Title

Sedimentary pigments as biomarkers of spatial and seasonal variations in Arctic pelagic-benthic coupling

Date of Completion

January 2008

Keywords

Biology, Oceanography|Biogeochemistry

Degree

Ph.D.

Abstract

The Arctic Ocean is characterized by broad continental shelves, which have high rates of primary productivity. In some areas, much of this production falls to the bottom, supplying rich and active communities of benthic organisms. Benthic-pelagic coupling over much of the Arctic shelves is thought to be particularly tight. Moreover in areas covered by ice, ice algae can be the main source of carbon for the food web and thus for the benthos. ^ Sedimentary pigments have demonstrated their usefulness in studies of ecosystem changes, and especially changes of organic matter inputs to the benthos. In order to characterize variation in pelagic-benthic coupling in the Arctic, sedimentary pigments were studied in the oligotrophic Beaufort Sea (CASES project) and in the more productive Barents Sea (CABANERA project). During 7 cruises from 2003 to 2005, sediment cores, water column POM and ice algae samples have been collected, representing a significant spatial coverage and seasonal variations. ^ Sedimentary pigments reflected changes in environmental factors, sources of primary productivity, food web structure, and benthic activity. The Beaufort Sea and Barents Sea showed very different pelagic-benthic coupling, reflecting the important contrast between the two ecosystems of primary productivity, secondary production, and hydrography. In the Barents Sea, spatial changes were highly influenced by currents while in the Beaufort Sea, spatial changes were due to depth and river influence. Physical parameters seemed more responsible of spatial changes. From a seasonal point of view, productivity regime, especially ice-algal production and the match/mismatch of grazing, seemed important in shaping organic matter inputs to the benthos. In the spring, ice-algal production largely influenced organic matter inputs to the benthos in both the Barents and Beaufort Seas. In the summer, grazing was responsible for inputs of degraded material in both ecosystems. In addition to biological parameters, environmental factors were also important in summer and/or fall. In the Barents Sea during summer, the different currents lead to phytoplankton taxonomy variations, and in the Beaufort Sea during fall, riverine inputs were found to be responsible for presence of allochtonous material in the sediment. ^