OCS Study BOEM 2017-062

Arctic Tracer Release Experiment (ARCTREX)

Applications for Mapping Spilled Oil in Arctic Waters

Final Report to the

U.S Department of the Interior Bureau of Ocean Energy Management

Cooperative Agreement No. M13AC00008

Peter Winsor1 pwinsor@alaska.edu

Harper Simmons1 hlsimmoins@alaska.edu

Robert Chant2 chant@marine.rutgers.edu

1

Institute of Marine Science 2Institute of Coastal and Marine Science

College of Fisheries and Ocean Sciences Rutgers University

University of Alaska Fairbanks 71 Dudley Rd, New Brunswick, NJ 08901

2150 Koyukuk Dr., Fairbanks, AK 99775 848.932.3348 (office)

907.474.7740 (office)

907.474.7204 (fax)
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Arctic Tracer Release Experiment (ARCTREX)

Applications for Mapping Spilled Oil in Arctic Waters 

This collaboration between

the U.S. Department of the Interior Bureau of Ocean Energy Management,

the University of Alaska Fairbanks,

and Rutgers University

was funded by the

U.S. Department of the Interior

Bureau of Ocean Energy Management

Alaska Outer Continental Shelf Region

Anchorage AK 99503

under Cooperative Agreement No. M13AC00008

as part of the Bureau of Ocean Energy Management

Alaska Environmental Studies Program

And

The Bureau of Safety and Environmental Enforcement (BSEE)

17 November 2017

Citation: Winsor, P., H. L. Simmons, R. Chant, 2017. Arctic Tracer Release Experiment 

(ARCTREX): Applications for Mapping Spilled Oil in Arctic Waters, Final Report to 

Bureau of Ocean Energy Management, M13AC00008, OCS Study BOEM 2017- 062, 

University of Alaska Fairbanks, Fairbanks, AK, 79 pp. 

Cover Image: Photo of a surface Rhodamine-WT dye injection in the Chukchi Sea, 2015. 

Visible in the center of the picture is a surface drifter that was just deployed off the aft 

deck of the R/V Norseman II.

The opinions, findings, conclusions, or recommendations expressed in this report are 

those of the authors and do not necessarily reflect the views of the U.S. Department of the 

Interior, nor does mention of trade names or commercial products constitute endorsement 

or recommendation for use by the Federal Government.
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Contents

List	of	Figures............................................................................................................................ v

List	of	Tables .........................................................................................................................viii

Abbreviations	and	Acronyms .............................................................................................ix

Executive	Summary ................................................................................................................ x

1. Applications	for	Mapping	Spilled	Oil	in	Arctic	Waters........................................1

1.1. Overview.................................................................................................................................. 1

1.2. Project	Goals........................................................................................................................... 2

1.3. Scientific	Project	Objectives.............................................................................................. 2

2. Northeastern	Chukchi	Sea—Physical	Setting.........................................................2

3. Methods...............................................................................................................................5

3.1. Dye	Releases........................................................................................................................... 5

3.2. Observational	Technologies ............................................................................................. 7

3.2.1. Ship-Based	Dye	and	Hydrographic	Measurements.....................................................7

3.2.2. Autonomous	Underwater	Vehicles ....................................................................................9

3.2.3. Satellite-Tracked	Drifters.................................................................................................... 10

3.2.4. Microstructure ......................................................................................................................... 11

3.2.5. Wind,	Waves,	and	Currents ................................................................................................ 12

3.2.6. Models	and	Remote	Sensing .............................................................................................. 14

3.3. Online	Data	Display............................................................................................................14

3.4. Protocol..................................................................................................................................15

4. Physical	Setting	during	Field	Experiments .......................................................... 16

4.1. 2014	Field	Experiment .....................................................................................................16

4.2. 2015	Field	Experiment .....................................................................................................28

5. Dye	Injection	Results................................................................................................... 35

5.1. 2014	Dye	Injection	#1 .......................................................................................................35

5.1.1. Dye	Patch	Evolution	and	Advection................................................................................ 35

5.1.2. Vertical	Dispersion................................................................................................................. 44

5.1.3. Horizontal	Dispersion........................................................................................................... 45
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5.2. 2014	Dye	Injection	#2 .......................................................................................................48

5.2.1. Dye	Patch	Evolution	and	Advection................................................................................ 48

5.2.2. Vertical	Dispersion................................................................................................................. 51

5.2.3. Horizontal	Dispersion........................................................................................................... 52

5.3. 2015	Dye	Injection	#3 .......................................................................................................55

5.3.1. Dye	Patch	Evolution	and	Advection................................................................................ 55

5.3.2. Vertical	Dispersion................................................................................................................. 57

5.3.3. Horizontal	Dispersion........................................................................................................... 58

6. Discussion ....................................................................................................................... 61

6.1. Internal	Waves	and	Vertical	Shear ...............................................................................64

6.2. Wind	Mixing..........................................................................................................................66

6.3. Modification	of	Advection	by	Vertical	Mixing ...........................................................68

6.4. Response	Agency	Interaction—Arctic	ERMA ............................................................69

7. Conclusions	and	Recommendations....................................................................... 71

8. Acknowledgments ........................................................................................................ 74

9. References....................................................................................................................... 74
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List of Figures

Figure 1. Mean depth-integrated streamlines in the Chukchi Sea, after Spall (2007)........ 3

Figure 2. Photo of a surface Rhodamine-WT dye injection, Chukchi Sea......................... 6

Figure 3. Photo of the Acrobat towed vehicle. ................................................................... 8

Figure 4. Glider positions during the 2014 field experiment.............................................. 9

Figure 5. Vertical sections of dye concentrations measured by AUVs during dye 

injections #1 (top) and #2 (bottom). ......................................................................... 10

Figure 6. An example of surface currents mapped by the Chukchi Sea HFR network. ... 13

Figure 7. 2014 map of the ARCTREX study area, Northeastern Chukchi Sea................ 17

Figure 8. Cross-shelf vertical sections of water properties, September 10, 2014............. 18

Figure 9. Temperature-salinity diagram for dye injection #1, September 2014............... 19

Figure 10. Temperature-salinity diagram for dye injection #2, September 2014............. 20

Figure 11. Environmental conditions from the Klondike ConocoPhillips meteorological 

buoy, September 2014. ............................................................................................. 21

Figure 12. Daily average surface currents from HFR, September 10, 2014..................... 22

Figure 13. Daily average surface currents from HFR, September 15, 2014..................... 23

Figure 14. Meteorological buoy and ADCP mooring data, September 8–13, 2014......... 24

Figure 15. Meteorological buoy and ADCP mooring data, September 13–17, 2014....... 25

Figure 16. Currents from the shipboard ADCP, September 2014. ................................... 26

Figure 17. Results of a two-layer dynamical model. ........................................................ 27

Figure 18. 2015 map of the ARCTREX study area, Northeastern Chukchi Sea.............. 28

Figure 19. Cross-shelf vertical sections of water properties, September 2015................. 29
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Figure 20. Sea ice concentration from special sensor microwave imager (SSMI), 2014 

and 2015.................................................................................................................... 30

Figure 21 Temperature-salinity diagram for dye injection #3, September 2015.............. 31

Figure 22. Environmental conditions extracted from NOAA’s WaveWatchIII model, 

September 2015. ....................................................................................................... 32

Figure 23. Daily average surface currents from HFR, September 9, 2015....................... 33

Figure 24. Meteorological buoy and ADCP mooring data, September 8–13, 2015......... 34

Figure 25. Mapped patches of dye for the first 75 hours after dye injection #1............... 36

Figure 26. Currents and dye trajectory, dye injection #1.................................................. 37

Figure 27. Surface density and drifter trajectories during dye injection #1...................... 38

Figure 28. Vertical transects of dye concentration measured in patch 1 of dye 

injection #1................................................................................................................ 40

Figure 29. Vertical transects of dye concentration measured in patch 7 of dye 

injection #1................................................................................................................ 41

Figure 30. Vertical transects of dye concentration measured in patch 12 of dye 

injection #1................................................................................................................ 42

Figure 31. Vertical transects of dye concentration measured in patch 17 of dye 

injection #1................................................................................................................ 43

Figure 32. Time series of mean patch temperature, salinity, and density of dye 

injection #1................................................................................................................ 44

Figure 33. Summary of 2014 VMP station 1 data. ........................................................... 45

Figure 34. Second moment of the dye patches of dye injection #1. ................................. 46

Figure 35. Drifters released during dye injection #1, September 10–11, 2014. ............... 47
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Figure 36. Mapped patches of dye for dye injection #2. .................................................. 49

Figure 37. Surface density during dye injection #2. ......................................................... 50

Figure 38. Time series of mean patch temperature, salinity, and density of dye 

injection #2................................................................................................................ 51

Figure 39. Evolution of dye injections #1 and #2............................................................. 52

Figure 40. Second moment of the dye patches of dye injection #2. ................................. 53

Figure 41. Drifters released during dye injection #2, September 15–16, 2014. ............... 54

Figure 42. Mapped patches of dye for dye injection #3. .................................................. 55

Figure 43. Time series of mean patch temperature, salinity, and density of dye 

injection #3................................................................................................................ 56

Figure 44. Vertical section of density with surface dye concentration, patch 19, dye 

injection #3................................................................................................................ 57

Figure 45. Summary of 2015 VMP stations 1–3. ............................................................. 58

Figure 46. Second moment of the dye patches of dye injection #3. ................................. 59

Figure 47. Drifters released during dye injection #3, September 9–11, 2015. ................. 60

Figure 48. Summary of dye injections.............................................................................. 61

Figure 49. Horizontal dispersion, all ARCTREX injections. ........................................... 63

Figure 50. Time series of mean patch density, shear, and velocity. ................................. 65

Figure 51. Analysis of wind mixing, September 2014, Klondike ConocoPhillips 

meteorological buoy.................................................................................................. 67

Figure 52. Analysis of wind mixing, September 2015, Klondike ConocoPhillips 

meteorological buoy.................................................................................................. 68

Figure 53. Arctic ERMA web display of dye injection #1, 2014. .................................... 71
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List of Tables

Table 1. Summary of dye injections................................................................................... 5

Table 2. Summary of VMP stations.................................................................................. 12

Table 3. Mooring dates and locations............................................................................... 14

Table 4. Dispersion estimates for each field experiment.................................................. 62
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Abbreviations and Acronyms

ACC Alaska Coastal Current

ACW Alaska Coastal Water

ADCP Acoustic Doppler Current Profiler

ARCTREX Arctic Tracer Release Experiment

AUV Autonomous Underwater Vehicle

BBL Bottom boundary layer

BOEM Bureau of Ocean Energy Management

BSEE Bureau of Safety and Environmental Enforcement

BSW Bering Sea Water

CPH Cycles Per Hour

CSESP Chukchi Sea Environmental Studies Program

CTD Conductivity, Temperature, Depth

ERMA Environmental Response Management Application

GIS Geographic Information System

HFR High Frequency Radar

NASA National Aeronautics and Space Administration

MODIS Moderate Resolution Imaging Spectroradiometer

NCEI National Centers for Environmental Information

NOAA National Oceanic and Atmospheric Administration 

MW Meltwater

PE Potential Energy

PSU Practical Salinity Units

S Salinity

SSMI Special Sensor Microwave Imager

SST Sea Surface Temperature

T Temperature

TSG Thermosalinograph

UAF University of Alaska Fairbanks

UTC Coordinated Universal Time 

VMP Vertical Microstructure Profiler

WW Winter Water

WW3 NOAA/NWS/NCEP WAVEWATCH III (WW3) model
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Executive Summary

Oil exploration and increased shipping traffic in Arctic waters significantly elevate the 

risk of oil spills. The Arctic Tracer Release Experiment (ARCTREX) was designed to 

test the ability of available observational technology to sample a simulated oil spill in the 

Chukchi Sea and to transmit data to a shore-based, online emergency management 

application. During the ice-free seasons of 2014 and 2015, three releases of RhodamineWT dye were performed and the subsequent plumes were sampled using fluorometers 

mounted on AUV gliders, a towed Acrobat vehicle, and a vessel-mounted through-flow 

thermosalinograph (TSG) along with a vessel-mounted ADCP and a free-falling VMP 

microstructure instrument (providing details on the vertical structure). These data were 

combined with ongoing industry and University of Alaska ocean observations including 

moored meteorological instruments and ADCP current meters, satellite-tracked drifters, 

and extended-range high frequency radars (providing two-dimensional surface current 

fields). Being able to view incoming data aboard the ship in real time was essential to the 

adaptive sampling we employed to map the plumes. During the field campaigns, data 

were transmitted to a version of NOAA’s Environmental Response Management 

Application (ERMA 2015) that is configured for the Arctic region; our successful 

collaboration with the Arctic ERMA staff provided quick visualization of our simulated 

oil spill, potentially improving communication and coordination among responders and 

environmental stakeholders during future events. Subsequent data analysis shows that 

each dye injection was performed in unique conditions, in areas of: (1) strong 

stratification with meltwater over cold/salty winter water, (2) active subduction of surface 

water inshore of a front, and (3) weak stratification caused by a year of record low sea 

ice. Our results show that dye is dispersed at an average rate of ~7.7 m2s

–1

, and that local 

ocean dynamics (particularly wind mixing and horizontal density gradients) have a 

profound impact on the fate of the dye, laterally and vertically, on time scales as short as 

a couple of hours. The diversity of environments and the extremely rough weather 

experienced during the field experiments allowed us to fully evaluate the performance of 

the instruments; the TSG and the towed undulating Acrobat vehicle are capable of 

tracking dye over time in great detail while being able to operate in stormy seas with 

significant wave heights approaching three meters. Dye was distributed throughout the 

surface mixed layer and, in one case, was subducted below the surface layer, requiring 

instruments capable of sustained subsurface measurements.
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1. Applications for Mapping Spilled Oil in Arctic Waters

1.1. Overview

Oil exploration and increased shipping through Arctic waters bring with them the 

increased possibility of oil spills. Previous oil spills in other areas have demonstrated the 

utility of real-time data in modeling and directing the oil spill response, and it was an 

open question whether the challenges created by the Chukchi Sea’s unique characteristics 

such as sea ice and extreme weather would allow the collection of this critical data. This 

study lays the groundwork for answering this question by using simulated oil spills to 

assess this capability in the Chukchi Sea.

