bluuebunny/crossref_metadata_2025 huggingface dataset:
Spreading of Labrador Sea Water in the eastern North Atlantic
Authors: Paillet Jérôme , Arhan Michel , McCartney Michael S.
Published: February 2004

The spreading of Labrador Sea Water (LSW) in the eastern North Atlantic south of 55°N is described on the basis of recent, high‐resolution hydrographic lines and using an inverse model of that basin general circulation. The isopycnic “salinity anomaly” relative to a standard θ/S curve is used to detect the main branches and limits of dominant influence of the intermediate water masses. The LSW crosses the Mid‐Atlantic Ridge at latitudes around 50°N with parts spreading farther eastward and southward. One southward pathway along the eastern side of the Mid‐Atlantic‐Ridge stands out as an eastern basin counterpart of the western Atlantic “Deep Western Boundary Current.” An entry into the Bay of Biscay in its northern part is also evidenced with striking similitudes between two data sets from 1974 and 1989–1990. At the southern limit of the LSW extension, in the vicinity of the Azores‐Biscay Rise, a marked front exists basinwide around 1800 m with the more saline Deep Mediterranean Water (DMW). The inverse model velocity field is consistent with most features of the tracer distributions and allows estimation of LSW transports: 6.3±1.2 Sv of LSW with salinities lower than 34.94 cross the 35°W meridian eastward between 44°N and 54°N, one fourth of which recirculates southwestward in the western basin, while another fourth turns northward across 54°N and the remaining half proceeds southward in the eastern basin. The model circulation suggests that DMW results from mixing between eastern basin LSW and the overlying Mediterranean Outflow Water, most probably through double diffusion. We finally describe several mesoscale structures of anomalously high LSW influence south of the LSW‐DMW front, notably one sampled by a RAFOS float. The velocity and potential vorticity fields suggest that these “LSW‐eddies” are formed through baroclinic instability at the LSW‐DMW front.
On the western boundary currents in the Philippine Sea
Authors: Qu Tangdong , Mitsudera Humio , Yamagata Toshio
Published: February 2004

In this study we describe the velocity structure and transport of the North Equatorial Current (NEC), the Kuroshio, and the Mindanao Current )MC( using repeated hydrographic sections near the Philippine coast. A most striking feature of the current system in the region is the undercurrent structure below the surface flow. Both the Luzon Undercurrent and the Mindanao Undercurrent appear to be permanent phenomena. The present data set also provides an estimate of the mean circulation diagram (relative to 1500 dbar) that involves a NEC transport of 41 Sverdrups (Sv), a Kuroshio transport of 14 Sv, and a MC transport of 27 Sv, inducing a mass balance better than 1 Sv within the region enclosed by stations. The circulation diagram is insensitive to vertical displacements of the reference level within the depth range between 1500 and 2500 dbar. Transport fluctuations are, in general, consistent with earlier observations; that is, the NEC and the Kuroshio vary in the same phase with a seasonal signal superimposed with interannual variations, and the transport of the MC is dominated by a quasi‐biennial oscillation. Dynamic height distributions are also examined to explore the dynamics of the current system.
Beam attenuation by microorganisms and detrital particles in the equatorial Pacific
Authors: Chung Sung Pyo , Gardner Wilford D. , Landry Michael R. , Richardson Mary Jo , Walsh Ian D.
Published: February 2004

The transmissometer has been actively used to monitor the variability of particulate matter in the surface ocean. Attenuation due to water (cw) is constant at a given wavelength, so variability in the signal is due primarily to particles (beam cp). Most of the beam cp signal appears to originate from particles <20 μ, which, in the euphotic zone, are most likely to be microorganisms. However, how much of the beam cp (λ = 660 nm) is attributable to any given organism category or the detrital component is poorly known. To answer this question, at least numerical abundances and optical (scattering) cross sections of each category are needed. During the two transect cruises (TT007 and TT011) of the Joint Global Ocean Flux Study (JGOFS) Equatorial Pacific (EqPac) program (12°N–12°S, 140°W), particulate matter attenuation (beam cp) and abundances of four microorganism categories (heterotrophic bacteria, Prochlorococcus, Synechococcus, and small autotrophic eukaryotes) with their forward angle light scattering (FALS) information (flow cytometer) were simultaneously measured from the same water samples. The bulk scattering coefficients of each population and total scattering coefficients (bp) of these four picoplankton populations (bp (PICO)) were calculated and compared with beam cp. In the equatorial Pacific, heterotrophic bacteria and Prochlorococcus were the most significant contributors to the beam c (16 and 7% of beam cp, respectively) via scattering, and autotrophic eukaryotes and Synechococcus were less important contributors (2 and 1%, respectively) in the equatorial Pacific. If absorption was also included, ∼30% of the beam cp could be accounted for by these four populations in the euphotic zone, supporting the argument that a transmissometer at 660 nm is an effective tool in measuring the net biological processes in the open ocean. A rough estimate for the beam cp signal from nonliving detrital particles was also made in surface waters of the region.
Radar‐derived interferometric surface currents and their relationship to subsurface current structure
Authors: Moller Delwyn , Frasier Stephen J. , Porter David L. , McIntosh Robert E.
Published: February 2004

