A sediment and organic carbon budget for the Canadian Beaufort Shelf

Abstract

The Arctic Ocean accounts for 20% of the world's continental shelves. Because the Arctic is sensitive to global change, budgets of organic carbon for its shelves are of immediate interest. The Mackenzie Shelf of the Canadian Beaufort Sea is the best North American proxy for the enormous 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 primary produced carbon. We have considered allochthonous inputs from the Mackenzie River, from coastal erosion, from smaller rivers, from groundwater, from the atmosphere and import by ice. The Mackenzie River dominates the supply to the Beaufort shelf of inorganic sediment (127 Mt a −1) and paniculate and dissolved terrestrial carbon (2.1 Mt a −1 POC, 1.3 Mt a −1 DOC). The combined input from all other sources contributes only about 5% of the Mackenzie load. Using sediment accumulation 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 shelf edge by various processes. Autochthonous primary production in the delta and on the shelf adds a further 3.3 Mt a −1 of particulate organic 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 improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf, measurement of organic carbon content of deltaic sediments, determination of primary production on the shelf, and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments.