Physical Oceanography of Alaska's Beaufort Sea

Presented by Tom Weingartner and Seth Danielson

With support from the Minerals Management Service, the Office of Naval Research and the Alaska Department of Environmental Conservation

Beaufort Map

Background: The Alaskan Beaufort Sea continental shelf spans approximately 600 km along-shore and 80 km in the cross-shore direction. Circulation patterns of the Chukchi and Beaufort Seas are schematically described in our transport pathway cartoon. The Beaufort shelf circulation is strongly influenced by ice, wind, fresh water (river discharge and ice melt) and air-sea heat fluxes. Tidal currents are generally quite small (< 5 cm/s). The shelf waters are covered by landfast and drifting pack ice during the winter but are often nearly ice-free in August and September. Other summers, however, very little open water develops [for example, 1983]. Mean winds are strong and normally directed from the northeast. Arctic rivers can discharge 90% of their total annual outflow in the weeks of the spring freshet. The Colville, Kuparuk and Mackenzie Rivers all discharge significant fresh water to the Beaufort coastal zone.

Major canyon systems bound the Alaskan Beaufort shelf to the west (Barrow Canyon) and to the east (Mackenzie Canyon). The shelf has low bathymetric relief but gouging and bulldozing by ice keels creates many small-scale features. Bottom gouging presents considerable risk to instruments deployed in the Beaufort. Before our field program, we did not know if it was possible to collect year-round measurements in the shallow Beaufort waters without great risk to the instruments. By developing a very compact mooring and choosing deployment locations with care, we have had reasonable success: to date, out of 16 deployments, only two have been destroyed by drifting ice. From these two, all instruments were nonetheless retrieved with at least some data intact.

Our short and squat moorings provide a platform from which we have made temperature, conductivity (salinity), pressure, transmissivity and current velocity measurements. Measurements are made every 20-60 minutes over the course of a year. The mooring design includes a popup buoy to facilitate revocery at the end of the deployment. An acoustic signal from the recovery vessel triggers a mechanism on the mooring to release the buoy. The buoy has a long tether attached, so the recovery crew can grab hold of the buoy and pull the entire mooring back on board.

With support provided by the Minerals Managements Service (MMS), we have deployed oceanographic moorings in the nearshore Beaufort Sea over the course of 1999-2002 (Phase I) and 2004-2007 (Phase II). All deployments and recoveries took place in August/September. Results from Phase I are documented in Weingartner, et al. [2005]. Additional analyses were funded by the Alaska Department of Environmental Conservation (ADEC) . In Phase I, four moorings were deployed within about 40km of Prudhoe Bay, to investigate local scales of coherence and variance. In Phase II, deployments in Smith Bay and Camden Bay as well as near Prudhoe Bay have provided us with an along-shore perspective. Phase II data are presently being collected, processed and analyzed.