ACCESSNUMBER: M11AC00001

STUDY TITLE: Satellite-tracked drifter measurements in the Chukchi and Beaufort seas

REPORT TITLE: Satellite-tracked drifter measurements in the Chukchi and Beaufort seas

CONTRACT NUMBERS(S): M11AC00001

SPONSORINGOCS REGION: Alaska

APPLICABLE PLANNING AREA: Chukchi Sea and Beaufort Sea

FISCAL YEAR(S) OF PROJECT FUNDING: 2011-2015

COMPLETION DATE OF REPORT: April 2015

COST (by fiscal year): $226,741 (FY12); $233,151(FY12) 

CUMULATIVE PROJECT COST: $459,892 

PROJECT MANAGERS: Thomas J. Weingartner

AFFILIATION: University of Alaska Fairbanks

ADDRESS: School of Fisheries and Ocean Sciences, PO Box 757220, Fairbanks, AK 99775-7220

PRINCIPAL INVESTIGATOR*: Thomas Weingartner

KEY WORDS: Surface circulation, satellite-tracked drifters, Chukchi Sea, Beaufort Sea, continental shelves.

BACKGROUND:

This study was initiated to better understand the surface circulation in the Chukchi Sea, which is not wellmeasured by subsurface moorings. In particular the circulation here results from a large-scale pressure gradient 

that impels waters northward over the shelf while the prevailing winds oppose this motion. This implies that 

there may be a large velocity shear over the water column with surface waters heavily influenced by the wind 

and subsurface waters moving largely in response to the pressure field. Shallow-drogued satellite-tracked drifters 

as used here provide a means to assess the surface circulation.

OBJECTIVES:

The overall goal of this program was to evaluate the near surface currents and their response to winds in the 

northeast Chukchi Sea where hydrocarbon exploration is underway and future development may take place. In 

particular, we sought to determine if:

1. The surface (upper 1 m) and near-surface (10 -15 m) circulation field diverges and differs from the subsurface circulation as captured by current meter measurements, and

2. The differences in the surface and sub-surface flows are related to the bathymetry, seasonally-varying 

winds, bathymetry and hydrographic conditions.

DESCRIPTION:

In August and/or September of 2011, 2012, and 2013 numerous satellite-tracked drifters were deployed in the 

northeast Chukchi Sea in conjunction with collaborators from the North Slope Borough. The drifters included 

non-drogued surface iSpheres (2012 only), 1-m drogued Microstar (MS) drifters, and 10-m drogued Surface 

Velocity Profiler (SVP) drifter. Drifter deployments were conducted with mixed drifter types in sets of 12 – 20 

drifters and tracked until the drifters were beached, ceased operating, or trapped in sea ice. There was 

considerable interannual variability in trajectories. In 2012, nearshore (within 10 miles of the Chukchi coast) 

drifters moved northeastward through Barrow Canyon. After exiting Barrow Canyon, these drifters moved 

eastward onto the Beaufort Sea shelf or the Beaufort slope, or northwestward along the Chukchi Sea slope. 

Drifters deployed offshore in the northeast Chukchi Sea in 2011 and 2012 generally moved eastward toward the 

coast and eventually entered Barrow Canyon. After exiting Barrow Canyon they also moved eastward along the 

Beaufort shelfbreak (or shelf) or northwestward along the Chukchi shelfbreak. Many of the drifters that moved 

westward on the Chukchi shelfbreak eventually turned southward and back onto the northeast Chukchi Sea shelf. 

All of the drogued drifters which returned to the northeastern Chukchi Sea shelf stop transmitting in this region. 
However, many of the iSphere drifters continued southward over the shelf in September and October and 

eventually came ashore in Ledyard Bay, along the coast of the Lisburne Peninsula. One iSphere was caught in the 

ice south of Pt. Hope and eventually crushed near the Siberian coast. The SVP drifters in 2012 had the greatest 

endurance and several were eventually trapped in, and drifted with, the sea ice for several months (through 

January-February) before being crushed or losing battery life. The ice carried these drifters as far afield as the 

western Chukchi Sea (near Wrangel Island) and the Mackenzie Shelf in the eastern Beaufort Sea. Several SVPs 

continued transmitting while locked in the landfast ice zone of the Beaufort Sea through winter and then made 

broad zonal excursions over this shelf in early summer before transmission was lost.

SIGNIFICANTCONCLUSIONS:

Linear regressions were used to examine the statistical relationship between drifter velocities and the local 

surface winds over six regions, defined on an ad hoc basis, as the Chukchi shelf, the inner Chukchi Sea shelf 

(Alaskan Coastal Domain; water depths <30m and exclusive of Barrow Canyon), within Barrow Canyon, the 

Chukchi-Beaufort continental slope, the Beaufort Sea shelf, and the Canada Basin. Only the iSphere drifters 

exhibited a strong statistical relationship in which the winds often explained more than 60% of the drifter velocity 

variance. For the MS drifters the winds explained >60% of the velocity variance only within the Alaskan Coastal 

Domain and the Beaufort Sea Shelf. The winds explained <30% of the velocity variance of the SVP drifters in all 

regions. The spatial differences in response likely reflect dynamical differences over the region. These differences 

can be ascribed to stratification, mesoscale motions associated with unstable meltwater fronts, instabilities in 

shelfbreak currents, and/or time-varying geostrophic currents within the regions. Drifters that entered the 

Canada Basin were entrained in eddies most likely spawned by shelfbreak current instabilities. There are also 

seasonal differences in the wind-driven response within the same general area of the shelf. We tentatively 

ascribe these differences to the absence/presence of fronts. Wind-current correlations among drifters far from 

fronts were substantially better than for those likely encountering fronts.

