winter, polynyas form in the Bering Sea near St. Lawrence 

 Island allowing surface water to supercool. Extremely cold 

 and highly saline waters have been found southwest of St. 

 Lawrence Island (Takenouti & Ohtani, 1974). Such cooling 

 reaches the bottom in the northern Bering Sea where the shelf 

 region is generally shallow (Ohtani, 1969). The cold water 

 would have a higher loading of CO,. Walsh et al. ( 1 985 ) have 

 shown that much of the production on the shelf may be 

 transported off the shelf. The off-shelf transport to deeper 

 water in the Bering Sea could act as a sink for carbon. Similar 

 transports occur off the shelves in the Arctic Ocean. The winter 

 is also when strengthened flows are expected to occur due to 

 meteorological forcing. Thus there would be an increased 

 transport of water and CO, through the Bering Strait. Thewinter 

 flows could supply source water for deep water mass formation. 

 These water masses could form either in the North Adantic or 



in the North Pacific via outflow along the Kamchatka Peninsula. 

 A salient point here is that in the Atlantic, the southward 

 transport of CO, is only 0.26 gigaton of C per year (Brewer 

 etal., 1989). This is a relatively small quantity in comparison 

 to the annual production of CO, (about 5.5 gigaton). Thus, 

 magnitude of the net Atlantic transport, while relatively small, 

 is of the same order as the estimated Bering Strait northward 

 transport (0.82 gigaton). Certainly not all the carbon in the 

 Bering Sea flux finds its way to the Norwegian Sea, but it could 

 be a significant contribution. Thus, the quantity of carbon 

 stored in the North Atlantic bottom water may be in good part 

 due to the flow from the Bering Sea. Additional storage of 

 carbon may result from transport of particulate carbon to the 

 deep basins of the Bering Sea. 



The Maine Undergraduate Science Consortium. MEDUSA, 

 Contribution No. 010. 



6.3 Intensity of Biosedimentation Processes 



BORIS V. GLEBOV' , VLADIMIR I. MEDINETS* , and VLADIMIR G. SOLOVIEV* 



* Institute of Global Climate and Ecology, State Committee for Hydrometeorology and Academy of Sciences. Moscow. USSR 



* State Oceanography Institute. Odessa. USSR 



Introduction 



Materials and Methods 



Marine organisms play an important part in the 

 sedimentation processes. The influence of biotic processes 

 upon sedimentation provides evidence of active participation 

 of marine organisms in the biological accumulation 

 (concentration) of chemical substances. They are also important 

 in the subsequent transfer of these substances through organic 

 products (organism remains, feces, etc.) or by the organisms 

 themselves to the deep layers of the ocean and the bottom. The 

 biotic processes directly or indirectly determine transformation 

 and distribution of essentially all the elements in the sea. 

 Changes occur in the physical and chemical form of the 

 elements during these transformations. The organisms may 

 accumulate essential elements as well as useless and even 

 detrimental ones. The chemical substances are circulated from 

 the external environment into the organisms and back by 

 typical routes. These processes thereby form relatively closed 

 biogeochemical cycles whose rates vary for different substances. 



The influence of marine organisms on geochemical 

 mobility may be broken into biological accumulation and 

 sedimentation stages (Lisitsyn, 1983). 



The essential regularity of these processes can be used to 

 develop methods of determining the biosedimentation rates on 

 the basis of vertical distribution of the elements differing from 

 each other in their biogeochemical activity. With this in mind, 

 it is logical to use natural radionuclides as tracers. Their 

 concentration can be measured in the medium with a highly 

 sensitive radiometric apparatus (McKee et al., 1984). 



From the middle of the sixties there began an intensive 

 study of the distribution in the ocean of the two genetically 

 connected natural radionuclides, -'^Uranium and -'""Thorium. 

 -'^Thorium is the product of -'*U a-decay. This process of 

 radioactive decay is the main source of -"Th in the sea. As 

 shown previously, these isotopes display a shift in the 

 radiochemical balance in ocean surface-water (Bhat et al.. 

 1969; Matsumoto, 1975). This shift is due to biological 

 accumulation and biosorption of Th by planktonic organisms 

 and suspended organic particles, which are then removed from 

 the surface layer as a result of sedimentation. 



The bioaccumulation factors of Th for different types of 

 plankton organisms in open ocean range from lO"* to 2 x 10' 

 (Barinov et al., 1967). The average values of accumulation 

 factors forTh in suspended organic particles are the same order 

 of magnitude (Cherry & Shannon, 1974). 



-"^Uranium is relatively evenly distributed in the oceanic 

 waters, where its concentration is about 3 |ig/l. Furthermore, 

 the accumulation factors in plankton and detritus are some 3 to 

 5 orders of magnitude lower than those of thorium. 



Thus, the shift in the radioactive balance is in fact 

 determined by the changes in the concentrations of -"Th due to 

 its transfer in the process of biosedimentation. Knowing the 

 vertical profile of these radionuclides, it is possible to calculate 

 the sedimentation rate of the suspended organic matter 

 (Polikarpov f/ 1//., 1976. 1980). 



224 