The core of ARCTREX is the field experiments performed aboard the R/V Norseman 

II—a series of dye releases and subsequent surveys with a suite of instruments. The 

releases were performed during the ice-free season in the vicinity of oil leases where an 

oil spill might likely occur. The study area is physically complex with rapidly changing 

weather and oceanic conditions and interannual variability that created diverse 

experimental conditions. The area also presents challenging logistical complications due 

to its remoteness and extreme weather. These challenges will be detailed in this report, as 

will assessments of the capabilities of the instruments we used for sampling. We stress 

that a dye release is not an ideal or even realistic simulation of oil in water, but does 

enable measurement of dispersion in the area of interest while it provides an opportunity 

to track a known substance over time and space with modern real-time enabled 

observational technology. 

Another important aspect of this study is our collaboration with the Bureau of Safety and 

Environmental Enforcement (BSEE) and NOAA’s Environmental Response 

Management Application ERMA (ERMA 2015) configured for the Arctic region, with 

the goal of feeding our real-time data into their response system. Real-time field data and 

prediction of the plume evolution is critical for proper response to an oil spill. ERMA is a 

web-based GIS tool that assists both emergency responders and environmental resource 

managers in dealing with incidents that may harm the environment. ERMA integrates and 

synthesizes data—some of which happens in real time—into a single interactive map, 

providing quick visualization of the situation and improving communication and 

coordination among responders and environmental stakeholders.

ARCTREX also advances fundamental knowledge of the Chukchi’s physical 

oceanography, including the dynamics of fronts and wind mixing. The field program was 

designed to provide multiple measurements of ocean surface properties using different 

observational platforms, and to characterize passive dispersion through the direct 

measurement of advection and patch spreading at small spatial and temporal scales.

Measurements of ocean turbulence and microstructure in concert with highly detailed 

observations of dispersion aids in the understanding of how this high-latitude shelf 

system evolves during the ice-free season. To our knowledge, no dye release study has 

previously been performed in this area, and as such we view this project as a test bed for 

future studies.
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1.2. Project Goals

• Develop a better understanding of small-scale transport processes important to 

fate and effects modeling used in oil impact analysis.

• Develop instrument and real-time mapping protocols that can guide oil spill 

responders in the event of a small offshore spill.

1.3. Scientific Project Objectives

• Conduct field tests of the dispersal and tracking of nontoxic Rhodamine dye off 

the Chukchi coast.

• Develop, test, and deploy instrumentation for Autonomous Underwater Vehicles 

(AUV) and other instrumentation that can be customized for use in the Arctic to 

detect the spatial and temporal locations of surface and subsurface spills.

• Track the dispersed dye plume by incorporating input from the AUVs, towed 

CTDs, and other real-time data collection sensors in the Chukchi Sea (e.g., 

surface currents from HF Radar, towed CTDs, drifters, real-time WRF highresolution wind fields, data from meteorological buoys and other offshore 

instruments) to assess the fate and transport of the dye plume.

• Evaluate the effectiveness of the suite of instruments to track the released dye 

under diverse environmental conditions.

• Calculate parameters that quantify small-scale transport processes based on 

measurable oceanographic and meteorological data.

2. Northeastern Chukchi Sea—Physical Setting

The Chukchi Sea borders the northern coast of Alaska (Figure 1). The shallow (~50m) 

Chukchi shelf extends ~800 km northward from Bering Strait to the shelf break at the 

200 m isobath. Though considered part of the western Arctic Ocean, the Chukchi shelf is 

oceanographically linked to the Pacific Ocean via mean northward flow through Bering 

Strait, which is sustained by a large-scale pressure gradient between the Pacific and 

Atlantic Oceans (Coachman et al. 1975; Aagaard et al. 2006). Also important to the 

Chukchi Shelf is the sea ice that typically covers it from October to May; the spring 

retreat of ice occurs earlier and fall ice formation is delayed there in comparison to most 

other Arctic shelves because of the northward heat flux through the strait; in September, 

sea ice is far from the ARCTREX study area. Major bathymetric features near the 

ARCTREX study area include Central Channel to the west, Hanna Shoal to the north, 

Barrow Canyon to the east, and the Alaska coast along the southwest.
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Figure 1. Mean depth-integrated streamlines in the Chukchi Sea, after Spall (2007).

Streamlines are white, bathymetry is shaded, and major bathymetric features are labeled.

Figure 1, from Spall (2007) is derived from model results, but it illustrates the mean 

circulation over the shelf. Although the mean flow is nominally northward over much of 

the shelf, the bulk of the transport occurs along the canyons. Water flushing the central 

and western Chukchi Sea then moves eastward north of Hanna Shoal, where a portion of 

it turns southward along the east side of Hanna Shoal and eventually enters the head of 

Barrow Canyon, according to models (Winsor and Chapman, 2004; Spall 2007). Mean 

current speeds within Herald and Barrow canyons are swift (~25 cm s–1 or larger), more 

moderate in the Central Channel (~10 cm s–1), and generally <5 cm s–1 elsewhere

(Weingartner et al. 2005; Woodgate et al, 2005; Pickart et al. 2010). 

The ARCTREX study area is influenced by several of the system’s current pathways and 

that, in turn, creates the mosaic of water masses encountered by our hydrographic surveys

and described historically (Paquette and Bourke 1974; Coachman et al. 1975; Johnson 

1989). Melting sea ice creates a surface layer of meltwater (MW) that is fresh and cold

(Aagaard 1988), but warms as the season progresses; this water is formed in place by 

melting or advected from the north. Two water masses are advected from the south by 

Bering Strait inflow—the fresh, warm, highly stratified Alaska Coastal Water (ACW) 

and the cooler, less stratified Bering Sea water (BSW) also called Chukchi Summer 

Water (Gong and Pickart 2015, 2016). The Alaska Coastal Current (ACC) brings ACW 

northwestward along the coast (Aagaard 1988; Münchow and Carmack 1997), but its 

influence can spread across the shelf during the upwelling events that occur in summer 

and fall (Weingartner et al. 2015). The ACC’s northwestward transport is at maximum in 

July, and in September is transitioning to its fall condition of near zero transport 

(Weingartner et al. 2017). BSW is offshore of ACW, spreading eastward from the Central 

Channel along its entire length (Weingartner et al. 2013). As these waters flow eastward,

they encounter dense (cold, salty) bottom waters that, because they were formed during 
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the previous winter over the northern Bering and Chukchi Seas (Aagaard 1988), are 

called winter water (WW). The model results (Figure 1) suggest that this dense water is 

most likely from the east side of Hanna Shoal.

In contrast to other continental shelves, tidal currents in the Chukchi Sea are weak 

(Sverdrup 1926; Hunkins 1965; Danielson 1996), but there are other processes that affect 

currents on the time and space scales of ARCTREX. While currents in the mean are 

forced by large-scale pressure gradients (Woodgate et al. 2006), current variations can be 

wind-forced. However, the contribution to the vertically averaged momentum balances 

by instantaneous winds is insignificant compared to geostrophic flow from pressure 

gradients generated by wind-driven convergences and divergences (Weingartner et al. 

2013). Atmospheric forcing also generates continental shelf waves that propagate 

northward from the Bering Strait, though these are more significant within the ACC than 

at mid-shelf locations like the ARCTREX study area (Danielson et al. 2014). In addition, 

wind-generated surface gravity waves create Stokes drift, which can be substantial on the 

Chukchi Shelf depending on the depth. Weingartner et al. (2017) found that Stokes drift 

makes a relatively small contribution to the momentum balance of 1 m drogued drifters, 

but integrated over a prolonged wind event, it can account for 20% of drifters’ 

displacement over 6 days. Undrogued drifters can travel in the opposite direction from 

even 1 m drogued drifters under strong wind conditions (personal observation). 

As we will show, dispersion in the Chukchi Sea is greatly influenced by lateral density 

fronts, which are prominent features of the Chukchi Shelf—especially north of ~71.5°N 

(Weingartner et al. 2015). In general, fronts are created by lateral differences in surface 

forcing and advection and are maintained in the vertical by turbulent mixing; they slump 

from the vertical, causing local instabilities and horizontal mixing (Ferrari and Bocaletti 

2004). Timmerman and Winsor (2013) found that in the Chukchi, horizontal temperature, 

salinity, and density variability extends down to O(1) km sub-mesoscales—the scale of 

ARCTREX’s dye patches—and that lateral isopycnal slumping of the fronts acts to 

restratify the water column north of the fronts. Lu et al. (2015) observed fronts in the 

Chukchi consisting of MW over WW in the north and BSW in the south, with lateral 

influxes (not vertical mixing) generating intrapycnocline lenses and layers of BSW 

between the MW/WW layers. Their idealized numerical model results showed that 

instability of the surface front generates eddies and meanders that give rise to these 

subsurface features. This complex of water masses is precisely what is seen during 

ARCTREX’s dye injection #1.

There are a number of processes that can alter the dispersion rate, including time 

dependence (Fischer et al. 1979; Young and Rhines 1982), incomplete vertical or lateral 

mixing (Bowden 1965; Okubo 1973), and lateral shear (Fischer 1972; Sumer and Fischer 

1977); see for example Geyer et al. (2008) for discussion. Kawaguchi et al. (2015) found 

the minimal dissipation rate of turbulent kinetic energy in the bottom layer is consistent 

with the area’s weak tides. The strong stratification of the northern Chukchi Shelf

(buoyancy frequencies in the pycnocline are greater than 10 cph) suppresses vertical 

mixing, so that MW moves over WW with little exchange of heat, salt, and dissolved 

nutrients. However, near-inertial internal waves and shear are generated by summer 
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storms and erode the pycnocline (Rainville and Woodgate 2009), and could enhance 

turbulent energy even in deep water such as the Arctic Ocean interior (Martini et al. 

2014). Observations in the two-layer system closer to the ice edge in September 2013 

demonstrated that when the winds are calm and the water is stratified, internal gravity 

waves propagate through the water column, causing mechanical overturning near 

pycnocline (Kawaguchi et al. 2015). During gale force winds, turbulence deepened the 

surface homogeneous layer. They also noted that drifting buoys moved with oscillations 

at the inertial period of 12.5 hours.

3. Methods

3.1. Dye Releases

The main purpose of the ARCTREX experiment was to map the evolution of a dye plume 

over time and space in order to simulate an oil spill event and to provide real-time data to 

the Arctic ERMA system. To do this, we conducted purposeful injections of a fluorescent 

dye, Rhodamine-WT, as a passive ocean tracer. We conducted two successful dye 

injections in September 2014 and another in September 2015, all in the upper mixed layer

(Table 1). A deep-water release was attempted in 2015 but was not successful (see 

below) so was not given an identifying number.

Table 1. Summary of dye injections

Id Date and 

Time 

(UTC)

Latitude

(°N)

Longitude

(°E)

Depth 

(m)

S

(PSU)

T

(°C)

Surveys Length 

(hours)

1 9/9/2014

23:05 71.2985 –162.6550 8 28.8 1.45 23 75

2 9/15/2014

03:30 70.6814 –162.0338 10 31.0 2.75 11 30

9/7/2015

05:00 71.6270 –162.9752 35.5 36.2 0.8

3 9/9/2015 

04:09 70.7183 –162.2080 5 31.1 6.8 19 42

To prepare for each dye injection, we first conducted hydrographic surveys of the study 

area to define the 3-D structure of the density field using a towed Acrobat vehicle and 

AUV gliders, and characterized turbulence with microstructure measurements (discussed 

in detail later). A solution of 50 kg of Rhodamine-WT in a 20% water solution was

mixed with propanol to achieve the anticipated in situ density. Use of this mixture 

together with rapid ~1000 to 1 dilution as the dye solution was injected through a 

diffusing nozzle precluded any subsequent anomalous density-driven flow. The dye was

injected by pumping it through a hose attached to the CTD rosette frame suspended 

below the ship. The surface injections occurred in the upper 5–7 meters of the water 
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column, in middle of the surface mixed layer. The dye quickly spread vertically to 

occupy the entire mixed layer, typically the upper 10–15 m of the water column. Dilution 

limited the duration of the tracer experiments to 1–4 days.

Figure 2. Photo of a surface Rhodamine-WT dye injection, Chukchi Sea. Visible in 

the center of the picture is a surface drifter that was just deployed off the aft deck of the R/V 

Norseman II. The drogue sank within 1 minute of deployment.

Surveys of the dye patch were performed with Chelsea Ltd. Aquatracka III fluorometers

mounted on a variety of instruments (see section 3.2). The Aquatracka III is able to detect 

Rhodamine-WT to 1 part in 1011 by weight, which was the expected background signal, 

and has a 4 decade logarithmic output. At low dye concentrations, ~10 × 10–11 signal 

contamination is possible due to fluorescence from a surface chlorophyll bloom. To 

estimate and remove this spurious signal, a separate chlorophyll fluorometer was used. A 

dye concentration >500 × 10–11 will produce a spurious chlorophyll signal but such 

concentrations persisted for only a few hours. Steaming at 6 knots, the dye patch was 

surveyed over 36–72 hours with a minimum of 11 separate surveys of each injection’s 

patch. Real-time data from instruments allowed us to anticipate the initial dye patch 

displacement and to adjust the ship course in order to achieve evenly spaced tracks 

through the patch. Integrated transect data from the acoustic Doppler current profiler

(ADCP) and Acrobat also helped adjust the ship position relative to the water column to 

a common reference time during subsequent data analysis.