The 2013 trajectories were markedly different from those of 2012. Few escaped the northeastern Chukchi Sea, 

but instead most drifted westward in response to the prevailing strong northeasterly winds of August and 

September 2013. About 60% of the zonal velocity variance for drifters deployed south of Hanna Shoal was due 

to the winds, while wind-current regressions north of Hanna Shoal were substantially poorer. Relative 

dispersion characteristics based on clustered drifter deployments in 2012 and 2013 indicate anisotropic 

dispersion, with the zonal relative diffusivity being about twice that of the meridional diffusivity. Relative 

dispersion increases according to a time2.5 power law after ~2 days, which is the Lagrangian decorrelation time 

scale.

STUDY RESULTS:

The drifter results reported here illustrate the rich complexity of the surface circulation of the Chukchi Shelf and 

its possible connections to the Arctic Basin and the Beaufort Sea. This complexity is a consequence of the spatial 

variability in stratification and bathymetry, which, when subjected to temporally varying winds produces a 

diversity of drifter (surface water) trajectories. By deploying drifters in a clustered manner we were also able to 

begin building a statistical climatology that quantifies relative dispersion. Relative dispersion describes how 

adjacent fluid parcels separate and move with respect to one another through time. It also captures small scale 

motions that are not well-resolved by other sampling techniques and/or numerical models. Hence the relative 

dispersion database that we are developing can be used to guide and evaluate numerical ocean circulation 

models that may be used in oil spill trajectory modeling. 

STUDYPRODUCTS:

Weingartner, T., S. Danielson, P. Winsor, and E. Dobbins, Satellite-tracked drifter measurements in the Northeast 

Chukchi Sea. CMI Annual Review, November 2012, Fairbanks, AK.

Winsor, P., T. Weingartner, T., H. Statscewich, R. Potter, E. Dobbins, K. Martini, and S. Danielson, High-Resolution 

Observations of Hydrography and Circulation of the Chukchi Sea. Alaska Marine Science Symposium, January 

2013, Anchorage, AK.
DeSousa, L., T. Weingartner, P. Winsor, S. Danielson, E. Dobbins, and C. Irvine, Interannual Variability in Surface 

Circulation in the Chukchi and Beaufort Seas: Satellite-tracked Drifter Measurements. Alaska Marine Science 

Symposium, January 2014, Anchorage, AK.

Irvine, C., K. Martini, L. DeSousa, P. Winsor, E. L. Dobbins, S. Danielson, and T. Weingartner, Satellite-tracked 

drifter measurements in the Chukchi and Beaufort Seas. Alaska Marine Science Symposium, January 2014, 

Anchorage, AK.

Weingartner, Thomas. Cayman Irvine, Peter Winsor, Liz Dobbins, Seth Danielson, Rachel Potter, Leandra de 

Sousa, Billy Adams, Robert Suydam, Willard Neatok, Warren Lampe, Leo Ferreira III, Guy Omnik, Henry & John 

Attunganna, Billy Sielak, Harris Aguvuluk, Lee Kayotuk, and Ian Kayotuk. A Lagrangian View of the Chukchi and 

Beaufort Seas. University of Alaska Institute of Marine Science Seminar, September 2014, Fairbanks, AK.

Related informal presentations were made to the oil industry and to residents of the communities of Barrow, Pt. 

Lay, Wainwright, Nuiqsuit, and Kaktovik in collaboration with the NSBW-Shell Baseline Studies Program.

Weingartner, T., C. Irvine, E. Dobbins, S. Danielson, L. de Sousa, B. Adams, R. Suydam, and W. Neatok (2015),

Satellite-tracked Drifter Measurements in the Chukchi and Beaufort Seas. Final Report. OCS Study BOEM

2015-022, University of Alaska Coastal Marine Institute and USDOI, BOEM Alaska OCS Region, 171 p.

Figure 1. Bathymetric map of the Chukchi Sea showing the approximate location of the Statoil (dark blue box), 

Burger (red box), and Klondike (green box) prospects. Approximate locations of UAF drifter releases in 2011 

(circles) and 2012 (squares) are shown. The approximate locations of NSBW drifter deployments in 2012 are shown 

by triangles. The orange arcs show the approximate radar masks for HFRs at Pt. Lay, Wainwright, and Barrow. The

solid black line extending northwest from Wainwright encompasses an array of six subsurface moorings present 

during the 2011 period. 

Icy Cape