OCS Study 

BOEMRE 2010-044 

 

Full-Water Column Current Observations 

in the Western Gulf of Mexico 

U.S. Department of the Interior 

Bureau of Ocean Energy Management, 

 Regulation and Enforcement 

Gulf of Mexico OCS Region 
OCS Study 

BOEMRE 2010-044 

Full-Water Column Current Observations 

in the Western Gulf of Mexico 

Authors 

J. Sheinbaum 

J. Ochoa 

J. Candela 

A. Badan 

Prepared under BOEMRE Contract 

M04PC00019 (1435-01-04-CT-32916) 

by 

Centro de Investigación Científica 

y Educación Superior de Ensenada 

Ensenada, Mexico 

Published by 

U.S. Department of the Interior

Bureau of Ocean Energy Management, 

 Regulation and Enforcement 

Gulf of Mexico OCS Region 

New Orleans

December 2010 
iii 

DISCLAIMER 

This report was prepared under contract between the Bureau of Ocean Energy Management, 

Regulation and Enforcement (BOEMRE) and the Centro de Investigación Científica y de 

Educación Superior de Ensenada (CICESE). This report has been technically reviewed by the 

BOEMRE, and it has been approved for publication. Approval does not signify that the contents 

necessarily reflect the views and policies of the BOEMRE, nor does mention of trade names or 

commercial products constitute endorsement or recommendation for use. It is, however, exempt 

from review and compliance with the BOEMRE editorial standards. 

REPORT AVAILABILITY 

This report is available only in compact disc format from the Bureau of Ocean Energy 

Management, Regulation, and Enforcement, Gulf of Mexico OCS Region, at a charge of $15.00, 

by referencing OCS Study BOEMRE 2010-044. The report may be downloaded from the 

BOEMRE website through the Environmental Studies Program Information System (ESPIS). 

You will be able to obtain this report also from the National Technical Information Service in the 

near future. Here are the addresses. You may also inspect copies at selected Federal Depository 

Libraries. 

 U.S. Department of the Interior U.S. Department of Commerce 

 Bureau of Ocean Energy Management, National Technical Information Service 

 Regulation and Enforcement 5285 Port Royal Road 

 Gulf of Mexico OCS Region Springfield, Virginia 22161 

 Public Information Office (MS 5034) Phone: (703) 605-6040 

 1201 Elmwood Park Boulevard Fax: (703) 605-6900 

 New Orleans, Louisiana 70123-2394 Email: bookstore@ntis.gov

 Telephone requests may be placed at 

 (504) 736-2519, 1-800-200-GULF, or 

Rush Orders: 1-800-553-6847 

 Fax: (504) 736-2620 

CITATION 

Sheinbaum J., J. Ochoa, J. Candela, and A. Badan. 2010. Full-water column current 

observations in the western Gulf of Mexico: Final report. U.S. Dept. of the Interior, Bureau 

of Ocean Energy Management, Regulation, and Enforcement, Gulf of Mexico OCS Region, 

New Orleans, LA. OCS Study BOEMRE 2010-044. 

ABOUT THE COVER 

Mooring on the deck of UNAM’s R/V Justo Sierra. Watercolor by A. Badan. Used by 

permission. All rights reserved. 
v 

ACKNOWLEDGMENT 

Thanks are due to Drs. Alexis Lugo-Fernandez, BOEMRE; H. Maske, CICESE; and all the 

people at SAIC, for their generous support throughout the development of the study. We would 

also like to thank Captain Leobardo Ríos and the crew of R/V Justo Sierra for their enthusiastic 

support at sea. This work would not have been possible without the ample participation of 

CICESE’s technical staff and students, in particular J.I. González, A. Ledo, M. Ojeda, B. Pérez, 

J. García, C. Flores, and T. Agüero. 

J. Sheinbaum 

J. Ochoa 

J. Candela 

A. Badan 
vii 

TABLE OF CONTENTS 

Page 

LIST OF FIGURES ..................................................................................................................... ix 

LIST OF TABLES .....................................................................................................................xiii 

ABBREVIATIONS AND ACRONYMS................................................................................... xv 

ABSTRACT............................................................................................................................... xvii 

1. INTRODUCTION ................................................................................................................... 1 

1.1. Background .................................................................................................................... 1 

2. SETTING AND DATA CHARACTERISTICS ................................................................... 5 

3. DATA ANALYSIS ................................................................................................................ 13 

3.1. Mean Current Profiles and Basic Statistics .................................................................. 13 

4. DESCRIPTION OF THE VARIABILITY ......................................................................... 21 

4.1. Eddy Field from Altimetry Data .................................................................................. 21 

4.2. Mooring Observations.................................................................................................. 29 

4.2.1. Flow Over the Shelf Break ............................................................................. 29 

4.2.2. Flow Over the Slope ....................................................................................... 33 

4.2.3. Abyssal Flow .................................................................................................. 45 

5. SPECTRAL CHARACTERISTICS OF THE VARIABILITY........................................ 51 

6. EMPIRICAL ORTHOGONAL FUNCTION ANALYSIS................................................ 59 

7. MEASUREMENTS OF VERTICAL MOTION OF ZOOPLANKTON......................... 71 

7.1. Proper Time Scale for Daily Migration Cycles............................................................ 73 

7.2. Comparison of the Euphotic Zone and 1,000 m Depth Mean Diel Cycles.................. 78 

7.3. Mean Cycles as a Function of Hours of the Day and Depth ........................................ 80 

7.4. Discussion on the Measured Diel Migrations from Near Surface to 1,200 m 

Depth ............................................................................................................................ 83 

8. SUMMARY AND CONCLUSIONS.................................................................................... 89 

9. REFERENCES ...................................................................................................................... 93 

APPENDIX A. TABLES OF BASIC STATISTICS ............................................................ 99 
ix 

LIST OF FIGURES 

Page 

Figure 1. Location of the WG moorings on the slope off the Mexican coast of the NW 

Gulf of Mexico.. ......................................................................................................... 6 

Figure 2. Longitude-depth section showing Moorings 1, 2, and 3. ........................................... 6 

Figure 3. Vertical distribution of instruments on the five moorings.......................................... 7 

Figure 4. Data records obtained by the instruments in each mooring...................................... 11 

Figure 5. NODC hydrographic stations. .................................................................................. 12 

Figure 6. Profiles of mean current magnitude, root mean square (RMS), and ratio of 

subinertial to total current variance measured by the instruments on each 

mooring..................................................................................................................... 15 

Figure 7. Mean current profile observed at each of the five moorings. ................................... 17 

Figure 8. Mean and low-pass variability ellipses of the measured currents at the indicated 

depths........................................................................................................................ 19 

Figure 9. Snapshots of absolute sea surface height from the AVISO product showing the 

evolution of one of the remnants of LC eddy Titanic, the intensification of 

cyclone C1 over the mooring area through merging with cyclonic structure C2, 

which accompanies LC Ulysses. .............................................................................. 22 

Figure 10. Snapshots of absolute sea surface height from the AVISO product showing first 

the splitting of eddy Ulysses, the northward along-slope movement of its 

southern byproduct UlyssesS, and its later merger with UlyssesN, forming a 

single anticyclone that covers the mooring array during April and part of May...... 24 

Figure 11. Snapshots of absolute sea surface height from the AVISO product showing the 

southeastward movement, splitting, and reattachment of "merged" eddy Ulysses, 

which formed in late March and April 2005. ........................................................... 26 

Figure 12. Snapshots of absolute sea surface height from the AVISO product showing 

cyclone C4 sitting over the mooring array. .............................................................. 27 

Figure 13. Arrival of LC eddy Vortex to the mooring array area. Vortex does not move into 

the mooring zone since its blocked by cyclone C4................................................... 27 

Figure 14. Trajectory of four LC eddys from December 2003 until November 2005............... 28 

Figure 15. Vector time series of the currents measured at the shelf edge, in 500 m of water, 

in the northwestern Gulf of Mexico.......................................................................... 30 

Figure 16. Snapshots of altimetry data from AVISO, which explain the observed current 

events in Figure 15.................................................................................................... 30 

Figure 17. Time series of total speed vs depth (top), speed of high-pass velocity series 

(middle), and time series of total (red) and high-frequency (black) kinetic energy 

for mooring MMS1................................................................................................... 31 
x 

Figure 18. Wind speed (top panel) and vector time series (lower panel) at NDBC station 

42002 located at 25.79° N 93.67° W. ....................................................................... 32 

Figure 19. Total (blue) and high-pass (red) temperature anomalies at 435 m (from the 

ADCP’s thermometer) (top panel)............................................................................ 33 

Figure 20. Vector time series of the currents measured over the slope, in 2,000 m of water, 

in the northwestern Gulf of Mexico, mooring 2. ...................................................... 35 

Figure 21. Vector time series of the currents measured over the slope, in 2,000 m of water, 

in the northwestern Gulf of Mexico, mooring 4. ...................................................... 35 

Figure 22. Vector time series of the currents measured over the slope, in 2,000 m of water, 

in the northwestern Gulf of Mexico, mooring 5. ...................................................... 36 

Figure 23. Time series of total speed vs depth (top), speed of high-pass velocity series 

(middle), and time series of total (red) and high-frequency (black) kinetic energy 

for mooring MMS2 in the top 400-500 m. ............................................................... 36 

Figure 24. Time series of total speed vs depth (top), speed of high-pass velocity series 

(middle), and time series of total (red) and high-frequency (black) kinetic energy 

for mooring MMS4 in the top 400-500 m. ............................................................... 37 

Figure 25. Time series of total speed vs depth (top), speed of high-pass velocity series 

(middle), and time series of total (red) and high-frequency (black) vertically 

averaged kinetic energy for mooring MMS5 in the top 400-500 m. ........................ 38 

Figure 26. Same as Figure 23 for mid-depths 800-1200 m and near-bottom depths 1960-

2020 m in mooring MMS2. ...................................................................................... 39 

Figure 27. Same as Figure 25 for mid-depths 800-1200 m and near-bottom depths 2000-

2050 m in mooring MMS5. ...................................................................................... 40 

Figure 28. Standardized sea surface height anomalies and temperatures at different depths 

(indicated by the legend) for mooring MMS1.......................................................... 41 

Figure 29. Same as Figure 28 but for mooring MMS4. ............................................................. 42 

Figure 30. Same as Figure 28 but for mooring 5. ...................................................................... 43 

Figure 31. Total (blue) and high-pass (red) temperature anomalies at around 700 and 1,250 

m depth at mooring 2 (first two panels) and mooring 5 (lower two panels). ........... 44 

Figure 32. Vector time series from mooring 3, located at the abyssal GoM at 3,500 m. .......... 46 

Figure 33. Absolute geostrophic velocity interpolated from AVISO data to the mooring 3 

position. .................................................................................................................... 46

Figure 34. Time series of total speed vs depth (top), speed of high-pass velocity series 

(middle), and time series of total (red) and high-frequency (black) vertically 

averaged kinetic energy for mooring MMS3 in the 800-1,200 m range and near 

the bottom (3,500-3,600 m). ..................................................................................... 47 

Figure 35. Standardized sea surface height anomalies and temperatures at different depths 

(indicated by the legend) for mooring 3. .................................................................. 49 
xi 

Figure 36. Total temperature anomalies (blue) and high-pass anomalies (red) at around 

1,200 m and 1,550 m depth. ..................................................................................... 50 

Figure 37. Rotary spectra, internal coherence, and phase between currents measured at 50, 

250, and 400 m on moorings MMS1 and MMS2..................................................... 52 

Figure 38. Rotary spectra, internal coherence, and phase between currents measured at 850, 

1,350, and 1,950 m on moorings MMS2 and MMS3............................................... 54 

Figure 39. Rotary spectra, internal coherence, and phase between currents measured at 50, 

850, 1,350, and 1,950 m on moorings MMS2 and MMS5....................................... 56 

Figure 40. Rotary spectra, internal coherence, and phase between currents measured at 850 

and 3,550 m on mooring MMS3............................................................................... 58 

Figure 41. First two EOF complex modes for the observed subinertial current interpolated 

at regularly spaced vertical levels on mooring MMS1............................................. 60 

Figure 42. First two EOF complex modes of the subinertial current vertical profile 

measured on mooring MMS2. .................................................................................. 62 

Figure 43. First two EOF complex modes of the subinertial currents measured on mooring 

MMS3. ...................................................................................................................... 63 

Figure 44. First two EOF complex modes of the sub-inertial current measured on mooring 

MMS4. ...................................................................................................................... 64 

Figure 45. First two EOF complex modes of the sub-inertial currents measured on mooring 

MMS5. ...................................................................................................................... 65 

Figure 46. First two complex EOF modes of the supra-inertial currents on mooring MMS1... 66 

Figure 47. First complex EOF modes of the supra-inertial currents on mooring MMS2.......... 67 

Figure 48. First two complex EOF modes of the supra-inertial currents on mooring MMS3... 68 

Figure 49. First two complex EOF modes of the supra-inertial currents on mooring MMS4... 69 

Figure 50. First two complex EOF modes of the suprainertial currents on mooring MMS5. ... 70 

Figure 51. Twenty diel cycles of the vertical velocity (upper frame) and echo intensity 

(lower frame) for the RDI 75kHz ADCP moored at a mean depth of 550 m in 

mooring MMS5. ....................................................................................................... 72 

Figure 52. As in Figure 51, five diel cycles are measured by another RDI 75kHz ADCP in 

the same mooring (WG-5), but looking upward from a depth of 1,250 m, 

showing depths from 1,250 to 750 m below the surface. ......................................... 73 

Figure 53. Time series of the diel cycle in vertical velocity averaged over two 150 m thick 

layers, one near surface and the other deep centered at 425 and 1,075 m................ 74 

Figure 54. Time series of the diel cycle in echo intensity, in similar format than Figure 53..... 75 

Figure 55. Color-coded diagram of the vertical velocity in the near surface layer, as a 

function of date, throughout the Canekito measuring period. .................................. 76 

Figure 56. Vertical velocity as in Figure 55, but using the sunrise/sunset times as 

06:00/18:00 as described in the text and shown in Figures 53 and 54. .................... 77 
xii 

Figure 57. Vertical velocity in the deep layer, near 1,000 m below the surface, with the 

same sunrise/sunset times as in Figure 56. ............................................................... 78 

Figure 58. Two functions are the mean diel cycle in vertical velocity for the data shown in 

Figures 56 and 57 (i.e., for two 150 m thick layers), here with the time axis 

defined in hours relative to sunrise (Sr) and sunset (Su).......................................... 79 

Figure 59. Functions shown display the anomaly in the mean echo intensity cycle following 

the same format as Figure 58; averaged over two 150 m thick layers and 473 

days or cycles, and with the time axis relative to sunrise and sunset. ...................... 80 

Figure 60. Color-coded mean vertical velocity diel cycle as a function of time, relative to 

sunrise and sunset as in Figure 58, and depth in m. ................................................. 81 

Figure 61. Anomaly in the mean echo intensity as a function of time and depth, following 

the same distribution as in Figure 60........................................................................ 82 

Figure 62. Mean vertical displacement as defined in the text, for the Canekito data. (a) the 

function for the near-surface region and (b) the function for the deep region.......... 83 

Figure 63. Plot shows, in the abscissa, the time in hours, relative to sunrise (Sr) and sunset 

(Ss) when the maxima in vertical migrating speed are reached at different depths 

in m, in the ordinate. ................................................................................................. 86 

Figure 64. Peak velocities in the mean diel cycle, negative during the downward and 

positive during the upward. ...................................................................................... 87 

Figure 65. Vector time series for the abyssal (mooring 3) and along slope moorings (2, 4, 

and 5) showing LC eddies Titanic (T), Ulysses (U), and Vortex (V), and 

cyclones C1 and C4 (see Section 4). ........................................................................ 90 

Figure 66. Temperature measurements at 500 and 800 m depth from all moorings with 

instruments at those depths....................................................................................... 90 
xiii 

LIST OF TABLES 

Page 

Table 1. Location and Deployment Depth of the 5 Moorings. ............................................... 12 

Table 2. Listing of the Quadratic Fit of Time (with 06:00 Defining Sunrise and 18:00 

Defining Sunset) at Maximum Migrating Speed Versus Depth for the Downward 

and Upward Phases of the Cycle. ............................................................................. 84 

Table A-1. Basic Statistics for Mooring 1. ................................................................................. 99 

Table A-2. Basic Statistics for Mooring 2. ............................................................................... 100 

Table A-3. Basic Statistics Mooring for 3. ............................................................................... 102 

Table A-4. Basic Statistics for Mooring 4. ............................................................................... 104 

Table A-5. Basic Statistics for Mooring 5. ............................................................................... 106 
xv 

ABBREVIATIONS AND ACRONYMS 

ADCP Acoustic Doppler Current Profiler 

AVISO Archiving, Validation and Interpretation of Satellite Oceanographic data 

BOEM Bureau of Ocean Energy Management, Regulation, and Enforcement 

CE Cyclonic Eddy 

CEOF Complex EOF 

CERSAT Centre ERS d’Archivage et de Traitement 

CICESE Centro de Investigación Científica y de Educación Superior de Ensenada 

CNES Centre National d’Etudes Spatiales, France 

CPD Cycles per Day 

CTD (or C/T/D) Conductivity/Temperature/Depth 

DOF Degrees of Freedom 

EEZ Exclusive Economic Zone 

EKE Eddy Kinetic Energy 

EOF Empirical Orthogonal Function 

ERS-2 Earth Resources Satellite - 2 

GDR Geophysical Data Record 

GEOSAT Geodetic Satellite 

GFO Geosat Follow-On 

GMT Greenwich Mean Time or UTC 

GoM Gulf of Mexico 

KE Kinetic Energy 

LC Loop Current 

LCE Loop Current Eddy 

NDBC National Data Buoy Center 

NOAA National Oceanic and Atmospheric Administration 

PI Principal Investigator 

PIES Inverted Echo Sounder with Pressure 

RMS Route Mean Square 

SAIC Science Applications International Corporation 

SNR Signal-to-Noise Ratio 

SSH Sea Surface Height 

SSHA Sea Surface Height Anomaly 

SST Sea Surface Temperature 

SUW Subtropical Underwater 

T Temperature 
xvii 

ABSTRACT 

Fourteen months of direct surface to bottom current measurements off the coast of 

Tamaulipas, Mexico, in the NW Gulf of Mexico during 2004 and 2005 capture the evolution of 

currents as several oncoming warm Loop Current eddies and cyclonic eddies reach the mooring 

array. Results show that current variability is mostly associated with these eddies as well as 

strong wind events (e.g. Hurricane Emily and Northern winds). In all five moorings, current 

standard deviations are larger than the mean. Interestingly, the most intense surface currents are 

found on the southernmost mooring (MMS5) at 2000 m depth and not at the shelf break. In 

general, current fluctuations are typically 20-40 cm/s at the surface and decrease with depth. In 

the upper layers, energy increases offshore, with a clear influence from eddies, to a depth of 

about 800 m. Further at depth, a weaker but steady southward flow appears to be locked near the 

slope in the form of a persistent current over the 2000 m isobath. Although low frequency 

fluctuations (periods > 3 days) are, as could be expected, more energetic than high frequency 

fluctuations, near-inertial and supra-inertial fluctuations are ubiquitous in all moorings and at all 

depths. In fact, it is found that at depths close to 1200 m there is a relative maxima in the high 

frequency contribution to total fluctuating energy. Whether this feature is produced by eddies 

focusing wind generated near surface inertial oscillations or it is produced by some sort of wave 

activity related to eddy instabilities or eddy-topography interactions processes is still to be 

resolved. 

In contrast to other studies, observations do not show a clear and coherent intensification of 

current variability near the bottom suggestive of topographic Rossby waves. We do find however 

coherent fluctuations at about 800-1200 m of periods near 20 days along the moorings located on 

the 2000 m isobath which may be related to baroclinic Kelvin waves. 

These observations were complemented with satellite altimetry. Two warm eddies released 

from the Loop Current (Titanic and Ulysses) entered the study area during the period of 

observations. A third one, Vortex, approached the region just prior to the retrieval of the 

instruments. The centroid of the eddies always remained in waters deeper than 2000 m, 

dissipating finally in a region between 21.25oN – 25.25oN latitude and 94oW – 97oW longitude, 

off the coast of Tamaulipas, Mexico. Besides these warm eddies, intense current events 

associated with cyclonic eddies in the area are captured by the array. High and low sea level 

values are clearly correlated with warm and cold temperature anomalies as deep as 1200-

1500 m. 