The surveys continued until the dye concentration signal to noise ratio was ~3. When 

50 kg of dye is evenly dispersed over a volume 10 km × 10 km × 10 m, the average 

concentration is 4 × 10–11; that is, a signal/noise ratio of ~4. The Aquatracka III 

fluorometer was able to perform as expected over the duration of the surveys, displaying 

sensitivity to the dispersed dye concentration over several orders of magnitude.

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at 16 Hz and a triplet Wetlabs EcoPuck sampling at 8 Hz, enabled us to perform repeated 

tow sections along and across the dye plume over time. The Acrobat transmitted data 

through a faired Kevlar cable to an onboard deck unit, and data was stored and plotted on 

the ship, so we were able to adapt the sampling scheme to real-time conditions. The 

Acrobat system was critical to our success in tracking dye over the entire water column 

and provided us with real-time data to allow for adaptive sampling of the growing dye 

patch. Once deployed, this system was also functional during high sea states.

Figure 3. Photo of the Acrobat towed vehicle. Also visible on the aft deck of the R/V 

Norseman II is the faired Kevlar cable that allows for real-time data transfer to the operator.

Through-flow ThermoSalinoGraph. We installed the same model large dynamic range 

Rhodamine fluorometer (Chelsea Ltd. Aquatracka III sampling at 1 Hz) in the R/V

Norseman II vessel’s through-flow ThermoSalinoGraph (TSG) system, and that enabled 

us to sample near-surface CTD and dye concentrations continuously while underway.

The TSG system collected salinity, temperature, and Rhodamine dye concentration every 

5 s with the intake located at ~3 m depth; with a typical survey speed of 6 knots, our 

horizontal resolution from the TSG was ~30 m. This system performed excellently and 

was critical to the success of our fieldwork. It provided us with the capability to map dye 

absence, presence, and concentrations continuously and, by measuring hydrographic 

surface properties, gave the detailed near-surface measurements of horizontal density 

fronts that proved critical in understanding the dye’s movement. The system was on 

continuously while we operated the ship, and the data was plotted in real time on a 

monitor onboard. Because it is constrained to the surface, its drawback was that it could 

not detect dye when the dye was subducted (dye injection #2) or released at depth (dye 

injection #4). The surface maps in the Results section were created using TSG data.

CTD/Rosette system. A third CTD system was also used during the sampling: a Seabird 

SBE55/SBE19+ CTD/Rosette system that was lowered from the surface at specific 

locations. It was used before the injections to determine the target density of the injection 

depth so that the Rhodamine dye could be made neutrally buoyant. In addition, during the 

dye release, the injection hose was attached to the rosette frame so that it could be 

lowered to that known depth/density surface. The CTD system enabled us to disperse the 

dye at a known depth while monitoring its salinity and temperature properties, but 
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because the ship had to stop when it was deployed, it had no utility during the dye 

surveys.

3.2.2. Autonomous	Underwater	Vehicles

Autonomous Underwater Vehicles. Slocum’s electric Autonomous Underwater Vehicle 

(AUV or glider) surveys independently of a ship in a vertical sawtooth pattern by using 

changes in its buoyancy to generate forward movement (Webb et al. 2001); it obtains

GPS positions upon surfacing, so it can navigate underwater by dead reckoning a 

compass bearing to a waypoint provided by operators on shore. Sampling is thus 

independent of the ship operations and weather conditions. Our gliders were each

equipped with a Sea-Bird Electronics (SBE) Glider Payload CTD (GPCTD) and a 

Rhodamine fluorometer with a 1 Hz sampling rate. A glider’s typical mean horizontal 

speed is 30–40 cm s–1 and the mean depth of the survey areas in the Chukchi Sea is 

~40 m, which resulted in a survey resolution for hydrography and dye concentration of 

~1 m vertically and ~300 m horizontally. Based on previous experience, we expected the 

glider’s sampling to be faster than the evolution of submesoscale features commonly 

found in the Chukchi Sea (Timmermans and Winsor 2013).

Figure 4. Glider positions during the 2014 field experiment.

For the 2014 ARCTREX field experiment, we deployed two gliders at the site of dye 

injection #1 (Figure 4) and programmed them to surface hourly, hoping that they could 

respond quickly to the dye patch position. However, the dye patch evolved faster than the 

gliders were able to make forward progress. Despite their ability to detect dye both at the 

surface and subsurface (Figure 5), we learned that individual gliders are not able to map a 

dye plume in time and space resolution needed for dispersion calculations. In 2015, no 
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gliders were deployed because the Rhodamine-equipped AUV glider had compass issues, 

probably due to damage caused in shipping. No glider transects or maps are included in 

the Results section of this report for these reasons.

Figure 5. Vertical sections of dye concentrations measured by AUVs during dye 

injections #1 (top) and #2 (bottom).

3.2.3. Satellite-Tracked	Drifters

We deployed satellite-tracked drifters (Microstars, Pacific Gyre Inc.) at the injection 

sites. Each drifter was drogued at 1 m depth and had a surface sphere that contained a 

temperature sensor, GPS, and Iridium satellite module for real-time data transfer to 

PacificGyre via Iridium SBD format. The drogue-to-surface float drag ratio is 50:1, 

which ensures that the floats represent ocean currents at the 1 m drogue depth. We 

expected the drifters to transmit the real-time position of the centroid of the dye patch

automatically to onshore stations, but the trajectories of the drifters and dye diverged, as 

will be discussed in the Results section. Horizontal dispersion as measured by drifters 

was calculated by assembling the pairwise distance between drifters (Weingartner et al.

2015), so it could only be calculated when the entire cluster returned data; if drifters 

entered the water late or died early, this shortened the time over which dispersion could 

be calculated.
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In 2014, a single drifter was deployed upon arrival at the first injection site to help 

characterize the currents there; this drifter eventually died in the sea ice four months later.

Another drifter was deployed immediately before dye injection #1, with 15 more released 

during the injection itself. For dye injection #2, those 15 drifters were recovered and redeployed at the second site with 13 additional drifters, for a total of 45 drifter 

deployments. These drifters sampled at five-minute intervals in hopes of computing 

dispersion via cluster analysis. However, we later discovered that waves breaking over 

the surface floats add noise to the GPS positions that is accentuated by the short sampling 

interval, making those calculations impractical. Hourly averaged position was used 

instead.

After the 2014 field experiment, all drifters were switched to hourly sampling and left to 

characterize wide-scale Chukchi circulation as part of BOEM’s Chukchi and Western 

Beaufort Circulation Study; all initially traveled northeast along Barrow Canyon but at 

the shelf break turned west, crossed the Chukchi Sea, and headed for the area near 

Wrangel Island, Russia (not shown); one of these drifters lasted until January 2016 and 

went as far west as 150°W, which is another story.

In 2015, one drifter was deployed before dye injection #3, and 9 more were deployed 

during the injection itself, for a total of 10. All reported sea surface temperature and 

position hourly, and all were left in the water after the 2015 field experiment. They also 

traveled west, many of them beaching on the Siberian coast; the last of these also died in 

January 2016.

3.2.4. Microstructure

Vertical microstructure profiler. We performed turbulence profiling using a 

lightweight VMP-250 vertical microstructure profiler built by Rockland Scientific. The 

profiler free-falls through the ocean interior, connected by a slack tether to avoid any 

drag or vibrations on the instrument; it was deployed and recovered using a small electric 

winch on the R/V Norseman II. The VMP measures profiles of the hydrographic 

finestructure and velocity microstructure, which can be used to quantify the rates of 

turbulent dissipation, ε, in the ocean (Gregg 1999; Lueck et al. 2002). These 

measurements allow us to measure the vertical component of the turbulent mixing, Kv,

using the method of Osborn (1980). Velocity microstructure was acquired using dual 

airfoil probes that measure shear and a FP07 thermistor for temperature; a Turner designs 

CYCLOPS-7 Rhodamine WT sensor measured dye concentration. The noise level for ε

measured by the VMP is ~5 × 10–10 W kg–1, as determined from examination of spectra 

in quiet patches.

A summary of VMP deployments is shown in Table 2 and Figure 6. In 2014, the VMP 

was deployed once before the first injection but was lost during the second deployment, 

with no data returned. In 2015, three deployments were performed before that year’s first 

dye injection, but bad weather precluded any more. The VMP profiles allowed us to 

characterize turbulence in the ocean, but it was not practical to use during the dye surveys

because the ship has to stop during profiles.
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Table 2. Summary of VMP stations.

Year Station Start Date and Time

(UTC)

Latitude

(°N)

Longitude

(°E)

Number of

Casts

2014 1 9/9/2014 20:33 71.2095 –162.4350 5

2015 1 9/7/2015 02:50 71.6548 –162.9780 12

2015 2 9/7/2015 20:30 71.5851 –162.8719 20

2015 3 9/9/2015 02:51 70.7117 –162.2248 10

3.2.5. Wind,	Waves,	and	Currents

High frequency radars. To obtain information about the background circulation over 

our study area, we utilized land-based high-frequency Radars (HFRs). The HFRs were 

deployed and maintained through the Bureau of Ocean Energy Management (BOEM) 

Grants 764 M12AC000008 and M09AC15207, the Alaska Ocean Observing System 

(AOOS)/U.S. Integrated Ocean Observing System, and the Alaska Coastal Impact Assistance 

Program (Dr. Weingartner, PI). Surface currents in the upper 1–2 m of the water column 

provided by HFR fields were mapped on a 6 km grid every hour during both the 2014 

and 2015 experiments (Figure 6). The two-dimensional current vectors were displayed 

online (www.chukchicurrents.com) and were updated in real time, so were available 

during field operations. The HFR data allowed us to identify circulation patterns and 

convergent features (fronts) in real time from the ship.

However, Figure 6 also illustrates one of the disadvantages of HFR measurements in 

regards to the ARCTREX experiment. Note that there is a data gap between Point Lay 

and Wainwright where all the dye releases occurred. This data gap occurs because the 

HFR stations are too far apart given the limitations of the Arctic’s power grid 

infrastructure (Weingartner et al. 2012; Fang et al. 2015). In 2015, a new station was 

established on Icy Cape to close this gap, but as of this time, processing of 2015 HFR 

data is not complete and should be considered preliminary. We have attempted to reduce 

this gap by using daily averages rather than hourly maps in the following sections, but the 

utility of HFR current maps is still limited.
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Figure 6. An example of surface currents mapped by the Chukchi Sea HFR 

network. Surface current vectors at 2100 UTC September 14, 2014, are colored according to 

current magnitude. Bathymetry is contoured at 10 m intervals (gray). The black box shows the 

location of CSESP’s Burger study area, and pink diamonds show the dye release sites in 2014 and 

2015. Additional instrumentation includes VMP stations (red), ADCP moorings (yellow), and 

meteorological buoys (green).

The R/V Norseman II is outfitted with a shipboard downward-looking ADCP current 

meter. Data were displayed on a screen during the cruise and were processed afterward 

using standard methods. Velocity data were corrected for ship heading and velocity and 

were edited for bad values.

Data from a variety of moored instruments were provided by the industry-sponsored 

Chukchi Sea Environmental Studies Program (CSESP), also archived as Accession 

#0164964 at the NOAA National Centers for Environmental Information (NCEI).

Meteorological buoys and moored ADCP and CTD instruments were located at various 

locations around the Chukchi Sea, primarily at the oil and gas lease prospects called 

Klondike and Burger by the ConocoPhillips and Shell, respectively (Table 3; Figure 6).

The Meteorological (Met) buoys were deployed during the ice-free seasons only; possible 

measured variables include sea surface temperature (SST), wind, surface current, and 

waves. ADCP data were processed by ASL Environmental Services (Mudge et al. 2017);

currents were output at surface, mid-water, and bottom depths only, making 

determination of vertical shear imprecise.
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Table 3. Mooring dates and locations.

ID Type Start Date End Date Latitude

(°N)

Longitude

(°E)

Klondike Met 08/03/2014 10/08/2014 70.8718 –165.2459

Klondike Met 07/21/2015 10/13/2015 70.8722 –165.2480

Burger Met 08/20/2014 10/07/2014 71.5020 –164.1335

Burger ADCP 08/5/2014 10/5/2015 71.2394 –163.2800

Site05 ADCP 08/6/2014 10/2/2014 70.9166 –161.4996

Site08 ADCP 10/16/2014 10/5/2015 71.2767 –161.5608

3.2.6. Models	and	Remote	Sensing

Moderate resolution imaging spectroradiometer (MODIS) remote sensing. Lastly, 

we utilized daily Level 2 Sea Surface Temperature (SST) product from NASA’s MODIS 

sensors to allow us to map surface thermal gradients and ocean fronts before and during 

our field experiments. These satellite images, together with the surface HFR current 

fields, aided us in determining the location for our dye release experiments. The MODIS 

imagery also helps visualize the complex frontal patterns between the nearshore,

relatively warm ACC and colder offshore water masses.

WaveWatchIII. For the period in 2015 when the industry meteorological buoy did not 

measure wave data, we acquired approximations of it from NOAA’s publicly available 

WaveWatchIII (WW3) model output (Tolmen 1997). WW3 produces NOAA’s 

operational ocean wave predictions and is also available as a hindcast. These have been 

shown to accurately reflect wind and wave measurements during the vast majority of 

conditions, the exception being storm events where peak wave heights may be 

underestimated by 1–2 m (Pingree-Shippee et al. 2016). WW3 wave output was 

interpolated to the location of the Klondike ConocoPhillips buoy: 70.8722°N, 

–165.248°E.

