A year in the physical oceanography of the Chukchi Sea

Published in Deep Sea Research, II, 2005
Woodgate, R. A., K. Aagaard, and T. J. Weingartner (2005), A year in the physical oceanography of the Chukchi Sea: Moored measurements from autumn 1990-1991, Deep-Sea Res., Part II, 52, 3116-3149, doi: 10.1016/j.dsr2.2005.10.016.

   Year-long time-series of temperature, salinity and velocity from 12 locations throughout the Chukchi Sea from September 1990 to October 1991 document the physical transformations and significant seasonal changes in the throughflow from the Pacific to the Arctic Ocean.
     In most of the Chukchi, the flow field responds rapidly to the local wind, with high spatial coherence over the basin scale - effectively the ocean takes on the lengthscales of the wind forcing. The mean flow is northwards, opposed by the mean wind, but presumably forced by a sea-level slope between the Pacific and the Arctic, which these data suggest may have significant variability on long (order a year) timescales. The high flow variability yields a significant range of residence times for waters in the Chukchi (i.e.\ 1-6 months for half the transit) with larger values in winter.
   Temperature and salinity (TS) records show a strong annual cycle of freezing, salinization, freshening and warming, with sizable interannual variability. The largest seasonal variability is seen in the east, where warm, fresh waters escape from the buoyant, coastally trapped Alaskan Coastal Current into the interior Chukchi. In the west, the seasonally present Siberian Coastal Current provides a source of cold, fresh waters and a flow field less linked to the local wind. Cold, dense polynya waters are observed near Cape Lisburne and occasional upwelling events bring lower halocline waters to the head of Barrow Canyon.
    For about half the year, the entire Chukchi is condensed down into a small region of TS-space at the freezing temperature, suggesting ventilation occurs to near-bottom driven by cooling and brine rejection in autumn/winter and by storm-mixing all year.
    The ca.\ 0.8~Sv annual mean inflow through Bering Strait exits the Chukchi in four outflows - via Long Strait, Herald Valley, the Central Channel and Barrow Canyon - each outflow being comparable (order 0.1-0.3~Sv) and showing significant changes in volume and water properties (and hence equilibrium depth in the Arctic Ocean) throughout the year. The clearest seasonal cycle in properties and flow is in Herald Valley, where the outflow is also little related to the local wind. In 1990-1991, the outflows ventilate above and below (but not in) the Arctic halocline mode of 33.1~psu. Volumetric comparison with Bering Strait indicates significant cooling during transit through the Chukchi, but remarkably little change in salinity. In fact, with the exception of (in this year small) polynya events, the salinity cycle in the Chukchi can be considered as being set by the input through Bering Strait. Thus, since density is dominated by salinity at these temperatures, Bering Strait salinities are a reasonable predictor of ventilation of the Arctic Ocean.

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

A Year in the Physical Oceanography of the Chukchi Sea: Moored measurements from Autumn 1990-1991