A separate issue, given the measurement of the vertical motion of zooplankton by ADCPs, is 

the determination of the mean diel cycle, from near the surface up to 1200 m deep. The deep 

cycle is, as the well known behavior from 500 m up to the surface, phase locked with the 

sunlight cycle. The downward peak velocity occurs earlier closer to the surface; at 220 m it 

reaches a maximum of 150 m/h half an hour before sunrise, while at 900 m it peaks at only 30 

m/h one hour and a half after sunrise. The cycle is nearly symmetric to solar noon, with upward 

peak velocities happening earlier at depth, a pattern expected if the vertical migration was 

triggered by critical light level that reached the greater depth closer to noon. Consequently with 

such differences in timing, in the mean, at greater depth the nightly shallower stay is longer for 

the deeper migrating biota. The peak vertical migration velocities showed relative maxima at 250 

and 1100 m depth, a sign of increased biological activity. 
1 

1. INTRODUCTION 

The Loop Current in the Gulf of Mexico extends periodically from the Yucatan Channel to 

the coast of Louisiana and, as it begins to retract, it usually pinches off and spins off a large 

anticyclonic eddy. The release of warm blobs is many times followed by a reattachment. The 

causes for the ultimate eddy release remains unclear. The release of eddies is at irregular 

intervals from six to 11 months (Sturges and Leben, 2000; Leben, 2005), and the eddies then 

drift in a general southwestern direction under the influence of the rotational beta effect, carrying 

with them some of the warmer, saltier, but less dense, Caribbean water into the western Gulf of 

Mexico. This translation takes from months to a year, during which the eddies shed and entrain 

some mass, but remain somehow identifiable, until they meet the shelf break off the TexasMexico coast, in the general vicinity of which they dissipate. The identification of one eddy is 

fuzzy; the breakup and merge of eddies is the rule. Any map of surface eddy kinetic energy 

shows clearly that eddies are of enormous importance in driving the circulation of the 

northwestern Gulf of Mexico. 

Additional factors that affect the circulation in the western Gulf are the seasonally varying 

winds that drive a southerly coastal current during Fall and Winter, but becomes a northerly flow 

during the summer as the winds blow from the south (Morey et al., 2005). In addition, there are 

semi-permanent current patterns of cyclonic circulation over the Texas and Louisiana shelves, 

and over the Campeche Bank (DiMarco et al., 2005). 

Equally important to the eddy release mechanism, and as poorly known, are the processes 

that accompany the dissipation of these eddies as they approach and interact with the shelf and 

slope off Texas and Mexico. It was widely believed that the eddies should dissipate in the ‘eddy 

graveyard’, the northwestern corner shelf of the Gulf of Mexico, in a series of interactions of the 

eddies with the shelf and slope topography, in the process shedding mass and redistributing 

vorticity, driving coastal jets and other forms of coastal motions in the process. The desire to 

better understand this evidently fundamental aspect of the gulf’s circulation is the main reason 

for the measurements in this project. The project consisted of a large number of current meter 

moorings deployed for over one year over the Texas shelf and slope and, through our component 

of the experiment, extending southwards into Mexican waters. As it turns out, the three eddies 

existing during the experiment entered and dissipated within our observation area in Mexican 

waters and therefore, were best recorded by the moorings here analyzed and reported. 

The data recovered document a wide spectrum of motions. The present report describes the 

subinertial currents recorded in the upper layers of the region of interest, which are related 

mostly to the presence of eddies, interacting among them and with the topography and decaying. 

Additionally, the transient intensification of inertial motions is also analyzed and described. 

There are several other motions of interest, such as isolated high-speed near-surface jets, which 

are not part of the analysis. All these forms of motion are of keen interest to the intense efforts by 

the oil industry in the region, as they impact directly the positioning and other operations of the 

platforms. 

A section of this report is devoted to the analysis of the vertical velocity and echo signal 

measured by ADCPs in relation to zooplankton vertical daily migrations. 

1.1. BACKGROUND

Eddies are a conspicuous feature of the circulation in many regions of the world, and have 

therefore motivated numerous observational and theoretical studies, especially in the Gulf of 
Mexico, where the life cycle of eddies is complicated by their interaction and dissipation near the

coast. 

Elliott (1982) initially suggested from hydrographic studies that the eddies released from the 

Loop Current are an integral part of the gulf’s circulation. The eddies detached from the Loop 

Current (LCE) are warm, anticyclonic, surface intensified eddies, shaped with a positive bulge in

the sea surface elevation, and a depression of the thermocline beneath, and carry the Caribbean

water trapped in them along their path to the western gulf, where they stir and mix their last 

fractions with the gulf’s waters. LCEs diameters range from 100 to 400 km, with typical ones 

close to 200 km (Elliott, 1982), with their influence often reaching 800 m depth (Vukovich and

Crissman, 1986), with tangential velocities from 50-70 cm/s at a distance of 50 to 80 km from 

the center of the eddy (Lewis et al., 1989). After detaching from the Loop Current, they travel to 

the west-southwest of the gulf (Ichiye, 1962; Elliott, 1982, Vukovich, 2007) with speeds of O(5 

km/day). The westward propagation of LCEs is in agreement with the influence of the beta effect 

(Cushman-Roisin et al., 1990), but they also interact with a variety of surrounding eddies, either

cyclones or anticyclones. In one case, Vukovich and Crissman (1986) observed that at 150 days

from release, the LCE maintained 45 percent of its original diameter, and at 300 days, it was

down to 30 percent of the original size. Some authors (Vukovich and Crissman, 1986, Vukovich, 

2007) have described how LCEs, as they travel, exchange mass and other properties with their 

surroundings, and argue that they typically reach western continental margin of the gulf having 

about 30-50 percent of their original size, where they rapidly dissipate. The descriptions in this

analysis show more complex processes because of the persistent merge and breakup of either 

cyclonic or anticyclonic eddies. Vukovich and Waddell (1991) followed the evolution of two 

eddies from the time they detached from the Loop Current to the time when they intersected the

coast of the western gulf, showing that when the eddies reach the coast, they become elliptical, a

much smaller, O(100 km) cyclonic structure develops next to the large eddy, and that as the eddy 

moves onto the slope, a jet of warmer water is driven between the eddy and the coast. 

The dissipation processes are fundamental, because they are accompanied with a 

redistribution of momentum, vorticity, and other properties. From a practical aspect, the traveling 

eddies can cause several disruptions to the operations of oil and gas industry. 

Theoretical studies include that of Zavala-Sanson et al. (1998) who examine, in a reduced 

gravity model, the collision of an anticyclonic eddy of non-zero potential vorticity with a 

meridional wall. They show that, under such model, the eddy slightly deforms when reaching the 

wall but most importantly expels mass in a southward jet adjacent to the boundary, which causes 

the eddy to move north, as a ‘rocket effects’. In this model the eddy’s translation that causes the 

approach and collision against the western boundary is purely a planetary beta effect. Even in a 

model in the f-plane (i.e. without the planetary beta effect), Nof (1999) reached similar 

conclusions with an eddy of vanishing potential vorticity. Nof’s (1999) model suddenly imposes

a vertical wall, cutting a western sector of a uniform, steady rotating eddy. This condition 

implied the generation of the southward jet adjacent to the wall, and the corresponding 

northward motion of the remaining rotating blob. In both models the southward jet has a Kelvinlike balance; an edge of water bulging against the wall, and flowing in geostrophic balance. The 

study of Csanady (1979) in a two-layer model argues that the decay time-scale of a warm eddy 

depends more on the lateral friction between the rotating water within the eddy and the 

surrounding waters, rather than from the loss of mass. In Zavala-Sanson et al., (1998) model, 

analytical approximations allow estimating the meridional motion of the eddy. This depends on 

the parameter r = ε / β , where O O β = β R/ f , O ε = ω / f , R is the radius of the eddy, ω its

2 
3 

angular frequency, Of and β O are the Coriolis parameter and its latitudinal gradient. If r > 1 , the 

motion of the eddy is to the south, consistent with the analytical solution, which balances the

motion of the eddy with the force from the wall (i.e. a Kelvin-like balance with the eddy itself). 

If r < 1, the eddy travels to the north until it looses enough mass then reverses to the south, since 

the motion of the eddy depends on the mass distribution along the wall. The amount of numerical 

models dealing specifically with the Loop Current Eddies, starting with the study by Hurlburt 

and Thompson (1980), is large, here we mention some that are relevant to the collision against 

topography. Itoh and Sugimoto (2001) used a primitive equation model in sigma coordinates to 

study the effect of a warm eddy approaching a western boundary. They found that for a situation 

similar to that of the western Gulf of Mexico, the eddy initially should move to the southwest for 

a few days, and then to the north. Even though the slope is small, it causes a similar effect as in 

models with a vertical wall. Hyun and Hogan (2008) make an analysis of historical altimetry 

data and the use of the Hybrid Coordinate Ocean Model (HYCOM) to asses the evolution of 

LCE reiterating the importance of the cyclone formation south of the collision location and the 

jet-like current along the shelf. Their numerical examples cover the three predominant paths

described by Vukovich and Crissman (1986) and other trajectories that have not been 

documented; entering Campeche Bay. Hyun and Hogan’s (2008) model includes realistic 

topography but sets a single LCE per run as initial condition, without the surrounding plethora of 

common structures in the gulf. The three predominant trajectories are either along the northern 

slope, a southerly trajectory, or an intermediate path through the center of the gulf, which is

direct to the area of the measurements here reported. Hyun and Hogan (2008) estimates show the 

varying reflection strength depending on the collision angle with the bottom gradient; maximum 

when normal to a steep slope. The LCE reflects, moving eastward after the first collision, then

reacquires westward motion colliding again, a process observed in this set of measurements and 

described by others like Vidal et al (1994) and Vukovich (2007) . The cyclones produced during 

the collision process play an essential role in the reflection and subsequent return to westward

motion of the LCEs (Zavala-Sanson et al, 1998, Hyun and Hogan, 2008). It seems then that the 

LCE ‘bouncing’ trajectory is largely dependent on the surrounding eddy field at the collision 

time, but the ultimate dissipation is against the western boundary. 
5 

2. SETTING AND DATA CHARACTERISTICS 

A set of 5 moorings were deployed in the western Gulf of Mexico (Figure 1) to complement 

measurements being done over the Texas and Louisiana shelf and slope. The deployment lasted 

for over 14 months from August 2004 to November 2005. The 5 moorings were designed to 

adequately sample the distribution of currents from the surface to the bottom at each of their 

locations which were around 500 m for mooring MMS1, 2000 m for moorings MMS2, MMS4 

and MMS5 and 3500 m for mooring MMS3. The northwest corner of the Gulf of Mexico 

consists of a 100 km-wide shelf that extends off the Texas coast to about 27°N and then stretches 

southwards, narrowing progressively along the Mexican coast, so that the shore is oriented northsouth, but the edge of the shelf and slope are oriented north-north-east. The slope is about 100 

km wide, with irregular topography joining the slope to the abyss at 3500 m depth (see Figure 2). 

Moorings 1, 2 and 3 sample this section, whereas moorings 4 and 5 (together with mooring 2) 

sample the along slope flow (Figure 1). Diagrams of the 5 moorings are shown in Figure 3. The 

instruments were located on the moorings in a way to efficiently monitor the currents throughout 

the water column, with a 75 kHz Long Ranger Acoustic Doppler Current Profiler (ADCP) from 

RDTeledyne looking up from 450 m depth to record currents in 8 m bins from the surface layer, 

a second Long Ranger at 1200 m depth recording in the same fashion from there to about 800 m 

depth, and a third, 300 kHz ADCP recording currents from 10 m off the bottom up into the 

bottom boundary layer (BBL) in 4 m bins. Intermediate depths not sampled by the ADCP’s were 

monitored with Aanderaa RCM11 current meters at intervals of 500 m, as shown in Fig. 3. In 

this way, mooring MMS1, being in 500 m of water, consisted of a single 75 kHz Long Ranger, 

moorings MMS2, MMS4, and MMS5, in 2000 m of water, included the three ADCP’s as 

described, plus Aanderaas at 750 and 1500 m. mooring MMS3, in 3500 m of water, included the 

three ADCP’s, plus Aanderaas at 750, 1500, 2000, 2500, and 3000 m. Most of the instruments 

worked as expected except for some mishaps. There was an unexpected pre-release of mooring 

MMS1, 24 hours after deployment, due to a mistakenly factory programmed release that was set 

to release 24 hours after being deployed. The factory Benthos Inc. did not informed about the 

state of the instrument upon delivery and without this information the release was used as 

expected. Therefore, the mooring was set adrift and, on top, the Argos beacon malfunctioned so 

no warning was obtained about the situation. Fortunately the mooring was rescued by a shrimp 

fisherman and taken to the Port of Brownsville. This mooring was then redeployed in December 

2004, with the aid of the same shrimp fisherman that had rescued it, and lasted until the middle 

of October 2005 when the batteries on the LR ADCP were exhausted. The two other important 

failures were two LR ADCP instruments, one on the top (~500 m) of mooring MMS3 and the 

other deployed at a depth of 1260 m on mooring MMS4 (Figure 3). Both of these instruments, 

also factory delivered before deployment, had problems related to faulty seals around the 

transducer heads that lead to partial water leakages into the instruments’ electronics shortly after 

deployment, with the consequence of complete data lose. Three other minor mishaps consisted in 

battery failure before recovery on the Aanderaa current-meters deployed at 820 and 2556 m on 

mooring MMS3 and 763 m on mooring MMS5. These resulted in measurement time series less 

than 14 months at these locations (Figure 4). 
Figure 1. Location of the WG moorings on the slope off the Mexican coast of the NW 

Gulf of Mexico. Depth contours in meters. 

Figure 2. Longitude-depth section showing Moorings 1, 2, and 3. 

6 
7 

Figure 3. Vertical distribution of instruments on the five moorings. 

Figure 3. Vertical distribution of instruments on the five moorings (continued). 
Figure 3. Vertical distribution of instruments on the five moorings (continued). 

8 
Figure 3. Vertical distribution of instruments on the five moorings (continued). 

9 
Figure 3. Vertical distribution of instruments on the five moorings (continued). 

10 
11 

Figure 4. Data records obtained by the instruments in each mooring. 

The pressure sensors on some instruments showed remarkably small vertical excursions of 

the moorings, with a maximum down-draft of 5.4 m for the moorings over the shelf and slope, 

and only one event in which the deeper 3500 m mooring dipped down by 71 m in mid-March 

2005, with a corresponding change in temperature of 0.12C, compared to the standard deviation 

of temperature of 0.55C, showing that the temperature correction for the vertical motion of the 

moorings was negligible (Hogg, 1991). 

Table 1 shows the location (longitude, latitude) and deployment depth of the moorings.
Table 1 

 

Location and Deployment Depth of the 5 Moorings. 

Mooring Longitude W (°) Latitude N (°) Depth (m)

MMS1 96.31 25.43 500 

MMS2 95.43 25.38 2000 

MMS3 94.88 25.27 3500 

MMS4 96.08 24.65 2000 

MMS5 96.30 24.04 2000 

Figure 5 shows positions of hydrographic stations from NODC data base. One can clearly see 

that there are only 4 or 5 useful hydrographic stations near the study area. Unfortunately, time

limitations during deployment did not allow us to carry out CTD casts. Such conditions make

estimation of full depth temperature profiles based on point observations from the moored

instruments not clearly valid. 

Figure 5. NODC hydrographic stations. Notice the lack of measurements near the mooring 

locations indicated by a triangle. 

12 
13 

3. DATA ANALYSIS 

3.1. MEAN CURRENT PROFILES AND BASIC STATISTICS

Figure 6 shows vertical profiles of mean current speed (left panel), standard deviation 

(middle panel) and the ratio of sub-inertial velocity variance to total variance. The magnitude of 

the mean currents are largest at the surface, as might be expected, however it is interesting to 

find that the largest mean current in the surface layer is observed in mooring MMS5 located in 

waters 2000 meters deep, while the largest variability in the surface layer is observed at the 

location of mooring MMS2, also installed in a location 2000 m deep (Figures 1 and 2). 

It is found that the mean current below 500 m have less than 5 cm/s magnitude and the root 

mean square deviations at those depths are less than 10 cm/s in all locations, however, moorings 

MMS2 and MMS5 show a relative increase of mean current magnitude near the bottom while 

mooring MMS4 has a relative mean current maximum at around 1500 m depth. Figure 7 shows 

that the mean currents near the bottom are toward the south west in all three 2000 m moorings, 

while the mean currents increase significantly towards the surface and are directed towards the 

north east on moorings MMS1, MMS4 and MMS5. At mooring MMS2 the surface current is the 

smallest of all and southeastward. Recall that unfortunately there are no near surface 

measurements for mooring MMS3. Looking at the deep currents we find that on mooring MMS2 

the mean current below 500 m, although small, increases toward the bottom while at mooring 

MMS4 there is a relative maximum at 1500 m. Moorings MMS3 and MMS5 both show a fairly 

uniform and small current from 1000 m down to the bottom. 

the total 

and 1300

Worth noticing also is the fact that in the deep moorings (>2000 meters), there is a general 

tendency for the relative proportion of supra-inertial to sub-inertial motions to grow towards the 

middle of the water column at depths around 1200 meters being larger there than towards the 

surface or the bottom (right hand panels Figure 6). 

The mean and (low pass) fluctuating currents denote three possible flow regimes in our study 

area. Mean currents were surprisingly small everywhere, flowing to the north and northeast only 

at about 10 to 20 cm/s near the surface over the edge of the shelf and slope (Figure 7), probably 

as an expression of the large anticyclonic gyre of the northwestern Gulf of Mexico (Nowlin and 

McLellan, 1967; Sturges and Blaha, 1976; DiMarco et al, 2005). Unfortunately, we lacked near 

surface data at the offshore mooring to confirm the offshore extension of the western boundary 

flow. From there, mean currents diminish quickly with depth, rotating clockwise over the shelf, 

so that by 400 m depth, the current is flowing to the south over the shelf’s edge, but still flowing 

offshore over the slope. Figure 8 shows variability ellipses at different depths and also depict the 

mean current vectors. The current fluctuations are larger than the mean close to 40 cm/s near the 

surface, and diminishing rapidly to about 10 cm/s close to 400-500 m, the bottom over the shelf, 

and offshore over the slope (Figure 8). The current fluctuations are prevalently along the 

topography over the shelf, but without a preferred direction at those depths (400-500 m) over the 

slope, going from parallel (mooring 2) to almost perpendicular (mooring 5) to the slope. 

Further at depth, below the shelf edge over the slope and the deep Gulf of Mexico, the 

topography separates two distinct regimes (Figure 8). Over the slope, current fluctuations are 

only about 10 cm/s, and oriented along the topography. Mean currents are even smaller, only a 

The sub-inertial currents dominate the observed variability representing more than 60 % of 

variance at all depths except for a mid-water interval on mooring MMS5 between 1000 

 meters depths where the ratio of sub-inertial to total variance gets as low as 47%. 
14 

few cm/s over most of the water column, but y near the bottom forming a 

flow is a

area whe er than the fluctuations. Farther offshore (Mooring 3), in 

the very deep Gulf of Mexico, the mean is insignificantly small, but the fluctuations are close to 

10 cm/s and in a predominant north-northeast direction throughout the water column. Such a 

barotropic distribution of the currents is to some extent similar to the current variability found in 

the deep central Gulf of Mexico (Rivas, et al, 2005, 2008) below the surface layers under the 

influence of eddies. However, in contrast to that study, we only find some intensification of the 

variability toward the bottom on mooring 3, but not in the moorings along the slope. This 

intensification is one of the signatures of topographic Rossby waves (Hamilton, 1990, 2007). 

A more thorough analysis of the current variability is carried out below (Sections 5 and 6) 

using rotary spectral analysis and complex empirical functions. But before we do that, it is 

necessary to look in more detail at the actual time series which feature a series of events related 

to the presence of eddies and/or strong wind forcing in the area. 

For completeness and reference, a set of 5 tables containing the basic statistics (mean, 

standard deviation, maxima, minima) of the horizontal velocity components is included in 

Appendix A. 

slightly intensif

southerly jet trapped to the slope, suggestive of the deep flow posed by Welsh and Inoue (2000) 

and DeHaan and Sturges (2005). Over the 2000 m isobath (Moorings 2, 4 and 5, Figure 6) mean 

 bit larger than the rms fluctuations just above the bottom, the only portion of our study 

re the mean flow becomes larg
15 

Figure 6. Profiles of mean current magnitude, root mean square (RMS), and ratio of subinertial to total 

current variance measured by the instruments on each mooring. Points at about the same

depth but with slight different values correspond to overlapping measurements by an Aanderaa

current meter and an ADCP. 
Figure 6. Profiles of mean current magnitude, root mean square (RMS), and ratio of subinertial to total 

current variance measured by the instruments on each mooring. Points at about the same depth

but with slight different values correspond to overlapping measurements by an Aanderaa current

meter and an ADCP (continued). 

16 
Figure 6. Profiles of mean current magnitude, root mean square (RMS), and ratio of subinertial 

to total current variance measured by the instruments on each mooring. Points at 

about the same depth but with slight different values correspond to overlapping

measurements by an Aanderaa current meter and an ADCP (continued). 

Figure 7. Mean current profile observed at each of the five moorings. The two panels show the

profile in two equivalent representations, on the left, vectors in 3-D space, and on the 

right, vectors in 2-D with the north-south/east-west component in the abscissa/ordinate

directions and each vector starting at its corresponding depth. 

17 
Figure 7. Mean current profile observed at each of the five moorings. The two panels show the profile in

two equivalent representations, on the left, vectors in 3-D space, and on the right, vectors in 2-D 

with the north-south/east-west component in the abscissa/ordinate directions and each vector

starting at its corresponding depth (continued). 