3.3. Online Data Display

During the experiment, data had to be transmitted to shoreside stations in order to be 

displayed on the web. Previous experiments by the University of Alaska Fairbanks

(UAF) have used Google Maps for data display, but that proved unworkable for this 

project because Google Maps lacks background map tiles at the spatial scales of the dye 

patches. Because of this, Arctic ERMA’s data display capabilities were indispensable. 

Transmission methods for our data differed by instrument and are summarized below.
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Gliders. Decimated data files were transmitted via Iridium to the onshore glider server, 

which is currently an Amazon cloud server administered by UAF. This preliminary data 

was automatically harvested by UAF, and glider positions were processed into tracklines 

in Google’s KML format by Python scripts on a Linux server. These KML files were 

copied to Arctic ERMA servers and converted to shapefiles for display in their system. 

The original data files also contain temperature, salinity, and Rhodamine dye 

concentration that were not included in the GIS files; instead, these data were 

dynamically displayed as vertical sections in time by PHP scripts on UAF’s website 

(http://www.ims.uaf.edu/artlab/), providing near real-time oceanographic data.

Drifters: Data was transmitted via Iridium to PacificGyre, which posted it on its website.

Automated scripts similar to those for the gliders created a KML file for each drifter, and 

these were copied to Arctic ERMA servers, converted to shapefiles, and displayed by 

them. PacificGyre’s data server also provides data in JavaScript Object Notation (JSON) 

format, a possible alternative format in the future.

The conversion of raw dye concentration data into gridded, synoptic realizations of the 

dye patch for delivery to Arctic ERMA was a manual process aboard the R/V

Norseman II. After 1–4 surveys of the dye patch, time limits for each new patch were 

determined. The relevant dye concentration data were extracted, gridded, and smoothed 

for contouring; the contours were then saved as polygons to shapefiles, one for each 

patch. These shapefiles were delivered to the ERMA server via SFTP as soon as they 

were generated. The same general process was used in 2014 and 2015, although—based 

on the experience in 2014—details of the shapefiles and metadata were changed to allow 

for an automatic update of Arctic ERMA when shapefiles were delivered.

3.4. Protocol

Details varied by instance, but the basic protocol followed for a dye-tracking experiment 

can be summarized as follows:

1. We used wide-scale measurements of MODIS and HFR to choose the injection 

sites based on likely oil spill locations and physical features of interest.

2. At an intermediate scale, Acrobat, glider, and shipboard ADCP transects were 

performed to define the physical setting.

3. A single drifter was deployed to give an initial prediction of the dye’s trajectory.

4. At the chosen injection site, VMP profiles were performed to define the mixing 

profile for later analysis.

5. A CTD profile was performed to define the target density for dye solution. The 

dye solution was mixed in accordance with the measured density.

6. The dye was released with a cluster of drifters.
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7. Continual surveys using ship-based measurements were performed to track the 

dye patch’s movement and to define the dye inventory. Surveys were performed 

with:

a. Shipboard ADCP

b. Towed Acrobat

c. Ship’s TSG

8. Drifter and glider position data were automatically transmitted to Arctic ERMA 

servers. Shapefiles of dye concentrations were manually produced on the ship and 

transmitted to Arctic ERMA.

4. Physical Setting during Field Experiments

4.1. 2014 Field Experiment

Figure 7 shows the study area for the 2014 observational effort in the northeastern

Chukchi Sea. The ship track for the 2014 experiment is shown in dark gray, and includes 

the two dye release surveys (in black boxes) and “butterfly” surveys around the locations 

of each dye injection. Also shown in Figure 7 is the average SST field obtained from 

NASA MODIS satellite imagery. The warmer ACW of the Alaska Coastal Current can be 

seen in the southeast portion of the map, and in the north is the colder MW. Note that the 

transition from warm to colder waters is not linear but rather contains local maximums 

and minimums suggestive of the meandering frontal system.
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Figure 7. 2014 map of the ARCTREX study area, Northeastern Chukchi Sea. The

two 2014 dye injection surveys described in this report are outlined by the black boxes. The ship 

track is shown in dark gray. The location of dye injections #1 and #2 are depicted by red stars and 

the location of the cross-shelf transect is in blue. The ConocoPhillips meteorological buoy, the 

location of our wind measurements, is the red dot located in the Klondike lease patch. Daily 

average SST from MODIS for September 15, 2014 is also shown. Isobaths are contoured at 

increments of 10 m depth.

Figure 8 shows cross sections of salinity, temperature, and density from the cross-shelf 

survey depicted in Figure 7. Far offshore, the stratification on the shelf can be 

characterized as a two-layer system with cold fresher waters (MW) overlaying very cold

salty waters (WW). On the innermost section of the transect is the Alaska Coastal 

Current, which transports warm, fresh ACW along the Alaska coast. Between these 

environments, the water column of the shelf includes an intermediate layer of water that 

is warm and moderately salty. At the surface, the cross-shelf structure of density is 

characterized by light waters offshore with densities less than 1023 kg m–3. Inshore of 

this are more dense waters exceeding 1024 kg m–3. The intersections of the isopycnals 

with the surface are the signature of the fronts common in the Chukchi Sea. Density is 

controlled by salinity, so temperature can be used as a tracer for the intrapycnocline 

intrusions seen offshore of the front. It is likely that the intermediate layer of warm water 

has moved northward from a front in a manner similar to that observed by Lu et al. 

(2015). In fact, the subduction of warm saline shelf waters underneath fresher offshore 

melt waters was observed during dye injection #2 as will be discussed later.
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Figure 8. Cross-shelf vertical sections of water properties, September 10, 2014.

Salinity (top), temperature (middle), and density (lower) collected by the Acrobat during the

initial transect from Wainwright to the site of the first dye injection site. The x-axis scale is km 

offshore, and the red dot is the approximate location of dye injection #1.
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Figure 9. Temperature-salinity diagram for dye injection #1, September 2014. Points 

are T-S properties measured by the Acrobat outside (black) and inside (blue-to-red indicating 

hours after the dye injection) the dye patch and across the entire butterfly survey (pink). The red 

dot marks the T-S of dye injection #1.

The salinity of the offshore upper layer MW is ~29 psu and temperature is < 2°C, and it

overlies dense WW with salinities exceeding 32 psu and temperatures < 0°C. Surface to 

bottom density difference exceeds 3 kg m–3. The temperature-salinity diagram in Figure 9

illustrates these water mass properties using data collected before and during the first dye 

injection, and Figure 10 does the same for the second dye release. Both the WW and MW

have distinct T-S properties with origins at 32.5 psu and –1.5°C and 28.5 psu and 1°C,

respectively. The mid-shelf waters have a more complex T-S structure with what appears 

to be several water masses including ACW at the highest temperatures and BSW at 

intermediate temperatures; this is all typical for the Chukchi Shelf. Note that prior to dye 
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injection #1, there is little mixing between the MW and WW; instead, mixing occurs 

between each of these water masses and the intermediate layer that sits at mid-depths 

between them. This changes over the course of dye injection #1 as the volume of the 

intermediate layer decreases, and mixing occurs more and more directly between the 

upper (MW) and lower (WW) layers. Dye injection #2 begins in BSW, but mixes with all 

available water masses.

Figure 10. Temperature-salinity diagram for dye injection #2, September 2014.

Points are T-S properties measured by the Acrobat outside (black) and inside (blue-to-red

indicating hours after the dye injection) the dye patch. The red dot marks the T-S of dye injection 

#2.
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Figure 11. Environmental conditions from the Klondike ConocoPhillips

meteorological buoy, September 2014. Wind vectors are presented along a time series of 

wind speed magnitude (top panel) with significant (black) and peak (blue) wave height (middle 

panel) and peak wave period (bottom panel). Red vertical lines depict the 2014 dye injections and 

the horizontal line indicates their duration. Arrow directions indicate the direction the wind is 

blowing toward.

As measured at the Klondike ConocoPhillips meteorological buoy, environmental 

conditions leading up to the 2014 ARCTREX experiment consisted of westerly (onshore) 

winds with speeds of 8–12 m s–1 from September 1–5 (Figure 11). A short lull in the wind 

on September 5 is associated with a change to easterly winds. From this period of very 

light winds on September 7, easterly wind speeds gradually ramped up to >10 m s–1 on 

September 9 and persisted with relatively constant intensity throughout the ARCTREX 

field experiment, eventually relaxing on September 15. Corresponding wave heights 

peaked on September 3 with significant wave heights reaching 3 m and peak wave 

heights near 6 m. During the dye injection #1, significant wave heights reached 1.5 m and 

peak wave heights were near 3 m. The conditions for field operations deteriorated slowly 

over the course of the experiment and during the second injection; significant wave 

heights reached 2.5 m with peak wave heights cresting over 4 m. Wave periods at 

Klondike steadily climbed from 5 to 7 seconds during the course of the two dye 
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injections. Note that the wind direction corresponds to an Ekman drift in the upper layer 

toward the west-northwest, which is relevant to the dye evolution discussed later.

The daily average surface currents from HFR for the days of dye injections in 2014

(Figure 12 and Figure 13) show that large areas of the shelf have coherent, alongshore 

flow fields, but that currents at dye release sites are onshore (September 10) or offshore 

(September 15). During this time period, the ACC is experiencing swings in direction, 

creating convergences and divergences offshore of Wainwright that result in the highly 

variable flow field there. Evidence of fronts exists where the currents abruptly change 

direction.

Figure 12. Daily average surface currents from HFR, September 10, 2014. The black 

box shows the location of the Burger lease patch, and the pink diamond shows the location of dye 

injection #1. Vector color indicates surface current speed.
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Figure 13. Daily average surface currents from HFR, September 15, 2014. The black 

box shows the location of the Burger lease patch, and the pink diamond shows the location of dye 

injection #2. Vector color indicates surface current speed.

The vertical structure of currents below these surface features can be estimated by 

examining the data from nearby moored ADCPs and meteorological buoys. These will 

not be exact versions of the currents during the dye releases, but will give a helpful 

estimation of vertical shear and variability in time. During the period of dye injection #1 

(Figure 14), the surface currents at the Klondike meteorological buoy shows the influence 

of the large-scale alongshore flow noted in the HFR figure. However, the surface currents 

at the Burger ADCP mooring show strong but highly variable current with a prominent 

inertial signal. Currents in the surface layer there are vertically uniform down to at least 

16 m, but the bottom layer exhibits steady onshore flow, meaning that there is strong 

vertical shear between the MW and WW layers. At Burger, conditions are consistent 

throughout the entire period of the first experiment, though given the spatial 

heterogeneity in this area, this may not be true at the dye injection site itself.

In contrast, the flow during the second dye injection is highly variable in time (Figure 

15). A very strong north/northeastward current event at the nearby Site05 ADCP mooring 

ends abruptly immediately prior to the dye injection, and there are hints in the surface 

currents at Klondike and in the hourly HFR maps (not shown) that this adjustment has a 

wide scale. Below the surface, currents are variable; currents are occasionally in opposing 
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directions at different depths, and there is a short period of inertial motion at mid-water 

that is not evident at the surface or bottom.

Figure 14. Meteorological buoy and ADCP mooring data, September 8–13, 2014.

Winds and currents are in vicinity of dye injection #1, and vectors are oriented in the toward

direction.
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Figure 15. Meteorological buoy and ADCP mooring data, September 13–17, 2014.

Winds and currents are in vicinity of dye injection #2, and vectors are oriented in the toward

direction.


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4.2. 2015 Field Experiment

Figure 18 shows the study area for ARCTREX’s 2015 observational effort. The ship 

track for the 2015 dye release surveys is shown in dark gray, and the 2015 dye injection 

described in this report is shown in the black box. Wind data during 2015 was obtained 

from the Klondike ConocoPhillips meteorological buoy, but there was no wave data 

collected this year and the inshore ADCP mooring, Site05, had been moved to another 

location. Also shown in the figure is the SST field from the MODIS satellite as an 

average over the time of the dye injection surveys. The warmer waters of the ACC can be 

seen in the southeast portion of the map, but the overall temperature gradient is lower 

because the very cold MW that was present in 2014 is absent in 2015, and the meanders 

and fronts are comparatively subtle. However, the study area for the injection does lie

within a weak gradient in SST.

Figure 18. 2015 map of the ARCTREX study area, Northeastern Chukchi Sea. The

2015 dye injection surveys described in this report are outlined by the black box. The ship track is 

shown in dark gray. The location of dye injection #3 is depicted by a red star, and the location of 

the cross-shelf transect is in blue. The ConocoPhillips meteorological buoy, the location of our 

wind measurements, is the red dot located in the Klondike lease patch. Average SST from 

MODIS is also shown, shaded in °C. Isobaths are contoured at increments of 10 m depth.
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Figure 19. Cross-shelf vertical sections of water properties, September 2015. Salinity 

(top), temperature (middle), and density (lower) collected by the Acrobat during the transect from 

the northern site to the site of dye injection #3, which is marked with a red dot.

Figure 19 shows cross sections of salinity, temperature, and density from the cross-shelf

survey offshore of dye injection #3 that is marked on Figure 18 above. Surface 

temperature ranges from 4–7°C. Inshore, the water is of similar temperature to water

farther inshore in 2014, suggesting that ACW has extended farther across the shelf, 

whereas offshore, the water is >3°C warmer. At depth offshore, the water is also warmer 

than in 2014 and fresher, so that stratification is greatly reduced even offshore. The 

greatest portion of the shelf is occupied by vertically homogeneous water that is 4–5°C 

and ~32 psu, making it impossible to replicate the 2014 experiments in the two-layer, 

frontally complex environment found then.
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Figure 20. Sea ice concentration from special sensor microwave imager (SSMI), 

2014 and 2015.

