ACCESS NUMBER: TO-15169

STUDY TITLE: Beaufort Sea Nearshore Under-Ice Currents: Science, Analysis and Logistics

REPORT TITLE: Beaufort Sea Nearshore Under-Ice Currents: Science, Analysis and Logistics

CONTRACT NUMBER: 1435-01-98-CA 30909; TASK ORDER (TO): 15169 

SPONSORING OCS REGION: Alaska 

APPLICABLE PLANNING AREA: Beaufort Sea 

FISCAL YEAR OF PROJECT FUNDING: 1999 

COMPLETION DATE OF REPORT: August 2001 

COST: FY 1999: $144,894; CUMULATIVE PROJECT COST: $144,894 

PROJECT MANAGER: Thomas J. Weingartner 

AFFILIATION: University of Alaska Fairbanks 

ADDRESS: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220 

PRINCIPAL INVESTIGATOR*: Thomas J. Weingartner 

KEY WORDS: Circulation, landfast ice zone, nearshore Beaufort Sea 

BACKGROUND: 

The development of offshore oil exploration and production facilities on the inner shelf of the Beaufort Sea 

might impact the nearshore biota and inhibit clean up of spilled pollutants. This project was undertaken to 

determine the circulation characteristics of Stefansson Sound throughout the year. Particular interest 

focused on obtaining direct current measurements from beneath the landfast ice that covers the area for 

up to nine months of the year. The results will help establish design criteria for spill clean up and guide 

the development of pollutant trajectory models for this region. 

OBJECTIVES: 

Our goals were to: 1) deploy three instrumented moorings in the vicinity of the Liberty and Northstar 

projects for a period of one year, 2) analyze current and wind records to quantify the correlation between 

the currents and winds, and 3) determine the vertical structure of the currents throughout the water 

column and how this structure changes throughout the year. 

DESCRIPTION: 

The moorings collected velocity, temperature, salinity, and transmissivity data at hourly intervals. 

(Transmissivity is an indirect measure of suspended sediment.) The moorings spanned an alongshore 

distance of about 40 km. Current measurements were made with a 1200 kHz upward-looking acoustic 

Doppler current profiler (ADCP) mounted on a rigid PVC frame resting on the seabed. Temperature, 

salinity, and transmissivity data were collected from temperature/conductivity recorders (SEACATs) 

installed on the frames. All instruments were about 1 m above the seabed in 6–8 m water depth. The 

ADCPs provide a measure of ice thickness and ice displacement throughout the deployment period. The 

latter capability allowed accurate determination of the formation and breakup of the landfast ice. Data 

recovery was excellent overall. 
ACCESS NUMBER: TO-15169

SIGNIFICANT CONCLUSIONS: 

The results show two seasonal circulation regimes. The open water/loose ice regime lasts from early July 

through mid-October, during which time the currents are swift, highly variable, and correlated with the 

alongshore winds. Current speeds typically exceeded 10 cm s–1 and maximum currents were greater than 

100 cm s–1. The region was covered by landfast ice from mid-October through the end of June. Currents 

at this time were feeble (~3 cm s–1) and the current variations were primarily tidal. Less than 1% of the 

current speeds exceeded 20 cm s–1 and less than 10% of the current speeds exceeded 10 cm s–1. 

Current fluctuations are horizontally coherent throughout the year over the 40 km separating the 

moorings. Vertical current shears are weak beneath the landfast ice, but can be large during the open 

water period. The mean winds are westward on annual average and drive a weak (<3 cm s–1), mean 

westward flow. Thus wind-driven flows will predominantly determine the dispersal of pollutants in this 

region. 

Two events were observed that involved very high suspended sediment concentrations (as determined 

from the transmissometer). The first occurred in early October 1999 during a storm event, but prior to 

freeze-up. The second event occurred in early June, when the landfast ice was intact and winds were 

weak. The June sediment signal is presumed to reflect the under-ice spreading of the Sagavanirktok 

River plume. Sediment transport includes both storm-forced re-suspension events during the open water 

season and settling from under-ice river plumes that might extend as far as 10 km from the river mouth. 

STUDY RESULTS: 

This work represents the first year-round measurements of under-ice currents in the nearshore Beaufort 

Sea, including both the freeze-up and break-up periods. This success was achieved because ADCPs 

were used for the measurements. These current meters can be moored near the seabed and are 

therefore less susceptible to destruction by deep ice keels. From the perspective of oil spill risk 

assessment and cleanup design, the most important result of this work is that current speeds beneath the 

landfast ice seldom (less than 1%) exceed 20 cm s–1. These findings were consistent among all of the 

moorings. The results reflect the inhibiting effects of landfast ice on the transfer of momentum from the 

atmosphere to the ocean. The current measurements might be biased toward low values because the 

measurements were made within the relatively protected lagoons inshore of the barrier island complex. 

The islands might restrict communication between the outer and inner shelf. Therefore, we recommend 

that sampling be undertaken outside of the barrier island complex to determine if there are substantial 

differences in under-ice current magnitudes inshore and offshore of the barrier islands. 

STUDY PRODUCTS: 

Weingartner T.J. 2000. Beaufort Sea nearshore under-ice currents: Science, analysis and logistics, p. 

75. In University of Alaska Coastal Marine Institute Annual Report No. 6. OCS Study MMS 2000-046, 

University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Weingartner T.J. 2000. Beaufort Sea nearshore under-ice currents: Science, analysis and logistics, p. 

37–41. In University of Alaska Coastal Marine Institute Annual Report No. 7. OCS Study MMS 2000-

070, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Weingartner T.J. 2001. Beaufort Sea nearshore under-ice currents: Science, analysis and logistics. 

University of Alaska Coastal Marine Institute Annual Research Review, February 2001, Fairbanks. 

Weingartner, T.J. 2001. Beaufort Sea nearshore under-ice currents: Science, analysis and logistics. 

MMS Information Transfer Meeting, April 2001, Anchorage. 

Weingartner, T.J. 2001. Going to extremes: Buoyancy forcing on arctic continental shelves. Gordon 

Conference on Coastal Ocean Circulation, June 2001, New London, NH. 

Dr. Weingartner was an invited speaker at this conference and presented some of the results from this 

project at the meeting. 

Weingartner T.J., and S.R. Okkonen. 2001. Beaufort Sea nearshore under-ice currents: Science, 

analysis and logistics. Final Report. OCS Study MMS 2001-068, University of Alaska Coastal Marine 

Institute, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region, 22 p. 

*P.I.’s affiliation may be different than that listed for Project Manager(s). 
ACCESS NUMBER: TO-15169

Focus area for Beaufort Sea Nearshore Under-Ice Currents: Science, Analysis and Logistics. 

Argo

Dinkum

McClure Prudhoe

Bay

Sagavanirktok

River Delta

–149 –148 30′ –148 –147 30′ –147

70 12′

70 24′

70 36′

–149 –148 30′ –148 –147 30′ –147

70 12′

70 24′

70 36′

Liberty

S t e f a n s s o n S o u n d

Deadhorse

Airport

ALASKA

Northstar

Map of Prudhoe Bay and Stefansson Sound, Alaska with the location of the three mooring sites indicated.