18 
Figure 7. Mean current profile observed at each of the five moorings. The two panels show the

profile in two equivalent representations, on the left, vectors in 3-D space, and on the 

right, vectors in 2-D with the north-south/east-west component in the abscissa/ordinate

directions and each vector starting at its corresponding depth (continued). 

Figure 8. Mean and low-pass variability ellipses of the measured currents at

the indicated depths. Note the different scales in each panel. 

19 
Figure 8. Mean and low-pass variability ellipses of the measured currents at the

indicated depths. Note the different scales in each panel (continued). 

20 
21 

ng. 

he Loop Current pinches off over itself sporadically and sheds a large warm, anticyclonic 

eddy that extends several hundred meters in depth and propagates in a west-southwest direction 

across the Gulf of Mexico until it intersects the coastal features of the western gulf. Given the 

breadth and depth of most eddies, this really happens rather far away from the shore itself, as the 

eddy begins to perceive the shoaling of the bottom over the slope and at the shelf’s edge. The 

path each eddy follows from its region of generation can vary somewhat, from a southerly 

trajectory through the middle of the gulf, to a more northerly one south of the northern 

escarpment. Although it has been suggested that eddies follow either of three distinct paths, they 

probably can travel through a range of directions between the two aforementioned extrem . 

Wh ew 

actually travel

ddies are ed through satellite altimetry, for which we use the sea surface 

elev

d altimetry data, the size and behavior of the eddy structures we 

identify in it, even its form and size, appear to be consistent with the mooring data. 

As the moorings were being deployed, eddy Titanic (eddies are named alphabetically in 

Inc.), whic 03, and traveled along a southern trajectory, was 

present on August 28 of the following year at 21.53oN; 95.64oW, when its center was in about 

200

4. DESCRIPTION OF THE VARIABILITY 

4.1. EDDY FIELD FROM ALTIMETRY DATA

Since, as will be shown in the next sections, most of the observed variability is related to the 

presence of eddies in the area, before describing the mooring observations we carry out a 

thorough analysis of altimetry data. The processes involved are very complicated and include 

eddy-eddy, eddy-topography interactions and strong wind forcing events. One may think there 

might be different interpretations of the altimetry data, but the figures leave little room to 

maneuver and clearly show what is happeni

T

es

at is clear is that eddies usually remain in water deeper than the shelf’s edge, and very f

 into the ‘eddy graveyard’ region in the extreme northwestern gulf. 

E conveniently detect

ation anomaly combined from the Topex-Poseidon, Jason-1, and GFO satellites, as offered 

by the AVISO website1

 (the altimeter products are produced by Ssalto/Duacs and distributed by 

AVISO, with support from Cnes). This information has a 1/3 of a degree spatial resolution, and 

3.5 days temporal resolution. From these data, three LC eddies were present or appeared at 

various phases of their development during the times our instruments were deployed and serve to 

illustrate the behavior of the eddies as they separate from the Loop Current, travel to the west, 

approach the coast and disappear. The current meter records then serve to document the effect of 

the eddies on the currents in the region of our observations. It is a pleasant surprise that even 

though use is made of interpolate

chronological order in the fashion of hurricanes by Eddy Watch, (a service of Horizon Marine, 

h had formed on December 31, 20

0 m of water off the coast of Veracruz (see Figure 9). It then traveled to the north, with its 

center remaining close to the 2000 m isobath, reaching 24.5oN; 96.25oW on September 15, 

becoming more elongated and weaker and difficult to identify by early October 2004. At about 

the same time on early October, a cyclone to the east of the now almost invisible Titanic and 

centered at 25.5oN; 95.5oW intensified. SSH anomalies (not shown) and the ssh field for early 

September suggest this cyclone is part of an anticyclone-cyclone pair, rotating clockwise on its 

axis. Whilst the anticyclone in this structure disappeared by the middle of October, the cyclone 

first intensified, then weakened (late October early November) and re-intensified through 

merging with other cyclonic anomalies particularly one to the east, related to eddy Ulysses (see 

 

1 http://las.aviso.oceanobs.com/las/servlets/dataset 
Figure 9). This intense cyclonic anomaly, labeled C1 for its importance, remained over the 

continental slope covering most of the mooring array (Moorings 1-4) until January 2005, when it 

started to elongate and weaken for a while, regaining strength and splitting in two, later in 

February (see Figure 10). 

Figure 9. Snapshots of absolute sea surface height from the AVISO product showing the

evolution of one of the remnants of LC eddy Titanic, the intensification of cyclone C1

over the mooring area through merging with cyclonic structure C2, which

accompanies LC Ulysses. Ulysses is blocked by cyclone C1 and plays an important 

role in its subsequent splitting. 

22 
Figure 9. Snapshots of absolute sea surface height from the AVISO product showing the 

evolution of one of the remnants of LC eddy Titanic, the intensification of cyclone C1

over the mooring area through merging with cyclonic structure C2, which 

accompanies LC Ulysses. Ulysses is blocked by cyclone C1 and plays an important 

role in its subsequent splitting (continued). 

23 
Figure 10. Snapshots of absolute sea surface height from the AVISO product showing first 

the splitting (top 6 panels) of eddy Ulysses, the northward along-slope

movement of its southern byproduct UlyssesS (middle 6 panels), and its later 

merger with UlyssesN, forming a single anticyclone that covers the mooring 

array during April and part of May (bottom 6 panels). 

24 
Figure 10. Snapshots of absolute sea surface height from the AVISO product showing first the 

splitting (top 6 panels) of eddy Ulysses, the northward along-slope movement of its 

southern byproduct UlyssesS (middle 6 panels), and its later merger with UlyssesN, 

forming a single anticyclone that covers the mooring array during April and part of 

May (bottom 6 panels) (continued). 

On Septemb

Current and pro ccompanied by a much weaker cyclonic elongated 

structure (C2) to the south of it. On late November, the eddy pair collided with the cold structure 

ssesS while it remained at that southerly position. In early March 2005, 

UlyssesS started traveling to the north and Uly es N began stretching to the west while C5

apparently rotated to . At the same time, 

around the middle of April, th orm a single large

anticyclonic eddy. It seems the ocities are observed

during April at several moorings

er 15, 2004, eddy Ulysses, one of the largest ever, detached from the Loop

ceeded directly to the west, a

C1, which merged with C2 to form a cyclonic structure that blocks Ulysses from reaching the 

continental margin (25.25oN; 95.5oW). On early December, with both cyclones fully merged, 

Ulysses began to stretch in two branches, with the northern half remaining close to where it was, 

but with the southern half (UlyssesS) traveling towards a southwesterly destination near 22oN; 

96oW, where it would remain from February to March 2005. The splitting process involved the 

intensification of a trailing cyclonic structure (C5) and cyclone C1 in a process resembling the 

formation of a LCE by a Tortugas and Campeche Bank cyclones strangling the LC. Ulysses 

clearly split in two at the very end of December, with C5 attached nearly in a stationary position

to the northeast of Uly

ss

the south and grew in size weakening in that process

e two halves of Ulysses merged again to f

array capture its rim, since very high vel

(see Figures 10 and 11).

25 
Figure 11. Snapshots of absolute sea surface height from the AVISO product showing the 

southeastward movement, splitting, and reattachment of "merged" eddy Ulysses, 

which formed in late March and April 2005 (see Figure 10). 

As these displacements were taking place, the fused cyclones (C1-C2) were pushed to the 

north over the shelf, where they became undetectable by late March when UlyssesN moves over 

the mooring array before merging with UlyssesS. The ssh data suggests that during May 2005, 

Ulysses begins to stretch and move on a clockwise path down to 22oN, strengthening at its

southeastern end, moving back west and splitting in two one more time (June 2005). Thereafter, 

while moving along the shelf back north, it merges once again with its weaker northern part 

forming a large stretched anticyclone along the western slope (August-September 2005). This 

stretched anticyclone remains detectable until middle October (see Figures 11 and 12). 

A few other cold structures had an impact on our measurements. Although their origin and 

time history is rather more fuzzy than the others mentioned before, we labeled them C4 basically 

because they do impact mooring observations in the last part of the observing period. Starting in 

early February, 2005, one notices that the northern split product of the merged cyclone C1-C2 is

rotating clockwise on the rim of UlyssesN. This cyclone merges with other anomalies to the east

of UlyssesN and later with other cyclonic features surrounding “remerged” Ulysses eddy formed 

26 
27 

October 2005.

in April 2005. Its associated cyclonic circulation impacted the mooring region from August

onwards particularly during

Figure 12. Snapshots of absolute sea surface height from the AVISO product showing cyclone 

C4 sitting over the mooring array. This eddy formed by several merging processes 

(see text for details). 

n the second half of September 2005, a third eddy, named Vortex, was released from the 

Loop Current. It traveled directly to the west, approaching the region of our moorings from a

northerly direction in by late October. Although cyclone C5 becomes smaller from late October 

and during November, it blocks eddy Vortex fully entering the mooring array zone. Hence it 

appears that only moorings MMS2 and MMS3 may have sampled eddy Vortex during that 

period. Unfortunately, there are no near surface measurements at mooring MMS3. The moorings 

were pulled out in December, so the effect of the eddy on the currents recorded lasted a bit less 

than 1.5 months (see Figure 13). 

O

Figure 13. Arrival of LC eddy Vortex to the mooring array area. Vortex does not move into the mooring

zone since its blocked by cyclone C4. 
28 

he behavior of the eddies can be summarized by the trajectories of the centroids (Figure 

14). Titanic lasted 11 months, and followed a southerly path, reached the slope, and proceeded

north. Ulysses lasted 12 months, followed a more central path, split into two halves, of which the 

mer ing a iginal eddy. It, nonetheless, seemed to possess 

larger amounts of energy, for it then repeated the clockwise path through the south before 

breaking up along the slope. Vortex followed a more northerly path, and took six months to 

move into the region of the moorings, when we ended the observational effort. The three eddies 

represented the various paths that have been proposed as typical behavior of the Gulf of Mexico 

eddies by Vukovich and Crissman (1986) from 11 years of data, and by Vukovich (2007) with 

23 years of data. It appears that the lifespan, length of path, and the minimal distance to the coast

of eddies is a function of their size, with Ulysses, the largest, lasting over a year, had to repeat 

the clockwise cycle near the coast to dissipate, and remained at more than 400 km form the 

coast. Vortex, the smallest, lasted only six months, and broke up before reaching the coast. 

Titanic was a medium sized eddy, lasted for 11 months, and got as close as 170 km from the

coast. A rule-of-thumb appears to be that the center of the eddies never penetrates regions where 

the water depth is less than 2000 m. The time the eddies lasted after reaching the coast for the 

first time, 5 months for Titanic, and 9 months for Ulysses, were all spent in a region delimited by 

the 23.5 – 24.8o N and 93.5– 97o W, off the coast of Tamaulipas, Mexico. When the eddy was

especially energetic, it cycled more than once around the area. 

T

southern one behaved essentially like Titanic had, moving north after reaching the slope and

g gain with the northern half of the or

Figure 14. Trajectory of four LC eddys from December 2003 until

November 2005. Red square shows the region where the

eddies either dissipated or loose its coherent circular form. 
29 

The cold, cyclonic eddies were typically smaller than the warm eddies, the exception being 

some merger cases such as the larger C1-C2 combination that was able to split eddy Ulysses in 

two halves, and remain for several months with a diameter of close to 100 km. 

The following section describes the mooring time series where it will be shown that the eddy 

events just described explain a great deal of the observed variability. 

4.2. MOORING OBSERVATIONS

In spite of the loss of two complete current profilers, we recovered a rich data set, useful to 

describe the regional circulation over the edge of the shelf and slope of the Northwestern Gulf of 

Mexico. The flow is predictably dependent on the bathymetry and depth, with three different 

regimes occurring over the shelf, the deep slope and the abyssal plain. It is shown below, that 

flow in all regions is affected by the presence of eddies and most of the high velocity events 

detected in the time series can be associated with them. However, obviously there are other 

processes affecting the variability besides the eddies, particularly strong wind events, among 

them “Nortes” and hurricane Emily that leave their mark in the time series. Spectra of the 

variability is red and the most energetic signals are sub-inertial, but high frequency signals 

(inertial and supra-inertial) are ubiquitous and in some cases as energetic as low frequency ones. 

Following is a description of the variability. Afterwards rotary spectra and complex EOF 

analysis (Sections 5 and 6) will help us in its interpretation. 

4.2.1. Flow Over the Shelf Break 

Figure 15 shows vector time series of low-pass subinertial currents at several depths in 

mooring MMS1 (which consisted of a single ADCP, see Figure 3). Recall these time series b 

unti nd 

redeploy the m e, 

at the 500 m d to be divided 

into two main layers, with the upper levels dominated by large O (30-40 cm/s) fluctuations of a 

month’s duration or longer that are very coherent in the vertical, extending down beyond 250 m 

depth and a predominant northerly flow during the summer, due to the presence of anticyclonic 

anomalies or simply because the wind-driven seasonal circulation of the region (Sturges, 1993). 

Below that level, events are shorter, close to a week in duration, reversals are frequent. Most 

fluctuations were smaller, of O(20 cm/s), and a few days to a week in duration, except for a large 

perturbation that began with a pulse of northerly flow and then dominated the entire water 

column during February 2005. The events seen in the top 250-270 m can be clearly associated 

with eddies as Figure 16 shows. The southward flow during February is associated with cyclone 

C1-C2 whereas the flow in March is related to the presence of eddy UlyssesN. In April, remerged eddy Ulysses is to the east of mooring MMS1 and cyclonic circulation occurs over the 

mooring. The northward flow during summer is also related to the second arrival of Ulysses in 

the area as Figure 11 above shows. The southward flow seen in the whole water column in the 

last part of the record is interesting because it appears first in the flow near the bottom in early 

September when the flow at the surface is still northward (associated with an anticyclonic feature 

in the altimetry). Later in October and November, cyclone C4 is over the mooring area so the 

flow is coherent throughout the water column. Both events occurred in summer, when the winds 

and wind stress curl are small (Sturges, 1993; DiMarco et al., 2005). Worth noticing is the fact 

that the flow below 300 meters is in general different from the one above but not opposite, in the 

egin

l December due to a problem with the acoustic release which forced us to recover a

ooring (see Section 1). As mentioned in Section 2, the flow over the shelf edg

epth location, is mostly north-south along the topography. It appears 
30 

sense of a first baroclinic mode, showing perhaps that the exchange between the flow on the

slope and the shelf edge is quite complex. 

Figure 15. Vector time series of the currents measured at the shelf edge, in 500 m of water, in the

northwestern Gulf of Mexico. 

Figure 16. Snapshots of altimetry data from AVISO, which explain the observed current events in

Figure 15. 

Figure 17 shows time series of total speed (top panel), high frequency speeds (periods less 

than 40 hours, middle panel) and total and high-pass vertically averaged kinetic energy. Figure 

18 shows time series of winds at the nearby NDBC station 42002. The middle panel in Figure 17 
31 

clearly sh t the end

of July 2005 due to t g area on

July 20. High frequen a inertial

motions lasted for about 10 days, until th e to 50% to 

the total kinetic energy. Other minor high frequency events occur between January and April and 

seem to be related with northern wind events (“Nortes”) as Figure 18 shows. The one occurring 

in April is interesting since it is slightly more energetic at about 200 m depth than at the surface. 

The full speed time series (Figure 17 top panel) depicts the complicated and highly variable 

structure of the flow. Worth noticing again is perhaps the last part of the record (September 

onwards) which shows the initial intensification of the flow at the bottom.

ows the generation of high frequency motion and its downward propagation a

he presence of hurricane Emily which crossed over near the moorin

cy kinetic energy (Figure 17 lower panel) shows that near and supr

e beginning of August and contributed clos

Figure 17. Time series of total speed vs depth (top), speed of high-pass velocity 

series (middle), and time series of total (red) and high-frequency

(black) kinetic energy for mooring MMS1. Speeds in m/s and kinetic 

energy in (m2/s2). 
Figure 18. Wind speed (top panel) and vector time series (lower panel) at NDBC station 42002

located at 25.79° N 93.67° W. The red curve on the top panel is the 12 hour running

mean. 

Figure 19 shows total (blue) and high-pass (red) temperature anomalies at 435 m (from the

ADCP’s thermometer, top panel). Lower panel is the absolute sea level obtained from linearly 

interpolating the AVISO data to the mooring position. Notice the lack of correlation between

bottom temperature and sea level. For example, during February 2005 while the flow is 

southward (cyclone C1-C2, Figures 15 and 16) and sea level is low, the temperature actually 

increases. Similarly, sea level increases from April to July and temperature basically ju t

fl

hurricane E

during Octob

s

uctuates. High frequency temperature fluctuations occur during high winds and clearly during

mily but also at other times when wind forcing is not particularly strong, such as

er 2005.

32 
Figure 19. Total (blue) and high-pass (red) temperature 

anomalies at 435 m (from the ADCP’s

thermometer) (top panel). Absolute sea level 

obtained from linearly interpolating the AVISO

data to the mooring position (lower panel). 

4.2.2. Flow Over the Slope 

Three moorings 2, 4 and 5 along the 2000 m isobath were supposed to document along-slope 

variations of the flow, while maintaining some degree of horizontal coherence. The records are 

surprisingly different from each other, with the upper 700 to 1000 m dominated by large events,

and no discernible influence of a surface wind-driven layer. The current pulses in this upper 

layer are large, about one month duration, coherent with depth, although the current vectors tend 

to diminish and rotate with depth. We will examine the relation of these events to the passing

eddies. Beneath, within the lower 1000 m, currents are smaller, only about 5 to 10 cm/s, but with 

very few reversals, so a net flow occurs near the bottom in the form of a steady southerly jet over 

the slope in the fashion of the cyclonic persistent circulation posited to exist at such depths by De 

Haan and Sturges (2005) and other authors. Altimetry data helps again to make sense of

simultaneous different flow directions observed at the three moorings. 

Figures 20, 21, and 22 show vector time series of low-pass filtered currents at different depths 

for moorings 2, 4 and 5 respectively. Currents decrease in the vertical but appear to be relatively

coherent on the top 800-1000 m on moorings 2 and 4 (Figures 20 and 21). Notice vertical 

coherence is less clear on mooring 5 even on the top 400 m, or in other terms, currents at 

mooring 5 in the top 1000 m rotate in the vertical much more than in moorings 2 and 4. 

Going back to Figure 9, one finds that from October to December cyclone C1 is over mooring 

2. Mooring 4 samples the southern rim of C1 and the northern rim of the anticyclone byproduct 

of Titanic. Mooring 5 appears to sample just anticyclonic features either associated with Titanic 

or the arrival of Ulysses. The vector time series in the top layer (0-800 m) agrees with this 

pict nd

nort 3

moorings agree with the presence of re-merged eddy Ulysses. Comparing altimetry with other 

periods the same result applies: flow directions in the moorings are consistent with the features

ure: flow is mostly southward in mooring 1, eastward-southeastward in mooring 4 a

hward-eastward in mooring 5. Similarly, during April and May flow direction in the

33 
34 

ca

ne can see the flow being 

some times in the same sense as the bottom flow e others in the opposite sense. Same thing 

occurs with events on the top 900 m: the flow below 1200 m (but above the bottom) is in the 

same direction as the near surface flow on some occasions but opposite or just different in others. 

The EOF analysis carried out below (see Section 6) clarifies what are the main modes of 

variability and suggests the main mode is quite barotropic. 

Figures 23-25 are similar to Figure 17. They show time series of total speed vs depth (top 

panel), speed of high pass velocity series (middle panel) and (lower panel), time series of total 

(red) and high frequency (black) kinetic energy for mooring MMS2, 4, and 5 respectively in the 

top 400-500 m. Notice color scales are slightly different to highlight events at different 

moorings, but that does not affect their comparison. The total speed plots clearly mark the eddy 

events discussed before and the vertical extent of speeds larger than 40 cm/s which in general are 

at depths shallower than 400 m. All the middle panels, which depict high frequency speeds, show 

the impact of hurricane Emily at the end of July. Notice that moorings 2 and 5 show more high 

frequency fluctuations than mooring 4. Mooring 5 shows an event in April at about 400 m depth. 

Whether this indicates focusing of surface generated inertial energy (Kunze, 1985, 1986) or the 

inertial motions are generated by the eddies alone remains to be determined. Observe that 

besides the high frequency motions generated by hurricane Emily almost all of the energy is 

subinertial at these depths. 

ptured by the altimetry data. The fact that these two different data sets (moorings and 

altimetry) agree, at least qualitatively, is quite encouraging. 

Flow at higher depths indicates the persistent along-slope southward flow near the bottom, 

being particularly strong in moorings 2 and 5 and less at mooring 4. This suggests not a different 

regime at mooring 4, just that we did not capture the core of the bottom current there. It is 

difficult to establish a pattern for the behavior of currents between the bottom and 1200-1400 

meters just looking at the vector time series (Figures 20, 21, and 22). O

som
Figure 20. Vector time series of the currents measured over the slope, in 2,000 m of water, in the 

northwestern Gulf of Mexico, mooring 2. 

Figure 21. Vector time series of the currents measured over the slope, in 2,000 m of water, in the 

northwestern Gulf of Mexico, mooring 4. 