The absence of MW can be attributed to 2015’s record low maximum sea ice extent. In 

February 2015, the maximum ice extent was the lowest in the satellite record, with 

below-average ice conditions everywhere except in the Labrador Sea and Davis Strait

(http://nsidc.org/arcticseaicenews/2015/03/2015-maximum-lowest-on-record/). In the 

Chukchi Sea, this translated to earlier and farther ice retreat (Figure 20). In July 2014, 

portions of the Chukchi shelf had as much as 50% sea ice coverage, but by July 2015, the 

ice had completely retreated. In September, sea ice was far from the study area in both 

years, but the impact was still felt. Less sea ice formed means less WW, and less sea ice 

melted means less MW, leading to low stratification in 2015.
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Figure 21 Temperature-salinity diagram for dye injection #3, September 2015.

Points are T-S properties measured by the Acrobat outside (black) and inside (blue-to-red

indicating hours after the dye injection) the dye patch. The red dot marks the T-S of dye 

injection #3.

The resulting differences in water masses are clearly evident in the 2015 T-S diagram 

(Figure 21), which depicts water mass properties from the cross-shelf section and during 

the dye release. Clearly, in 2015, the MW is absent. Dye injection #3 was performed in 

water whose properties were confined to 6–7°C temperature and 31–31.25 psu water, 

much warmer and saltier than in 2014 indistinguishable from the ACW as shown in 

Figure 21 above. The relatively small amount of WW encountered had end member 

properties of 32.2 psu and ~ –1°C, barely cold enough to quality as WW. Instead, the 

water of the dye injection was mixing only with slightly colder BSW at depth.
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Figure 22. Environmental conditions extracted from NOAA’s WaveWatchIII model, 

September 2015. Model output has been interpolated to the location of the Klondike 

ConocoPhillips meteorological buoy. Wind vectors are presented along a time series of wind 

speed magnitude (top panel) with significant wave height (middle panel) and peak wave period

(bottom panel). Red vertical lines depict the 2015 dye injections and the horizontal line indicates 

their duration. Arrow directions indicate the direction the wind is blowing toward.

Wind and wave data during September 2015 are represented by output from the WW3

model (Figure 22). In contrast to 2014, the wind and wave conditions leading up to the 

first dye injection on September 7, 2015, were relatively calm. Winds were easterly with 

5–7 m s–1 speeds, with the exception of a single, short-lived event on September 4, which 

reached speeds of 10 m s–1. Leading up to ARCTREX, significant wave heights hovered 

around 1 m. Just after the deep-water injection on September 7, 2015, wind speeds 

increased rapidly, from 4 to 8 m s–1, and associated wave heights increased from 0.5 to

1.75 m. After this first burst of wind, a second wind event occurred with wind speeds 

ramping up very rapidly from 4 to 14 m s–1 from the northeast; peak wind speeds were 

observed on September 9, the same day as the dye injection #3. Modeled wave heights 

increased from 1 to 2 meters during the second injection of 2015. Although sea states 

with greater than 2 m were safely operated in during the 2014 experiment, it was 

determined that the sea state after the rapid wind event on September 9 did not permit 

safe back-deck operations. We feel that this particular wind event was not accurately 
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described by the model output of WW3. Wind speeds remained at or above 10 m s–1 until 

midday on September 12, when they relaxed.

Figure 23. Daily average surface currents from HFR, September 9, 2015. The black 

box shows the location of the Burger lease patch, and the red square shows the location of dye 

injection #3. Vector color indicates surface current speed.

Figure 23 shows the daily average HFR field for the release on September 9, 2015. Note 

that the HFR station in Point Lay was moved to Icy Cape in 2015 in an attempt to fill the 

data gap in the convergence/divergence zone, moving the edge of the coverage closer to 

the dye injection site; also, data for this year have not been fully processed, so should be 

considered preliminary. However, it can be seen that once again, the dye injection 

occurred in an area of offshore flow, when other areas of the shelf have alongshore flow.

It appears the ACC is weak, if not reversed, perhaps a consequence of the upwelling 

favorable winds that blew during the first half of September (Figure 22). By September 

11, the ACC has fully reversed, and currents are toward the west or southwest over the 

entire HFR coverage area.
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Figure 24. Meteorological buoy and ADCP mooring data, September 8–13, 2015.

Winds and currents are in vicinity of dye injection #3, and vectors are oriented in the toward

direction.
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Mooring data is substantially reduced in 2015 due to the end of CSESP and the retreat of 

Shell from the Chukchi Sea. The Klondike meteorological buoy shows upwelling 

favorable winds prior to and after dye injection #3, while currents shift from southeast to 

southwest. There is no ADCP mooring near the 2015 ARCTREX survey site, but at the 

Burger ADCP mooring, currents are weak and variable before strengthening to nearly 

vertically homogeneous eastward flow. It is unlikely, though, that these currents 

accurately describe conditions farther inshore beyond showing that currents in early 

September 2015 respond dramatically to the strong and persistent southwestward wind—

a condition different from the pressure gradient forced currents in 2014.

5. Dye Injection Results

5.1. 2014 Dye Injection #1

The dye study commenced with an injection of 50 kg of Rhodamine-WT dye into the 

surface mixed layer on September 10, 2014. The dye was tracked with shipboard surveys 

as the patch moved south/east throughout the 75-hour dye study. An Acrobat survey in a

butterfly pattern measured wider-scale T-S properties toward the end of the first dye 

study (more detail in Figure 27). There is a long gap before the penultimate survey (#22) 

of dye injection #1 because we interrupted the dye survey to perform the survey of 

hydrography in the region.

5.1.1. Dye	Patch	Evolution	and	Advection

The majority of the analysis in this report focuses on dye injection #1 in 2014 because 

that dye release was tracked over 75 hours and provides the most detailed view of the 

evolution of a dye patch. Figure 25 below shows a sequence of dye patches, surface 

density, and drifter trajectories for the first dye experiment, where we made a total of 23 

surveys of the dye patch. The red dots in Figure 25 depict the dye’s centroid for each of 

the 23 patch surveys. The red arrows show the winds, which are from the east-northeast,

while the blue arrow shows the mean current in the upper 10 m of the water column. For 

a select number of patches we also plot the dye’s distribution along surface density field 

and the ship tracks that were used to map each patch. Both the drifters and the dye patch 

travel north somewhat before moving quickly to the southeast. The dye patch is then 

sharply strained along a density front for patches 11–13; we call this a “frontal straining 

event” in later discussion. It should be noted that a large portion of the dye patch was not 

included in the surveys after patch 16 due to the patch’s extended tail.

In general, the movement of the dye is parallel to isopycnals, consistent with geostrophic 

flows, although there are numerous cases that deviate from this. During the first 8–9 

surveys (the first 12 hours), the movement of the patch nearly completes a clockwise loop 

consistent with the inertial period motion seen in the current meter records. Between 

patches 10 and 14 there is a rapid movement of the dye to the south-southeast that 

coincides with sharper surface density gradients; this motion is consistent with 

geostrophy. During patches 15–21, the patch slows again as surface density gradients 
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weaken and its motion turns eastward. There was a gap between surveys of the patch 

because of the ~24 hour butterfly pattern survey, after which time the surveys of the last 

two patches (22 and 23) indicate an abrupt change of direction to the south. Over this 

entire trajectory, the mean density of the dye patch increased. However, between patches

16 and 17, we stopped sampling approximately 30% of the dye—the long tail of dye 

apparent in the western end of patch 16.

Figure 25. Mapped patches of dye for the first 75 hours after dye injection #1. The 

centers of mass of dye patches are shown by red dots. Shaded contours of dye concentration, 

contours of density, and the gray ship tracks of the sampling transects are offset from actual 

position but connected to them with heavy black lines and identified with the patch number. 

Tracks of drifters for same time period are shown in purple.

Drifters were initially deployed in the middle of the dye patch, and there is general 

agreement between the trajectories of the two. Initially, both dye and drifters went toward

the south-southeast, though the dye seems to have experienced inertial motion whereas 

the drifter trajectories do not show it. However, between patches 15–21, the drifters went 

farther south than the dye patch, and this separation increased over time. Eventually the 

drifters slowed their southerly motion and followed a clockwise trajectory suggestive of 

inertial period motion themselves.
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The general movement to the west by the drifters is consistent with the effects of wind on 

the drifters. It is likely that near-surface currents, which the 1 m drogued drifters follow, 

are more downwind than the mean currents in the mixed layer, which are more influential

on the advection of the dye patch. Interestingly, the initial trajectory of the drifters, unlike 

the dye, shows no evidence of inertial motion; neither the wind nor shear in the mixed 

layer seems to explain this difference. It is also important to note that both the drifters 

and the dye moved in the opposite direction of the Ekman driven flows, which would be 

to the north-northwest. This suggests that the flows are driven by pressure gradients 

rather than winds. This conjecture is also consistent with the observation that the dye 

patch accelerated in the presence of elevated density gradients, with the momentum 

balances calculated earlier, and with established knowledge of the Chukchi Sea.

Figure 26. Currents and dye trajectory, dye injection #1. Vectors indicate the direction 

of mean density gradient (black), mean current in upper 10 m from shipboard survey (blue) and 

the mean speed and trajectory of the dye (purple) for patches 1–21. Patch trajectory is based on a 

centered difference estimate and thus is only estimated for patches 2–20.

To illustrate the relationship between the density gradient and advection more concisely,

Figure 26 shows a timeline of the density gradient (black arrow), along with estimates of 

the advection based on the mean current in the upper 10 m from the shipboard ADCP 

(blue arrow) and the trajectory of the dye (purple arrow) for the first 20 patch surveys.

The magnitude and direction of the density gradient is relatively constant for the first 4–5 

patches during which time both velocity vectors rotate clockwise approximately 180 

degrees. This is consistent with translation due to inertial motion. Thereafter, the density 

gradient rotates counterclockwise as the dye moves into an area of stronger density 

gradient; during this, the flow rapidly accelerates and is 90 degrees to the left of the 

density gradient, consistent with geostrophic flow in a surface front. Finally, the 

horizontal density gradient weakens and reverses, and currents weaken and become more 

westward. 
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Figure 27. Surface density and drifter trajectories during dye injection #1. Surface 

density (color) is shown with drifter trajectories (black). The dotted red line depicts the shape of 

the frontal boundary inferred by surface density map. Numbers indicating hours after injection are 

positioned at the location of the dye patch centroid.

Figure 27 shows the surface density measured by the ship’s TSG during the first dye 

experiment with the trajectories of the dye and the drifters. The large-scale structure of 

the density field is characterized by low-density water to the northwest and high-density 

waters to the south. Strong east/west density gradients are evident in the middle of the 

survey where the patch accelerated. However, the structure of this frontal system is 

complex, and in the vicinity of the dye’s trajectory it appears to be associated with a 

lateral intrusion of MW into the warmer mid-shelf waters; the intrusion is 4–5 km long 

and 2 km wide and is indicated by the red-dotted line in the figure. The dye patch crossed 

this intrusion into the warmer and more saline fluid, then drifted to the east more slowly. 

It appears that in contrast, the drifters remained in the MW as evidenced by the densities 

measured when the drifters were retrieved. The dye patch’s crossing of density surfaces is 

enabled by the fact that its density dynamically changes due to mixing processes, as will 

be discussed.

To relate conditions within the dye plume to those of the wider shelf, an earlier figure, 

Figure 9, shows the T-S properties from the cross-shelf survey, the evolving dye patch 

(blue to red indicating the time after injection), and the butterfly survey performed before 

the final two patch surveys. Initially, the dye patch appears to mix with BSW. While 

some of this is horizontal mixing due to the dye crossing the front into warmer water 

between hours 10–20, both the changing T-S properties of the dye and the crossing of 
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horizontal density gradients are likely primarily due to vertical mixing processes. The 

vertical cross-shelf sections (Figure 8) show that underlying the surface MW water mass 

is a subsurface intrusion of warm/salty BSW that is mixed into the surface layer from 

below. After hour 40, this intruded layer has been mixed away and now the mixed layer 

(and dye) begins incorporating WW from below. The mixing becomes increasingly 

diapycnal toward the end of the experiment. Data collected during the butterfly survey 

indicate only mixing between the upper-layer MW and the lower-layer WW. Note that 

this differs from the T-S properties that we observed in the larger-scale survey before dye 

injection #1, which indicates relatively little mixing between these water masses. We 

suggest that it is the strong and persistent winds during the dye experiment that generated

mixing between winter and melt waters. In contrast, the weaker winds prior to the crossshelf survey allowed the shelf water to intrude between the layers of WW and MW,

creating a buffer that limited direct mixing between these water masses. 

Figure 28–Figure 31 show vertical transects of dye concentration of selected patches. The 

transects were selected to be as parallel to the local density gradient as possible and still 

contain the maximum dye concentration. The horizontal coordinates were defined such 

that the origin of the x-axis is the maximum dye concentration. Patches 1–7 are similar; 

the surface layer is weakly stratified with a horizontal gradient of ~1 kg m–3 m–1. Beneath 

the upper layer lies a 5–7 m thick layer of warmer BSW water that is associated with the 

intrusions seen in the vertical sections of physical properties (Figure 8). Below this layer 

is the cold salty WW. Over the first 7 patches, the maximum temperature of the 

intermediate layer varies from 2 to 2.5°C and its thickness varies from 3–6 m.

