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

Rebecca A Woodgate, Knut Aagaard, and Tom Weingartner

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ONR N00014-99-1-0345
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NSF  0125082

Published in Geophysical Research Letters, February 2005
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.

Preprint (downloadable as pdf)


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   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.  

© Polar Science Center, University of Washington, 2004

  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.

© Polar Science Center, University of Washington, 2004

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

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