35 
Figure 22. Vector time series of the currents measured over the slope, in 2,000 m of water, in the

northwestern Gulf of Mexico, mooring 5. 

Figure 23. Time series of total speed vs depth (top), speed of high-pass velocity series (middle),

and time series of total (red) and high-frequency (black) kinetic energy for mooring 

MMS2 in the top 400-500 m. Speeds in cm/s and kinetic energy in (m2/s2). 

36 
37 

Figure 24. T ,

a

M

ime series of total speed vs depth (top), speed of high-pass velocity series (middle)

nd time series of total (red) and high-frequency (black) kinetic energy for mooring 

MS4 in the top 400-500 m. Speeds in cm/s and kinetic energy in (m2/s2). 
38 

Figure 25. Time series of total speed vs depth (top), speed of high-pass velocity series (middle), 

and time series of total (red) and high-frequency (black) vertically averaged kinetic 

energy for mooring MMS5 in the top 400-500 m. Speeds in m/s and kinetic energy in

(m2/s2). 

Figures 26 and 27 show speeds, high frequency speeds and their energy contributions at other 

depths for moorings 2 and 5, respectively. The feature to notice here is that there appears to be a 

maximum in the relative contribution of high frequency energy to the total energy at depths 

between 800 and 1200 m. That can be appreciated looking at the size of the black curve relative 

to the red curve in the lower panels of Figures 26 and 27. We mentioned this feature already 

when discussing Figure 6 in Section 3. The other thing worth mentioning is that high frequency 

energy is present throughout the water column in all moorings. This will clearer below, (Section 

5) with the spectral analysis. Figures for mooring 4 are not shown since the mid-depth ADCP 

instrument (measuring between 700-1200 m depth) failed. 

Figures 28, 29, and 30 show standarized times series (i.e. the series are divided by their 

standard deviation) of of sea surface height anomalies and temperatures for moorings 2, 4, and 5 

respectively. In contrast to mooring MMS1 (see Figure 19), temperature variations in the top 800 

meters seem to be highly (above 0.5) correlated with sea surface height anomalies. Between

1200- s the

temperature anom more

mixed, with their sign being opposite to the anomalies above in some cases. Moorings 4 and 5 

1500 m correlations are low although the sign of the anomalies is generally the same a

alies above and those from sea level. Anomalies near the bottom are
39 

capture a strong warming signal at depth during the second half of April 2005 consistent with the

passage of “ re-merged” eddy Ulysses near core region over them (see Figure10). 

Figure 26. Same as Figure 23 for mid-depths 800-1200 m and near-bottom depths

1960-2020 m in mooring MMS2. Notice the higher contribution of highfrequency motions to the total energy at depths between 800 and 1,200

m for which the KE ratio (high pass KE/total KE) is about 25%. 
40 

Figure 27. Same as Figure 25 for mid-depths 800-1200 m and near-bottom depths

2000-2050 m in mooring MMS5. Notice the higher contribution of highfrequency motions to the total energy at depths between 800 and

1200 m. 
Figure 28. Standardized sea surface height anomalies and temperatures at different depths

(indicated by the legend) for mooring MMS1. Series are offset by 5 units to ease

visualization and comparison. Standard deviations, in cm for sea surface height and 

degrees C for temperature, are indicated. Temperature anomalies above 800 m have

correlation coefficients with ssh anomalies higher than 0.5. 

41 
42 

Figure 29. Same as Figure 28 but for mooring MMS4. Notice the strong warming produced by 

the passage of eddy Ulysses during April 2005, which is absent in mooring 2. 
Figure 30. Same as Figure 28 but for mooring 5. Notice the strong warming produced by the 

passage of eddy Ulysses during April 2005, which is absent in mooring 2. 

Figure 31 shows time series of temperature anomalies (blue) and high-pass anomalies (red) at 

around 750 m and 1250 m on moorings 2 and 5. Besides the increase in high frequency 

variations associated with hurricane Emily at the end of July, one can see there are other events 

(e.g. eddy Ulysses in mooring 5 during April) where suprainertial energy increases. Abrupt

temperature variations associated with eddies seem to give rise to larger high frequency 

temperature fluctuations. Notice also that inertial-suprainertial motions related to hurricane

Emily appear to last longer at mooring 5 than at mooring 2 at 1250m.

43 
Figure 31. Total (blue) and high-pass (red) temperature anomalies at around 700 and

1,250 m depth at mooring 2 (first two panels) and mooring 5 (lower two panels). 

Note time series at 700 m on mooring 5 is shorter than the others. Observe

high-frequency fluctuations at 1,250 m associated with Hurricane Emily appear 

to last longer at mooring 5 than at mooring 2. Abrupt temperature changes 

associated with eddies seem to enhance high-frequency variations. 

44 
45 

4.2.3. Abyssal Flow 

Finally, mooring MMS3 depicts the current regime offshore, over the deep gulf. 

Unfortunately the ADCP sampling currents at the near surface (top 500 m) was faulty so the 

analysis is based on currents below 700 m. Figure 32 shows vector time series for this mooring 

for comparison with Figures 20, 21, and 22 (all along the slope). First thing one notices is that 

currents are much more coherent in the vertical than the ones along the slope. The other obvious 

feature is the absence of the persistent southward flow near the bottom. Another singular event 

occurred in March of that year, when a strong, bottom-intensified, southerly current was present 

from 787 m to the bottom, and caused the mooring to sink by more than 70 m, the largest event 

of that kind during the period of measurements. To relate the mooring observations with eddy 

features it is interesting to compare them with the surface geostrophic flow obtained from 

altimetry data which is shown in Figure 33. During September-October there is consistency 

throughout the water column between the surface geostrophic flow and the deeper mooring 

velocities. Figure 9 shows cyclone C1 moving to the west at that time, so the mooring samples 

the western branch of C1 during September and its eastern branch during October. During 

November and December, the surface flow shows the signature of eddy Ulysses over the 

mooring and the flow rotating clockwise. In early November, the deeper flow is quite weak to 

the north above 1000 m and to the south below that depth. As time progresses, the flow rotates 

anticyclonically. At the end of December, southeastward flow is seen at 700 m rotating 

clockwise with depth while the flow at the surface is to the northeast. The rapid changes in flow 

direction in early Febr per mooring currents 

signal the interaction between cy the flow going from 

northeast to northwest very rapidl fied event occurs with currents 

rotating clockwise (south-southwest) while at the surface the flow goes northwest-northeast. In 

the period April-May-June the flow is similar in the whole water column. This is the period 

where “re-merged” eddy Ulysses is over the whole mooring array. The rapid changes seen 

during early May signal the rapid rotation of this eddy (see Figure 11). From July to the end of 

September the surface flow is determined by a cyclonic feature (C5) and the flow rotates 

southwest-southeast. Meanwhile the deeper flow during this period is basically to the northwest 

until the end of September when it starts rotating clockwise. October signals the arrival of eddy 

Vortex. Surface geostrophic flow and mooring currents coincide at the beginning and end of the 

month with flow going north then north-west whilst in the middle of the month the deep flow is 

to the southeast. Note that the flow at a point may rotate cyclonically even when an anticyclone 

is present due to the orientation of the eddy. 

uary 2005, seen both at the surface and at the dee

clone C1-C2 and UlyssesN eddies, with

y. In March the bottom intensi
Figure 32. Vector time series from mooring 3, located at the abyssal GoM at 3,500 m. 

Figure 33. Absolute geostrophic velocity interpolated from AVISO data to the mooring 3 position. 

For comparison with Figure 32 since the mooring lacks near-surface measurements. 

Figure 34 is similar to Figures 26 and 27, and shows time series of total speed (top panel), 

high-pass speeds (middle panel) and total (vertically integrated) kinetic energy (red) and highpass kinetic energy (black) on mooring 3. Similar to the results in moorings 2 and 5 (Figures 26 

and 27) the relative contribution of high-frequency motions to the total energy is larger in the

800-1200 m depth. We see again the signature of hurricane Emily, though this time in the very 

last days o July and first couple of days of August. Besides hurricane Emily one sees again an 

increase in high frequency energy during the winter season probably associated with northern 

wind events and during April when there is a strong warming in the water column associated 

with eddy Ulysses and a northern event (see Figure 35 below and Figure 18). 

46 
Figure 34. Time series of total speed vs depth (top), speed of high-pass velocity series

(middle), and time series of total (red) and high-frequency (black) vertically 

averaged kinetic energy for mooring MMS3 in the 800-1,200 m range and near 

the bottom (3,500-3,600 m). Speeds in m/s and vertically averaged kinetic 

energy in (m2/s2). Note the higher relative contribution of high-pass motions to

total kinetic energy in the 800-1,200 m range, similar to moorings 2, 4, and 5

along the slope, given by the total KE ratio (high-pass KE /total KE vertically 

and time integrated). 

47 
48 

Figure 34. Time series of total speed vs depth (top), speed of high-pass velocity series

(middle), and time series of total (red) and high-frequency (black) vertically

averaged kinetic energy for mooring MMS3 in the 800-1,200 m range and near 

the bottom (3,500-3,600 m). Speeds in m/s and vertically averaged kinetic energy 

in (m2/s2). Note the higher relative contribution of high-pass motions to total kinetic 

energy in the 800-1,200 m range, similar to moorings 2, 4, and 5 along the slope, 

given by the total KE ratio (high-pass KE /total KE vertically and time integrated) 

(continued). 
49 

Figure 35. Standardized sea surface height anomalies and temperatures at different depths

(indicated by the legend) for mooring 3. Series are offset by 5 units to ease

visualization and comparison. Standard deviations, in cm for sea surface height and

degrees C for temperatures, are provided to estimate actual variations. Notice the 

strong warming at the end of April associated with “re-merged” eddy Ulysses. 

Figure 35 shows standardized sea surface height anomalies and temperature anomalies at 

different depths (indicated by the legend). Series are offset 5 units to ease comparison. The main

feature in this plot is the strong warming that occurs at the end of April 2005 in the 1200-2000 m 

depth, although the signal can be detected all the way to the bottom at 3600 m. Comparing 

mooring 3 with moorings 4 and 5 over the slope (Figures 29 and 30) we see that, relative to its 

overall variance, the warming in mooring 3 at 800 m -and probably above that level too- is not as 

strong as the warming at deeper levels, whereas in moorings 4 and 5 the relative warming is 
50 

similar in the 1500-500 m range. In absolute terms, the warming at 800 m is about 1.5 degrees 

whereas below it is of about 0.7 and 0.25 degrees at 1200 m and 1500 m respectively. The event, 

we repeat, is related to the presence of eddy Ulysses over the mooring. Correlation coefficients 

between ssh anomalies and temperature anomalies is higher than 0.7 in the top 4 instruments

(from 800 to 2000 m). Hence cold (warm) anomalies do indicate the presence of cyclones 

(anticyclones). 

To determine when high frequency temperature fluctuations enhance, the next figure shows 

full (blue) and high-pass (red) temperature anomalies at 1200 and 2000 m depth. Besides the

strong high-frequency event during April, notice that there is no clear enhancement of high-pass 

temperature variations associated with hurricane Emily as it occurs in moorings 2 and 5 (see 

Figure 31). Although there too, the effect of the hurricane is clearer in the velocity data rather 

than the temperature data. Overall, comparing Figure 36 with Figure 31, there seems to be less 

high-pass temperature variations at depth in mooring 3 than in moorings 2, 4, and 5. 

Figure 36. Total temperature anomalies (blue) and high-pass anomalies (red) at around

1,200 m and 1,550 m depth. Note the increase of high-frequency fluctuations in

the middle of April 2005. 
51 

5.

To dissect and quantify the spectral content and structure of the variability described in the 

previous section, we first carry out rotary spectral analysis of the velocity vector time series and 

spectral analysis of the temperature data. The spatial structure of the variability is studied using 

Empirical Orthogonal Function analysis in Section 6. 

Rotary cross spectra (Mooers, 1973, Gonella, 1972) are calculated between current 

observations at the same depth on different moorings and between different depths at the same 

mooring. Besides the spectral density at positive and negative frequencies the following plots 

also show internal coherence square, that relate components rotating in the same sense on the 

current series being analyzed, and their phase relation, with negative phase for positive 

frequencies and positive phase for negative frequencies indicating that the input series leads the 

output series by that phase amount. 

Figure 37 shows cross spectra, between two adjacent moorings MMS1 and MMS2 at 50, 250 

and 400 m. Only at 50 m there is some coherence of motions around the inertial frequency, 

which is lost at depth since the inertial energy decreases rapidly with depth on the shallow 

mooring (MMS1) where there is not a discernible inertial peak at the 400 m depth. The vector 

cross spectra analysis shows little coherence in the across shore directions at all depths. Also 

cross spectra between mooring MMS2 and MMS3 at depths of 850, 1350 and 1950 m depth, in 

the across shelf direction, do not show significant coherence at any of the resolved frequency 

bands (Figure 38). 

In the along 2000 m isobath direction there is significant coherence of currents only at the 

1/20 cpd band between moorings MMS2 and MMS5 at depths between 1150 to 1750 m (Figure 

39). The associated phase for this frequency band, ~25 degrees for the negative frequency and ~-

30 degrees for the positive frequency, indicate a signal propagating from mooring MMS2 to 

mo is 

quite plausibl et 

al (2003), when analyzing the transports through Yucatan Channel, with direct observations and 

num rical model simulations, found that both observations and models gave a significant 

coherence only at the 1/20 cpd band when calculating the cross-spectra between the transports 

above and below the 6 0

C isotherm, which they interpreted as possibly the signal of a first 

baroclinic Kelvin wave traveling cyclonically around the gulf trapped to the slope. 

There is significant coherence of currents at subinertial frequencies below 760 meters on the 

deep mooring MMS3 (Figure 40), which was installed at a depth around 3550 m (Figure 3). This 

aspect is also evident on the subinertial EOFs calculated for this mooring and discussed in the 

following section. An interesting feature of the spectra calculated at all depths on the deep 

moorings (>2000 m) is the evidence of a distinguishable inertial peak. 

 SPECTRAL CHARACTERISTICS OF THE VARIABILITY 

oring MMS5, cyclonically around the gulf, with a phase speed of about 1.7 m/s, which 

e for an internal Kelvin wave propagating around the gulf. Interestingly, Candela 

e
Figure 37. Rotary spectra, internal coherence, and phase 

between currents measured at 50, 250, and 400 m on

moorings MMS1 and MMS2. 

52 
53 

7. Rotary spectra, internal coherence, and phase between currents measured at 50, 

250, and 400 

Figure 3

m on moorings MMS1 and MMS2 (continued). 
Figure 38. Rotary spectra, internal coherence, and phase between 

currents measured at 850, 1,350, and 1,950 m on moorings 

MMS2 and MMS3. 

54 
55 

Figure 38. Rotary spectra, internal coherence, and

phase between currents measured at 850,

1,350, and 1,950 m on moorings MMS2 

and MMS3 (continued). 
56 

Figure 39. Rotary spectra, internal coherence, and phase between 

currents measured at 50, 850, 1,350, and 1,950 m on moorings

MMS2 and MMS5. 
Figure 39. Rotary spectra, internal coherence, and phase between

currents measured at 50, 850, 1,350, and 1,950 m on

moorings MMS2 and MMS5 (continued).

57 
58 

Rotary spectra, internal coherence, and 

phase between currents measured at 850 

and 3,550 m on mooring MMS3. 

Figure 40.
59 

6. EMPIRICAL ORTHOGONAL FUNCTION ANALYSIS 

Using Empirical Orthogonal Function (EOF) analysis of the currents in each mooring, one 

can decompose the variance of the currents into vertically coherent patterns that can help 

simplify understanding the behavior of the variability observed on each mooring. 

Depending on the degree of polarization of the current data being analyzed one can either 

arrange the data along independent components (zonal and meridional), maintaining the analysis 

in the real domain, or combine the horizontal currents into a complex vector. For the case when 

the observed currents are not well polarized, the complex arrangement usually results in a more 

compact and clear representation of the patterns. In our present case, the variability ellipses along 

each mooring, shown in Figure 8, indicate that in most of the water column the currents are quite 

circular in nature not showing a strong polarization or a well defined direction of variability. 

Therefore, a complex EOF analysis is preferable. Also to evenly weight current observations in 

the vertical and to take into account the longest measurement interval, currents were linearly 

interpolated to nominal depths using only the longest common time series in each mooring. 

The first two modes of the subinertial currents are shown in Figures 41-45. The first mode 

usually represents more than about 80% of the variability of the currents in the vertical profile at 

each mooring, showing a surface intensified structure at all moorings except at the deep mooring 

MMS3 where there are no measurements above 760 m (Figure 43). The first mode at this 

mooring, which represents 90% of the variability, presents a uniform vertical profile from 760m 

to the bottom. The second modes on all moorings represent around 10% of the variability and 

show, by orthogonality requirements of the method, a structure resembling a first baroclinic 

mode. An interesting aspect is that the subinertial EOF modes, in all of the 5 moorings, do not 

reflect a clear signal of the passage of hurricane Emily over the mooring array. 

The first two modes of the suprainertial currents are shown in Figures 46-50. Between the 

two modes around 50% of the suprainertial variability is taken account for. The spatial vertical 

at all loca

strong atm

and 0 of e winter season, due to excitation of 

inertial motions (Pollard 1970), but also when Loop Current associated eddies (or their remains) 

are in the vicinity of the mooring location, like the presence of eddy Ulysses on April 2005, that 

also excite inertial like motions in the water column. 

structure is quite complicated for the two modes. Contrary to the subinertial modes, what is clear 

tions, is the fact that the suprainertial variability increases both whenever there is a 

ospheric event, like the passage of hurricane Emily over the mooring array on the 19 

 2 July 2005, or strong “Norte” events during th
60 

Figure 41. First two EOF complex modes for the observed subinertial current interpolated at 

regularly spaced vertical levels on mooring MMS1. The upper two panels show the

dimensioned spatial structure of the mode in two equivalent representations, on the 

left, vectors in 3-D space, and on the right, vectors in 2-D with the north-south/eastwest component in the abscissa/ordinate directions and each vector starting at its 

al

com

both and here presented 

with the time evolution of its magnitude and phase. 

corresponding depth. The lower panel shows the time series (also called princip

ponents) of the mode. Since the EOFs are for a complex time series, i.e. u+i*v, 

the spatial structure and principal components are complex 
61 

Figure 41. First two EOF complex modes for the observed subinertial current interpolated at

regularly spaced vertical levels on mooring MMS1. The upper two panels show the 

dimensioned spatial structure of the mode in two equivalent representations, on the 

left, vectors in 3-D space, and on the right, vectors in 2-D with the north-south/eastwest component in the abscissa/ordinate directions and each vector starting at its 

corresponding depth. The lower panel shows the time series (also called principal

components) of the mode. Since the EOFs are for a complex time series, i.e. u+i*v,

both the spatial structure and principal components are complex and here presented

with the time evolution of its magnitude and phase (continued). 
62 

Figure 42. First two EOF complex modes of the subinertial current vertical profile measured on

mooring MMS2. Currents have been linearly interpolated to nominal depths between

50 and 1,950 m every 50 m.
63 

Figure 43. First two EOF complex modes of the subinertial currents measured on mooring MMS3. 

Currents have been linearly interpolated to nominal depths between 750 and 3,550 m

every 100 m.
64 

Figure 44. First two EOF complex modes of the sub-inertial current measured on mooring

MMS4. Currents have been linearly interpolated to nominal depths between 50 and

1,950 m every 50 m. 
65 

Figure 45. First two EOF complex modes of the sub-inertial currents measured on mooring MMS5. 

Currents have been linearly interpolated to nominal depths between 50 and 1,950 m

every 50 m. 
66 

Figure 46. First two complex EOF modes of the supra-inertial currents on mooring MMS1. 
67 

Figure 47. First complex EOF modes of the supra-inertial currents on mooring MMS2. 

Currents have been linearly interpolated to nominal depths between 50 and 1,950

m every 100 m. 
68 

Figure 48. currents on mooring MMS3. 

Currents have been linearly interpolated to nominal depths between 750 and 3,550 m 

every 100 m.

First two complex EOF modes of the supra-inertial
69 

Figure 49. First two complex EOF modes of the supra-inertial currents on mooring MMS4. 

Currents have been linearly interpolated to nominal depths between 50 and 1,950 m

every 100 m.
70 

Figure 50. First two complex EOF modes of the suprainertial currents on mooring MMS5. Currents 

have been linearly interpolated to nominal depths between 50 and 1,950 m every 

100 m. 
71 

 one in 3500 m have two upward looking LR75KHz RDI ADCPs close to 500 m and 

12

° 39.00’ W from May 12, 2003, to August 27, 

20

ustic backscatter intensity. Without the purpose of estimating biomass, in what follows 

we

recorded, from 

Au

nd echo intensity as a function of depth and time. These two figures, made with 

the 

7. MEASUREMENTS OF VERTICAL MOTION OF ZOOPLANKTON 

A well known capability of ADCP measurements is the observation of diel vertical migration 

(there are many many references, see for example Ott, 2005; Luo et al., 2000; Tarling et al., 

2001), it was used since the beginnings of ADCPs (Plueddemann and Pinkel, 1989). Two ADCP 

measurements are significant in relation to the amount of plankton and its vertical migration; the 

echo intensity and the vertical component of velocity. Here we present an analysis, related to 

such capabilities, as a subset of the measurements pertinent to this report. The moorings in 2000 

m and the

00 m below the surface. For completeness, we also include in this analysis measurements from 

the Canekito deployment (at 25° 05.47’ N, 90

04) in 3500 m depth. The novel feature shown with these measurements, given their length, is 

the precise relative timing from surface to 1200 m of the mean diel migration cycle. To our 

knowledge, no other report has shown the timing in the mean cycle for all levels from the surface 

to 1200 m. With a limited amount of measured cycles, given the high variability and noise in the 

data, the different start, intensity, duration and end in the mean upward and downward migration 

phases cannot be established to the precision here shown. 

