Simulating the Sea Ice Carbon Pump in the Beaufort Gyre

The Arctic Ocean is undersaturated in CO₂, and currently acts as a carbon sink. Carbon fluxes in the Arctic are not only impacted by the presence or absence of sea ice, but also by its melting and freezing. During sea ice formation carbon-rich, dense brine is rejected, while ice melt dilutes surface water and reduces CO₂. This combination of processes should lead to a net uptake of atmospheric CO₂ concentration. The magnitude of the resulting uptake is determined by how much of the brine sinks below the mixed layer. This carbon export mechanism is referred to as the Sea Ice Carbon Pump (SICP). Since the Arctic is rapidly warming, multi-year and seasonal sea ice are declining. This decline is more prominent for the annual sea ice minimum in summer than the annual maximum in winter, leading to an overall increase in the seasonal growth and melt of sea ice, and potentially the SICP. Yet, its importance and impact on carbon fluxes in the Arctic Ocean remain an open question. Here we look at how to best parametrize this process in numerical ocean models and at quantifying its importance. To do so, we are using a 1D version of the biogeochemical model PISCES constrained by mooring observations of physical, carbonate and ice properties in the Beaufort Gyre. The validated model is then used in sensitivity studies to investigate how the change of ice characteristics due to the replacement of multi-year by first-year ice, such as bulk salinity and DIC to alkalinity ratios, might impact the efficiency of the SICP. Finally, we use a 3D circulation-ice-biogeochemical ocean model to evaluate regional impacts.