CONTEXT
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Marine biological productivity in Arctic is highly constrained by sea ice, which limits the penetration of sunlight and air-sea interactions. The September extent of the Arctic Ocean icepack has decreased by nearly 40% over the last 3 decades . It is largely expected that the resulting increase in the penetration of sunlight in the water column will boost PP of phytoplankton and, possibly, increase the overall biological productivity in the Arctic Ocean. Several Arctic surveys using ocean colour remote sensing confirm an 20% increase in primary productivity (PP) between 1998 and 2009. However, over longer time periods, the trajectory of primary productivity is uncertain. The Beaufort Gyre is getting more oligotrophic because of increasing vertical stratification. Using a coupled physical-biological model, Slagstad et al. (2011) showed that the Arctic Basin and the Eurasian shelves will become more productive in a seasonally ice-free Arctic Ocean, but that the highly productive Barents Sea will remain stable. In contrast, Wassmann and Reigstad (2011) argued that new production in the former will remain low, and energy transfer to higher trophic levels will decrease in the latter. The temporal match/mismatch between the phytoplankton spring bloom (PSB) and the life cycle of secondary producers is key to the efficiency of energy transfer through the food chain. So, it seems that overall primary production will actually increase in the Arctic Ocean, but when considering where and how, it gets more complex and to figure out the impact on carbon fluxes and on the food chain seems elusive when based on simple arguments.
As in most parts of the World Ocean, the PSB provides a large fraction of the annual primary production and, most importantly, nearly all of the new primary production exportable through the food chain and towards the bottom sediments. In the Arctic Ocean, the PSB often develops around the ice-edge. This highly transient phenomenon lasts about 3 weeks at any given location in the seasonal ice zone (SIZ). According to Perrette et al. (2011), ice-edge blooms represent most of the annual primary production in the Arctic Ocean. The SIZ is currently increasing in size and may cover the entire Arctic Ocean as early as twenty years from now. Therefore, one may expect ice-edge blooms to cover a much larger area than previously dbecause of a significant northward expansion. However, we currently do not know the fate of the possible additional phytoplankton biomass build-up along the retreating ice cover. Will it sustain more secondary production and higher trophic transfer to the pelagic compartment, thus benefiting Arctic megafauna? Or will it sink rapidly and create new benthic hotspots, possibly enhancing carbon sequestration in the sediment?.