Multiple studies have dealt with the estimation of zooplankton biomass via the echo intensity 

of echo sounders and ADCPs, which are themselves echo sounders (see for example Weeks et 

al., 1995, Flagg and Smith, 1989, Record and de Young, 2006, Jiang et al, 2007). Following 

clouds of scatterers, shown as bands in the echo intensity profiles vs time graphs, the vertical 

migration speed might also be determined (see for example Tarling et al., 2001). The 

simultaneous measurements of acoustic backscatter intensity and vertical velocity have been 

combined in biomass balance equations (see Record and de Young, 2006, Putzeys and 

Hernández-León, 2005, and their references). In particular, Roe et al (1996) show a method to 

estimate the amount of biomass with the use of simultaneous RDI ADCP and hydrographic data, 

and Jiang et al (2007) made net tows to produce calibration curves between zooplankton biomass 

and aco

 use the raw recorded RDI ADCP echo intensity as a biological-related signal. 

The ADCP measures the velocity of scattering particles relative to the ADCP’s variable 

velocity but, since its vertical velocity is estimated via the pressure gauge, the scatterers’ vertical 

motion relative to the sea surface, which in this case are mostly zooplankton, is easily derived. 

For the observations here considered the corrections, due to ADCP motion, turn out to be 

insignificant for diel migrations; while migrations speeds are order 2/1 cm/s at 300/900 m depth 

the standard deviation of the ADCPs vertical velocity, via its pressure sensor, is order 0.05 cm/s. 

The recordings of the Long Ranger RDI ADCPs where programmed for averages of 18 

‘pings’ evenly distributed during half hour and there where 442 full days 

gust 24, 2004 to November 11, 2005. Figures 51 and 52 show color-coded diagrams of the 

vertical velocity a

aid of the ADCP’s manufacturer software (RD Instruments), are examples of the daily 

regularity. It will be shown how the timing in the migration varies with depth. Near surface 

plankton reaches its maximum velocity in downward migration earlier than deep plankton, and 

vice versa in the upward migration, therefore the nightly shallower stay of zooplankton is longer 

with depth. 
72 

Figure 51. Twenty diel cycles of the vertical velocity (upper frame) and echo intensity (lower frame)

for the RDI 75kHz ADCP moored at a mean depth of 550 m in mooring MMS5. The depth

interval goes from 550 (Range scale 0) to 50 m (Range scale 500) below the surface. 
73 

Figu

surf

fun

7.1 PER TIME SCALE FOR DAILY MIGRATION CYCLES

5 to

the available records averaged over 150 m thick layers as function of time corresponding to the 

e

recognized. They show the well-known correlation of daylight and migration cycles. The

daylight cycle is shown in these figures via the black trace; a function that is larger/lower during

re 52. As in Figure 51, five diel cycles are measured by another RDI 75kHz ADCP in the same

mooring (WG-5), but looking upward from a depth of 1,250 m, showing depths from 1,250 to 

750 m below the surface. 

The analysis here presented first shows how a time axis based on shifting the GMT is 

appropriate for computing the mean diel cycle (Section 7.1). Then the major differences for near 

ace and deep layers are shown (in Section 7.2.). Last, the mean diel cycle is shown as a 

ction of hour of the day and depth (Section 7.3), followed by a discussion (Section 7.4). 

. PRO

In order to produce a low noise signal in vertical velocity time series, we average ADCP bins

20, which are neither too close or far from the ADCP. Figures 53 and 54 show fractions of

mooring WG-5. 

The ADCPs were programmed for recordings of 18 ‘pings’ averaged over half hour. Th

near surface oscillations are more regular than in the 1000 m deep layer. Figures 53 and 54 show 

two examples where diurnal variations in vertical velocity and echo intensity are easily 
74 

and er edge of the disk of the sun is on the horizon. We checked 

our formulas with tables published by the U.S. Naval Observatory 

daylight/night with jumps at sunrise and sunset. We used the conventional definition for sunrise 

sunset; the times when the upp

(http://www.usno.navy.mil/USNO) having a maximum difference in a full year of 1.8 min and a 

dard deviation of less than one min. The sunrise and sunset, which by definition are close to

00 and 18:00 in local times, are for 96o 18.071’ W

stan

06: , the longitude of WG-5, close to 12:00 and 

Figure 53. Time series of the diel cycle in vertical velocity 

race

24:00 GMT (Figures 53 and 54). Echo intensities shown in Figure 54 were vertically averaged in

the same way as the velocities shown in Figure 53. 

averaged over two 150 m thick layers, one near 

surface and the other deep centered at 425 and

1,075 m. The time is in GMT and the black t

indicates the sunlight cycle (see text). 
75 

ification at sunrise and sunset during the

and upward migrations in the near 

is g

roperly average the available individual daily cycles and thus produce a mean cycle, a

smo ides

hou

57) ear surface than in the deep measurements, and 

the am ace than at depth. 

Figure 54. Time series of the diel cycle in echo intensity, in 

similar format than Figure 53. Notice the echo

intens

downward 

surface layer and the intensification during 

daylight in the deep layer signal. 

The timing of migrations is very much phase locked with the sunrise (downward migration) 

and sunset (upward migration) to the point that the daylight length shows when the stack of days 

raphed over the full set of days recorded. Figures 55-57 are from the Canekito data. 

To p

time scale based in the sunrise and sunset times is needed. Using the local time, the mean will 

average on times shifted from the natural reference that sets the cycles, and produce an overothed estimate of the mean cycle. Shifting the first half of the daily cycle so 06:00 coinc

with sunrise in the downward migration phase, and shifting again the second half cycle so 18:00 

rs coincides with the sunset upward migration the alignment is quite clear (Figures 56 and 

. There is a higher degree of regularity in the n

plitude of the velocity cycle is larger in the near surf
76 

Figure 55. Color-coded diagram of the vertical velocity in the near surface layer, as a function of date, 

throughout the Canekito measuring period. There are 473 days and the migrations show the

modulation by the daylight length; shorter in winter, longer in summer. The modulation also 

shows weaker velocities in winter than in summer. 
77 

Figure 56. Vertical velocity as in Figure 55, but using the sunrise/sunset times as

as described in the text and shown in Figures 53 and 54. In comparison 

06:00/18:00

with Figure

55 the alignment is quite evident. 
78 

Figure 57. Vertical velocity in the deep layer, near 1,000 m below the surface, with the 

same sunrise/sunset times as in Figure 56. The deep layer has a weaker

velocity cycle and is less regular than the near surface layer. 

7.2. COMPARISON OF THE EUPHOTIC ZONE AND 1,000 M DEPTH MEAN DIEL 

CYCLES

Having the sunrise (Sr) and sunset (Su) as reference, it is appropriate to define the time axis 

relative to such times. An on purpose over sampled linear interpolation, with a uniform time 

interval of 3 min from 5 hours before sunrise or sunset to 5 hours after, allows to stack all days 

and average them to yield the mean cycle, as shown in Figures 58 and 59. 
79 

Figu . Tw ctio e t an ycle in tica city for the data show ures 5

and (i.e. wo th ers), wit tim def h lative

sun (Sr) su u) blue gre ces or t r-surface (Figu

56) dee gu aye

T tanda via o cal ities e n urface and deep layers are 1.21 and 

0.58 whi ce t iel is ved .29 .37 . T ly accou

for 94% and 59% of the variance in the upper and deep vel refo r ty in

near ace ch r the deep layer. The deep and near ce veloc

cycles show t stes grations at different

zooplankton es ma s dur twi he de

zooplankton has its m um downward motion well after sunrise. In aximu

upward migra pee cu ier pth i ses

T cho siti me series, Fig 4, si var y bstantial 

iffe means. The standard deviations of the f

rface, and 7.5 for the deep layer, but their means are 150 and 106, respectively. Hence, we plot 

the anomalies. 

re 58 o fun ns ar he me diel c ver l velo n in Fig 6

57 , for t 150 m ick lay here h the e axis ined in ours re to

rise and nset (S . The and en tra are f he nea re

and p (Fi re 57) l rs.

he s rd de tions f verti veloc in th ear s

cm/s le on he d cycle remo are 0 and 0 cm/s he dai cycles nt

er le s, the re the egulari the

surf is mu grate than in surfa mean ity

he fa t mi times. In the downward phase, the near surface 

reach the ximum peed ing light before the sunrise, but t ep

axim contrast, the m m

tion s d oc rs earl as de ncrea .

he e

rent

inten es ti as in ure 5

ull series shown in Figure

show milar iabilit

 54 are 5.2 for the near 

but su

d

su
80 

Figu . Fun s dis e a ly in e ho sity fo the sa

form s 58; ed 150 m th yers and 473 days o and w

the a ativ nris d sun Th e een the ne

surf n p la otic highe o ity during da fo ep lay

contrasting the die avior e n ur yer.

F s 58 9 th dis beha fo ll dee r urpos f

this a sis is anifest these differen s a c uo n f d

7.3. EAN L S A H Y A E

Having mo h of the ADCPs used in this section allows splitting the 

functions show F 58 9 in each lev in A s w o ed with a 

verti soluti i.e siz 0 m keep such in this section. Figures 60 and 61 are the 

resul veraging af ear olations; one ep ch l ement of

the A is c e d e vel xed ive he ce, e d in t

with over-sampling as describe e p us se .

re 59 ction shown play th noma the m an ec inten cycle llowing me

at a Figure averag over two ick la r cycles, ith

time

ace a

xis rel

d dee

e to su

yers. N

e an

e the

set.

r ech

e blu

intens

and gr traces

ylight

are for

r the de

arer,

with well-stu d beh in th ear-s face la

igure and 5 show e main tinct vior r sha ow vs p laye s, the p e o

naly to m ces a ontin us fu ction o epth.

M CYC ES A FUNCTION OF OURS OF THE DA ND D PTH

re than 400 days in eac

n in igures and 5 el. S ce the DCP ere pr gramm

cal re on ( ., bin e) of 1 we

t of a ter lin interp in d th, su that the vertica displac

DCP onsid red an ach le is fi relat to t surfa and th secon ime 

d in th revio ction
81 

Figu . Col ed n v locity diel cycle as a ct time ti nrise

sun s in re 5 m. The labe to cor

WG r Ca ito. lor , in c c, a e fra G ies to the 

data from 60 to th ace divid 3 a es dee le

re 60 or-cod mea ertical ve fun ion of , rela ve to su and

set a Figu 8, and depth in l on p is ac ding to the mooring, with

-0 fo nek

0 m

The co

e surf

scale

, and

m/se

ed by

t th

ppli

gap in

to the

me W

p cyc

-0, appl

.
82 

Figure 61. A aly e o nsity as unc of time and d follo e same

uti in 60 color-c d sc ap all .

vert ve ies oop ton at 0 t 00 epth ne m/s≈144 

m/ 00 m/ va th hug mpared with low frequency water mo s. This

also the case for the zooplankton’s peak vertical velocities at 120 ep alue o

cm m/h≈ m/ th e m larger an ng cted w cy wa

motion. 

the os s g t tensit such m iel th verti

displacement function is defined such that partic raje ies w th an cycle

a f on of an ep d en us computed show the vertical positioni

during the daily cycle, of some -weighted zooplankton. Careful interpretation and 

sta nts sh be w h t depth n cy s. E erti loc sured

the ADCP is a weighted m a varie scatters if to eighti

fac er pa e, tu t fl tions the ter ec na ds on

com tion o ope in g t itted ic s l a e si rdn orm

the icles, e of which are passively drifting with the water, othe e t plankt

slip thru wa ig 2a s that eig f n of the zooplankton which 

st ring d ght 00 s a hted u ard ra f 80 hi ame kind 

of fraction found at 100 m es . de om 1100

nom in th mean ech inte a f tion epth, wing th

distrib on as Figure . The ode ale plies to frames

Peak ical locit of z lank 10 o 5 m d s are ar 4 c

h≈35 day, lues at are e co vement is

800 to 0 m d ths; a v f 1

/s≈36 860 day, erefor uch than ythi expe for lo frequen ter

With purp e of howin he in y of ean d cycle e mean cal

les t ctor follo e me velocity as

uncti time d d th. The isplacem ts th ng,

mean

teme ould used ith suc ime- mea cle ach v cal ve ity mea by

ean of large ty of , with d ficult asses w ng

tor p rticl and rbulen uctua in wa . The ho sig l depen a

bina f pr rties cludin he em son igna nd th ze, ha ess and f of

part som rs, lik he zoo on,

ping the ter. F ure 6 show a w hted ractio

ays du ayli at 3 m, ha weig pw mig tion o m, w le the s

 on daylight only migrat 20 m In the ep, fr 900 to m
83 

depth, there is also depth-dependent amplitude of the migration cycle, varying between 20 and

40 m (Figure 62b). 

F 2. Mean vertic sp nt a fined in tex r th ekit . (a ction f

the near-surf d (b) the function for the deep regi

7.4. DISCUSSION ON THE MEASURED DIEL MIGRATIONS FROM NEAR SURFACE 

TO 1,200 M DEPTH

The novel finding of these measurements is about the mean daily cycle in migrations as a 

function of depth, from the surface to 1200 m below. Before the advent of ADCPs, the vertical 

velocities in zooplankton migrating below 500 m were inferred, not measured. These include old 

conflicting inferences, for example: Angel et al (1982) argue that most of the species living at 

and below 1000 m show no diel migration, and Hu (1978) measured differences in stomach 

weight of euphausiids, as deep as 1100 m, inferring nocturnal (shallower) preferred feeding. In 

another examples, Andersen and Sardou (1992) and Andersen et al (1992) measured day to night 

concentrations differences in zooplankton catches by net tows, as deep as 1000 m, and inferred 

vertical excursions. Examples of recent measurements via ADCPs near or deeper than 1000 m 

are the studies of Van Haren (2007) and Kaltenberg et al (2007). The study of Van Haren (2007) 

showed the existence of daily, seasonal and monthly periodicities in ADCPs backscatter strength 

up to 1300 m deep. In the study of Kaltenberg et al (2007) the migration of deep scattering 

igure 6 al di

ace regio

laceme

n an

s de the t, fo e Can

on. 

o data ) the fun or

a b
84 

layers (DSLs) in the Gulf of Mexico, for about 50 diel cycles, are analyzed. There is also

theoretical studies that extend well-known hypothesis applicable in the euphotic zone; Putzeys 

and Hernández-León (2005) mode cle decaying in amplitude and 

without significant time delay up m. We find no single reference 

t e d ents here

presented show me l up 0 .

dee cy o e lock ith unl yc t r-stud

migration at depths from 500 m t belo he s ce. measurements raise sev l

que s, a th ) oe down d/u d m on in the deep layers 

and starts d d/e r t near face r? hy th inten

pat in th p nt be ior ve nea ac ? And 3) 

What signal is used for the circadian sync niza at s n 0 able 2 

summarizes e paramet t cycle, in particular the tim the p

mi ns sp It t b ed he ec nten diff e (F s 5 9) is

to lence se th m ctivi whi rsi clin t /shallow 

fauna throughout the daylight phase of the cycle her th ce of

zoo kton.

Table 2 

 

ing Q c Fi ime (w 06:00 Definin rise :0

Defining S t) a mum Migrating Speed Versus D or th nw

d U d Pha of th cle.

D T t M D ard S d at M m U S

l the zooplankton migration cy

to a maximum depth of 1000

hat specifies th mean

an die

iel migration below 600 m depth. The velocity m

cycles

easurem

to 120 m depth

The p diel cle sh ws to b phase ed w the s ight c le, as is he bette ied

o just w t urfa The era

stion mong em: 1 why d s the war pwar igrati exists 

elaye arlier elative o the sur laye 2) W does e echo sity

tern e dee layer shows so differe hav relati to the r surf e layer

hro tion depth ear 1 00 m? T

som ers of he mean diel ing of eak

gratio eed. migh e argu that t ho i sity erenc igure 8 and 5 due

turbu cau d by e swim ing a ty, ch pe sts/de es for he deep

, rat than e con ntration the

plan

List of the uadrati t of T ith g Sun and 18 0

unse t Maxi epth f e Dow ard

an pwar ses e Cy

epth ime a aximum ownw pee Time aximu pward peed

Meter Hour Min Hour Min

0 5 02 18 50 

100 5 14 18 39 

200 5 27 18 27 

300 5 41 18 16 

400 5 57 18 03 

500 6 13 17 51 

600 6 31 17 38 

700 6 50 17 25 

800 7 10 17 12 

900 7 31 16 58 

1000 7 54 16 44 

1100 8 18 16 29 

1200 8 42 16 14 

In the eu ic z a cue circad sync niz is k to sunl t

cycle, but this cue is questionable at 1000 m d . Bra r e 987 m ear n

do rd ra on 5 h o 10− ⋅ /cm nd et 8 ated that 

at 400 m depth the m u igh iation .3⋅ W/ hes es e prof

of Young et 198 re ten h an inction coefficient (including absorption and 

sca g) o 30 m d t asu nts o arke Kelly (1965). The radiation at depth 

is m y com ed b ue (47 nm avel h i acu r 0 Hz in 

fre cy) t olo r oce wa Ass g er w r

transparency with an extinction coefficient close which has been reported for deep sea 

phot one, main for ian hro ation nown be the igh

epth dne t al (1 ) esti ated a n oon

wnwa diati at 67 m dept f 1.4 12 W 2

, a Young al (19 0) estim

axim m sunl t rad is 2 8 0− cm

2 1 , t e valu and th iles

al ( 0) a consis t wit ext

tterin f ~1/ an he me reme f Cl and

ostl pos y bl light 0±10 of w engt n the v um, o ~6.4 ⋅1 14

quen he c r of less absorption in clea

to 1/50 m

an

,

ters. umin a great ate
85 

value (see among others Bolesta 1997; Capone . 2002; Riccobene et al 2007), these water 

pro rties imply that a flux is close to

2

w f f er r s st th g

d ig a 0 m wit hin ve e

 have eyes designed in relation to the surrounding bioluminescence not the 

l evi es tha w 00 m

ht pl o in vis f f (De n, . T ore, daylight is a 

nable or fo e t ng nchr ation ha in th p

e die le, efined by the measured velocity, has some a tries. For 

le, th xim ed s l del from shallow to deep levels in the downward 

ion th th w gra In wor the ima d wimm

ds occ with tim ing downwards. In addition, during 

e ownward phase, the shallower zooplankton starts earlier, and through the upward phase the 

deeper individuals start earlier, therefore there is a convergence of individuals in both phases. 

The black thin trace in Figure 63 is the cubic fit of the timing in maximum migration speed as a

function of depth. Table 2 lists values of such times. Confidence intervals on the timing of 

maximum migration speed are ±9 and ±14 min at 80% and 95% levels. The extrapolations of 

such timings imply the collapse of migrations at ~2000 m, where the downward and upward 

migrations would occur at the same time; at ~13:00 hs. 

The peak migration speed looked as a function of depth, shows two relative extremes, one at

250 m the other at 1100 m (Figure 64). This is a sign of an increased biological activity at such 

depths, the extreme at 1100 m probably related to deep scattering layers as described by 

Kaltenberg et al (2007). 

et al

pe t noon in subtropical areas the daylight energy 15 10−

W/cm at 1000 m

amplitu

. Even

ible sm

ith a

ll at 10

actor o

0 m co

100 in

pared

ror fo

h anyt

uch e

g abo

imates,

500 m

e dayli

ters. Fishes living 

ht cycle

e is negl

deeper than 1000 m

sunlight (Land, 2000; Warrant, 2000). The genera denc favor t belo 900-10 the

daylig ays n role the ion o ishes nto 1990) heref

questio fact r th riggeri or sy oniz mec nism e dee diel cycle. 

Th l cyc as d slight symme

examp e ma a spe show onger ays

migrat

pw r

an in

urs

e up

less

ard mi

e difference than

tion. other

 when swimm

ds, max spee when s ing

u

th

a

d
86 

Figure 63. sh th issa, the time in rs, tive nrise (Sr) an et (Ss

n th xima in vertic grating ed reac t dif d m, in

ord Th on s trace fit e f M(z) 1 to the

sh s b ts. 

Plot ows, in e absc hou rela to su d suns )

whe e ma al mi spe are hed a ferent epths in

the inate. e thin c tinuou is a of th orm T =a0+a z+a2z2

data own a lack do
87 

F Peak veloc in an cycle, tive own an ve dur

th ward re eep and 5 nea ace P

igure 64. ities the me diel nega during the d ward d positi ing

e up . The are 4 d r-surf ADC s.

