ACCESS NUMBER: M07PC13368

STUDY TITLE: Modeling of Circulation in the North Aleutian Basin

REPORT TITLE: Modeling of Circulation in the North Aleutian Basin

CONTRACT NUMBER: M07PC13368

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA: North Aleutian Basin

FISCAL YEARS OF PROJECT FUNDING: FY 2007-FY2009

COMPLETION DATE OF REPORT: August 2010

COSTS BY FY: FY 2007: $278,000

CUMULATIVE PROJECT COST: $278,000

PROJECT MANAGER: Enrique Curchitser

AFFILIATION: Rutgers University

ADDRESS: Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road, New 

Brunswick, NJ 08901

PRINCIPAL INVESTIGATOR(S)*: Enrique Curchitser, Thomas Weingartner, Katherine Hedstrom

KEY WORDS: North Aleutian Basin, Bering Sea, numerical model, sea ice, circulation, ROMS.

BACKGROUND: In order to carry out Oil Spill Risk Analysis, the Bureau of Ocean Energy Management, 

Regulation and Enforcement (BOEMRE, ex. MMS) put out a solicitation for a state-of-the –art coupled 

circulation-sea ice model for the North Aleutian Basin region of the Bering sea. This region exhibits 

complex phenomena over a broad range of spatial and temporal scales, including tidal mixing, 

topographically steered flows, shelf-slope exchanges through canyons, mesoscale eddy mixing, flows 

through narrow passes and the yearly formation, drift, and melting of sea ice. This work is the result of 

that solicitation.

OBJECTIVES: The primary aim of the work done under this award was to modify and use a state-of-theart coupled circulation-sea ice numerical ocean model to simulate several decades of the currents in the 

North Aleutian Basin which can be used as inputs to oil-spill models and to perform extensive model 

evaluation against available data. The gridded model output was to be delivered to BOEMRE as well as 

a model manual.

DESCRIPTION: The main research tool used for this work is a state-of-the-art coupled ocean/sea ice 

model based on the Regional Ocean Modeling System (ROMS). ROMS is a free-surface, hydrostatic 

primitive equation ocean circulation model, which has been coupled to a dynamic/thermodynamic sea ice 

model. The model was implemented for the Bering Sea region at 10 km resolution permitting extensive 

sensitivity studies and multi-decadal length integrations while resolving the significant dynamics of the 

region. The model was used for the period of 1985 to 2005 in hindcast mode, storing output every 3 

hours for the duration of the simulation.

SIGNIFICANT CONCLUSIONS: The coupled circulation-sea ice model exhibits predictive skill in this 

region. However, the skill is not uniform in all variables or on all scales. Sea ice cover is generally well 

represented in the model. Model kinetic energy is similar to observations at frequencies lower than three 

days and at tidal frequencies, but the inertial peak is missing in the model and the noise floor between 10 
ACCESS NUMBER: M07PC13368

and 100 hours is biased low. We speculate that this is primarily due to the wind forcing dataset which 

itself does not resolve the inertial frequency. The seasonal and interannual temperature and salinity 

variability in the model matches well with time series observations at NOAA mooring M2. A comparison 

with transect data shows the model reproduces the seasonal transitions in the water column from a wellmixed shelf regime, to a highly-stratified two-layer system during the summer at the mid-shelf, although 

the depth and strength of stratification are still difficult parameters to resolve. The near-shore remains well 

mixed throughout the year both in the data and the model results; energy for mixing is supplied from both 

wind and tide forcing.

STUDY RESULTS: Model simulations using the coupled circulation-sea ice model were carried out for 

the twenty-year period of 1985-2005 and archived. Extensive model evaluation was carried out with an 

analysis of 1. Tidal heights and currents, 2. Sub-tidal currents, 3. Temperature and salinity variability, 4. 

Density gradients and 5. Sea ice cover. The extensive model-data comparison shows significant skill in 

the model capability to reproduce observed circulation and sea ice patterns in the Bering sea.

STUDY PRODUCTS: Under this study, an existing model was modified and twenty years of gridded 

coupled circulation-sea ice model data were generated, archived and delivered to BOEMRE. Extensive 

data products were assembled and used for model evaluation. A model manual was written for the 

coupled model and submitted together with a final report. Several manuscripts are currently in 

preparation describing the results of the work.

*P.I.’s affiliation may be different than that listed for Project Manager(s).

Map of focus area for Modeling of Circulation in the North Aleutian Basin.