Radar‐derived ocean surface currents are analyzed in conjunction with in situ acoustic Doppler current profiler (ADCP) measurements. The interferometric measurements were collected by an X‐band imaging Doppler radar in a manner analogous to those of along‐track interferometric synthetic aperture radar (ATI‐SAR). While the advent of ATI‐SAR has provided a new, potentially powerful technique for current mapping, the relationship between surface currents and interferometric velocity measurements is not yet clearly understood. This paper presents comparisons between radar‐derived and in situ current measurements. To develop a precise method for estimating the surface current from interferometric measurements, the influence of long wave orbital velocities and the influence of Bragg resonant waves are studied. We find that coupling between the orbital velocity and backscattered power (i.e., the modulation transfer function) can bias surface current estimates, potentially by up to 20 cm s−1 in an upwind viewing orientation. Furthermore, experimental observations verify a cos2n (θ/2) analytical model for the directional spreading of Bragg resonant waves. Extending our analysis to include subsurface currents, case studies are presented under varying environmental conditions for which the vertical current structure changes considerably. Analysis of radar imagery yields both radial surface currents and vector subsurface current estimates derived from long wave dispersion characteristics. Combining these with coincident ADCP measurements yields a vertical profile of current. Using these measurement techniques, we make several observations within the upper meter of the ocean. These profiles reveal the sensitivity of X‐band interferometric measurements to wind‐drift and the near‐surface current structure.
Large structures and temporal change in the Azores Front during the SEMAPHORE experiment
Authors: Tychensky A. , Le Traon P.‐Y. , Hernandez F. , Jourdan D.
Published: February 2004

The Structure des Echanges Mer‐Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) mesoscale experiment took place from July to November 1993 in the northern Canary Basin, where the circulation is dominated by the eastward flowing Azores Current (AC). A large data set was acquired from three hydrographic arrays (phases 1, 2, 3), current meter moorings, surface drifters drogued at 150 m, and 2000 m deep RAFOS floats. The analysis confirmed the large‐scale observations previously made in this region but also provided new insights into fine‐scale dynamics of the AC. The front was observed over the 6‐month period. It was narrow (100 km) and mostly surface intensified (velocities reaching 40–50 cm s−1). Whereas at the beginning of the experiment (phase 1) the AC was mainly zonal with weak oscillations, large meridional meanders were observed from phase 2 until the end of the experiment. They seem to be related to the arrival of two Mediterranean eddies (Meddies), which interacted with the AC [Käse and Zenk, 1996; Tychensky and Carton, this issue]. The front had a deep dynamical signature (down to 2000 m), with a 16–18 sverdrup (Sv) volume transport (0–2000 m depth integrated). The southward recirculation branch of the AC near 22°–23°W [Klein and Siedler, 1989] corresponds to meridional transport of 5–6 Sv. Then, 4.5 Sv of these waters are recirculating westward (along 31°–32°N). Some interesting new oceanographic results were obtained by examining the RAFOS float trajectories over the abyssal plain. The circulation is similar to that observed at the surface, with mean velocities of about 1–3 cm s−1 and eddy kinetic energy <4 cm2 s−2. In agreement with the analysis of current meter data this reveals a significant barotropic component in the Azores‐Madeira flow field of roughly 3–3.5 cm s−1.
Subtidal energetics in the Faroe‐Shetland Channel: Coarse‐grid model experiments
Authors: Oey L.‐Y.
Published: February 2004

This paper compares various forcings that contribute to the regional subtidal energetics of the ocean passageway northwest of Scotland, in the Faroe‐Shetland Channel (FSC), where inflow of warm and saline North Atlantic water mixes with outflow of cold and less‐saline Nordic Sea waters. On the scales resolvable by the (coarse) grid sizes of Δx = Δy = 20 km and 20 vertical sigma layers, changes in currents' energetics caused by wind, Atlantic inflow (doubled), decreased horizontal mixing, surface heat flux, and open‐boundary density specifications were 28, 43, 40, 16, and 5%, respectively, of the kinetic energy of a background quasi‐steady slope current. The subtidal currents were not sensitive to the atmospheric pressure forcing and the surface relaxation to monthly climatology nor to the inclusion of additional (apart from M2) tidal constituents K1, O1, and S2. Wind‐induced motions resulted in transport fluctuations of about 1.5 Sv in the FSC, maximum in winter and minimum in summer, and alongshore and cross‐shore current variances of 0.1 and 0.05 m s−1, respectively, in fair agreement with observations. Spectral peaks at periods of 23–30 hours were found and were shown to correspond to resonant continental shelf waves in the channel.
Coupling of internal waves on the main thermocline to the diurnal surface layer and sea surface temperature during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment
Authors: Walsh E. J. , Pinkel R. , Hagan D. E. , Weller R. A. , Fairall C. W. , Rogers D. P. , Burns S. P. , Baumgartner M.
Published: February 2004