89 

8. SUMMARY AND CONCLUSIONS 

The high degree of consistency between the mooring observations and the altimetry data 

clearly indicate that flow variability in the study area is determined by the passage, formation, 

regeneration and dissipation of both cyclonic and anticyclonic eddies. Strong wind events do 

leave their signature (and may even be responsible for the formation of some of these eddies, see 

Donohue et al., 2008) but arrival of LC eddies, eddy-eddy and eddy-topography interactions 

appear to be the key features that explain many of the observations in the sense that every 

notable event can be traced to the presence of an eddy, cyclonic or anticyclonic. 

Figure 65 provides a summary of the main eddy events detected at the moorings showing 

vector time series at 60 meters and around 800 m depth on the different moorings. LC eddies 

Titanic (T), Ulysses (U) and Vortex (V) impacted the mooring area at the beginning, middle part 

and end of the observational record (see Section 4). Cyclones C1 and C4 had very complicated 

histories since their generation, involving several intensification and merging events. They had a 

strong impact on the mooring observations. As discussed in Section 4, during SeptemberOctober 2004, anticyclonic eddy Titanic affected the southern moorings 5 and 4 while cyclone 

C1 was over moorings 2 and 3. Late November marks the arrival of eddy Ulysses which was 

blocked by cyclone C1 and together with cyclone C5 (not shown in this Figure but see Section 4) 

split the eddy in two forming UlyssesS and UlyssesN eddies at the end of December 2004. 

Cyclonic circulation dominated the mooring area during January and February. In March eddy 

UlyssesS moves northward along the slope and UlyssesN stretches to the west so that by April 

the two branches merge again and for the following 7 months (until mid September) this “remerged” eddy Ulysses defines the circulation over the array. Last three months of observations 

are marked by the presence of cyclone C4, the result of several merging events including cyclone 

C1, and the arrival of LC eddy Vortex. 

Temperature time-series are highly coherent with altimetry data and therefore consistent with 

the eddy field (except for mooring 1) as discussed in Section 4. The most dramatic event 

captured by moorings 3, 4 and 5 is the warming associated with eddy Ulysses (“re-merged”) 

which occurred during April 2005, as depicted in Figure 66 which shows temperature 

measurements from the different moorings at around 500 and 800 m depth. The warming 

signatures of LC Titanic and Ulysses at the end of 2004 and the cooling signal associated with 

cyclones can also be identified (see Section 4 for details). 

Topography determines also the basic characteristics of the flow. Currents at mooring 1 on the 

shelf break are highly coherent on the top 300 m and also agree with eddy events when the 

altimetry suggests so. Below that depth, flow variability is different, and its basic dynamics not 

very clear. Mid-depth and near bottom intensified current events occur on this mooring (Section 

4.2.1). Flow along the slope is sampled by moorings 2, 4 and 5. Currents are highly coherent in 

the top 1000-1200 m and show the signature of eddies. But the other feature seen in these 3 

moorings is the southward bottom intensified mean along-slope flow (see Section 4). In contrast 

to other measurements however, there is no clear bottom intensification of the variability, which 

does not suggest the presence of strong topographic Rossby waves seen in other areas of the 

GoM along the slope (e.g. Hamilton, 2007, Oey and Lee, 2002, Rivas et al. 2008). 
90 

Figure 65. Vector time series for the abyssal (mooring 3) and along slope moorings (2, 4, and 5) 

showing LC eddies Titanic (T), Ulysses (U), and Vortex (V), and cyclones C1 and C4 (see 

Section 4). 

Figure 66. Temperature measurements at 500 and 800 m depth 

from all moorings with instruments at those depths. 

Observe the rapid warming event associated with eddy 

Ulysses in moorings 3, 4, and 5 during April 2005. 

On the abyssal plane (mooring 3) the flow is very coherent from 800 m down to the bottom. 

The top ADCP on this mooring failed so there are no near surface observations. Comparison 

with surface geostrophic currents derived form altimetry, we found some eddy events reaching 
91 

all the way to the bottom and some others in which substantial veering of the current must occur 

between the surface and 800 m if one believes the surface geostrophic currents are correct. In 

contrast to along-slope moorings, no persistent southward flow is found on this mooring 

(Section 4, Figure 22). 

High pass filtering the time series shows inertial and supra-inertial oscillations are present 

basically at all depths in the mooring observations. These high frequency motions are excited by 

strong wind events at the surface such as northern-winds or “Nortes” during winter and 

particularly by hurricane Emily which passed over the array on July 19-20 2005. However high 

frequency signals, particularly at depth, also seem highly correlated with eddy events. In some 

cases it may be argued the deep signals perhaps reflect vertical eddy-focusing (Kunze 1985) of 

wind generated inertial energy. But in other cases the high frequency variations just seem to be 

related to the eddies themselves. An interesting result is that all moorings show that the relative 

contribution of inertial and supra-inertial motions to total kinetic energy increases at depths 

between 1000 and 1500 m (see Sections 2 and 4). Whether this is related to eddy focusing of 

wind generated inertial energy or whether it is related to eddy interactions or instabilities remains 

to be found. 

Rotary spectral analysis (Section 5) shows low frequency motions are the most energetic and 

also confirm the ubiquitous presence of inertial and higher frequency motions in all mooring 

sites. However, the analysis does not provide clear evidence of coherent signals among different 

moorings, except for a 20 day period signal between 800-1200 m depth along the slope 

(moorings 2 and 5), suggestive of a baroclinic Kelvin wave (Candela et al 2003); although much 

work still needs to be done to understand the character and details of this signal. There is also 

some coherence between moorings on the inertial frequency band though some times just above 

the significance level and with mixed results depending on the pair of moorings chosen for the 

analysis. 

Strong vertical coherence is however found within each mooring consistent with the visual 

inspection of the vector time series (Section 4). 

Complex Empirical Orthogonal Function analysis of the velocity anomalies carried out at 

each mooring (see Section 6) shows that the first two modes explain nearly 90-99% of the 

variance, with the first mode representing 79% to 90% of the variance and the second mode 

explaining between 5-13%. The vertical structure of the first mode is highly equivalent 

barotropic (i.e. surface intensified but unidirectional) and barotropic at mooring 3 which only 

accounts for currents below 800 m. Orthogonality constraints make the second mode look more 

baroclinic (i.e. with surface directions opposite to deeper ones). This is interesting considering 

that full vector time series at the moorings (Section 4, Figures 20-23) sometimes do show some 

veering of the current with depth. High amplitudes of the principal components associated with 

the vertical vector pattern are related, perhaps not surprisingly, to eddy events (e.g. eddy Ulysses, 

April 2005, just to highlight one the strong ones). In contrast, complex EOF analysis of the highpass velocity fluctuations show that the first two modes explain less than 50% of the variance in 

the inertial-suprainertial band. Vertical structure as well as time dependence (see Section 6) is 

much noisier than more energetic EOFs just described, with substantial vertical veering and 

temporal fluctuations. These modes (their principal components) clearly highlight the periods 

when inertial energy is present and coincide with strong wind-forced events or .the presence of 

eddies. 

The presence of eddies detected by altimetry data provides a clear framework to interpret the 

mooring observations and allows to explain the connection between observed currents at 
92 

different locations. However, such spatial and temporal coherence is very difficult to grasp with 

rotary spectra and horizontal EOF analysis (i.e. EOFs for all mooring data simultaneously): First, 

variability is event-driven and each event, even if it represents a similar feature such as a cyclone 

or anticyclone, varies from one another simply by the movement and orientation of such an eddy 

within the array. Second, this event-driven variability makes it difficult for global methods such 

as spectral analysis and horizontal EOFs, to identify similar eddy patterns in the whole time 

series, when we know each eddy will behave very differently during the record. 

Finally, with regards to the vertical motion of zooplankton discussed in Section 7 the main 

conclusions are: 

The deep diel cycle, near 1000 m below the surface, has slight differences with the better 

known migrations from the surface to 500 m below it. The mean cycle as a function of depth 

shows two relative maxima of vertical velocity: at 250 and 1100 m deep, a sign of localized 

biological control and vertical ecosystem structure. The downward phase of the migration is 

delayed in the deep, relative to the near surface, region. The peak downward velocity at 1100 m 

occurs 164 min after the same event at 250 m. The cycle is nearly symmetric to solar noon, with 

upward peak velocities happening earlier at depth, a pattern expected if the vertical migration 

was triggered by critical light level that reached the greater depth closer to noon. The peak 

upward velocity at 250 m occurs 33 min after sunset, but the same event at 1100 m happens 

earlier; 92 min before sunset. These delays imply that the shallower nightly stay is longer for the 

deep fauna than for the near surface. Although the migration velocities are about one fourth 

smaller at 1075 m relative to the ones at 475 m, the swimming time is during two short pulses in 

the upper layer compared with longer pulses in the deep. The higher echo intensity occurs during 

the swimming periods, regardless of depth or being upward or downward. 
93 

9. REFERENCES 

Andersen, V. and J. Sardou. 1992. The diel migration and vertical distribution of zooplankton 

and micronekton in the Northwestern Mediterranean Sea. 1. Euphausiids, mysids, decapods 

and fishes. J. Plankton Res. 14:1129-1154. 

Andersen, V., J. Sardou, and P. Nival. 1992. The diel migration and vertical distribution of 

zooplankton and micronekton in the Northwestern Mediterranean Sea. 2. Siphonophores, 

hydromedusae and pyrosomids. J. Plankton Res. 14:1155-1169. 

Angel, M.V., P. Hargreaves, P. Kirkpatrick, and P. Domanski. 1982. Low variability in 

planktonic and micronektonic populations at 1,000 m depth in the vicinity of 42°N, 17°W; 

evidence against diel migratory behavior in the majority of species. Biol. Oceanogr. 1:287-

319. 

Bolesta, J.W. 1997. Upper limits to the diffuse neutrino emission from galactic nuclei. Ph.D. 

Thesis, University of Hawaii, Honolulu. 

Bradner H., M. Bartlett, G. Blackinton, J. Clem, D. Karl, J. Learned, A. Lewitus, S. Matsuno, D. 

O'Connor, W. Peatman, M. Reichle, C. Roos, J. Waters, M. Webster, M. Yarbrough. 1987. 

Bioluminescence profile in the deep Pacific Ocean. Deep Sea Research. 34(11):1831-1840. 

Candela, J., S. Tanahara, M. Crepon, B. Barnier, and J. Sheinbaum. 2003. Yucatán Channel 

flow: Observations versus CLIPPER ATL6 and MERCATOR PAM models. J. Geophys. 

Res. 108(C12):3385, doi:10.1029/2003JC001961. 

Capone, A., T. Digaetano, A. Grimaldi, R. Habel, D. Lo Presti, E. Migneco, R. Masullo, F. 

Moro, M. Petruccetti, C. Petta, P. Piattelli, N.Randazzo, G. Riccobene, E. Salusti, P. 

Sapienza, M.Sedita, L. Trasatti, and L. Ursella. 2002. Measurements of light transmission in 

deep sea with the AC9 trasmissometer. Nuclear Instruments and Methods in Physical 

Research. A487:423-434. 

Chassignet, E.P., H.E. Hurlburt, O.M. Smedstad, C.N. Barron, D.S. Ko, R.C. Rhodes, J.F. 

Shriver, A.J. Wallcraft, and R.A. Arnone. 2005. Assessment of data assimilative ocean 

models in the Gulf of Mexico using ocean color. In W. Sturges and A. Lugo-Fernández, eds. 

Circulation in the Gulf of Mexico: Observations and models. AGU Monograph No. 161. Pp. 

87-100. 

Clarke, G.L. and M.G. Kelly. 1965. Measurements of diurnal changes in bioluminescence from 

the sea surface to 2000 meters using a new photometric device. Limnology and Oceanology. 

10:54-76. 

Csanady, G.T. 1979. The birth and death of a warm core ring. J. Geophys. Res. 84:777-780. 

Cushman-Roisin, B., B. Tang, and E.P. Chassignet. 1990. Westward Motion of Mesoscale 

Eddies. J. Phys. Oceanogr. 20:758–768. 
94 

DeHaan, C.J. and W. Sturges. 2005. Deep cyclonic circulation in the Gulf of Mexico. J. Phys. 

Oceanogr. 35(10):1801-1812. 

Denton, E.J. 1990. Light and vision at depths greater than 200m. In Herring P.J., A.K. 

Campbell, M. Whitfield, and L. Maddock, eds. Light and life in the sea. Cambridge 

University Press, Cambridge, MA. Pp. 127-148. 

DiMarco, S.F., R.O. Reid, W.D. Nowlin Jr. 2005. A statistical description of the near-surface 

velocity field from drifters in the Gulf of Mexico. In Sturges, W., and A. Lugo-Fernandez, 

eds. Circulation of the Gulf of Mexico: Observations and Models. Geophysical Monograph 

Series, Volume 161. American Geophysical Union. Pp. 101-110. 

Donohue, K., P. Hamilton, R. Leben, R.Watts, and E. Waddell. 2008. Survey of deepwater 

currents in the northwestern Gulf of Mexico. Volume II: Technical report. U.S. Dept. of the 

Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 

OCS Study MMS 2008-031. 375 pp. 

Elliot, B.A. 1982. Anticyclonic rings in the Gulf of Mexico. J. Phys. Oceanogr. 12:1291-1309. 

Flagg, C.N. and S.L. Smith. 1989. On the use of the acoustic Doppler current profiler to 

measure zooplankton abundance. Deep-Sea Res. 36:455-474. 

Gonella, J. 1972. A rotary-component method for analyzing meteorological and oceanographic 

vector time series. Deep-Sea Res. 19:833–846. 

Hamilton, P. 1990. Deep currents in the Gulf of Mexico. J. Phys. Oceanogr. 20:1087-1104. 

Hamilton, P. 2007. Deep-current variability near the Sigsbee Escarpment in the Gulf of Mexico. 

J. Phys. Oceanogr. 37:708-726. 

Hamilton, P. and A. Lugo-Fernández. 2001. Observations of high speed deep currents in the 

northern Gulf of Mexico. Geophys. Res. Letters. 28(14):2867-2870. 

Hogg, N.G. 1991. Mooring motion corrections revisited. J. Atmos. Oceanic Technol. 

8(2):289-295. 

Hu, V.J.H. 1978. Relationships between vertical migration and diet in four species of 

Euphausiids. Limnology and Oceanography. 23(2):296-306. 

Hurlburt, H. and J.D. Thompson. 1980. A numerical study of loop current intrusions and eddy 

shedding. J. Phys. Oceanogr. 10:1611–1651. 

Hyun, K.H. and P.J. Hogan. 2008. Topographic effects on the path and evolution of loop 

current eddies. J. Geophys. Res., 113, C12026, doi:10.1029/2007JC004155. 

Ichiye, T. 1962. Circulation and water mass distribution in the Gulf of Mexico. Geofis. lnt. 2: 

47-76. 
95 

Itoh, S. and T. Sugimoto. 2001. Numerical experiments on the movement of a warm-core ring 

with the bottom slope of a western boundary. J. Geophys. Res. 106(C11):26,851-26,862. 

Jiang, S., T.D. Dickey, D.K. Steinberg, and L.P. Madin. 2007. Temporal variability of 

zooplankton biomass from ADCP backscatter time series data at the Bermuda Testbed 

Mooring site. Deep-Sea Res. 54(4):608-636. 

Kaltenberg, A.M., D.C. Biggs, and S.F. DiMarco. 2007. Deep scattering layers of the Northern 

Gulf of Mexico observed with a shipboard 38-kHz acoustic Doppler current profiler. Gulf 

Mex. Sci. 25(2):97-102. 

Kunze, E. 1985. Near-inertial wave propagation in geostrophic shear. J. Phys. Oceanogr. 

15:544-565. 

Kunze, E. 1986. The mean and near-inertial velocity fields in a warm-core ring. J. Phys. 

Oceanogr. 16(8):1444-1461. 

Land, M.F. 2000. On the functions of double eyes in midwater animals. Phil. Trans. R. Soc. 

Lond. B. 355:1147-1150. 

Leben, R.R. 2005. Altimeter-derived loop current metrics. In: Sturges, W. and A. LugoFernández, eds. Circulation in the Gulf of Mexico: Observations and models. AGU 

Monograph No. 161. Pp. 181-201. 

Lewis, J.K., A.D. Kirwan, Jr., and G.Z. Forristall. 1989. Evolution of a warm-core ring in the 

Gulf of Mexico: Lagrangian observations. J. Geophys. Res. 94(C6):8163-8178. 

Lohrmann, A., B. Hackett, and L.P. Røed. 1990. High resolution measurements of turbulence, 

velocity and stress using a Pulse-to-Pulse Coherent Sonar. J. Atmos. Oceanic Technol. 7:19-

37. 

Luo, J., P.B. Ortner, D. Forcucci, and S.R. Cummings. 2000. Diel vertical migration of 

zooplankton and mesopelagic fish in the Arabian Sea. Deep-Sea Res. II, 47:1451-1473. 

Maximenko, N.A. and P.P. Niiler. 2004. Hybrid decade-mean global sea level with mesoscale 

resolution. In: N. Saxena, ed. Recent Advances in Marine Science and Technology. 

Honolulu: PACON International. Pp. 55-59. 

Mooers, C.N.K. 1973. A technique for the cross spectrum analysis of pairs of complex-valued 

time series, with emphasis on properties of polarized components and rotational invariants. 

Deep-Sea Res. 20:1129–1141. 

Morey, S.L., J. Zavala-Hidalgo, and J.J. O'Brien. 2005. The seasonal variability of continental 

shelf circulation in the northern and western Gulf of Mexico from a high-resolution 

numerical model. In Sturges, W. and A. Lugo-Fernandez, eds. New developments in the 

circulation of the Gulf of Mexico. Geophys. Mongr. Ser. 161. AGU, Washington, D. C. 

doi:10.1029/161GM16. 
96 

Nof, D. 1999. Strange encounters of eddies with walls. J. Mar. Res. 57:739–761. 

Nowlin, W.D., Jr. and H. J. McLellan. 1967. A characterization of the Gulf of Mexico waters in 

winter. J. Mar. Res. 25:29-59. 

Nowlin, W.D., Jr., D.F. Paskausky, and H.J. McLellan. 1969. Recent dissolved-oxygen 

measurements in the Gulf of Mexico deep waters. J. Mar. Res. 27:39-44. 

Nowlin, W.D., A.E. Jochens, S.F. DiMarco, and R.O. Reid. 2000. Physical oceanography. In: 

Continental Shelf Associates, Inc., ed. Deepwater Gulf of Mexico environmental and 

socioeconomic data search and synthesis. Vol. 1: Narrative report. U.S. Department of the 

Interior, Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 

OCS Study MMS 2000-049. 360 pp. 

Oey, L.-Y. and H.-C. Lee. 2002. Deep eddy energy and topographic Rossby waves in the Gulf 

of Mexico. J. Phys. Oceanogr. 32:3499-3527. 

Ott, M.W. 2005. The accuracy of acoustic vertical velocity measurements: Instrument biases 

and the Zooplankton migration. Cont. Shelf Res. 25(2):243-257. 

Plueddemann, A.J. and R. Pinkel. 1989. Characterization of the pattern of diel migration using 

Doppler sonar. Deep-Sea Res. 36:509-530. 

Pollard, R.T. 1970. On the generation by wind of inertial waves in the ocean. J. Mar. Res. 

17:795-812. 

Putzeys, S. and S. Hernández-León. 2005. A model of zooplankton diel vertical migration off 

the Canary Islands: Implication for active carbon flux. J. of Sea Res. 53:213-222. 

RD Instruments. 1998. ADCP coordinate transformations. formulas and calculations. RDI Tech. 

Manual P/N 951-6079-00. 26 pp. 

Record, N.R. and B. de Young. 2006. Patterns of diel vertical migration of zooplankton in 

acoustic Doppler velocity and backscatter data on the Newfoundland Shelf. Can. J. Fish. 

Aquat. Sci. 63:2708-2721. 

Ricobenne, G., A. Capone, S. Aiello, M. Ambriola, F. Ameli, I. Amore, M. Anghinolfi, A. 

Anzalone, C. Avanzini, G. Barbarino, E. Barbarito, M. Battaglieri, R. Bellotti, N. Beverini, 

M. Bonori, B. Bouhadef, M. Brescia, G. Cacopardo, F. Cafagna, L. Caponetto, 2007. Deep 

seawater inherent optical properties in the Southern Ionian Sea. Astroparticle Physics. 27:1-

9. 

Rivas, D., A. Badan and J. Ochoa. 2005. The ventilation of the deep Gulf of Mexico. J. Phys. 

Oceanogr. 35:1763-1781. 

Rivas, D., A. Badan, J. Sheinbaum, J. Ochoa, and J. Candela. 2008. Vertical velocity and 

vertical heat flux observed within loop current eddies in the Central Gulf of Mexico. J. Phys. 

Oceanogr. 38:2461-2481. 
97 

Roe, H.S.J., G. Griffiths, M. Hartman, and N. Crisp. 1996. Variability in biological distributions 

and hydrography from concurrent Acoustic Doppler Current Profiler and SeaSoar surveys. 

ICES J. of Mar. Sci. 53:131-138. 

