7.1 Benthic Processes on the Shallow 

 Continental Shelf 



JACQUELINE M. GREBMEIER 



Graduate Program in Ecology, University of Tennessee. Knoxville, Tennessee, USA 



Introduction 



Participation in the Third Joint US-USSR Bering & Chukchi 

 Seas Expedition from 24 July to 3 September 1988 extended 

 studies of pelagic-benthic coupling and benthic carbon cycling 

 in the northern Bering and Chukchi Seas (Grebmeier et al., 

 1988; 1989; Grebmeier & McRoy, 1989) into Soviet waters 

 previously inaccessible to US scientists. Scientific studies 

 included benthic community structure and biomass, faunal 

 bioturbation, benthic carbon cycling, and carbon accumulation 

 in the sediments. In addition, data were collected and analyzed 

 in cooperation with L. Cooper and M. DeNiro (University of 

 California, Santa Barbara) to investigate a new technique for 

 studying multiyear variation in water mass movement in polar 

 seas using stable oxygen isotope measurements of tunicate 

 cellulose and bottom seawater (Grebmeier et a!.. 1990). 



The shelf of the northern Bering and Chukchi Seas is 

 shallow (30-70 m) and normally ice-covered from November 

 to May. Northerly-flowing currents transport Pacific Ocean 

 water through Bering Strait into the Chukchi Sea and Arctic 

 Ocean ( Fig. 1 ). Three major water masses develop during the 

 open- water season, each having different salinity, nutrient, and 

 phytopiankton dynamics (Walsh et al.. 1989). The high 

 nutrient load (20-33 |i M NO, -N) of the subsurface Anadyr 

 Water provides a continuous source of nutrients for high 

 primary production in the water column on the west side of the 

 shelf from the Gulf of Anadyr to north of Bering Strait, but 

 nutrient depletion limits production along the Alaska coastline 

 after the spring bloom. 



Past studies have shown a direct relationship between the 

 particulate organic matter tlux to the benthos and planktonic 

 production in the surface waters of the ocean (Eppley & 

 Peterson. 1979; Deuser et at.. 1981; Davies & Payne, 1984). 

 The quantity and quality of freshly produced or consolidated 

 organic carbon reaching the benthos is influenced by many 

 factors, such as mixed layer and water column depth, 

 zooplankton grazing, and bacterial decomposition in Ihe water 

 column (Parsons ef«/., 1977). Supply of organic matter to the 

 benthos is a major factor influencing benthic community 

 structure, biomass, and metabolism (Mills. 1975; Graf t-r al.. 

 1982; Jorgensen, 1983; Smith el al.. 1983; Smetacek. 1984; 

 Was.sman, 1984; Grebmeier t-r «/.. 1988. 1989: Grebmeier & 

 McRoy. 1989). Sediment oxygen uptake rates provide 

 information on aerobic utilization of carbon in sediments and 

 have been shown to increase with elevated carbon fluxes to the 

 sediments (Hargrave, 1973; Davies. 1975). Recent studies 

 using shipboard sediment oxygen uptake experiments in the 

 shallow shelf of the northern Bering and Chukchi Seas show 



the value of this measurement in delineating areas of high 

 organic carbon flux to the benthos, which are coincident with 

 areas of high water column production, benthic faunal biomass, 

 and sediment carbon remineralization (Blackburn, 1987; 

 Grebmeier & McRoy. 1989). These total sediment oxygen 

 uptake rates are used as an indicator of food supply to the 

 benthos. 



Fig. 1 . Study area in tlie northern Bering and Chukchi Seas showing local 

 water circulations, water ma.sses, and bathymetry (modified from 

 Coachman cfo/., 1975; Walsh « a/.. 1989). 



Marine benthic systems in polar regions can exhibit high 

 abundance and biomass in spite of cold temperatures and only 

 seasonal pulses of particulate organic matter to the benthos 

 (White. 1977;Stoker. 1978; Petersen & Curtis. 1980; Grebmeier. 

 1987; Grebmeier& McRoy. 1989). High latitude shelves have 

 a higher percentage of water column production reaching the 

 benthos compared to both tropical and temperate regions, 

 supporting larger benthic populations (Petersen & Curtis. 

 1980). In eariy spring, food supply to the benthos in the 

 northern Bering and Chukchi Seas consists of ice algal cells, 

 water column phytopiankton, and cells resuspended from the 



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