PMEL Publications Abstract

FY 2012

Stratification on the Eastern Bering Sea Shelf revisited

Ladd, C., and P.J. Stabeno

Deep-Sea Res. II, 65–70, doi: 10.1016/j.dsr2.2012.02.009, 72–83 (2012)

The timing and magnitude of stratification can have profound influences on the marine ecosystem. On the Eastern Bering Sea shelf, in the absence of strong wind mixing, stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface. Temperature and salinity both influence the stratification of the Eastern Bering Sea shelf with their relative importance varying spatially and temporally. In the northern middle shelf domain (north of ∼60°N), salinity stratification is often as important as temperature stratification. On the southern middle shelf, while the influence of temperature on stratification dominates during summer, the influence of salinity stratification plays a role in the interannual variability. Mooring 2 (M2; 56.9°N, 164.1°W) has been deployed at ∼70 m depth in the southern middle shelf domain since 1995. Data from this mooring show that stratification typically begins to set up in May and to break down in September/October, but these dates can vary by >30 d. While no trend is found in the timing of the spring setup, the fall stratification breakdown exhibited a trend toward later breakdown (∼2 d later per year from 1996 to 2009). Results suggest that it may be difficult to forecast stratification on the Eastern Bering Sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification. Contrary to intuition, the strength of summer stratification is not correlated with depth averaged temperature. Warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification. This decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change, as we cannot assume that projections of a warmer climate simply imply higher stratification in the future.

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