Phytoplankton productivity on the Canadian Shelf of the Beaufort Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 277:37-50 (2004) - doi:10.3354/meps277037 Phytoplankton productivity on the Canadian Shelf of the Beaufort Sea Eddy C. Carmack1,*, Robie W. Macdonald1, Steve Jasper2 1Institute of Ocean Sciences, 9860 West Saanich Road, Sidney, British Columbia, V8L 4B2, Canada 2Essjay Ventures Inc., 72 Beech St., Comox, British Columbia, V9M 3W7, Canada *Email: carmacke@pac.dfo-mfo.gc.ca ABSTRACT: For the first time, the seasonal cycle of phytoplankton productivity on a broad, seasonally ice-covered arctic shelf (the Canadian Shelf of the Beaufort Sea) is examined. This shelf is the most riverine of the panarctic shelves. During 5 surveys between April and September 1987, field observations (salinity, temperature, nutrients, photosynthetically active radiation PAR, chlorophyll a) and shore-based data (air temperature, river discharge, sea-ice cover, PAR) were collected. Productivity was measured using 14C and converted to daily production with PAR and vertical light extinction values. Due to inflow from the Mackenzie River, phosphorus limits production over the inner shelf (depth z 80 m) shelf. Light limitation due to landfast ice delays the onset of water-column productivity in spring in the inner shelf by about 1 mo compared to the outer shelf. In spring, maximum productivity occurred near the surface and decreased exponentially with depth. In summer, as nutrients became depleted in the upper mixed layer, a deep chlorophyll maximum developed toward the bottom of the winter mixed layer (20 to 40 m). Productivity during spring (ice cover) was about 10 mgC m-2 d-1, rising typically to about 200 mgC m-2 d-1 by late July. Maximum productivities, ~600 mgC m-2 d-1, were observed above the head of Kugmallit Canyon, suggesting enhanced upwelling. The total production for 1987 was estimated at 12 to 16 gC m-2, characteristic of oligotrophic waters. This range is consistent with new-production estimates based on nutrient draw-down over the shelf and on vertical carbon fluxes at the shelf break measured by sequential traps or 234Th disequilibria. Light limitation due to snow and ice cover may control the timing of primary production, but the availability of nutrients ultimately sets the annual limit. Nutrient availability is determined partly by cumulative vertical convection during winter, and partly by upwelling. Projected loss of ice cover over the Arctic¹s marginal seas is likely to have its greatest impact by widespread initiation of conditions for shelf-break upwelling. KEY WORDS: Arctic · Nutrients · Primary production · Shelf Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 277. Online publication date: August 16, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.