3.1 Biogenic Nutrient Content 



TERRY E. WHITLEDGE' , MIKHAIL 1. GORELKIN^ , and SERGEI M. CHERNYAK* 

 "Marine Science Institute. University of Texas at Austin. Port Aransas. Texas. USA 



'Institute of Global Climate and Ecoloi;\. State Committee for Hydrometeoroloi^y and Academy of Sciences. Moscow. USSR 



Introduction 



The early investigation of the biogenic nutrient content of 

 Bering Sea waters have shown these elements that are necessary 

 for phytoplunkton grow ih lo often be present in surface waters 

 in quite high concentrations (Barnes & Thompson, 1938). 

 More recently, the Processes and Resources of the Bering Sea 

 Shelf (PROBES) program did an exhaustive study of the 

 physical-biological ecosystem dynamics of the southeastern 

 Bering Sea Shelf. Over a five-year period, the nutrient content 

 across the shelf was observed to be related to three frontal 

 systems that governed the nutrient dynamics in the open ocean, 

 outer shelf, middle shelf, and inner shelf (Coachman, 1986; 

 WhitledgC(Vu/., 1986). 



The later program of Inner Shelf Transfer and Recycling 

 (ISHTAR) further investigated the transport of water and 

 nutrients through the northern Bering Sea into the Chukchi Sea 

 and studied the primary production/decomposition processes 

 that occurred in the Alaskan Coastal water, Bering Shelf water 

 and Anadyr water (Walsh et al.. 1990). The Third Joint US- 

 USSR Bermg & Chukchi Seas Expedition in 1988 was a 

 tremendous enhancement to the ISHTAR sampling program, 

 which had previously lacked a complete and quasi-synoptic 

 sampling of all of the above water masses. 



The biogenic nutrient content is indicative of the potential 

 primary production that ma\ occur in seawater and therefore is 

 used to assess one ol the major factors controlling primary food 

 production in the marine environment. The concentration of 

 nitrogen, in the form of nitrate and ammonium, is particularly 

 useful because most oceanic environments contain small 

 concentrations of nitrogen relative to phosphorus and silicon 

 and is often thought lo limit rales of primary production 

 (Ryther & Dunstan, 1971 ). The uptake of biogenic nutrients 

 along with carbon dioxide and light is important as fuel for 

 primary production processes. The production of nutrients by 

 regenerative processes must also be considered because the 

 nutrients present in seawater are replenished on a continuous or 

 periodic basis. These regeneration processes maintain the 

 long-term primary production of an ecosystem especially on 

 continental shelves where benthic regeneration also contributes 

 nutrients to the euphotic zone. The biogenic nutrient content of 

 water in the Bering and Chukchi Seas in general is high, 

 reflecting its origin in the North Pacific Ocean. The deep 

 Bering Sea, where few biological measurements have been 

 taken, maintains high nutrient concentrations throughout the 



year, and plant biomass represented by chlorophyll is small. 

 The continental shelf, which comprises about 45% of the area 

 of the Bering Sea, varies from high to low nutrient concentrations 

 as the annual cycle of primary production occurs (Whitledge 

 etui, 1986). 



The primary purpose of this paper is to describe the 

 nutrient, oxygen, and pH variations of the south and east 

 regions of the deep Bering Sea, the northern Bering Sea Shelf 

 and the southern Chukchi Sea ( Frontispiece). All of these areas 

 were sampled on the Third Joint US-USSR Bering & Chukchi 

 Seas Expedition in 1 988 as a part of a program to investigate the 

 ecology and health of the Bering and Chukchi Seas. 



Methods 



Water samples were collected on the upcast with a Sea- 

 Bird CTD/rosette sampler. Water samples were immediately 

 collected in polyethylene scintillation vials and were analyzed 

 on a model 300 Alpkem segmented flow analyzer at 80 samples 

 per hour. The analytical techniques were adapted to small 

 volume glassware from previously described methods 

 (Whitledge et al.. 1981 ). The basic analytical methods were 

 described by Armstrong et al. (1967) for nitrate, phosphate, 

 and silicate. Ammonium was measured by the 

 phenohypochlorile method of Koroleff (1970) as adapted to a 

 continuous analyzer by Slawyk and Maclsaac (1972) and 

 modified by Patton and Crouch (1977). Standard Winkler 

 titrations were used to determine the concentration of dissolved 

 oxygen. 



Results 



Northern Shelf Regions 



The physical transport of water from the North Pacific inio 

 the deep Bering Sea moves eastward and north in a counter- 

 clockwise gyre until it nears the coastline of the Soviet Union 

 where it bifurcates and a northern segment Hows through the 

 Gulf of Anadyr toward Bering Strait (Whitledge et al.. 1988). 

 This long-term net movement of water carries a large quantity 

 of biogenic nutrients from the deep Bering Sea onto the shallow 

 northern shelf of the Bering and Chukchi Seas where primary 

 production processes consume them. The northern tlow of 

 water varies from about 0.5 to 1.0 Sv and produces 

 bathymetrically induced upwelling as a result of the 30-50 m 

 water depths of the shelf. 



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