Bering Strait Climatology paper GRL 2004

Published in Geophysical Research Letters, February 2005
Citation: Woodgate R. A., K. Aagaard, T. J. Weingartner (2005), Monthly temperature, salinity, and transport variability of the Bering Strait through flow, Geophys. Res. Lett., 32, L04601, doi:10.1029/2004GL021880.
Copyright 2005 American Geophysical Union. Further reproduction or electronic distribution is not permitted.

The Bering Strait throughflow is important for the Chukchi Sea and the Arctic and Atlantic oceans. A realistic assessment of throughflow properties is also necessary for validation and boundary conditions of high resolution ocean models. From 14 years of moored measurements, we construct a monthly climatology of temperature, salinity and transport. The strong seasonality in all properties (~ 31.9 to 33 psu, ~ -1.8 to 2.3°C and ~ 0.4 to 1.2 Sv) dominates the Chukchi Sea hydrography and implies significant seasonal variability in the equilibrium depth and ventilation properties of Pacific waters in the Arctic Ocean. Interannual variability is large in temperature and salinity. Although missing some significant events, an empirical linear fit to a local (model) wind yields a reasonable reconstruction of the water velocity, and we use the coefficients of this fit to estimate the magnitude of the Pacific-Arctic pressure-head forcing of the Bering Strait throughflow.

Figures
For details, see paper

Figure 1. Sea-surface temperature for 26th August 2004 in the Bering Strait region, with mooring sites, A1, A2, A3 and A3' (black dots). (MODIS/Aqua level 1 image courtesy of Ocean Color Data Processing Archive, NASA/Goddard Space Flight Center.) Note the warm Alaskan Coastal Current in the east. White areas indicate clouds.

Table 1. Climatological near-bottom temperature (T), salinity (S) and principal component (V) of velocity (heading 329°) at A3, with estimated errors in brackets (grey areas on Figures 2, 3, 4, and 5). Standard deviations (thin black lines on Figures 2, 3, 4, and 5) are ~3 times these errors. Estimated transports (Vol) have errors ~ 25%. Water column means are probably ~ 0.5 to 1 psu fresher and 1 to 2°C warmer than these values during summer/autumn (~ May - October). AM = annual mean.

Figure 2. Salinity (top) and temperature (bottom) from ~ 9 m above bottom at site A3 and A3'. Horizontal axis is time starting in August with letters indicating calendar months. Black stars mark the 14-year monthly climatology of Table 1; thin black lines, the standard deviation; and the grey band, errors obtained from variance of the monthly means. Colored curves are 30-day running mean (with errors) from the various years (red= deployed in 1990 or 1991; magenta=1992, 1993; yellow=1994, 1995, green=1997, 1998, cyan=1999, 2000; blue=2001, 2002, black=2003). A3' (deployed summer 1992 to summer 1995) data is not included in the climatology. Water column means are probably ~ 0.5 to 1 psu fresher and 1 to 2°C warmer than these values during summer/autumn.

Figure 4. Principal component of velocity (true heading 329°) at A3 and A3', illustrated as per Figure 2. Estimated transports (labeled on right axis) are as per Figure 5.

Figure 3. Fourteen year 30-day smoothed time-series of salinity (top) and temperature (bottom) from ~ 9 m above bottom at A1 (cyan), A2 (blue), A3 (red) and A3' (green - summer 1992 to summer 1995). Line width indicates errors. Grey area and black lines are the climatology of Figure 2. Water column means are probably ~ 0.5 to 1 psu fresher and 1 to 2°C warmer than these values during summer/autumn.

Figure 5. Fourteen year 30-day smoothed time-series of principal component of velocity (top) at A3 and A3' (true heading 329°) and (middle and bottom) at A2 (true heading 0°). Velocity climatologies from A3 and A2 (with errors and standard deviation) are marked in top and middle figures. A3' (deployed summer 1992 to summer 1995) data is not included in the climatology. Thin black line on bottom figure marks 30-day smoothed reconstruction of velocity from a linear fit to the NCEP 6 hourly winds (i.e. reconstructed velocity (cm/s) = 32 + 3.4 x NCEP 10 m wind component (m/s) at heading of 330°). (Coefficients obtained from a least squares fit, see Wetal). Grey here indicates errors in the coefficients. Colors are as per Figures 2 and 4. Conversions to transports (using cross-section areas of ~ 2.6 km2 at A2 and ~ 3.9 km2 at A3) are marked on the right axis. These transports are subject to ~ 20% errors in addition to those indicated by error bars on the plots.

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

Monthly Temperature, Salinity and Transport Variability of the Bering Strait Throughflow

Rebecca A Woodgate, Knut Aagaard, and Tom Weingartner