A SEDIMENT AND ORGANIC-CARBON BUDGET FOR THE CANADIAN BEAUFORT SHELF

The Arctic Ocean accounts for 20% of the world's continental shelves. Because the Arctic is sensitive to global change, budgets of organic c arbon for its shelves are of immediate interest. The Mackenzie Shelf o f the Canadian Beaufort Sea is the best North American proxy for the e normous Eurasian Shelves (large area, large river input), and the only site for which a complete organic carbon budget can be attempted, due to an extensive data base, A mass balance for the Mackenzie Shelf has been constructed for sediments, terrestrial organic carbon. and prima ry produced carbon. We have considered allochthonous inputs from the M ackenzie River, from coastal erosion, from smaller rivers, from ground water, from the atmosphere and import by ice. The Mackenzie River domi nates the supply to the Beaufort shelf of inorganic sediment (127 Mt a (-1)) and particulate and dissolved terrestrial carbon (2.1 Mt a(-1) P OC, 1.3 Mt a(-1) DOG), The combined input from all other sources contr ibutes only about 5%, of the Mackenzie load, Using sediment accumulati on data we estimate that about half of the sediment supply is trapped in the delta; about 40% on the shelf and the remainder escapes the she lf edge by various processes. Autochthonous primary production in the delta and on the shelf adds a further 3.3 Mt a(-1) of particulate orga nic carbon. A box model has been constructed to account for sediment, terrestrial organic carbon and primary produced carbon. Whereas about 60% of the terrestrial POC is preserved in delta and shelf sediments, it appears that most (97%) of the primary produced carbon is recycled and not preserved in sediments. Confidence in the budget should be imp roved by focusing future research on the determination of modern sedim entation rates on the delta and shelf, measurement of organic carbon c ontent of deltaic sediments, determination of primary production on th e shelf, and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments. (C) 1998 Elsevier Sc ience B.V.