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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C10017, doi:10.1029/2005JC003335, 2006

Eddy-induced cross-slope exchange maintaining summer high productivity of the Bering Sea shelf break

Kohei Mizobata

International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA


Jia Wang

International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USA


Sei-ichi Saitoh

Laboratory of Marine Bioresource and Environment Sensing, Graduate School of Fisheries Sciences, Hokkaido University, Hokkaido, Japan


Abstract

Eddy-related cross-slope exchange along the Bering Sea shelf break was investigated using a hydrographic observations data set and a numerical model. Results of observations in summer of 2001 showed a shelf break front that formed at a shelf break near an anticyclonic eddy, high nitrate-nitrite concentrations in the subsurface layer, and high chlorophyll a (Chl-a) concentrations (≥6 mg m−3) in the surface layer. A hydrographic observation in summer of 2002 exhibited relatively high Chl-a concentrations at the surface around the anticyclonic eddy. Tracer experiments revealed two types of cross-slope exchange. Under isopycnals, nutrient-rich water in the basin is transported to the shelf and there is about a 64.53% increase in integrated nitrate-nitrite on-shelf flux (50 m depth ∼bottom), when mesoscale eddies are formed and propagated along the shelf break. At the surface, high Chl-a waters in the shelf are advected to the deep basin area by eddy transport and propagation. These indicate that (1) mesoscale eddies supply nutrients and sustain primary productivity at the shelf break, and (2) eddies expand the high Chl-a area to the basin, then to the highly productive area, so that the Green Belt is maintained.

Received 30 September 2005; accepted 14 July 2006; published 31 October 2006.

Keywords: Bering Sea eddy; cross-slope exchange; on-shelf flux; hydrographic observation; numerical model.

Index Terms: 4520 Oceanography: Physical: Eddies and mesoscale processes; 4219 Oceanography: General: Continental shelf and slope processes (3002); 4273 Oceanography: General: Physical and biogeochemical interactions; 4255 Oceanography: General: Numerical modeling (0545, 0560); 4855 Oceanography: Biological and Chemical: Phytoplankton.

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Citation: Mizobata, K., J. Wang, and S. Saitoh (2006), Eddy-induced cross-slope exchange maintaining summer high productivity of the Bering Sea shelf break, J. Geophys. Res., 111, C10017, doi:10.1029/2005JC003335.