Multiyear record of rates of Arctic biological production offers a glimpse of the possible response of the biological pump to changing sea ice cover

Profound changes are occurring in the Arctic Ocean as climate warms. Most dramatically perhaps, the summer sea ice extent has decreased significantly. How is the carbon cycle changing concurrent with these environmental changes? Biological productivity is one of the main drivers of the carbon cycle in the ocean. Net community production (NCP) reflects the total amount of CO₂ drawn down by the ocean’s biological pump. Gross primary production (GPP) is a measure of the photosynthetic flux and thus represents the total amount of CO₂ removed by photosynthesis. Gas tracers – namely O₂/Ar ratios and triple oxygen isotopes – can be used to quantify in situ rates of net community production and gross primary production. Here we present rates of NCP and GPP from the Beaufort Gyre region of the Canada Basin in late summer and early fall for four years (2011 – 2014). We examine the relationship between these rates of biological productivity and environmental variables such as ice cover, sea surface temperature and salinity, mixed layer depth, etc. Additionally, the cruise in 2014 was in the fall rather than the late summer, allowing investigation of seasonal modulation of productivity. Overall, the data show higher rates of GPP following the record low ice coverage in summer of 2012, suggesting that the large scale melting event in 2012 may have produced a step change in total photosynthesis, caused by lack of ice that year and lack of multiyear ice the subsequent year. In spite of large differences in GPP, the rates of NCP are very similar between the years, suggesting a tightly coupled autotrophic/heterotrophic network so that even when photosynthesis increases, there is little change in carbon export. If this finding is substantiated in other seasons and other regions of the Arctic, it has significant implications - that the changing climate may not change the net carbon balance or CO₂ fluxes in and out of the Arctic Ocean even though it might change local production.