Patterns in sea surface temperature (SST) on 5‐km scales were observed from low‐flying research aircraft on a light wind day during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment. An inverse trend was observed between the SST and the sea surface mean square slope (mss). However, low correlation coefficients indicate that the dominant process causing the spatial variation of SST under these light wind conditions is neither well controlled by the wind speed nor well monitored by the mss. The SST spatial pattern persisted for at least 1 hour and propagated toward the NE at about 1 m s−1, a factor of 1.6 faster than the speed of the surface current. Coupling between internal gravity waves propagating on the seasonal thermocline and the diurnal surface layer is examined as a possible explanation for the observed SST variability in space and time.
WOCE line P1W in the Sea of Okhotsk: 2. CFCs and the formation rate of intermediate water
Authors: Wong C. S. , Matear R. J. , Freeland H. J. , Whitney F. A. , Bychkov A. S.
Published: February 2004

From August 30 to September 21, 1993, temperature, salinity, nutrient, and CFC data were collected along a section starting in the Pacific Ocean near Bussol' Strait in the Kuril Islands, crossing the basin and shelf region of the Sea of Okhotsk, and ending near the coastal town of Okhotsk at the northwest corner of the Sea of Okhotsk (World Ocean Circulation Experiment (WOCE) line P1W). Water on the continental shelf had potential density (σθ) as great as 27.0, with high CFC concentrations and low temperature and salinity. The Sea of Okhotsk Intermediate Water (SOIW) ranging from 26.8 to 27.4 σθ had uniform water properties along isopycnal surfaces that were distinctly different from either the North Pacific Intermediate Water (NPIW) or the shelf water found at the same density. Since the SOIW was colder and fresher than the NPIW, we postulate that SOIW is formed by sinking plumes and diapycnal mixing. Shelf‐derived water (SDW) as dense as 27.0 σθ is formed on the shelf during the winter by cooling and brine rejection during ice formation. Prevailing winds move the SDW off the shelf, where it sinks to an equilibrium depth and subsequently mixes isopycnally with North Pacific Water (NPW) flowing into the Sea of Okhotsk through the Kuril Islands. The observations on the shelf suggest that SDW directly modifies SOIW to 27.0 σθ. Using potential temperature (θ), salinity (S), and CFC data, we calibrated a simple box model to determine the input of SDW into the SOIW. Model results required a minimum of 0.9 Sv (1 Sv = 106 m3 s−1) of SDW in the formation of SOIW and produced a minimum export of 2.7 Sv of SOIW from the Sea of Okhotsk. Our minimum calculated export of SOIW into the North Pacific Ocean makes the Sea of Okhotsk a significant source of the salinity minimum present in the NPIW. Below 27.2 σθ the box model failed because the CFC concentrations of the SDW were too high. This suggests that SDW directly ventilates the SOIW to a maximum of 27.2 σθ. The unique properties of the SOIW below 27.2 σθ must be the result of diapycnal mixing in the Sea of Okhotsk and isopycnal mixing with inflowing NPW.
Short wave damping in the simultaneous presence of a surface film and turbulence
Authors: Milgram Jerome H.
Published: February 2004

Spatial decay rates of short gravity waves and gravity‐capillary waves in the frequency range of 3 to 8 Hz were measured in a laboratory wave tank equipped with a submerged oscillating grid to generate turbulence. Experiments were conducted with: clean fresh water, fresh water with an oleyl alcohol insoluble surfactant surface film, fresh water with a Triton X‐100 soluble surfactant surface film, and with sea water having a surface film of its own natural surfactants. With each material, decay rate tests were conducted with and without turbulence. The principal purpose of the study was to determine the extent to which turbulence modified the wave decay due to the presence of surface films. This is of importance for modeling the energy balance of short sea waves which influence microwave backscattering used for remote sensing of the ocean. The results show that the wave decay rate is equal to the sum of the rates due to surfactant alone and with turbulence alone. It is concluded that the statistically stationary component of the turbulence that exists near the free surface does not significantly modify the decay mechanism associated with the presence of the surfactant.
Characteristics of pack ice stress in the Alaskan Beaufort Sea
Authors: Richter‐Menge J. A. , Elder B. C.
Published: February 2004

Ice stresses in a multiyear floe were continuously monitored over 6 months in the fall‐winter‐spring of 1993–1994. Stresses sensors were installed at sites near the edge and at the center of the floe, which was located in the pack ice of the Alaskan Beaufort Sea. Compressive stresses in the major principal stress component varied significantly among the measurement sites, being of greater magnitude and exhibiting more high‐frequency variations at the edge than at the center of the floe. Maximum compressive stresses, measured at a site 400 m from the edge of the floe, ranged from 100 to 300 kPa. Tensile stresses (maximum of 50 kPa) and the minor principal stress component (±50 kPa) were relatively constant at all measurement sites. A cross‐correlation analysis indicates that the minor principal stress is strongly correlated to changes in the ice temperature. This result suggests that the minor principal stress component provides a good first‐order approximation of thermally induced stresses. Correlation between the major principal stress component and the ice temperature at the center site was also high, but weakened near the edges of the floe where the ice‐motion‐induced stresses became more significant. Attempts to filter the major principal stress signal to separate the thermal and ice‐motion‐induced stresses were unsuccessful. This result implies that the ice‐motion‐induced stresses, distinguished by variations in magnitude of the order of hours, also have a significant low‐frequency content similar to the thermal stresses. These low‐frequency changes occur over a period of days. Seasonal variations in the characteristics of the stress were also evident and are likely to reflect the developing continuity of the pack as the winter season progresses.
Arctic sea ice as a granular plastic
Authors: Overland James E. , McNutt S. Lyn , Salo Sigrid , Groves Joanne , Li Shusun
Published: February 2004