The evolution of the dye patch’s temperature and salinity relative to the surrounding

density field that was evident in the T-S diagram (Figure 9) can also be seen in Figure 

28–Figure 31. Most notable is a continued increase in the dye’s salinity and density, as 

the homogeneous water mass that the dye was injected into evolves through mixing with 

its surrounding waters. For example, in patch 1 the core of the dye has a salinity of 28.86 

psu while by patch 7 the salinity has increased to 28.90 psu. These fields have been 

corrected for advection, but nevertheless, the dye moves relative to the background salt 

field by approximately 1 cm s

–1 (see section 6.3). Between patches 8–12, the upper layer 

entrains the middle layer into the tracer patch at mid-depth which causes a permanent

increase in the dye’s salinity and a temporary increase in the dye’s temperature. After 

patch 12, the intermediate layer has vanished and the temperature, salinity, and density of 

the upper layer have increased. Thereafter, the MW and WW mixed and the upper layer 

temperature have decreased while its density and salinity continue to increase. It is 

interesting to note that the horizontal density gradient in the upper layer has reduced 

significantly in the final patches.
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Figure 28. Vertical transects of dye concentration measured in patch 1 of dye 

injection #1. Dye concentration (color) is plotted with contours of density (top), salinity

(middle), and temperature (bottom). The transects are parallel to the local density gradient. The 

horizontal coordinate system is such that the origin of the x-axis represents the maximum dye 

concentration.
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Figure 29. Vertical transects of dye concentration measured in patch 7 of dye 

injection #1. Plots as in Figure 28.
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Figure 30. Vertical transects of dye concentration measured in patch 12 of dye 

injection #1. Plots as in Figure 28.
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Figure 31. Vertical transects of dye concentration measured in patch 17 of dye 

injection #1. Plots as in Figure 28.

Changes in the physical properties of the dye patch can be summarized by plots of the

mean temperature, salinity, and density over time (Figure 32). Density and salinity 

increase over time, consistent with the surface boundary layer mixing with denser water 

below. Temperature increases around the time of the frontal straining event, when the dye 

patch extended along a density front during patches 11–13. The temperature increases 

between patches 9–13 from 1.52°C to 1.6°C, and this increase occurred as the ~6 m thick 

layer of intermediate water of 2.2°C mixed into the 15 m thick upper layer of 1.52°C. 

Simple mixing of these two layers explains the observed increase in the dye’s 

temperature. Thereafter, the water of the dye patch cools—though some of this variability 

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Figure 33. Summary of 2014 VMP station 1 data. The upper panel shows the vertical 

structure of dissipation over time. Lower panels show mean vertical profiles (from left to right) of 

dissipation, temperature, salinity, N2, density, and diffusivity. The green dashed line in panel g 

represents background molecular levels of diffusivity.

VMP data show a two-layer system with enhanced turbulence levels in a 15–20 m thick

turbulent surface mixed layer. At the base of the mixed layer, Kv measured by the VMP 

compares favorably with that computed from dye concentration gradients. In contrast, the 

bottom layer, from 20–30 m, had low levels of turbulence with almost no enhancement 

above background molecular levels, and no indication of a bottom boundary layer (BBL). 

It is likely that the BBL was not detected because the VMP was not able to get close 

enough to the bottom, but that one exists in a thin layer within a meter or so of the 

bottom. It should be noted that the turbulence and mixing levels were well within the 

resolvable range of the instrument, but were smaller in the bottom layer than what is 

typically found on continental shelves. In contrast to the tidally dominated Irish Sea 

(Simpson et al.1996), surface forcing dominates the weak tidal forcing of the Chukchi 

Shelf.

5.1.3. Horizontal	Dispersion

Figure 34 shows the time rate of change of the dye’s second moment (D2), from which a 

horizontal dispersion coefficient, KH, can be estimated, 

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Figure 35. Drifters released during dye injection #1, September 10–11, 2014.The top 

panel contains the trajectories of each drifter in the cluster (gray) and the mean SST measured by 

the drifters plotted along the positions of the center of mass (color). Below are time series of the 

velocity of the center of mass, the second moment (i.e., spreading) of the drifter cluster (blue) +/–

one standard deviation (purple), and the mean SST measured by the drifters.
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5.2. 2014 Dye Injection #2

5.2.1. Dye	Patch	Evolution	and	Advection

During dye injection #1, the dye patch remained coherent and sampling could continue

for several days. With a short amount of cruise time remaining, we decided to try 

sampling in a more dynamically active region where the dye would disperse more 

quickly. A location at a frontal boundary between offshore MW and northward flowing 

BSW mid-shelf water was chosen for dye injection #2. Prior to the dye release, the R/V

Norseman II steamed south, crossing the front at approximately 162°W, 70.7°N; dye was 

injected inshore of the front in weakly stratified water. The dye injection system pumped 

~45 kg of Rhodamine-WT fluorescent dye into the surface layer at ~10 m depth while the 

ship was allowed to drift. The injection took about ~20 min. After the injection, the dye 

was surveyed over the course of ~1 day with 11 synoptic realizations of the dye (patches) 

measured. Over the course of the experiment, winds were generally to the west or 

southwest at 7–8 m s

–1

. 
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Figure 36. Mapped patches of dye for dye injection #2. The centers of mass of dye 

patches are shown by numbered red dots. Shaded contours of dye concentration, contours of 

density, and the ship tracks of the sampling transects are offset from the actual positions but 

connected to them with heavy black lines and identified by patch number. Insets show Patch 6

northward (Inset A) and westward (Inset B) vertical sections with shaded contours of dye 

concentration in kg m–3, and the 30.9 and 31.2 psu salinity isohalines in green.

Immediately following the initial injection, the dye remained within the surface mixed 

layer and was clearly visible from the bridge of the R/V Norseman II for about two hours.

However, the dye patch was then subducted and advected under the fresher water north 

of the injection site (Figure 36). The inset panels of Figure 36 show how the dye had

evolved by patch 8. The tilting isohalines (green) in the westward elevation profiles 

represent the subsurface expression of the front. Instead of spreading evenly through a 

surface layer, the dye contours parallel the isohalines as they deepen northward. The 

northward view reveals that this subduction occurs along a downward spiral, creating a 

complex shape that is not easy to integrate over. The subducted dye was tracked with the 

towed Acrobat system only, because the hull-mounted TSG was positioned at 

~3 m depth.
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Figure 37 shows the density measured by the TSG at the surface along the ship track 

immediately before and during dye injection #2. The surface expression of the front is 

evident as an abrupt transition between waters with density of 1024.5 and ~1024 kg m–3.

Over the course of the surveys, the front, along with the dye, is advected toward the 

north, resulting in a checkerboard of different locations for the front as the surveys 

progress. Currents in this area of the shelf are variable, but this northward advection is in 

accordance with surface currents measured by both the HFR (Figure 13) and nearby 

industry ADCP mooring Site05 (Figure 15).

Figure 37. Surface density during dye injection #2. Ship tracklines colored according to 

surface density (as sigma-t = density minus 1000) measured by the TSG before and during dye 

injection #2. The dotted line indicates the approximate location of the front, and the black arrows 

indicate its approximate path.

Figure 38 shows the mean temperature, salinity, and density of each dye patch for the 

first 30 hours. After a brief increase in density, it and salinity remain relatively constant, 

with ranges of only .08 kg m–3 and 0.03 respectively, which indicates the subducted water 

is maintaining its identity as it traverses; the variability in these properties reflects the 
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difficulty of integrating over the dye’s irregular shape. Temperature increases by ~0.2°C, 

which is twice the increase during injection #1.

Figure 38. Time series of mean patch temperature, salinity, and density of dye 

injection #2.

5.2.2. Vertical	Dispersion

Calculation of the vertical eddy diffusivity during dye injection #1 was possible because 

the dye filled the mixed layer relatively uniformly, but the active subduction of dye 

injection #2 created significant patchiness without a well-defined salinity gradient at the 

dye patch’s base. However, comparison of the vertical structure of the two injections and 

the evolution of the patches can give hints regarding the vertical dispersion of the second 

injection.

Figure 39 shows density profiles and dye concentrations for both injections (upper 

panels) along with the dye evolution in density coordinates over time (bottom panels).

Injection 1 occurred in a surface mixed layer of a two-layer system offshore of a front. 

The dye patch filled the upper mixed layer and remained at the surface layer throughout 

the experiment, though its density increased. The upper layer expanded by 5 m over the 

course of the experiment, and so the thickness of the dye also increased, dispersing

linearly over the first 40 hours. Dye mixed mainly into higher density water throughout 

the experiment (Figure 39, lower left). 

In contrast, during the second injection onshore of a front, the dye patch quickly 

subducted under the fresher body of water to the north (Figure 36). During the surveys,

the mean density of the dye patch increased by 0.05 kg m–3 in the first 5 hours, then 

remained fairly constant (Figure 39), implying that the water mass the dye followed into 

the middle of the water column mixed little with the upper and lower layers. However, in 

this less stratified environment, the dye mixed into fresher/light water above as well as 

the denser water below, which is consistent with the warming of the dye patch 

noted earlier.
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Figure 39. Evolution of dye injections #1 and #2. Left, top: injection #1 density profile and 

dye concentration. Left, bottom: dye evolution in density coordinates. Right, top: injection #2 

density profile and dye concentration. Right, bottom: dye evolution in density coordinates.

5.2.3. Horizontal	Dispersion

We were only able to calculate horizontal dispersion of dye injection #2 for the first 30 

hours due to the complexity of the patch shape and its subduction. The characteristics of 

the patch evolution make it difficult to reliably compute dye inventories complete enough 

to make stable calculations of statistical moments of the dye distribution. However, the 

second moment of the dye patch (Figure 40) shows a steady increase during that time; KH

was calculated to be 3.7 m2s

–1 before the subduction and 34 m2

s

–1 after subduction—an 

order of magnitude increase.
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Figure 40. Second moment of the dye patches of dye injection #2.

In sharp contrast to the analysis of the dye, plots of drifter statistics (Figure 41) show that 

the variance of the drifter cluster remains low throughout the entire experiment. There is 

little evidence of an inertial signal in velocity, unlike the first dye injection. Unlike the 

mean temperature of the dye patch (Figure 38), SST increases by almost 2°C but then 

decrease again, confirming the complex structure of the front at the surface. The second 

moment of the drifter cluster, as calculated via pairwise comparisons, is an order of 

magnitude smaller than that of the dye patch, and even decreases as the drifters converge 

at the end of the day. The horizontal eddy diffusivity, KH, calculated via equation (1)

oscillates around zero as the drifters diverge and converge. It is clear from the 

comparison that the subduction of the dye greatly enhanced its dispersion, and that 

conditions at the surface were very different from those within the intrusion.
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Figure 41. Drifters released during dye injection #2, September 15–16, 2014. The top 

panel contains the trajectories of each drifter in the cluster (gray) and the mean SST measured by 

the drifters plotted along the positions of the center of mass (color). Below are time series of the 

velocity of the center of mass, the second moment (i.e., spreading) of the drifter cluster (blue) +/–

one standard deviation (purple), and the mean SST measured by the drifters.
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5.3. 2015 Dye Injection #3

The 2015 dye study commenced with a surface injection of Rhodamine dye in the center 

of the box outlined in Figure 18. The dye was tracked with shipboard surveys as the patch 

evolved throughout the 42-hour dye study. The larger-scale survey was done before the 

dye release to measure T-S properties in the vicinity of the dye study. Dye concentration 

measurements are restricted to those by the TSG at 3 m depth, though the physical 

variables were measured throughout the water column by the Acrobat.

5.3.1. Dye	Patch	Evolution	and	Advection

In 2014, the dye injections were performed on either side of the front between MW and 

mid-shelf water. The setting for dye injection #3 was near the location of dye injection 

#2, but in 2015, the water was much warmer, slightly fresher, and distant from any MW.

Again, we performed an injection into the surface layer and seeded the patch with 10

satellite-tracked drifters. Bad weather made data collection particularly challenging; 

winds were up to 22 knots and there were 6–7 ft seas. Despite this, we were able to 

successfully survey the dye extent 19 times and transmitted these maps to Arctic ERMA

in near real time. The injection parameters for 2015 dye injection #3 are summarized in 

Table 1 and VMP parameters are summarized in Table 2.

Figure 42. Mapped patches of dye for dye injection #3. The centers of mass of dye 

patches are shown by numbered red dots. Shaded contours of dye concentration, contours of 

density, and the ship tracks of the sampling transects are offset from the actual positions but 

connected to them with heavy black lines and identified with the patch number.
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The dye moved to the northeast initially, then sharply reversed direction and went eastsoutheast (Figure 42). The mapped surface dye patches show that immediately after 

injection, the dye has a Gaussian distribution; the core of the dye path is contained within 

a 400 × 400 m2 area, and at detectable concentrations, the entire patch occupies an area of 

800 × 800 m2. In the survey of the final patch, the dye has been stretched and extended 

along isopycnals. Dispersion and straining has elongated the patch extensively, with the 

dye now covering an approximate area of 2 × 60 km2 oriented, for the most part, along 

the surface density gradient.

The wind was strongly northeasterly through most of the 2015 field season, though both 

the dye and drifters (shown below) moved up-wind initially. It isn’t until patch 10, 15

hours after the injection, that the dye trajectory reverses direction. Once it does, it is 

swiftly advected in the direction of the wind, accelerating even as the wind slackens 

through patch 19.

Figure 43. Time series of mean patch temperature, salinity, and density of dye 

injection #3.
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During the surveys, the dye patch’s density and salinity increased, and its temperature 

decreased (Figure 43). There is little variation in the rate of these changes, reflective of 

the more homogeneous nature of the physical environment relative to that of 2014. The 

changes that occur are consistent with vertical mixing and deepening of the mixed later.