Schmitz, W. J., Jr. 2005. Cyclones and westward propagation in the shedding of anticyclonic 

rings from the Loop Current. In: W. Sturges and A. Lugo-Fernández, eds. Circulation in the 

Gulf of Mexico: Observations and models. AGU Monograph No. 161. Pp. 241-261. 

Sturges, W. 1993. The annual cycle of the western boundary current in the Gulf of Mexico. J. 

Geophys. Res. 98(C10):18053-18068. 

Sturges, W. 2005. Deep-water exchange between the Atlantic, Caribbean and Gulf of Mexico. 

In: W. Sturges and A. Lugo-Fernández, eds. Circulation in the Gulf of Mexico: Observations 

and models. AGU Monograph No. 161. Pp. 263-278. 

Sturges, W. and J.P. Blaha. 1976. A western boundary current in the Gulf of Mexico. Science 

192:367-369 

Sturges, W. and R. Leben. 2000. Frequency of ring separations from the Loop Current in the 

Gulf of Mexico: A revised estimate. J. Phys. Oceanogr. 30(7):1814-1819. 

Tarling, G.A., J.B.L. Matthews, P. David, O. Guerin and F. Buchholz, A.J., and R. Pinkel. 2001. 

The swarm dynamics of northern krill (Meganyctiphanes norvegica) and pteropods 

(Cavolinia inflexa) during vertical migration in the Ligurian Sea observed by an acoustic 

Doppler current profiler. Deep-Sea Res. 48:1671-1686. 

Van Haren, H. 2007. Monthly periodicity in acoustic reflections and vertical motions in the 

deep ocean. Geophys. Res. Letters 34:L12603, doi:10.1029/2007GL029947. 

Vidal, V.M.V., F.V. Vidal, A.F. Hernández, E.Meza, and J.M. Pérez-Molero. 1994. Baroclinic 

flows, transports, and kinematic properties in a cyclonic-anticyclonic-cyclonic ring triad in 

the Gulf of Mexico. J. Geophys. Res. 99(C4):7571-7597. 

Vukovich, F.M. 1988. Loop Current Boundary Variations. J. Geophys. Res. 93(C12):15,585-

15,591. 

Vukovich, F.M. 1995. An updated evaluation of the Loop Current's eddy-shedding frequency. 

J. Geophys. Res. 100(C5):8655-8659. 

Vukovich, F.M. 2007. Climatology of ocean features in the Gulf of Mexico using satellite 

remote sensing data. J. Phys. Oceanogr. 37(3):689, doi: 10.1175/JPO2989.1. 

Vukovich, F.M., and B.W. Crissman. 1986. Aspects of warm rings in the Gulf of Mexico. J. 

Geophys. Res. 91(C2):2645-2660. 

Vukovich, F.M. and E. Waddell. 1991. Interaction of a warm ring with the western slope in the 

Gulf of Mexico. J. Phys. Oceanogr. 21(7):1062-1074. 
98 

Warrant, E. 2000. The eyes of deep-sea fishes and the changing nature of visual scenes with 

depth. Phil. Trans. R. Soc. Lond. B. 355:1155-1159. 

Weatherly, G.L., N. Wienders, and A. Romanou. 2005. Intermediate-depth circulation in the 

Gulf of Mexico estimated from direct measurements. In: Sturges, W. and A. LugoFernández, eds. Circulation in the Gulf of Mexico: Observations and models. AGU 

Monograph No. 161. Pp. 315-324. 

Weeks, A.R., G. Griffiths, H. Roe, G. Moore, I. S. Robinson, A. Atkinson, and R. Shreeved. 

1995. The distribution of acoustic backscatter from zooplankton compared with physical 

structure, phytoplankton and radiance during the spring bloom in the Bellingshausen Sea. 

Deep-Sea Res. 42(4-5):997-1019. 

Welsh, S. E. and M. Inoue. 2000. Loop Current rings and the deep circulation in the Gulf of 

Mexico. J. Geophys. Res. 105(C7):16951-16959. 

Young, R.E., E.M. Kampa, S.D. Maynard, F.M. Mencher, and C.F.E. Roper. 1980. 

Counterillumination and the upper depth of midwater animals. Deep-Sea Res. 27:671-691. 

Zavala-Sanson, L., F. Graef, and E. G. Pavía. 1998. Collision of anticyclonic, lens-like eddies 

with a meridional western boundary. J. Geophys. Res. 103(C11):24,881-24,890. 
99 

APPENDIX A. TABLES OF BASIC STATISTICS 

Table A-1 

 

Basic Statistics for Mooring 1. 

Depth mean u std u min u max u mean v std v min v max v MMS # 

of obs 

Sample 

interval 

55 6.8 15.7 -60.2 92.8 8.5 27.6 -72.3 130.9 14481 30

65 6.6 15.7 -54.3 87.5 8.2 27.3 -70.7 119.0 14481 30

75 6.4 15.3 -55.1 70.8 8.2 26.9 -66.8 90.2 14481 30

85 6.2 14.8 -47.2 74.3 8.5 26.5 -67.5 73.1 14481 30

95 6.1 14.4 -45.2 65.3 8.8 26.0 -64.9 74.4 14481 30

105 5.9 14.0 -48.9 68.2 8.7 25.6 -63.9 71.0 14481 30

115 5.6 13.5 -54.8 65.5 8.4 25.4 -71.0 77.7 14481 30

125 5.3 13.0 -49.8 73.9 8.0 25.0 -71.1 79.8 14481 30

135 5.0 5.0 5.0 5.0 5.0 24.6 -63.1 86.0 14481 30

145 4.8 11.9 -35.5 69.2 7.3 24.1 -62.3 70.4 14481 30

155 4.6 11.2 -31.3 62.8 7.3 23.8 -67.9 64.8 14481 30

165 4.5 10.8 -29.3 58.5 7.3 23.6 -75.2 60.6 14481 30

175 4.5 10.5 -28.7 49.4 7.2 23.3 -73.5 59.6 14481 30

185 4.1 10.2 -28.6 50.4 7.0 23.2 -74.9 58.4 14481 30

195 4.0 10.1 -31.5 44.5 6.7 23.1 -71.1 62.8 14481 30

205 3.8 9.8 -40.4 49.0 6.3 22.8 -68.8 57.5 14481 30

215 3.4 9.4 -33.1 42.9 6.1 22.6 -67.6 58.3 14481 30

225 3.1 8.9 -26.3 40.5 5.6 22.3 -62.7 56.9 14481 30

235 2.8 8.6 -26.0 42.3 5.1 22.0 -62.4 59.4 14481 30

245 2.5 8.2 -24.5 47.2 4.5 21.8 -63.0 59.2 14481 30

255 2.1 7.8 -27.0 39.6 4.0 21.4 -61.7 58.8 14481 30

265 1.9 7.4 -32.1 32.8 3.3 20.9 -60.1 55.5 14481 30

275 1.6 7.0 -28.8 28.4 2.7 20.5 -65.6 57.3 14481 30

285 1.4 6.6 -27.8 26.2 2.1 20.0 -63.1 55.7 14481 30

295 1.0 6.4 -25.0 25.5 1.4 19.5 -61.4 56.4 14481 30

305 0.9 6.1 -23.2 26.3 0.8 18.8 -61.7 55.3 14481 30

315 0.6 5.7 -21.4 26.7 0.1 18.1 -61.4 52.9 14481 30

325 0.4 5.5 -22.1 24.0 -0.5 17.4 -61.5 52.9 14481 30

335 0.2 5.2 -22.8 29.8 -1.0 16.7 -58.6 51.6 14481 30

345 0.0 5.0 -25.0 22.5 -1.5 16.0 -58.1 50.9 14481 30

355 -0.2 4.8 -20.2 19.8 -1.9 15.3 -58.0 50.3 14481 30

365 -0.3 4.6 -20.3 19.6 -2.2 14.5 -55.4 50.6 14481 30

375 -0.4 4.5 -19.3 17.8 -2.6 13.8 -52.1 43.1 14481 30

385 -0.6 4.3 -19.3 18.9 -2.8 12.9 -47.4 41.6 14481 30

395 -0.7 4.3 -18.9 17.0 -3.0 12.1 -43.0 39.5 14481 30

405 -0.7 4.1 -17.7 19.2 -3.1 11.1 -41.5 39.4 14481 30

415 -0.7 4.1 -17.6 20.0 -3.3 10.0 -37.8 37.1 14481 30

425 -0.6 4.0 -17.8 14.9 -3.1 8.7 -36.0 31.6 14481 30
100 

Table A-2 

 

Basic Statistics for Mooring 2. 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v 

MMS 

# of 

Obs 

Sample 

Interval 

45 6.0 26.2 -68.0 102.4 -2.4 33.1 -97.9 115.8 21126 30

55 6.0 25.9 -68.8 103.6 -2.1 32.6 -95.8 117.5 21126 30

65 6.0 25.5 -70.3 104.6 -1.6 32.0 -91.4 115.8 21126 30

75 5.9 25.1 -72.0 102.3 -1.3 31.1 -92.1 121.3 21126 30

85 5.6 24.5 -73.6 102.5 -1.1 30.2 -86.5 119.3 21126 30

95 5.3 23.8 -67.7 100.7 -1.0 29.2 -83.7 111.1 21126 30

105 4.9 23.0 -57.8 97.3 -1.2 28.1 -74.5 100.5 21126 30

115 4.5 22.2 -53.3 99.6 -1.3 26.8 -74.7 98.3 21126 30

125 4.1 21.3 -51.7 95.0 -1.5 25.8 -71.0 92.3 21126 30

135 3.8 20.6 -51.3 90.6 -1.7 24.8 -68.5 85.6 21126 30

145 3.5 19.8 -50.6 84.7 -2.0 23.8 -69.6 80.7 21126 30

155 3.2 19.1 -50.3 81.7 -2.4 22.9 -68.4 72.5 21126 30

165 2.8 18.5 -49.1 80.2 -2.6 22.2 -64.8 70.1 21126 30

175 2.6 18.0 -49.9 71.3 -2.8 21.5 -62.2 64.9 21126 30

185 2.4 17.5 -52.4 69.6 -2.9 20.9 -61.1 63.6 21126 30

195 2.2 16.9 -53.8 68.9 -3.1 20.3 -60.6 61.9 21126 30

205 1.9 16.5 -50.8 64.7 -3.1 19.7 -60.5 58.2 21126 30

215 1.7 16.0 -48.8 64.7 -3.1 19.1 -60.9 58.9 21126 30

225 1.6 15.7 -49.1 58.5 -3.2 18.6 -57.3 54.4 21126 30

235 1.4 15.3 -48.4 56.4 -3.3 18.1 -55.2 52.2 21126 30

245 1.3 15.0 -48.4 57.6 -3.4 17.8 -58.2 50.8 21126 30

255 1.2 14.6 -49.2 57.0 -3.4 17.4 -61.3 49.4 21126 30

265 1.1 14.4 -47.3 52.5 -3.5 17.1 -57.0 47.2 21126 30

275 1.1 14.1 -45.6 52.5 -3.5 16.7 -57.7 47.8 21126 30

285 1.0 13.8 -46.7 51.8 -3.7 16.4 -55.5 44.1 21126 30

295 0.8 13.5 -47.5 48.5 -3.7 16.1 -54.7 42.0 21126 30

305 0.7 13.2 -45.3 46.7 -3.6 15.9 -53.6 38.5 21126 30

315 0.7 13.0 -45.4 44.1 -3.6 15.6 -54.3 41.4 21126 30

325 0.6 12.7 -42.8 41.7 -3.5 15.3 -52.5 38.2 21126 30

335 0.6 12.5 -44.5 40.7 -3.4 15.1 -50.4 38.6 21126 30

345 0.5 12.4 -44.8 43.1 -3.5 14.8 -51.1 39.3 21126 30

355 0.5 12.2 -44.3 41.2 -3.5 14.6 -49.6 36.9 21126 30

365 0.5 11.9 -41.2 40.9 -3.5 14.4 -47.7 36.2 21126 30

375 0.4 11.7 -43.8 42.8 -3.5 14.1 -45.6 35.5 21126 30

385 0.3 11.5 -41.3 41.3 -3.5 13.8 -47.5 37.7 21126 30

395 0.3 11.3 -41.5 42.7 -3.5 13.5 -44.6 34.7 21126 30

405 0.2 11.0 -42.8 42.9 -3.5 13.3 -44.4 33.1 21126 30

415 0.2 10.8 -38.9 40.5 -3.4 13.0 -40.8 32.7 21126 30

425 0.1 10.6 -40.2 36.7 -3.4 12.8 -41.7 31.9 21126 30

435 0.1 10.3 -40.3 34.1 -3.4 12.5 -41.8 33.4 21126 30

445 0.1 10.2 -40.4 33.7 -3.4 12.3 -40.6 34.0 21126 30

455 0.1 10.0 -40.4 35.1 -3.3 12.1 -41.0 31.5 21126 30

465 0.0 9.7 -36.1 33.4 -3.4 11.8 -42.4 29.5 21126 30

475 0.0 9.4 -35.2 33.4 -3.3 11.6 -39.3 29.0 21126 30

485 -0.1 9.1 -33.4 32.7 -3.3 11.2 -37.9 28.8 21126 30

495 -0.1 8.6 -35.1 32.4 -3.2 10.6 -37.3 31.1 21126 30
101 

Table A-2 Basic Statistics for Mooring 2 (continued). 

Depth Mean u Std u Min u Max u Mean 

v 

Std v Min v Max v 

MMS 

# of 

Obs 

Sample 

Interval 

732 -0.7 5.6 -24.3 15.8 -2.9 7.0 -30.6 16.1 10562 60

730 -0.8 6.4 -26.1 21.1 -3.2 7.7 -35.1 23.7 21125 30

740 -0.8 6.4 -30.0 20.4 -3.2 7.6 -30.3 23.6 21125 30

750 -0.9 6.2 -28.8 20.9 -3.2 7.5 -34.6 21.8 21125 30

760 -0.9 6.2 -25.9 20.4 -3.2 7.4 -30.8 20.1 21125 30

770 -1.0 6.1 -27.2 19.1 -3.2 7.3 -31.7 19.4 21125 30

780 -1.0 6.0 -26.9 19.5 -3.2 7.3 -31.3 20.3 21125 30

790 -1.1 6.0 -25.4 19.2 -3.1 7.2 -30.4 21.0 21125 30

800 -1.1 5.9 -25.3 22.0 -3.0 7.1 -33.5 21.2 21125 30

810 -1.1 5.9 -24.2 19.6 -3.0 7.1 -30.4 19.5 21125 30

820 -1.1 5.8 -24.9 19.6 -3.1 7.0 -34.3 21.8 21125 30

830 -1.2 5.8 -26.2 20.3 -3.1 7.0 -32.7 19.8 21125 30

840 -1.2 5.8 -27.7 20.1 -3.1 6.9 -32.3 19.0 21125 30

850 -1.2 5.7 -23.5 18.5 -3.1 6.9 -30.8 18.2 21125 30

860 -1.2 5.6 -22.9 20.4 -3.2 6.8 -30.9 19.2 21125 30

870 -1.3 5.6 -25.1 18.0 -3.2 6.8 -29.2 20.2 21125 30

880 -1.3 5.6 -23.8 18.1 -3.2 6.7 -31.2 18.4 21125 30

890 -1.3 5.5 -24.4 18.5 -3.3 6.7 -31.8 17.2 21125 30

900 -1.3 5.5 -23.3 17.8 -3.3 6.6 -32.3 16.7 21125 30

910 -1.4 5.5 -25.9 18.1 -3.3 6.7 -32.0 17.8 21125 30

920 -1.4 5.5 -23.9 17.4 -3.3 6.7 -34.5 17.8 21125 30

930 -1.4 5.4 -23.4 18.4 -3.4 6.7 -34.9 17.8 21125 30

940 -1.5 5.3 -25.4 19.1 -3.4 6.6 -34.4 20.2 21125 30

950 -1.4 5.2 -26.2 19.5 -3.4 6.5 -34.6 17.8 21125 30

960 -1.5 5.2 -27.1 18.8 -3.4 6.5 -33.7 16.0 21125 30

970 -1.5 5.2 -26.1 20.8 -3.4 6.4 -33.3 17.1 21125 30

980 -1.5 5.2 -26.5 17.9 -3.4 6.3 -31.3 16.8 21125 30

990 -1.5 5.2 -26.5 17.3 -3.3 6.3 -30.2 17.8 21125 30

1000 -1.5 5.1 -24.6 18.3 -3.3 6.2 -30.9 16.6 21125 30

1010 -1.6 5.1 -30.0 17.3 -3.3 6.2 -30.8 19.9 21125 30

1020 -1.6 5.1 -25.3 16.4 -3.4 6.1 -31.5 16.7 21125 30

1030 -1.6 5.0 -27.5 16.9 -3.3 6.1 -30.5 16.7 21125 30

1040 -1.6 5.0 -25.9 17.8 -3.3 6.0 -31.4 16.8 21125 30

1050 -1.6 5.0 -25.0 21.1 -3.3 6.0 -27.9 15.5 21125 30

1060 -1.6 4.9 -23.3 21.2 -3.3 5.9 -28.4 15.4 21125 30

1070 -1.6 4.9 -24.2 18.4 -3.3 6.0 -26.5 18.2 21125 30

1080 -1.6 4.8 -21.9 19.6 -3.3 5.8 -27.3 16.4 21125 30

1090 -1.6 4.9 -21.2 17.5 -3.3 5.8 -28.1 15.9 21125 30

1100 -1.7 4.8 -21.8 19.1 -3.3 5.8 -35.5 16.2 21125 30

1110 -1.7 4.8 -21.9 18.1 -3.2 5.7 -29.6 16.4 21125 30

1120 -1.7 4.8 -22.0 18.5 -3.2 5.7 -24.6 15.8 21125 30

1130 -1.7 4.7 -22.1 16.9 -3.2 5.6 -26.0 16.1 21125 30

1140 -1.6 4.6 -22.1 15.1 -3.2 5.6 -25.3 18.1 21125 30

1150 -1.6 4.5 -22.8 17.1 -3.1 5.3 -23.5 17.1 21125 30

1160 -1.7 4.4 -22.8 16.6 -3.0 5.1 -23.3 14.6 21125 30

1170 -1.5 4.4 -25.2 15.4 -3.0 5.1 -22.2 16.7 21125 30
102 

Table A-2 Basic Statistics for Mooring 2 (continued). 

depth mean u std u min u max u mean v std v min v max v MMS # 

of obs 

Sample 

interval 

1544 -2.2 3.5 -16.3 9.2 -3.5 4.0 -24.9 6.2 10562 60

1957 -1.9 3.7 -23.2 22.7 -6.3 5.6 -24.8 16.8 21125 30

1965 -1.9 3.4 -22.5 23.1 -6.3 5.4 -25.1 12.4 21125 30

1973 -1.8 3.3 -22.2 23.7 -6.4 5.3 -26.1 12.5 21125 30

1981 -1.7 3.3 -21.6 23.6 -6.4 5.3 -25.1 11.3 21125 30

1989 -1.6 3.3 -23.0 24.4 -6.5 5.3 -25.4 10.7 21125 30

1997 -1.5 3.3 -23.0 25.7 -6.4 5.2 -25.8 10.0 21125 30

2005 -1.4 3.3 -22.4 25.5 -6.2 5.0 -26.5 9.9 21125 30

2013 -1.2 3.1 -22.5 24.7 -5.7 4.7 -26.6 9.2 21125 30

2021 -0.7 3.0 -20.9 24.2 -4.1 4.4 -24.8 9.5 21125 30

Table A-3 

 