An important consideration in understanding sea ice mechanics is the integration of observed sea ice behavior on a floe neighborhood scale (1–10 km) into ice dynamics on a regional scale O(50 km). We investigate sea ice kinematics from October 1993 through April 1994 using relative motions from 13 drifting buoys with Global Positioning System navigation in a 20‐km array centered on the Sea Ice Mechanics Initiative ice camp, and we compare these motions to synthetic aperture radar (SAR)‐ derived ice velocities over a 100‐ by 500‐km region in the Beaufort Sea. There is excellent correspondence between the deformation of the buoy array and that from the SAR. Inferred ice dynamics from analysis of the two major northerly wind convergence events of the winter are consistent with a granular hardening plastic conceptual model for Beaufort sea ice. Under continued northerly winds the ice from the Alaskan shore to the camp failed in shear and convergence, in a progressive manner away from the coast. The continuum scale O(10 km) is an order of magnitude larger than the grain, i.e., floe, size O(1 km). The ice motion often forms aggregates of 20–200 km separated by narrow (<10 km) shear zones, similar to granular materials. At moderate forcing, i.e., wind stress multiplied by fetch, the ice appears to fail along slip lines that occur at an acute angle to each other and to the direction of the wind forcing, characteristic of a plastic material at critical state. With longer fetch the ice appears to fail in compression, perpendicular to the wind direction. Sea ice appeared to harden on a regional scale after the first event. During the second northerly wind event there was a sea ice breakout toward the west, apparently due to a lack of lateral confining stress. Our observations suggest that the ice floes advect through relatively stationary stress fields, created by the wind forcing and coastal boundaries. For example, while the SAR and advanced very high resolution radiometer images indicated the presence of the shear feature at the same geographic location for nearly a week, buoys would show shearing only for several days as they transited across the region of shear. There is a high correspondence between the major internal ice deformation events and persistent weather patterns on a 3‐ to 5‐day temporal scale. This implies that SAR data collection and analysis for regional sea ice dynamics should be consistent with the wind forcing and have a sampling of less than 3 days.
Influence of coagulation, sedimentation, and grazing by zooplankton on phytoplankton aggregate distributions in aquatic systems
Authors: Boehm Alexandria B. , Grant Stanley B.
Published: February 2004

Phytoplankton growing at the surface of lakes and oceans are removed from the water column by gravitational sedimentation and/or zooplankton grazing. Both of these processes are influenced by the aggregation state of the phytoplankton, which, in turn, may be altered through particle‐particle coagulation. In this study, we present a mathematical analysis of these phenomena in an attempt to better understand the physical and biological factors that control phytoplankton concentrations in aquatic systems. During phytoplankton blooms, grazer concentrations are relatively low, the concentration of phytoplankton in the mixed layer is high, and phytoplankton production at the surface is countered by coagulation and sedimentation. In this case, dynamic scaling theory indicates that the concentration of total phytoplankton aggregates N0 and the volume fraction of phytoplankton N1 should decay as power laws of depth z: N0 ≈ z−γ and N1 ≈ z−ε. The values of the power law exponents γ and ε are determined by the physical and chemical processes responsible for coagulation and sedimentation in a given system. Under nonbloom conditions, the concentration of grazers is relatively high, the phytoplankton concentrations are relatively low, and phytoplankton generated at the surface are quickly transferred to higher‐trophic levels by grazing. In this case, N0 and N1 decay with depth in an approximately exponential fashion. These results suggest that the principle mechanism by which phytoplankton are removed from the water column in natural aquatic systems may be differentiated by the depth evolution of N0 and N1.
Primary production and chlorophyll a in the northwestern Pacific Ocean in summer
Authors: Shiomoto Akihiro , Ishida Yukimasa , Tamaki Mamoru , Yamanaka Yasumasa
Published: February 2004

Primary production was measured in the Western Subarctic Gyre (WSG) and adjacent regions in July 1993 and 1994. The primary production integrated from the surface to the 2% light depth (16–40 m) ranged from 255 to 1198 mg C m−2 d−1 in the WSG. Mean ± standard error (SE) of the primary production was estimated to be 663±86 mg C m−2 d−1 (n = 11) in both years. Chlorophyll a (chl) concentration in the upper 2% light depth ranged from 0.32 to 6.95 μg L−1, and the mean ± SE was calculated to be 1.03±0.15 μg L−1 (n = 44). The mean ± SE of chl standing stock integrated in the upper 2% light depth was calculated to be 28.6±2.9 mg m−2 (n = 11). The mean primary production in the WSG was roughly equal to the values in the adjacent regions, whereas the mean chl concentration and standing stock were about 1.5 times higher in the WSG than in the adjacent regions. In addition, the primary production integrated from the surface to the 0.2% light depth (26–62 m) was estimated in the WSG. The depth‐integrated primary production in the upper 0.2% light depth ranged from 278 to 1397 mg C m−2 d−1, and the mean ± SE was calculated to be 751±94 mg C m−2 d−1. On the basis of recent observations in the summertime Alaskan Gyre (AG), depth‐integrated primary production in the upper 0.2–1.7% light depth (60–80 m) ranged from 290 to 1550 mg C m−2 d−1, and the mean ± SE was calculated to be 642±55 mg C m−2 d−1 (n = 19). Chl concentration in the surface layer reported previously in the AG was about 0.4 μg L−1. There was no substantial difference between the areal primary production in the WSG and AG, whereas the chl concentration in the surface layer was higher in the WSG than in the AG. In addition, primary productivity (primary production per unit of chl) at the surface tended to be lower in the WSG (mean ± SE of 33.4±2.5 μg C (μ chl)−1;n = 11) than in the AG (51.3±5.6 μg C (μg chl)−1 d−1; n = 19). The difference in phytoplankton species composition between the gyres may be related to the differing primary productivity.
South Atlantic Ocean circulation: Simulation experiments with a quasi‐geostrophic model and assimilation of TOPEX/POSEIDON and ERS 1 altimeter data
Authors: Florenchie P. , Verron J.
Published: February 2004

