Circulation in the Beaufort Sea

Rebecca Woodgate (UW), Knut Aagaard (UW), Ed Carmack (IOS), Tom Weingartner (UAF)

Corresponding author: Rebecca Woodgate (woodgate@apl.washington.edu)

OVERVIEW

We are presently investigating the circulation over the continental slope and adjacent abyssal plain of the Beaufort Sea using moored time series of temperature, salinity, and current velocity. Our goals are to quantify the vertical and cross-shore spatial and temporal scales of variability in velocity and density across the slope, estimate the transport within the eastward-flowing subsurface boundary current, and determine the statistics of eddies and other smaller scale features over the adjacent abyssal plain, with an eye toward how these modify the properties of the interior ocean.

Maps (by year 1986-1997) of mooring locations along
the Beaufort slope and in the Beaufort Sea

Between 1986 and 1997, moorings were deployed in the Beaufort Sea as part of a joint US-Canadian project.

The coverage varies from year to year as can be seem from this schematic of the mooring locations.

The boundary current along the Beaufort slope shows frequent reversals, at least in part associated with long wave propagation, but the mean flow is clearly cyclonic, even though the flow of ice and near-surface water is westward. Both plumes and eddies may help move shelf waters offshore across the slope, where the boundary current is the dominant feature. In addition to dispersing shelf waters, the boundary current likely also acts as a source of offshore waters for the shelf during pulses of onshore flow associated with upwelling events near the shelf break. In the Beaufort Sea the latter can reach 400 m in amplitude.

Seaward of the Beaufort Sea slope and below the mixed layer, the most energetic part of the velocity field resides in eddies with a typical horizontal length scale of 10-20 km. We find that in the pycnocline, the time history of the T/S correlation at a fixed location is complex, with clouds of outlier points. The temperature excursions are particularly large, probably because for cold water, temperature has a lesser effect on density than does salinity, and temperature excursions are therefore less constrained by buoyancy forces. Combined velocity and T/S records provided convincing evidence of baroclinic eddies embedded in the pycnocline, and the data show the frequent passage of both horizontally and vertically paired counter-rotating eddies drifting past the monitoring site. Sharp frontal passages are also visible in these data, and the overall impression is of an interior ocean with considerable horizontal and vertical structure, and with a decidedly grainy T/S field. We also find long-term (months or more) changes in the elevation of isopycnal surfaces by tens of meters, with corresponding changes in the thickness of the upper layer. These changes likely represent either shifts in the location of the Beaufort gyre or changes in the circulation strength, or both.

REFEREED PUBLICATIONS (back to top)

Aagaard, K., The Beaufort Undercurrent, in The Alaskan Beaufort Sea:
Ecosystems and Environment, edited by P. Barnes and E. Reimnitz, pp. 47-
71, Academic Press, New York, 1984.

We gratefully acknowledge financial support for this work from the Office of Naval Research (ONR), High Latitude Dynamics program, and the Minerals Management Service (MMS).

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