Quantifying the fate of organic matter produced during an under-ice bloom using a 1-D Ecosystem model

Courtney Payne1, Laura Bianucci2, Gert van Dijken1 and Kevin R Arrigo1, (1)Stanford University, Earth System Science, Stanford, CA, United States, (2)Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC, Canada
In the last few decades, as sea ice thinned and melt ponds proliferated in the Chukchi Sea, light penetration through ice and into the underlying water column has increased. This has allowed massive under-ice phytoplankton blooms to form in the top 30 m of the water column. Extremely high column-integrated phytoplankton biomass (~1300 mg chlorophyll a m-2) and primary production rates (as high as 3.7 g C m-2 d-1) were recorded in 2011. Phytoplankton physiology and the post-bloom subsurface chlorophyll maximum associated with these blooms are well characterized. However, no in situ observations have been made of the fate of the organic matter generated during these blooms. Changes in the apportioning of organic matter between pelagic and benthic communities could have regional consequences for upper trophic level organisms. We will use a coupled physical-biochemical 1-D Ecosystem model to simulate the annual cycle of phytoplankton growth, including under ice blooms. We will quantify the relative proportion of phytoplankton that either cycles through the pelagic food web following grazing by zooplankton or sinks to the benthos. Additionally, experiments demonstrate how climate change, which affects overlying air temperatures and ice conditions (including retreat timing in the spring and sea ice thickness), could influence the partitioning of organic matter between the pelagic and benthic habitats.