Simulation experiments of South Atlantic Ocean circulations are conducted with a 1/6°, four‐layered, quasi‐geostrophic model. By means of a simple nudging data assimilation procedure along satellite tracks, TOPEX/POSEIDON and ERS 1 altimeter measurements are introduced into the model to control the simulation of the basin‐scale circulation for the period from October 1992 to September 1994. The model circulation appears to be strongly influenced by the introduction of altimeter data, offering a consistent picture of South Atlantic Ocean circulations. Comparisons with observations show that the assimilating model successfully simulates the kinematic behavior of a large number of surface circulation components. The assimilation procedure enables us to produce schematic diagrams of South Atlantic circulation in which patterns ranging from basin‐scale currents to mesoscale eddies are portrayed in a realistic way, with respect to their complexity. The major features of the South Atlantic circulation are described and analyzed, with special emphasis on the Brazil‐Malvinas Confluence region, the Subtropical Gyre with the formation of frontal structures, and the Agulhas Retroflection. The Agulhas eddy‐shedding process has been studied extensively. Fourteen eddies appear to be shed during the 2‐year experiment. Because of their strong surface topographic signature, Agulhas eddies have been tracked continuously during the assimilation experiment as they cross the South Atlantic basin westward. Other effects of the assimilation procedure are shown, such as the intensification of the Subtropical Gyre, the appearance of a strong seasonal cycle in the Brazil Current transport, and the increase of the mean Brazil Current transport. This last result, combined with the westward oriention of the Agulhas eddies' trajectories, leads to a southward transport of mean eddy kinetic energy across 30°S.
Simulation of heat storages and associated heat budgets in the Pacific Ocean: 1. El Niño‐Southern Oscillation timescale
Authors: Auad Guillermo , Miller Arthur J. , White Warren B.
Published: February 2004

We use a primitive equation isopycnal model of the Pacific Ocean to simulate and diagnose the anomalous heat balance on El Niño‐Southern Oscillation, ENSO, timescales associated with heat storage changes observed in the expendable bathythermograph (XBT) data set. We focus on the analysis of the total (diabatic plus adiabatic) and diabatic anomalous heat balances in six areas of the tropical and subtropical North Pacific Ocean in the upper 400 m. The diabatic (i.e., from the model conservation temperature equation) and adiabatic (i.e., from the model mass conservation equation) anomalous heat balances add up to the total anomalous heat balance. We computed the adiabatic/diabatic ratios to infer the relative importance of both contributions in different areas and found that they are smaller than 2.0 in only two regions (western equatorial and central North Pacific). The larger ratios (>2) were found along the corridor where adiabatic anomalies propagate westward in the form of Rossby waves and at the eastern equatorial Pacific. For those areas where the adiabatic/diabatic ratio is higher than about 2 the total anomalous heat balance is dominantly between the temporal change of heat and the three‐dimensional divergence of the heat flux. At the central North Pacific area the total anomalous heat balance is between the temporal changes in anomalous heat, the surface heat flux and the vertical advection of heat. Different ENSO events are not always controlled by the same physical processes in the different areas. In many cases these differences are associated with the relative importance of adiabatic to diabatic processes. For instance, the western equatorial Pacific is controlled in general by diabatic processes, while the eastern equatorial Pacific is dominated by adiabatic physics most of the time.
The changing structure of the upper ocean in the western equatorial Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment
Authors: Inall Mark E. , Richards Kelvin J. , Eldin Gerard
Published: February 2004

