An Altimetric Census of Mesoscale Eddy-like Features in the Bering Sea

Stephen R. Okkonen
Box 1025
Kasilof, Alaska 99610

Affiliation:

Institute of Marine Science
University of Alaska Fairbanks
Fairbanks, Alaska 99775

Objective

To use existing satellite altimeter measurements of sea surface height (SSH) in the Bering Sea to catalog the distribution and variability of mesoscale eddy-like features in the space-time domain.

Results

Figure 1. A time-longitude plot of the slope of sea surface height (SSH) anomalies
along a segment of TOPEX orbital ground track D79. This ground track passes from
northwest to southeast just seaward of the shelf break in the central Bering Sea.
Only positive slopes are shown for clarity. The contour interval is 1 microradian.
Long-lived mesoscale SSH anomalies, exhibiting a northwestward component of
propagation, are readily apparent.

Maps of SSH variability in the Bering Sea constructed for the periods of both altimeter missions indicate that eddy-like activity along the shelf break region of the deep basins is greater than that which occurs in the central basins. The region of principal interest and effort for the present study is the shelf break region in the central Bering Sea, a region of high primary productivity and along which flows the Bering Slope Current. Both altimeter data sets reveal mesoscale features near the shelf break region which exhibit propagation both along the shelf break and away from the shelf break. The features which are observed to propagate along the shelf break are interpreted to be topographic planetary waves, whereas the mesoscale features which are observed to propagate into the central Aleutian Basin are interpreted to be baroclinic planetary waves. The topographic planetary waves have a representative wavelength and period of about 100 km and 2 months, respectively. These waves are most developed in the spring and early summer months. The baroclinic planetary waves are characterized by wavelengths of hundreds of kilometers and periods of hundreds of days. There is evidence for dispersion of these latter waves as representative wavelengths and periods increase as the waves propagate away from the shelf break.

Very little eddy activity, coherent with that occurring seaward of the shelf break, is observed on the continental shelf. The occurrence of short wavelength (tens of kilometers) phenomena in the deep basins during the autumn and early winter months suggest that stratification of the upper waters in the Bering Sea is strongest at this time.

Remaining Work

My present efforts are directed at investigating (1) what relationship may exist between wind forcing and the nature of the mesoscale response and (2) cross-shelf influence of the shelf break planetary wavefield.