Basic Statistics Mooring for 3. 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v Mms # 

of Obs 

Sample 

Interval 

820 1.1 5.5 -21.9 31.6 0.1 6.3 -18.2 26.9 8862 60

767 1.6 6.8 -28.8 40.8 0.5 8.0 -28.5 32.7 21142 30

777 1.6 6.8 -30.2 41.4 0.5 7.8 -27.6 36.4 21142 30

787 1.5 6.8 -29.3 39.7 0.5 7.8 -27.5 33.6 21142 30

797 1.5 6.7 -27.2 36.9 0.5 7.7 -23.0 32.9 21142 30

807 1.5 6.7 -28.9 35.9 0.5 7.5 -24.0 31.5 21142 30

817 1.4 6.6 -25.3 35.7 0.6 7.5 -22.3 31.5 21142 30

827 1.3 6.6 -27.8 40.1 0.7 7.4 -22.6 32.3 21142 30

837 1.3 6.6 -30.1 36.2 0.7 7.4 -22.0 35.2 21142 30

847 1.2 6.6 -27.4 37.7 0.7 7.3 -23.3 31.6 21142 30

857 1.2 6.6 -26.9 36.9 0.7 7.2 -23.6 32.3 21142 30

867 1.1 6.6 -26.8 39.2 0.7 7.2 -24.7 31.6 21142 30

877 1.0 6.6 -23.9 39.3 0.7 7.1 -23.8 32.7 21142 30

887 1.0 6.5 -24.1 37.3 0.7 7.1 -22.0 34.6 21142 30

897 0.9 6.5 -23.6 36.0 0.8 7.0 -21.2 35.0 21142 30

907 0.9 6.5 -21.3 35.5 0.8 7.0 -21.3 35.7 21142 30

917 0.8 6.4 -20.8 37.8 0.8 6.9 -23.8 33.5 21142 30

927 0.8 6.3 -19.8 36.5 0.8 6.8 -21.0 35.2 21142 30

937 0.8 6.3 -20.4 39.8 0.8 6.7 -20.4 34.3 21142 30

947 0.7 6.3 -21.3 37.8 0.8 6.7 -22.0 34.4 21142 30

957 0.7 6.3 -20.5 38.3 0.8 6.6 -20.9 37.2 21142 30

967 0.6 6.3 -20.3 37.2 0.9 6.5 -20.8 32.9 21142 30

977 0.6 6.3 -21.7 37.2 0.9 6.5 -20.5 32.2 21142 30

987 0.5 6.2 -21.4 36.1 0.9 6.4 -18.8 31.4 21142 30

997 0.4 6.2 -20.6 35.0 0.9 6.5 -20.2 33.0 21142 30

1007 0.4 6.1 -20.2 36.4 0.9 6.5 -18.7 33.0 21142 30

1017 0.4 6.1 -21.0 38.8 0.9 6.4 -20.9 32.7 21142 30

1027 0.4 6.1 -19.0 39.2 0.9 6.4 -23.2 33.3 21142 30

1047 0.3 6.0 -20.4 33.4 0.9 6.2 -19.5 34.6 21142 30
103 

Table A-3 Basic Statistics Mooring for 3. 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS # 

of Obs 

Sample 

Interval 

1057 0.3 6.0 -20.1 33.8 0.9 6.1 -20.6 31.2 21142 30

1067 0.2 5.9 -19.1 35.7 0.9 6.2 -21.6 27.2 21142 30

1077 0.2 5.9 -20.8 33.2 0.9 6.1 -21.7 28.4 21142 30

1087 0.2 5.9 -21.0 34.1 0.9 6.0 -23.3 29.9 21142 30

1097 0.2 5.9 -19.6 36.6 0.9 6.0 -22.6 32.2 21142 30

1107 0.1 5.9 -21.8 33.4 0.9 6.1 -21.9 30.5 21142 30

1117 0.1 5.8 -20.6 35.5 0.9 6.0 -22.1 32.1 21142 30

1127 0.0 5.8 -20.9 28.3 0.9 6.0 -20.3 27.8 21142 30

1137 0.0 5.8 -20.1 30.3 0.8 6.0 -23.6 25.8 21142 30

1147 -0.1 5.8 -20.4 31.0 0.8 6.0 -23.3 27.4 21142 30

1157 -0.1 5.8 -21.2 30.8 0.8 5.9 -23.2 26.1 21142 30

1167 -0.1 5.7 -20.5 32.0 0.8 5.9 -21.3 22.6 21142 30

1177 -0.2 5.7 -23.4 29.7 0.8 5.9 -22.4 24.3 21142 30

1187 -0.2 5.7 -20.4 32.4 0.8 5.8 -21.2 25.1 21142 30

1197 -0.2 5.6 -24.3 31.6 0.7 5.8 -20.8 30.8 21142 30

1207 -0.2 5.5 -21.6 31.2 0.8 5.6 -24.7 26.0 21142 30

1217 -0.2 5.4 -19.2 30.5 0.7 5.5 -20.3 30.7 21142 30

1541 -0.8 4.3 -18.0 15.3 0.7 4.3 -18.5 16.7 10561 60

2048 -0.9 4.7 -19.0 14.9 0.7 4.6 -21.1 16.6 10561 60

2556 -0.6 3.2 -12.2 11.2 0.4 4.1 -10.4 12.8 4640 60

3038 -1.0 5.0 -17.8 16.3 0.8 5.2 -21.0 19.6 10561 60

3510 -1.1 5.5 -19.8 17.0 0.9 5.7 -21.1 20.5 21142 30

3518 -1.1 5.4 -19.4 16.6 0.9 5.6 -22.1 20.1 21142 30

3526 -1.1 5.3 -19.4 16.2 0.9 5.5 -21.1 19.7 21142 30

3534 -1.1 5.2 -18.7 15.9 0.9 5.5 -20.4 19.9 21142 30

3542 -1.0 4.9 -17.7 16.1 0.8 5.2 -19.5 19.8 21142 30

3550 -0.9 4.5 -17.5 15.3 0.7 4.8 -19.9 19.9 21142 30

3558 -0.1 4.5 -18.9 15.5 2.2 4.9 -19.8 20.7 21142 30
104 

Table A-4 

 

Basic Statistics for Mooring 4. 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS# 

of Obs 

Sample 

Interval 

50 12.3 27.7 -109.0 154.0 6.4 20.8 -78.8 104.1 21199 30

60 12.0 27.1 -102.6 158.5 6.1 20.3 -79.4 94.6 21199 30

70 11.7 26.4 -97.8 148.4 6.0 19.7 -73.5 77.8 21199 30

80 11.4 25.6 -91.3 140.8 5.9 19.0 -64.4 74.8 21199 30

90 11.0 24.6 -77.3 144.2 5.7 18.4 -62.9 71.6 21199 30

100 10.6 23.6 -56.6 132.8 5.5 17.7 -63.7 67.0 21199 30

110 10.2 22.5 -48.9 120.8 5.1 17.0 -65.2 62.9 21199 30

120 9.8 21.3 -49.7 111.4 4.9 16.2 -62.8 56.5 21199 30

130 9.2 20.1 -50.9 105.6 4.6 15.6 -55.1 59.3 21199 30

140 8.7 19.1 -42.1 104.5 4.3 14.9 -49.2 50.6 21199 30

150 8.2 18.2 -39.1 98.7 4.0 14.3 -47.7 47.1 21199 30

160 7.6 17.3 -35.1 92.5 3.8 13.7 -45.8 48.0 21199 30

170 7.1 16.3 -35.8 93.7 3.5 13.1 -40.9 46.2 21199 30

180 6.7 15.5 -32.5 90.7 3.2 12.7 -41.3 44.4 21199 30

190 6.3 14.7 -36.0 81.0 2.9 12.2 -40.2 41.4 21199 30

200 5.9 14.0 -33.8 73.6 2.7 11.8 -38.8 41.4 21199 30

210 5.6 13.4 -32.6 67.1 2.5 11.5 -40.1 37.4 21199 30

220 5.4 12.9 -30.9 65.2 2.2 11.2 -38.5 36.5 21199 30

230 5.1 12.5 -30.9 59.0 2.0 10.9 -38.4 34.4 21199 30

240 4.9 12.1 -28.0 56.4 1.9 10.6 -40.9 37.1 21199 30

250 4.7 11.7 -28.2 56.2 1.7 10.5 -40.2 42.7 21199 30

260 4.5 11.3 -30.1 54.0 1.6 10.4 -38.5 45.4 21199 30

270 4.3 11.0 -28.2 50.1 1.5 10.2 -36.3 44.9 21199 30

280 4.2 10.7 -26.5 54.9 1.4 10.1 -37.5 43.6 21199 30

290 4.1 10.4 -26.5 48.3 1.4 9.8 -33.4 39.3 21199 30

300 3.9 10.2 -30.4 46.3 1.3 9.7 -34.0 43.5 21199 30

310 3.8 9.8 -27.4 47.4 1.3 9.5 -36.9 45.1 21199 30

320 3.7 9.6 -24.7 43.7 1.2 9.4 -31.2 47.2 21199 30

330 3.6 9.4 -23.5 44.7 1.1 9.3 -33.4 46.1 21199 30

340 3.4 9.2 -27.0 43.3 1.2 9.2 -33.0 47.2 21199 30

350 3.2 9.1 -25.0 39.6 1.1 9.1 -32.1 48.7 21199 30

360 3.1 8.8 -23.8 39.2 1.1 9.0 -33.9 47.4 21199 30

370 3.0 8.6 -23.5 41.7 1.0 9.0 -31.7 47.1 21199 30

380 2.9 8.4 -24.8 39.2 1.0 8.9 -34.4 44.3 21199 30

390 2.8 8.3 -24.8 38.4 0.9 8.8 -31.5 44.8 21199 30

400 2.8 8.1 -21.9 36.8 0.9 8.8 -31.5 46.6 21199 30

410 2.8 8.0 -22.3 34.1 0.9 8.6 -30.7 38.3 21199 30

420 2.7 8.0 -21.8 34.9 0.8 8.5 -31.3 37.3 21199 30

430 2.7 7.8 -23.9 35.6 0.7 8.5 -31.0 37.4 21199 30

440 2.6 7.8 -24.9 35.6 0.7 8.4 -31.3 33.6 21199 30

450 2.5 7.6 -22.9 34.8 0.6 8.3 -31.6 34.0 21199 30

460 2.4 7.5 -22.7 36.7 0.5 8.2 -30.2 31.5 21199 30

470 2.3 7.3 -22.0 33.8 0.5 8.0 -29.2 30.2 21199 30

480 2.2 7.0 -23.3 31.7 0.3 7.7 -29.2 31.7 21199 30

708 0.5 4.8 -17.3 21.3 -0.4 5.6 -22.5 16.0 10599 60
105 

Table A-4 Basic Statistics for Mooring 4 (continued) 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS# 

of Obs 

Sample 

Interval

1572 -2.1 2.8 -16.1 7.3 -2.3 3.3 -17.6 11.2 10599 60

1941 -0.7 3.1 -13.2 13.7 -1.3 3.0 -12.7 15.9 21199 30

1949 -0.6 3.1 -12.5 14.5 -1.3 2.9 -13.0 15.1 21199 30

1957 -0.5 3.1 -12.5 14.4 -1.2 2.9 -12.3 15.1 21199 30

1965 -0.4 3.2 -12.3 14.4 -1.2 2.9 -12.6 14.9 21199 30

1973 -0.3 3.1 -12.1 13.5 -1.1 2.8 -12.2 14.5 21199 30

1981 -0.1 3.0 -12.3 13.8 -1.0 2.7 -13.4 15.2 21199 30

1989 0.2 2.8 -12.1 11.6 -0.9 2.4 -12.1 14.2 21199 30

T
106 

Table A-5 Basic Statistics for Mooring 5. 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS# 

of Obs 

Sample 

Interval

45 18.1 25.5 -53.9 113.9 10.3 14.6 -48.4 110.2 21239 30

55 18.7 26.0 -43.6 117.2 10.3 14.6 -52.1 108.3 21239 30

65 19.2 26.3 -51.7 108.8 10.3 14.6 -53.3 104.9 21239 30

75 19.3 26.4 -48.1 115.3 10.2 14.6 -60.3 101.5 21239 30

85 19.2 26.2 -38.9 117.2 10.0 14.5 -54.8 89.2 21239 30

95 18.8 25.7 -36.3 111.5 9.6 14.3 -56.1 82.3 21239 30

105 18.3 25.1 -34.4 110.1 9.3 14.0 -53.7 74.7 21239 30

115 17.7 24.2 -32.5 102.5 9.1 13.6 -54.5 68.1 21239 30

125 17.0 23.3 -33.8 95.4 8.8 13.2 -52.6 65.6 21239 30

135 16.4 22.2 -30.6 90.1 8.3 12.7 -53.1 61.5 21239 30

145 15.6 21.2 -30.5 81.6 7.9 12.1 -49.0 57.3 21239 30

155 14.9 20.4 -28.4 82.5 7.4 11.6 -44.6 53.4 21239 30

165 14.3 19.7 -28.0 80.6 7.0 11.2 -40.9 52.4 21239 30

175 13.8 19.1 -28.5 80.9 6.6 11.0 -38.5 52.7 21239 30

185 13.3 18.6 -27.9 78.8 6.2 10.8 -36.2 53.6 21239 30

195 12.8 18.0 -33.5 78.9 6.0 10.6 -33.7 59.4 21239 30

205 12.3 17.6 -26.6 72.3 5.7 10.4 -36.8 60.8 21239 30

215 11.9 17.1 -31.5 72.5 5.4 10.3 -37.2 57.9 21239 30

225 11.6 16.7 -30.8 68.1 5.2 10.3 -36.5 59.5 21239 30

235 11.2 16.3 -32.6 69.6 5.0 10.2 -31.5 58.7 21239 30

245 10.9 15.8 -29.5 65.8 4.7 10.0 -31.1 59.7 21239 30

255 10.6 15.4 -32.0 67.5 4.5 9.8 -32.2 57.0 21239 30

265 10.3 15.1 -33.6 63.7 4.3 9.7 -30.5 59.5 21239 30

275 10.1 14.7 -33.9 69.0 4.1 9.6 -29.9 54.1 21239 30

285 9.8 14.3 -32.2 67.8 4.0 9.4 -27.2 55.6 21239 30

295 9.7 13.9 -30.9 67.4 3.8 9.3 -29.6 49.6 21239 30

305 9.3 13.7 -24.7 61.8 3.7 9.1 -29.2 48.4 21239 30

315 9.1 13.3 -25.6 60.7 3.6 9.0 -27.3 47.9 21239 30

325 8.9 13.0 -26.7 57.1 3.5 8.8 -27.7 49.0 21239 30

335 8.7 12.8 -28.1 52.0 3.4 8.8 -28.9 49.3 21239 30

345 8.5 12.5 -33.3 50.0 3.3 8.6 -33.6 46.2 21239 30

355 8.3 12.2 -31.7 51.7 3.3 8.5 -35.6 45.7 21239 30

365 8.1 12.0 -40.0 53.3 3.2 8.4 -36.5 46.6 21239 30

375 8.0 11.9 -39.7 50.4 3.1 8.4 -38.3 46.8 21239 30

385 7.8 11.7 -38.5 50.2 3.0 8.3 -33.1 45.7 21239 30

395 7.7 11.6 -33.3 50.5 3.0 8.2 -32.0 46.6 21239 30

405 7.5 11.3 -35.1 47.6 2.9 8.2 -31.6 46.0 21239 30

415 7.4 11.1 -28.6 50.2 2.8 8.0 -30.2 46.5 21239 30

425 7.2 10.9 -26.3 46.5 2.7 7.8 -27.3 45.2 21239 30

435 7.1 10.6 -27.5 52.4 2.7 7.6 -23.4 44.8 21239 30

445 6.9 10.4 -26.3 47.0 2.5 7.5 -21.4 42.1 21239 30

455 6.7 10.1 -22.4 47.2 2.4 7.4 -21.4 39.5 21239 30

465 6.6 9.8 -24.4 44.0 2.3 7.3 -23.2 40.4 21239 30

475 6.4 9.6 -21.6 40.8 2.3 7.2 -21.4 38.7 21239 30

485 6.2 9.4 -23.0 41.8 2.1 7.0 -21.3 37.1 21239 30

495 6.1 9.2 -22.4 43.8 2.0 6.9 -25.5 33.9 21239 30

505 5.8 8.9 -19.7 39.8 1.9 6.8 -21.6 33.2 21239 30
107 

Table A-5 Basic Statistics for Mooring 5 (continued). 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS# 

of Obs 

Sample 

Interval

515 5.6 8.7 -22.7 39.2 1.8 6.6 -21.5 31.8 21239 30

525 5.3 8.3 -21.1 37.2 1.6 6.4 -20.8 30.5 21239 30

763 1.6 4.6 -25.8 21.0 0.6 4.5 -20.4 25.6 8613 60

755 2.7 6.5 -32.1 36.0 0.1 5.9 -27.7 31.5 21244 30

765 2.5 6.3 -31.0 27.1 0.0 5.8 -25.6 33.2 21244 30

775 2.5 6.2 -30.6 28.6 0.0 5.7 -26.7 33.6 21244 30

785 2.3 6.2 -29.7 28.0 -0.1 5.7 -26.4 32.8 21244 30

795 2.2 6.2 -27.0 30.8 0.0 5.8 -26.4 30.8 21244 30

805 2.1 6.2 -26.8 29.4 -0.1 5.8 -26.4 26.4 21244 30

815 2.1 6.2 -25.1 30.1 -0.1 5.8 -24.2 26.6 21244 30

825 2.1 6.1 -23.4 28.1 -0.1 5.8 -26.3 24.7 21244 30

835 2.0 6.0 -24.7 27.3 -0.2 5.7 -26.9 26.0 21244 30

845 1.9 6.0 -21.6 25.8 -0.3 5.7 -25.4 26.4 21244 30

855 1.9 5.9 -24.1 25.4 -0.2 5.6 -24.0 27.1 21244 30

865 1.8 5.8 -20.5 30.5 -0.2 5.5 -25.1 28.7 21244 30

875 1.7 5.7 -20.7 29.4 -0.3 5.5 -21.4 26.4 21244 30

885 1.7 5.6 -21.5 25.9 -0.4 5.4 -24.1 26.2 21244 30

895 1.5 5.5 -21.4 24.8 -0.5 5.3 -20.1 25.3 21244 30

905 1.5 5.4 -21.8 22.9 -0.5 5.3 -19.0 27.9 21244 30

915 1.4 5.3 -23.1 22.5 -0.6 5.2 -19.7 26.1 21244 30

925 1.3 5.3 -23.6 21.4 -0.6 5.1 -18.8 22.4 21244 30

935 1.2 5.2 -25.1 21.6 -0.7 5.1 -20.4 21.5 21244 30

945 1.1 5.0 -22.1 20.5 -0.7 5.0 -20.4 21.0 21244 30

955 1.0 4.9 -24.5 20.7 -0.8 4.9 -19.7 21.6 21244 30

965 0.9 4.8 -20.2 19.0 -0.9 4.9 -21.7 24.2 21244 30

975 0.8 4.8 -17.9 19.2 -0.9 4.9 -21.6 20.4 21244 30

985 0.7 4.7 -20.2 19.2 -1.0 4.8 -21.6 20.0 21244 30

995 0.7 4.6 -20.3 18.8 -1.0 4.8 -22.7 20.7 21244 30

1005 0.6 4.5 -18.2 16.2 -1.1 4.7 -22.2 17.8 21244 30

1015 0.5 4.5 -21.1 18.3 -1.1 4.7 -20.0 21.5 21244 30

1025 0.5 4.5 -25.3 18.7 -1.1 4.7 -23.6 17.3 21244 30

1035 0.4 4.4 -18.9 18.2 -1.2 4.7 -23.2 17.4 21244 30

1045 0.4 4.4 -18.8 18.5 -1.3 4.6 -24.2 17.3 21244 30

1055 0.4 4.3 -16.4 18.4 -1.2 4.6 -22.2 19.2 21244 30

1065 0.3 4.3 -16.7 16.0 -1.2 4.6 -22.6 20.8 21244 30

1075 0.3 4.2 -17.3 17.8 -1.2 4.6 -22.0 18.7 21244 30

1085 0.2 4.2 -17.6 19.6 -1.2 4.6 -21.2 20.7 21244 30

1095 0.2 4.3 -18.2 17.8 -1.3 4.6 -21.2 22.7 21244 30

1105 0.1 4.2 -18.3 16.8 -1.3 4.6 -19.3 23.8 21244 30

1115 0.1 4.2 -19.3 17.5 -1.3 4.5 -22.2 20.1 21244 30

1125 0.0 4.2 -17.0 16.8 -1.3 4.5 -19.9 22.6 21244 30

1135 0.0 4.2 -18.4 18.0 -1.3 4.4 -19.2 19.2 21244 30

1145 0.0 4.2 -17.8 15.9 -1.3 4.4 -20.5 18.9 21244 30

1155 -0.1 4.2 -16.7 16.3 -1.3 4.4 -19.6 19.5 21244 30

1165 -0.1 4.2 -18.1 16.8 -1.4 4.4 -19.5 17.7 21244 30

1175 -0.1 4.2 -19.7 18.9 -1.4 4.3 -19.2 17.7 21244 30

1185 -0.1 4.1 -18.9 20.1 -1.4 4.2 -22.2 20.2 21244 30
108 

Table A-5 Basic Statistics for Mooring 5 (continued). 

Depth Mean u Std u Min u Max u Mean v Std v Min v Max v MMS# 

of Obs 

Sample 

Interval

1195 0.0 4.0 -21.0 17.2 -1.4 4.2 -19.8 16.7 21244 30

1205 -0.1 3.9 -20.9 16.6 -1.4 4.1 -19.8 16.3 21244 30

1215 -0.3 3.8 -22.2 15.3 -1.3 3.9 -21.7 15.3 21244 30

1572 -0.4 2.6 -11.4 13.9 -1.5 2.8 -12.5 12.2 10622 60

1998 -0.3 1.8 -9.0 11.2 -2.5 3.1 -18.5 10.6 21244 30

2006 -0.3 1.7 -9.2 12.1 -2.6 3.1 -18.5 10.0 21244 30

2014 -0.2 1.7 -8.9 11.6 -2.6 3.1 -18.5 9.5 21244 30

2022 -0.2 1.6 -8.3 11.7 -2.6 3.1 -18.2 9.0 21244 30

2030 -0.1 1.6 -7.7 11.8 -2.5 3.0 -17.5 8.1 21244 30

2038 0.0 1.5 -7.7 10.3 -2.4 2.9 -17.7 8.1 21244 30

2046 -0.4 1.5 -7.6 10.7 -1.4 2.8 -16.5 7.8 21244 30