Benthic oxygen consumption on continental shelves off eastern Canada

Abstract

The consumption of phytoplankton production by the benthos is an important component of organic carbon budgets for continental shelves. Sediment texture is a major factor regulating benthic processes because fine sediment areas are sites of enhanced deposition from the water column, resulting in increased organic content, bacterial biomass and community metabolism. Although continental shelves at mid- to high latitudes consist primarily of coarse relict sediments ( Piper, Continental Shelf Research, 11, 1013–1035), shelf regions of boreal and subarctic eastern Canada contain large areas of silt and clay sediments ( Fader, Continental Shelf Research, 11, 1123–1153). We collated estimates of benthic oxygen consumption in coarse (<20% silt-clay, <0.5% organic matter) and fine sediments (20% silt-clay, 0.5% organic matter) for northwest Atlantic continental shelves including new data for Georges Bank, the Scotian Shelf, the Grand Banks of Newfoundland and Labrador Shelf. Estimates were applied to the areal distribution of sediment type on these shelves to obtain a general relationship between sediment texture and benthic carbon consumption. Mean benthic oxygen demand was 2.7 times greater in fine sediment than in coarse sediment, when normalized to mean annual temperature. In terms of carbon equivalents, shelf regions with minimal fine sediment (Georges Bank, the Grand Banks of Newfoundland-northeast Newfoundland) consumed only 5–8% of annual primary production. Benthos of the Gulf of Maine (100% fine sediment) and the Scotian Shelf (35% fine sediment) utilized 16–19% of primary production. Although 32% of the Labrador Shelf area contained fine sediments, benthic consumption of pelagic production (8%) was apparently limited by low mean annual temperature (2°C). These results indicate that incorporation of sediment-specific oxygen uptake into shelf carbon budgets may increase estimates of benthic consumption by 50%. Furthermore, respiration and production by large macrofauna allow an even greater proportion of primary production to enter benthic pathways. Fine sediment areas (shelf basins or “depocenters”) are postulated to be sites of enhanced biological activity which must be considered in the modelling of shelf carbon budgets and the role of the benthos in demersal fisheries.