As part of the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) the French vessel Le Noroit completed a series of 18 sections from 5°S to 5°N on 156.5°E, using a towed undulating CTD (SeaSoar) and a hull‐mounted acoustic doppler current profiler (ADCP). Here we present results from the cruise. We describe both the mean structures and the response of the upper ocean to changing meteorological conditions in terms of changes in the dynamic and thermodynamic structure over a 10° latitude band and over a period of approximately 70 days. The mean thermal and haline structures were consistent with the ongoing El Niño conditions of 1992–1993. Only between 1°N and 3°N did salinity play a greater role than that of temperature in the mean stratification of the upper 80 m. The zonal currents were weak in the mean but highly variable, correlating significantly in the 0–60 m depth range with the zonal winds. We show that a cyclonic, cold core structure, identified at 2°S around January 9, will heavily influence any heat budget performed there. Meteorological conditions varied dramatically during the experiment, with strong westerlies, strong easterlies, and periods of little wind observed. Throughout these conditions and at all latitudes a diurnal thermal cycle was seen. The maximum depth of the diurnal thermocline varied from 30 to 35 m, being shallower at more southerly latitudes. The near‐surface temperature showed a mean diurnal signal of approximately 0.4°C. The halocline depth also exhibited a diurnal signal of around 17 m, suggesting that salinity stratification plays a role in limiting vertical mixing at all latitudes, and more so in northern latitudes. Thicker barrier layers were found north of the equator; we show that barrier layers thicker than approximately 25 m correspond to significantly reduced entrainment cooling of the mixed layer (0(0.1°C)). The observed spatial and temporal variability is discussed in the context of the analyses made by others within the intensive flux array near 2°S.
Spectral reflectance and absorption of a massive red tide off southern California
Authors: Kahru Mati , Mitchell B. Greg
Published: February 2004

Spectral reflectance and absorption of a massive Lingulodinium (Gonyaulax) polyedra red tide in March 1995 off southern California are compared to a “baseline” of biooptical measurements from the California Cooperative Oceanic Fisheries Investigations. The red tide was characterized by increased absorption and therefore reduced remote sensing reflectance (Rrs) in the 340–400 nm spectral range. The increased ultraviolet absorption was probably caused by mycosporine‐like amino acids in the particulate fraction as well as increased absorption by dissolved organic matter. The chlorophyll a (chl a) specific particulate absorption of the L. polyedra bloom in the visible spectral range remained relatively constant for the chl a range 1–150 mg m−3 indicating accumulation of cells with similar optical characteristics. The difference in the Rrs versus chl a relationship of the red tide and “normal” California Current phytoplankton diminished with increasing wavelength from 340 nm and disappeared at 412 nm. Ratios of Rrs at 340 nm (or 380 nm) and 412 nm (or 443 nm) provided differentiation of the red tide starting at chl a concentration of 1–2 mg m−3. The forthcoming Japanese Global Imager (GLI) satellite sensor has, among others, the 380 nm band. If the signal to noise ratio and atmospheric correction for the 380 nm band are sufficient to retrieve the dynamic range of the water leaving radiance, then it might be possible to differentiate red tides from other phytoplankton blooms with the algorithm described here.
Introduction to special section: Maurice Ewing Symposium on Applications of Trace Substance Measurements to Oceanographic Problems
Authors: Schlosser Peter , Smethie William M. , Toggweiler J. Robert
Published: February 2004

On October 16–20, 1995, a Maurice Ewing Symposium on Applications of Trace Substance Measurements to Oceanographic Problems was held at Biosphere 2 in Oracle, Arizona. The objectives of this symposium were (1) to review the status of tracer methodology for oceanographic research (technological advances and progress in applications), (2) to evaluate the potential of the individual tracers for regional and global studies of water mass formation and circulation in the ocean, and (3) to outline the role of tracers in calibration and improvement of global circulation models.

Trace substances of natural and anthropogenic origin have been used to study circulation and mixing in the ocean for roughly the past 4 decades. In such studies the penetration and subsequent spreading of anthropogenic trace substances released to the ocean are observed and evaluated in terms of flow paths and mean transit and residence times of specific water masses. These studies are basically regional or global dye experiments. Additionally, the radioactive character of several natural tracers is used to determine the mean residence times of deep waters.
On the births of film drops from bubbles bursting on seawater surfaces
Authors: Spiel Donald E.
Published: February 2004

The parameters describing the birth of film droplets originating from bubbles bursting on seawater surfaces are presented. Results are given for bubble sizes Db from 2 to 14.6 mm equivalent volume diameter. It is shown, contrary to earlier reports, that the films of all bubbles with Db up to at least 14.6 mm burst in an orderly manner in which a hole appears at a well‐defined location, usually the film's edge, and propagates from there gathering up the film's mass into a toroidal ring as it progresses. This process is enabled because surface tension provides the force required to sustain the centripetal accelerations. Film drops are created when beads, of sufficient size, form along the length of the toroidal ring and surface tension is insufficient to maintain the centripetal accelerations at these accumulation points. Pieces of the ring break loose and leave the toroidal ring along paths tangential to the bubble's cap. It is shown that only bubbles larger than 2.4 mm diameter can launch film droplets by this means and that this begins when the film has rolled up through an angle of about 31° independent of both bubble size and (theoretically) surface tension. Film drop spray patterns recorded on MgO‐coated cylindrical shells surrounding the burst bubbles yield film drop numbers and trajectories. In addition, film drop size distributions, their speed of launch, and the speed at which the film opens have been determined as a function of bubble size. The droplet sizes cited here are substantially larger than most previous estimates, and with a high probability, these droplets follow downward trajectories which lead them to impact the surface. A strong inference may be drawn that these impacts give birth to secondary droplets that are smaller than their parents and which have upward velocity components.
Component separation of oceanic helium
Authors: Roether Wolfgang , Well Roland , Putzka Alfred , Rüth Christine
Published: February 2004

A new procedure to quantify the components of oceanic helium (“terrigenic” 3He and 4He released from the ocean floor and “tritiugenic” 3He from tritium decay) is described. Terrigenic He and nonatmospheric 3He (i.e., terrigenic and tritiugenic combined) are obtained in terms of measured concentrations of the He isotopes and also of neon (Ne) (which improves the separation considerably), assuming terrigenic He to vanish in the mixed layer. For the subsequent separation of terrigenic and tritiugenic 3He, additional information is required and 3He due to natural tritium represents a complication. The procedure is applied to data from a hydrographic section in the South Atlantic (19°S, 1991) and one in the Eastern Mediterranean (1987). The 1σ data precisions and a systematic error accounting for uncertainties in mixed‐layer He are approximately 0.3%. Sections of the new representations of oceanic He and 3He and comparisons to the nearest classical quantities (i.e., 3He, He) are presented. In the South Atlantic the 3He distribution reflects the hydrographic structure. East of 20°W the average 3He/4He ratio of terrigenic He below 800 m is 4.5±0.8 times the atmospheric ratio, which implies a substantial contribution of crustal He. In the upper waters, tritiugenic 3He (0.5 tritium units, ±20%) is separated from terrigenic 3He. In the Eastern Mediterranean, tritiugenic 3He is quantified throughout the water column in the presence of substantial levels of terrigenic He; the release rate of terrigenic He from the sea floor is found to be 3.1±1.2 1010 atoms m−2 s−1, similar to the rate for continental crust, with a mantle He contribution of 5±1.2% only. Recommendations for future work are to reduce the mentioned systematic error and the uncertainty margins of the He and Ne solubilities and of 3He due to natural tritium.
Radiocarbon variability in the western equatorial Pacific inferred from a high‐resolution coral record from Nauru Island
Authors: Guilderson Thomas P. , Schrag Daniel P. , Kashgarian Michaele , Southon John
Published: February 2004

We have generated a high resolution coral Δ14C record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical Pacific. Prebomb (1947–1956) Δ14C values average −63‰ and have a total range of 30‰. Values begin to increase in 1957, reaching a maximum of 137‰ in mid‐1983. Large interannual variability of up to 80‰ closely follows the El Niño‐Southern Oscillation (ENSO). During each ENSO warm phase, Δ14C values begin to increase, reflecting the reduction of low‐14C water upwelling in the east and the invasion of subtropical water into the western equatorial tropical Pacific. Maximum Δ14C values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical Pacific, whereas the rapid return to more negative Δ14C is in phase with eastern Pacific ENSO indices. The highest‐amplitude excursions occur during the 1965/1966 and 1972/1973 events, when the 14C contrast is highest between the eastern Pacific and subtropics. The 1982/1983 El Niño, although a larger ENSO event, has a lower Δ14C amplitude, reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in Δ14C between thermocline and subtropical surface waters at that time. This coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in Pacific shallow circulation over interannual and decadal timescales.
Baroclinically driven estuarine flow: A perturbation approach
Authors: Driscoll E. A. , Janowitz G. S. , Pietrafesa L. J.
Published: February 2004

The residual circulation and density in a shallow estuary of constant depth and width and flowing at high Rayleigh number (Ra) and small internal Froude number (Fr), based on riverine flow (U∞) and the horizontal density variation, are studied. Criteria under which direct tidal effects on the residual flow can be neglected are established. The effects of varying the bottom boundary condition on the velocity field from free slip to no slip are examined using a linear bottom stress boundary condition. The governing equations are nondimensionalized, expanded in a power series in the small parameter, and the zeroth‐ and first‐order equations governing the density field are solved; these solutions yield the zeroth‐ and first‐order results for the velocity field. The equation governing the density field at lowest order is nonlinear and is solved numerically. The results show that for sufficiently large Ra, the mean transport of salt is balanced by baroclinic advection near the mouth and by horizontal turbulent transport farther upstream. For these large Ra the horizontal structure as well as the vertical structure of the flow is strongly affected by the bottom boundary condition with the salinity disturbances determined under the free‐slip condition extending twice as far upstream as the no‐slip results. For smaller Ra, though still large compared to 1, the mean transport is balanced by horizontal mixing throughout the system, and the bottom boundary condition does not affect the horizontal structure. The penetration distance of oceanic waters, with the internal Fr fixed, increases as Ra increases above 24, reaches a maximum upstream penetration distance of Kh/U∞ when Ra reaches 65, and decreases as Ra increases further. The ratio of entrained oceanic waters to riverine inflow is inversely proportional to the internal Fr to the 2/3 power for very large Ra and becomes proportional to Ra as the latter decreases.
The development of layering, fluxes through double‐diffusive interfaces, and location of hydrothermal sources of brines in the Atlantis II Deep: Red Sea
Authors: Anschutz Pierre , Turner J. S. , Blanc Gérard
Published: February 2004