In the vertical sections of density (Figure 44), it appears the mixed layer did deepen

slightly. The wave-like oscillations of the pycnocline in that figure are due to the ship’s 

traversing the sloping isopycnals that the dye patch is stretched along, but there is a 

deepening of mixed layer depth below the dye patch from roughly 14 m deep in the 

transects across patch 14 (not shown) to 15–16 m deep in the transects across patch 19.

Figure 44. Vertical section of density with surface dye concentration, patch 19, dye 

injection #3. The top panel is surface dye concentration measured by the ship’s TSG system 

along the ship track as it performed the survey of patch 19. High values occur when crossing the 

dye patch. The bottom panel is a vertical section of density along the ship track.

5.3.2. Vertical	Dispersion

Because of the lack of dye concentration measurements at depth in 2015, vertical 

diffusion calculations based on dye are not available. However, the VMP was deployed at

three stations consisting of multiple full-depth casts to approximately 35 m. The first two 

stations were at the site of the deep dye injection, ~1° north of dye injection #3, but the 

third station was conducted immediately prior to and near the surface release. Turbulence 

microstructure was returned consistently from 5 m to 30 m. The first two stations showed 

a more distinct two-layer structure, as can be seen in Figure 45, panels e and h. 
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Turbulence and mixing was present throughout the water column. The dissipation (ε) and 

mixing (Kv) decrease from a near-surface maximum, with an increase near the bottom 5 

meters, likely due to the instrument penetrating into the near-bottom log-layer. It should 

be noted that the three turbulence stations suggest that the vertical structure of turbulence 

on the Chukchi is highly heterogeneous in space and time.

Figure 45. Summary of 2015 VMP stations 1–3. The upper three panels show the vertical 

structure of dissipation over time for the three stations occupied. Lower panels show mean 

vertical profiles (from left to right) of dissipation, temperature, salinity, N2, density, and 

diffusivity.

5.3.3. Horizontal	Dispersion

Comparison of KH calculated from the second moment of the dye (Figure 46) and drifters 

(Figure 47) shows the two methods of measurement give consistent values; averaged over 

the 2 day experiment, KH = 7.4 m2s

–1 for dye and 7.1 m2

s

–1 for the drifters. That is likely 

because the dye calculations had to be based on surface measurements alone in 2015, so 

both measured the same environment. This is echoed in the similarity of SST measured 

by drifters and the mean temperature of the dye patch shown earlier. The trajectories of 

the two differ, however, because the drifters are more responsive to wind and waves than 

the dye is. For a surface-constrained tracer, such as oil, in an area without strong fronts, a 
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valuable measure of horizontal dispersion can be gained from drifters alone, even if they 

don’t follow the same trajectory as the tracer.

Figure 46. Second moment of the dye patches of dye injection #3.
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Figure 47. Drifters released during dye injection #3, September 9–11, 2015. The top 

panel contains the trajectories of each drifter in the cluster (gray) and the mean SST measured by 

the drifters plotted along the positions of the center of mass (color). Below are time series of the 

velocity of the center of mass, the second moment (i.e., spreading) of the drifter cluster (blue) +/–

one standard deviation (purple), and the mean SST measured by the drifters.
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6. Discussion

In this section we discuss the three dye releases and highlight similarities and differences 

between the three field efforts. All three releases were conducted in the surface mixed 

layer and the dye quickly occupied the entire mixed layer after initial injection. Diapycnal 

mixing was low to moderate during all three dye releases despite considerable wind 

forcing. In all cases, advection was a prominent process with the patches becoming 

anisotrophic as they stretched along density gradients.

Figure 48. Summary of dye injections.

During the first dye release in 2014, the pycnocline was strong with a density difference 

of ~3.5 kg m–3 between the surface layer and bottom layer, and with, at least initially, an 

intermediate layer of warmer water. The surface waters consisted mainly of meltwater 

(MW) with low salinities (29 psu or less) from in situ ice melt and moderately cold 

temperatures (~2°C). The strong two-layer system inhibited diapycnal mixing and 

entrainment, though during the course of the experiment, the intermediate layer was 

mixed away and there was some mixing between the MW and winter water (WW). The 

VMP profiles show no turbulent mixing in the bottom layer WW. This is also evident 

from the evolution of the dye, which remained within the mixed layer as it was advected 

toward the south and southeast.

The second dye release in 2014 occurred inshore of a front in an area with strong 

horizontal density and temperature gradients. Initially, the dye patch evolved in a similar 
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manner to the first, but then there were notable differences. The dye remained visible at 

the surface for about two hours as it dispersed through the mixed layer, but then the dye 

subducted at a front between offshore MW and the northward advecting ACC. The dye 

transitioned into an intrapycnal subsurface dye patch with a complex shape and trajectory 

that could only be tracked for ~1 day (Figure 36). The subsequent dispersion was about 

three times larger during the subduction phase.

In September 2015, following a year of record low sea ice, the dye release took place in 

less stratified water with fewer surface frontal features. Turbulence and mixing was 

present throughout the water column as measured directly using the VMP instrument, 

with near-surface and near-bottom local maxima in mixing. The near-bottom maxima 

was likely due to the presence of a well-developed bottom boundary layer. The dye was 

strained and dispersed over the 19 realizations of the patch that we performed, while the 

mixed layer deepened.

Dispersion was estimated for each main dye release by making a detailed inventory of the 

dye patch over time and is summarized in Table 4 and Figure 49.

Table 4. Dispersion estimates for each field experiment.

Dye Injection

#

Average dispersion

(m2s

–1

)

Comment

1 7.7 Surface release and for period with 

well-defined dye patch

2 33.2 Surface release with subsequent 

subduction

3 7.4 Surface release with high wind and wave 

environment
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Figure 49. Horizontal dispersion, all ARCTREX injections.

The overall mean dispersion from all three experiments was found to be ~7.5 m2s

–1

. The 

average dispersion from dye injection #1 in 2014 was estimated at 7.7 m2s

–1 over the 

duration of patch surveys where >90% of the released dye was detected. This is close to 

the overall mean dispersion from all three experiments. Dispersion during the second 

release in 2014 was close to an order of magnitude higher during the time period when 

dye was subducting along isopycnals in the frontal region. We estimate that the 

dispersion during this phase was ~34 m2s

–1

, with pre-subduction values being ~3.7 m2s

–

1

. Dispersion values for the third experiment were 7.4 m2s

–1

, close to those of the first 

surface experiment in 2014. Estimates of dispersion determined from the ARCTREX 

project fall within those reported in the literature for shelf and coastal environments by 

Sundermeyer and Ledwell (2001) and Ledwell et al. (2004).

The field observations showed that dye distributions were significantly influenced by 

shearing and straining on scales of the mixed-layer depth in the vertical (5–15 m) and 1–

50 km in the horizontal. For example, during dye injection #1 in 2014, the dispersion 

estimated during different legs of the survey was 2.9 m2 s

–1 immediately after injection, a 

period that was dominated by inertial motions. Later on, the patch experienced 

horizontally sheared geostrophic flow and the dispersion was estimated to be 24.4 m2 s

–1

. 

Simultaneous increases in the horizontal second moments of the dye patches were 

superimposed on these larger-scale distortions.

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Figure 50. Time series of mean patch density, shear, and velocity. The upper panel 

shows density of dye over the survey. The middle panel shows shear squared between the upper 

and lower layers of the water column. The lower panel is current east-west (U, black) and northsouth (V, red) velocity from shipboard ADCP data.

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Figure 51. Analysis of wind mixing, September 2014, Klondike ConocoPhillips 

meteorological buoy. Top panel: wind speed. Middle panel: rate of energy transfer from the 

wind into the water column (∂E/∂t). Bottom panel: the sum of wind energy per event. Red vertical 

lines indicate the times of the two Rhodamine dye injections.
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Figure 52. Analysis of wind mixing, September 2015, Klondike ConocoPhillips 

meteorological buoy. Top panel: wind speed. Middle panel: rate of energy transfer from the 

wind into the water column (∂E/∂t). Bottom panel: the sum of wind energy per event. Red vertical 

lines indicate the times of the two Rhodamine dye injections.

These findings are consistent with Hauri et al. (2013), in which they found that periodic 

late-season wind events, most frequently occurring in September and October, contained 

the potential to overcome stratification and mix the water column. It also reflects the

results of Kawaguchi et al. (2015), who observed wind-forced mixing that stirred the 

upper water column and resulted in a deepening of the surface homogeneous layer. Thus 

it is likely that during dye injections #1 and #3, the observed deepening of the mixed 

layer is due to wind mixing.

6.3. Modification of Advection by Vertical Mixing

Throughout ARCTREX’s experiments, dye patches advected and strained along the 

direction of local isopycnals. However, modifications of the dye patches’ physical 

properties also caused them to move relative to the background salinity/density fields; 

they moved faster than isohalines when fronts or horizontal density gradients were 

advected normal to their orientation. We can investigate the contribution of vertical 

mixing to this process by using the value of Kv that was previously estimated assuming 

only vertical mixing changes the mean salinity of a dye patch. In this case, we apply a

1-D salt balance equation to the mixed layer’s average salinity in the direction of the 

horizontal density gradient (i.e., perpendicular to isopycnals), which is:

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2. On the ship, altered details of dye patch shapefiles allowed production to be

partially automated, speeding the dissemination of patch locations via the Internet.

3. The color-scheme representation of dye concentrations was improved. The units 

of dye concentration in 2014 had not been explained precisely enough prior to the 

experiment, leading to delays in the shapefile production.

4. An API interface was developed within ERMA that simplified the input of new 

data streams into the interface. This improved input of the dye shapefiles, but 

ironically delayed the posting of drifter tracklines. On our end, getting the 

filenames to ERMA before the experiment started would have allowed time for 

the necessary changes to the code to propagate to the production server.
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Figure 53. Arctic ERMA web display of dye injection #1, 2014. The Arctic ERMA GIS 

layer shows mapped dye patch extensions over time in an interactive web display.

Figure 53 shows an active GIS layer from NOAA’s ERMA website during the 

ARCTREX project. Each dye patch in this visualization was transmitted to ERMA, 

enabling them to produce a time series of the dye patch evolution. The ability for us to 

send near real-time data from the field, and for ERMA to ingest this into their 

management system, was a great success. We anticipate that future experiments will be 

able to display three-dimensional data in various GIS layers on the ERMA website from 

field campaigns or during a real incident. 

7. Conclusions and Recommendations

The Arctic Tracer Release Experiment (ARCTREX) project was designed to explore 

applications for mapping spilled oil in Arctic waters. This experiment tested the capacity 

of available real-time observational technology to map a dye plume that simulated an oil 

spill and to provide real-time data in space and time to response agencies. We utilized the 

existing infrastructure of the University of Alaska’s ongoing ocean-observing efforts in 

the Chukchi Sea, including real-time, two-dimensional surface current fields from 

extended-range high frequency radar and existing observing assets such as AUV gliders 
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and a towed Acrobat vehicle. To these we added detailed microstructure measurements of 

ocean turbulence, satellite-tracked surface drifters, shipboard and moored ADCP current 

meters, remotely sensed sea surface temperature and sea ice concentration, and dedicated 

dye measurements sampled with fluorometers to map a dye plume and its evolution over 

three periods during field seasons in 2014 and 2015.

Our results show that it is feasible to track a passive dye in detail using the technologies

listed above. The effort requires high-end knowledge of operating instruments and ships 

and becomes significantly more difficult if there is no surface expression of the dye, such 

as the subducting dye in release #2 in 2014. In this case, for instance, simulating 

dispersed oil that has sunk down into the water column and mapping the detailed threedimensional evolution of the plume in time and space becomes challenging. We also 

successfully transmitted data to NOAA’s Arctic ERMA and UAF’s web pages in near 

real time, proving that this capacity does exist in the Chukchi Sea with available 

technology. The results from the three dye releases show that dye patches are advected 

and strained horizontally over the full depth of the mixed layer. Dye injection #2 in 2014 

also showed that in addition to horizontal dispersion, fronts in the Chukchi Sea can 

significantly alter the fate of dye (and likely dispersed oil), and can generate conditions 

that make tracking the dye significantly more difficult. Surface features rapidly disappear 

due to subduction and are only able to be tracked using undulating subsurface 

instruments.

Other findings include:

Currents: HFR data were used onboard to identify regions of convergent flow and to 

find a suitable location for deploying dye; these data were also successfully added to 

ERMA’s real-time data feed. However, they did not resolve currents on the scale of the 

dye patches. Of more utility at these scales were the vertical current profiles measured by 

the shipboard ADCP and even the moored ADCP current meters.

Drifters: Satellite-tracked drifters were deployed throughout the ARCTREX project.

Generally, the paths of the 1 m drogued surface drifters diverged from the position of the 

centroid dye concentration of each patch after 12–24 hours. We attribute this behavior to 

the shallow drogue depth of the drifters, which would make them subject to more windwave interaction and Stoke’s drift compared to the dye patch, which is spread over the 

entire mixed layer. However, there were conditions when drifters provided useful 

parameterization of surface processes, even though the trajectories of dye and drifters 

diverged.

Gliders: AUV gliders were able to detect dye in the water column, transmitted their data 

in real time, and operated successfully in harsh weather conditions, but were not able to 

maneuver with the agility necessary to define dye patch for dispersion calculations.

Multiple gliders operating in concert would be able to estimate patch locations in a 

response situation.
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Environmental conditions presented a number of challenges to the field operations. 

