| Summary: | Canadian Arctic Shelf Exchange Study (CASES); Natural Sciences and Engineering Research Council of Canada (NSERC); Fonds Quebecois de la Recherche Sur la Nature et les Technologies (FQRNT); Department of Earth and Planetary Sciences at McGill University; To establish the relative importance of terrigenous and marine organic matter in the southern Beaufort Sea, we measured the concentrations and the stable isotopic compositions of organic carbon and total nitrogen in sediments and in settling particles intercepted by sediment traps. The organic carbon content of surface! sediment in the Chukchi and southern Beaufort Seas ranged from 0.6 to 1.6% dry wt., without a clear geographical pattern. The C(ORG):N(TOT) ratio ranged from 7.0 to 10.4 and did not vary significantly downcore at any one station. Values delta(13)C(ORG) and delta(15)N(TOT) in the sediment samples were strongly correlated, with the highest values, indicative of a more marine contribution, in the Amundsen Gulf In contrast, the organic matter content, elemental (CORG:NTOT ratio) and isotopic (delta(13)C(ORG); and delta(15)N(TOT)) composition of the settling particles was different from and much more variable than in the bottom sediments. The isotopic signature of organic matter in the Beaufort Sea is well constrained by three distinct end-members: a labile marine component produced in situ by planktonic organisms, a refractory marine component, the end product of respiration and diagenesis, and a refractory terrigenous component. A three-component mixing model explains the scatter observed in the stable isotope signatures of the sediment trap samples and accommodates an apparent two-component mixing model of the organic matter in sediments. The suspended matter in the water column contains organic matter varying from essentially labile and marine to mostly refractory and terrigenous. As it settles through the water column, the labile marine organic matter is degraded, and its original stable isotope signature changes towards the signature of the marine refractory component. This process continues in the bottom sediment with the result that the sedimentary organic matter becomes dominated by the refractory terrigenous and marine components. (C) 2009 Elsevier Ltd. All rights reserved.
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