The brines in the Atlantis II Deep of the Red Sea occur in horizontally uniform, well‐mixed layers, with the hottest and saltiest water at the bottom, separated from the successively cooler and fresher layers above by very sharp vertical temperature and salinity gradients. Data acccumulated over 3 decades are used to test the widely accepted hypothesis that all heat and salt for the brine layers are supplied from below and that the layered brine structure is the result of double diffusion. Using the changes in temperature and salinity in each layer over successive time intervals, one can deduce the corresponding fluxes of heat and salt across the interfaces. It is found that the required flux of salt cannot be sustained by double diffusion alone. An alternative calculation shows that most of the salt in the successively forming upper layers must have been injected directly from the bottom of the deep through one or more vents located above the level of the lowest brine interface. For the bottom layer, however, it is not possible to obtain the observed salinity and temperature changes unless hot saline water is injected directly into that layer and some of the heat and a smaller fraction of the salt are transferred upward through the interface. This process will also maintain convection in each of the layers and keep them well mixed, as is observed. The new interpretation in terms of separate inputs at various levels in the Atlantis II Deep is also supported by recent geochemical evidence.
Spectral analysis of highly aliased sea‐level signals
Authors: Ray Richard D.
Published: February 2004

Observing high‐wavenumber ocean phenomena with a satellite altimeter generally calls for “along‐track” analyses of the data: measurements along a repeating satellite ground track are analyzed in a point‐by‐point fashion, as opposed to spatially averaging data over multiple tracks. The sea‐level aliasing problems encountered in such analyses can be especially challenging. For TOPEX/POSEIDON, all signals with frequency greater than 18 cycles per year (cpy), including both tidal and subdiurnal signals, are folded into the 0–18 cpy band. Because the tidal bands are wider than 18 cpy, residual tidal cusp energy, plus any subdiurnal energy, is capable of corrupting any low‐frequency signal of interest. The practical consequences of this are explored here by using real sea‐level measurements from conventional tide gauges, for which the true oceanographic spectrum is known and to which a simulated “satellite‐measured” spectrum, based on coarsely subsampled data, may be compared. At many locations the spectrum is sufficently red that interannual frequencies remain unaffected. Intra‐annual frequencies, however, must be interpreted with greater caution, and even interannual frequencies can be corrupted if the spectrum is flat. The results also suggest that whenever tides must be estimated directly from the altimetry, response methods of analysis are preferable to harmonic methods, even in nonlinear regimes; this will remain so for the foreseeable future. We concentrate on three example tide gauges: two coastal stations on the Malay Peninsula where the closely aliased K1and Ssa tides are strong and at Canton Island where trapped equatorial waves are aliased.
The effect of included participates on the spectral albedo of sea ice
Authors: Light B. , Eicken H. , Maykut G. A. , Grenfell T. C.
Published: February 2004

Sediments and other participates are often entrained into sea ice formed over shallow shelves in the Arctic, causing significant changes in the albedo of the ice and in the amount of shortwave radiation absorbed and transmitted by the ice. A structural‐optical model was used in conjunction with a four‐stream radiative transfer model to examine the effects of such particulates on the optical properties of sea ice. Albedo data from well‐characterized ice with moderate particulate loading were combined with model calculations to infer a spectral absorption coefficient and effective size for the particulates. Results indicate that sediment particles contained in the ice have an effective radius (R) of ∼9 μm, assuming absorption coefficients similar to those of Saharan dust. With these values, model predictions are in close agreement with spectral albedo observations over a broad range of particulate loading. For particle size distributions commonly observed in sea ice, the calculations indicate that particles with R>30 μm have little effect on the bulk optical properties of the ice. The albedo data also suggest that even apparently “clean” ice contains trace amounts (5–10 g m−3) of particulates that reduce albedos by as much as 5–10% in the visible part of the spectrum. The calculations show that particulates in sea ice primarily affect radiative transfer at visible wavelengths, whereas apparent optical properties in the near‐infrared tend to be governed by ice structure rather than by the presence of particulates. Particle‐bearing layers occurring below ∼20–30 cm are found to have little effect on albedo, although they can still have a substantial effect on transmission. Estimates of total particle loading cannot be obtained from reflectance data without some additional information on particle size, vertical distribution, and ice structure.
Tidal correction of TOPEX/POSEIDON altimetry for seasonal sea surface elevation and current determination off the Pacific coast of Canada
Authors: Foreman M. G. G. , Crawford W. R. , Cherniawsky J. Y. , Gower J. F. R. , Cuypers L. , Ballantyne V. A.
Published: February 2004

Altimetry from the TOPEX/POSEIDON satellite is analyzed for the waters off British Columbia, Canada. Tides are removed using harmonic constants from two coastal and two global models, and the accuracy of this detiding is assessed by using these same models and one digital filter to remove the tide from the time series of three representative coastal tide gauges. It is demonstrated that inaccurate M2, S2, and K1 tide removal from TOPEX/POSEIDON altimetry can introduce systematic biases to the calculation of seasonally averaged fields. Average summer and winter sea surface heights are calculated from the detided altimetry, and estimates of their accuracy nearshore are computed using concurrent time series from 11 tide gauges. Finally, these seasonal elevations are blended with those from the 11 tide gauges, and the associated surface currents are calculated using a diagnostic finite element model. These currents are compared with those calculated from historical conductivity and temperature versus depth measurements and those measured by historical near‐surface current meters.