Delicate instruments such as the gliders, CTD, and VMP had to be very carefully lifted 

over the side of the ship, and as wave heights reached 2.5 m, over-the-side operations had 

to be halted several times to ensure safe working conditions both for the equipment and 

for the operators. The shallow Chukchi Sea wave environment tends to be quite choppy 

compared to deep water like the Gulf of Alaska, where long-period swells and 2–3 m seas 

are still quite feasible to work in. Over-the-side operations tend to be very hectic when 

the wave periods are between 5–7 s as we experienced in the Chukchi Sea. While 

working on the back deck, constant vigilance was required to ensure the safe movement 

of personnel and instrumentation. In addition, the communications channels between the 

bridge and back deck personnel needed to be clear and consistent, as slight changes in 

ship velocity or heading would result in very different conditions at the water line. All 

told, the Acrobat was the most resilient instrument deployed by the ARCTREX 

experiment. Once it was in the water and 200–300 m of tow cable was spooled out, the 

instrument was fairly impervious to sea state or ship motion. At times, the sea state was 

too rough for safe recovery for the Acrobat so the decision was made to leave it in the 

water and continue surveying until the weather pattern shifted toward calmer conditions.

Additionally, we had planned to use a drone to survey the dye from the air, but high 

winds made this impractical.

From this extensive fieldwork and analysis, recommendations emerge for future direction

and research:

• Advanced observational-modeling framework: Currently, NOAA ERMA utilizes 

slab models or simpler circulation models in oil spill response applications. The 

results presented here show the need for a more complex treatment of ocean 

physics and dynamics. We recommend that coupled detailed observations and 

three-dimensional ocean modeling of dye and/or oil-in-water be performed.

• Oil-like dye: The dye used in this study, Rhodamine-WT, is excellent for detailed 

studies of a fully passive tracer. However, it is not a perfect simulation of oil in 

water, not even when dispersed. For more realistic oil spill applications, we 

encourage development efforts for a more positively buoyant dye with oil-like 

properties. Alternatively, smaller ocean experiments with oil in water would be 

illuminating.

• Detailed physical oceanography studies: Our fieldwork highlights the complex 

nature of ocean fronts and small-scale (<300 m horizontal) physics on passive 

tracers and their evolution in time and space. A dedicated study at these scales is 

recommended to build on the work presented here. This includes a critical need 

for near-shore dye studies of the fate of an oil spill and interaction with buoyant 

coastal waters.

• Lab experiments on buoyant dispersed oil droplets and their interaction with a 

turbulent environment: The fate of dispersed oil droplets in a turbulent boundary 

layer is not well studied and would be advised in order to parameterize this 

process into general circulation models.
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8. Acknowledgments

We would like to acknowledge the captain and crew of the RV Norseman II for their skill 

and flexibility in conducting these exercises in adaptive sampling. Cayman Irving 

produced the drifter analysis as part of his work on the U.S. Dept. Interior, Bureau of 

Ocean Energy Management (BOEM) Cooperative Agreement #M12AC00008 

("Characterization of the Circulation on the Continental Shelf Areas of the

Northern Chukchi and Western Beaufort Seas"). Chase Stoudt provided the figures of 

SSMI sea ice concentration. Elizabeth Dobbins, Hank Statscewich, and Eli Hunter

provided additional data analysis and text, and prepared the report. Shell, ConocoPhillips, 

and Statoil provided data from their current meter moorings, and ASL Environmental 

Services analyzed these data. Gliders were partly funded by the Alaska Ocean Observing 

System (AOOS). Additional funding for the HFR array was provided by BOEM 

(#M12AC00008).

9. References

Aagaard, K. 1988. Current, CTD, and pressure measurements in possible dispersal 

regions of the Chukchi Sea. Final Report. U.S. Department of the Interior, Alaska Outer 

Continental Shelf Region, 255–333.

Aagaard, K., T.J. Weingartner, S.L. Danielson, R.A. Woodgate, G.C. Johnson, and T.E.

Whitledge. 2006. Some controls on flow and salinity in Bering Strait. Geophysical 

Research Letters 33 (19): L19602. https://dx.doi.org/10.1029/2006GL026612.

Bowden, K. 1965. Horizontal mixing in the sea due to a shearing current. Journal of 

Fluid Mechanics 21 (1): 83–95. https://doi.org/10.1017/S002112065000058.

Coachman, L.K., K. Aagaard, and R.B. Tripp. 1975. Bering Strait: The Regional 

Physical Oceanography. Seattle: University of Washington Press.

Danielson, S.L. 1996. The Chukchi Sea Tidal Currents (Master’s thesis). Fairbanks, 

Alaska: University of Alaska Fairbanks.

Danielson, S.L., T.J. Weingartner, K.S. Hedstrom, K. Aagaard, R. Woodgate, E. 

Curchitser, and P.J. Stabeno. 2014. Coupled wind-forced controls of the Bering–Chukchi 

shelf circulation and the Bering Strait throughflow: Ekman transport, continental shelf 

waves, and variations of the Pacific–Arctic sea surface height gradient. Progress in 

Oceanography 125:40–61. https://dx.doi.org/10.1016/j.pocean.2014.04.006.

Denman, K.L., and M. Miyake. 1973. Behavior of the mean wind, the drag coefficient, 

and the wave field in the open ocean. Journal of Geophysical Research 78 (12): 1917–

1931. https://dx.doi.org/10.1029/JC078i012p01917.

OCS Study BOEM 2017-062

76

Kawaguchi, Y., S. Nishino, and J. Inoue. 2015. Fixed-point observation of mixed layer 

evolution in the seasonally ice-free Chukchi Sea: Turbulent mixing due to gale winds and 

internal gravity waves. Journal of Physical Oceanography 45:836–853. 

https://dx.doi.org/10.1175/JPO-D-14-0149.1.

Ledwell, J.R., T.F. Duda, M.A. Sundermeyer, and H.E. Seim. 2004. Mixing in a coastal 

environment: 1. A view from dye dispersion. Journal of Geophysical Research

109:C10013. https://dx.doi.org/10.1029/2003JC002194. 

Lueck, R.G., F. Wolk, and H. Yamazaki. 2002. Oceanic velocity microstructure 

measurements in the 20th century. Journal of Oceanography 58:153–174. 

https://dx.doi.org/10.1023/A:1015837020019.

Martini, K.I., H.L. Simmons, C.A. Stoudt, and J.K. Hutchings. 2014. Near-inertial 

internal waves and sea ice in the Beaufort Sea. Journal of Physical Oceanography

44:2212–2234. https://dx.doi.org/10.1175/JPO-D-13-0160.1. 

Mudge, T.D., A. Slonimer, J. Barrette, N. Milutinovic, D. Sadowy, and K. Borg. 2017.

Analysis of ice and metocean measurements, Chukchi Sea 2014–2015, for BOEM. 

Project report. Bureau of Ocean Energy Management, Anchorage, Alaska. ASL 

Environmental Sciences Inc., Victoria, B.C.

Münchow, A., and E.C. Carmack. 1997. Synoptic flow and density observations near an 

Arctic shelf break. Journal of Physical Oceanography 27:1402–1419.

https://doi.org/10.1175/1520-0485(1997)<1402:SFADON>2.0.CO;2.

Okubo, A.1973. Effect of shoreline irregularities on streamwise dispersion in estuaries 

and other embayments. Netherlands Journal of Sea Research 6:213–224.

https://doi.org/10.1016/0077-7579(73)90014-8.

Osborn, T.R. 1980. Estimates of the local rate of vertical diffusion from dissipation 

measurements. Journal of Physical Oceanography 1:83–89. 

https://dx.doi.org/10.1175/1520-0485(1980)010<0083:EOTLRO>2.0.CO;2.

Paquette, R.G., and R.H. Bourke. 1974. Observations on the coastal current of Arctic 

Alaska. Journal of Marine Research 32 (2): 195–207.

Pickart, R.S., L.J. Pratt, D.J. Torres, T.E. Whitledge, A.Y. Proshutinsky, K. Aagaard, 

T.A. Agnew, G.W.K. Moore, and H.J. Dail. 2010. Evolution and dynamics of the flow 

through Herald Canyon in the western Chukchi Sea. Deep Sea Research Part II: Topical 

Studies in Oceanography 57 (1–2): 5–26. https://dx.doi.org/10.1016/j.dsr2.2009.08.002.

Pingree-Shippee, K.A., N.J. Shippee, and D.E. Atkinson. 2016. Overview of Bering and 

Chukchi Sea wave states for four severe storms following common synoptic 

tracks. Journal of Atmospheric and Oceanic Technology 33:283–302. 

https://dx.doi.org/10.1175/JTECH-D-15-0153.1.
OCS Study BOEM 2017-062

77

Rainville, L., and R.A. Woodgate. 2009. Observations of internal wave generation in the 

seasonally ice-free Arctic. Geophysical Research Letters 36:L23604. 

https://dx.doi.org/10.1029/2009GL041291. 

Simpson, J.H., W.R. Crawford, T.P. Rippeth, A.R. Campbell, and J.V. Cheok. 1996. The 

vertical structure of turbulent dissipation in shelf seas. Journal of Physical 

Oceanography 26:1579–1590. https://dx.doi.org/10.1175/1520-

0485(1996)026<1579:TVSOTD>2.0.CO;2.

Spall, M.A. 2007. Circulation and water mass transformation in a model of the Chukchi

Sea. Journal of Geophysical Research 112:C05025.

https://dx.doi.org/10.1029/2005JC003364.

Sumer, S.M., and H. B.Fischer. 1977. Transverse mixing in partially stratified flow. 

Journal of the Hydraulics Division 103:587–600.

Sundermeyer, M.A., and J.R. Ledwell. 2001. Lateral dispersion over the continental 

shelf: Analysis of dye release experiments. Journal of Geophysical Research 106 (C5):

9603–9621. https://dx.doi.org/10.1029/2000JC900138.

Sverdrup, H.U. 1926. Dynamics of Tides on the North Siberian Shelf. Results from the 

Maud Expedition. Geofysiske Publikasjoner 4(5).

Timmermans, M.-L., and P. Winsor. 2013. Scales of horizontal density structure in the 

Chukchi Sea surface layer. Continental Shelf Research 52:39–45. 

https://doi.org/10.1016/j.csr.2012.10.015

Tolman, H.L. 1997. User manual and system documentation of WAVEWATCH-III 

version 1.15. NOAA / NWS / NCEP / OMB Technical Note 151.

Webb, D.C., P.J. Simonetti, and C.P. Jones. 2001. SLOCUM: an underwater glider 

propelled by environmental energy. IEEE Journal of Oceanic Engineering 26:447–452. 

https://dx.doi.org/10.1109/48.972077.

Weingartner, T., K. Aagaard, R. Woodgate, S. Danielson, Y. Sasaki, and D. Cavalieri. 

2005. Circulation on the north central Chukchi Sea shelf. Deep Sea Research Part II: 

Topical Studies in Oceanography 52 (24–26): 3150-3174.

https://dx.doi.org/10.1016/j.dsr2.2005.10.015.

Weingartner, T., P. Winsor, R.A. Potter, H. Statscewich, and E.L. Dobbins. 2012. 

Application of high frequency radar to potential hydrocarbon development areas in the 

northeast Chukchi Sea. Final report. U.S. Department of the Interior, Alaska Outer 

Continental Shelf Region Contract M09AC15207, OCS Study BOEM 2012-079.
OCS Study BOEM 2017-062

78

Weingartner, T., E. Dobbins, S. Danielson, P. Winsor, R. Potter, and H. Statscewich. 

2013. Hydrographic variability over the northeastern Chukchi Sea shelf in summer-fall 

2008–2010. Continental Shelf Research 67:5–22. 

https://dx.doi.org/10.1016/j.csr.2013.03.012.

Weingartner, T., C. Irvine, E. Dobbins, S. Danielson, L. DeSousa, B. Adams, R. Suydam, 

and W. Neatok. 2015. Satellite-tracked drifter measurements in the Chukchi and Beaufort 

Seas. Final report. U.S. Department of the Interior, Alaska Outer Continental Shelf 

Region Contract M11AC00001, OCS Study BOEM 2015-022.

Weingartner, T.J., R.A. Potter, C.A. Stoudt, E.L. Dobbins, H. Statscewich, P.R. Winsor, 

T.D. Mudge, and K. Borg. 2017. Transport and thermohaline variability in Barrow 

Canyon on the Northeastern Chukchi Sea Shelf. Journal of Geophysical Research

122:3565–3585. https://dx.doi.org/10.1002/2016JC012636.

Winsor, P., and D.C. Chapman. 2004. Pathways of Pacific water across the Chukchi Sea: 

A numerical model study. Journal of Geophysical Research 109:C03002.

https://dx.doi.org/10.1029/2003JC001962.

Woodgate, R.A., K. Aagaard, and T.J. Weingartner. 2005. A year in the physical 

oceanography of the Chukchi Sea: Moored measurements from autumn 1990–1991. Deep 

Sea Research Part II: Topical Studies in Oceanography 52 (24–26): 3116–3149.

https://doi.org/10.1016/j.dsr2.2005.10.016.

Woodgate, R.A., K. Aagaard, and T.J. Weingartner. 2006. Interannual changes in the

Bering Strait fluxes of volume, heat and freshwater between 1991 and 2004. Geophysical

Research Letters 33:L15609. https://dx.doi.org/10.1029/2006GL026931.

Young, W.R., P.B. Rhines, and C.J.R. Garrett. 1982. Shear-flow dispersion, internal 

waves and horizontal mixing in the ocean. Journal of Physical Oceanography 12:515–

527. https://doi.org/10.1175/1520-0485(1982)012<0515:SFDIWA>2.0.CO;2