international date line and the influence of refractory terrestrial 

 material on this food source, coming into the marine systems 

 from Alaskan rivers, is supported by previous work (Grebmeier 

 et al., 1988; Walsh et ai, 1989). 



Natural Radioisotope (-'"Pb) Content in Surface Sediments 



A preliminary study of spatial ''"Pb-ex distribution in 

 surface sediments at select stations in the Gulf of Anadyr, 

 northern Bering Sea, and southern Chukchi Sea indicated a 

 higher concentration of the particle-reactive radionuclide -'"Pb 

 in the higher silt and clay content sediments of the Gulf of 

 Anadyr and southern Chukchi Seas (Fig. 11). This limited data 

 set had a high correlation between surface sediment TOC and 

 -'"Pb content (n = 9, r- = 0.7 1 . 0.00 1 < p < 0.005 ), indicating that 

 regions of higher organic carbon content in the sediments were 

 also regions of higher sedimentation and accumulation of 

 organic matter from the overlying water column to the sediments. 

 The highest -'"Pb-ex concentration in the Gulf of Anadyr 

 occurred at the mouth of Kresta Bay, suggesting enhanced 

 deposition of terrigenous and marine material at this site. In the 

 Chukchi Sea. the highest -'"Pb-ex (3.8 dpm/g) occurred in the 

 "hot spot" of high primary and benthic secondary productivity, 

 and the lower total organic carbon in the sediments (1.3%) 

 relative to surrounding stations may result from the high 

 benthic consumption of organic matter at this site. The lowest 

 -'"Pb-ex concentrations were measured in the sandy sediments 

 of the northern Bering Sea (0.6-1.0 dpm/g), along with low 



organic carbon content (0.3%). However, this area is a region 

 of high water column chlorophyll and benthic biomass. Recent 

 studies by Blackburn ( 1987) suggest that efficient grazing by 

 the benthic amphipods, along with rapid mineralization of 

 organic matter in the sediments, results in lower sediment 

 organic carbon content in this region. The present study, in 

 addition to earlier -'"Pb studies (Grebmeier, unpubl. data), 

 supports a reduced sediment accumulation in this region, 

 although carbon flux to the benthos is high (Grebmeier & 

 McRoy, 1989; M. Fukuchi, personal communication). 



An additional study was undertaken to determine the 

 sedimentation rates based on vertical cores within each of the 

 main study areas (Fig. 12). Preliminary data, based on natural 

 log-normal distributions of -'"Pb-ex in sediment .sections with 

 depth down the sediment core in the Gulf of Anadyr and 

 southern Chukchi Sea, indicate low but variable sediment 

 accumulation rates. Sedimentation rates ranged from 

 0.01-0.03 mm/yr in the southern Chukchi Sea to 0.04 mm/yr 

 in the Gulf of Anadyr. The difference between these two 

 regions is evident in the highly variable -'"Pb-ex values in the 

 top 0- 1 cm in the southern Chukchi Sea stations ( Stations 45, 

 55), due to the extremely high mixing of these sediments by the 

 high benthic fauna populations (Fig. 7; Grebmeier, 1987; 

 Grebmeier & McRoy, 1989). In comparison, the one station 

 analyzed in the central Gulf of Anadyr ( Station 22 ) occurred in 

 a low benthic faunal abundance region in the central gulf 

 ( Fig. 7 ), such that the surface sediment was little mixed and the 

 -'"Pb-ex profile was undisturbed. Further studies are needed on 

 longer cores in both the Gulf of Anadyr and Chukchi Sea to 

 evaluate organic carbon sedimentation and accumulation in the 



Excess Pb-210 (dpm/g) 

 1.0 2.0 3,0 



4,0 



3. 4 



E 



73 



12 



16 



47-100 



+ 



47-045 



47-055 



Fig. 1 1. Distribution of-"'Pb-ex (dpm/g) und total orgunii; carbon (%)al select 

 .stations during August 1988. 



Fig. 12. Verticle profile of -'"Pb-ex (dpm/g) at select stations in the Gulf of 

 Anadyr: Station 22 ( AK47-022^ ); and southern Chukchi Sea: Station 

 45 (AK47-045 •) and Station .S.^i (AK47-055 o ). An additional 

 -'"Pb-ex concentration for a surface sample (0-3 cm) in the northern 

 Bering Sea is presented for coinparison: Station 100 (AK47-I00 +). 



sediments of these arctic regions. Previous data from the sandy 

 sediments of the northern Bering Sea indicate little or no 

 sediment accumulation in this region, with sedimentation rates 

 a magnitude lower than values in the other two regions 

 (Grebmeier, unpubl. data). These data support the conclusion 

 presented earlier — that although organic matter is settling to 

 the benthos in this region, highly efficient benthic faunal 



250 



