We use a modern Earth system model to approximate the relative importance of ice vs. temperature on Arctic marine ecosystem dynamics. We show that while the model underestimates upper water column nitrate across the region. This nitrate bias is likely responsible for the apparent underestimation of ice algae production. Despite this shortcoming, the model appears to be a useful tool for exploring the impacts of environmental change on phytoplankton production and carbon dynamics over the Arctic Ocean. Our experiments indicate that under a warmer scenario, the percentage of ocean warming that could be apportioned to a reduction in ice area ranged from 11 to 100 %, while decreasing ice area could account for 22-100 % of the increase in annual ocean primary production. The change to CO₂ air-sea flux in response to ice and temperature changes averaged an Arctic-wide 5.5 Tg C y⁻¹ (3.5 %) increase, into the ocean. This increased carbon sink may be short-lived, as ice cover continues to decrease and the ocean warms. The change in carbon fixation from phytoplankton in response to increased temperatures and reduced ice was generally more than a magnitude larger than the changes to CO₂ flux, highlighting the importance of fully considering changes to the marine ecosystem when assessing Arctic carbon cycle dynamics. Our work demonstrates the importance of ice dynamics in controlling ocean warming and production, and thus the need for well-behaved ice and BGC models within Earth system models if we hope to accurately predict Arctic changes.

Arctic sea ice cover, ocean temperature, annual primary production and annual CO₂ flux in each model scenario. A) Summer fraction of model grid cell covered in sea ice in each sea ice reduction experiment S1 (i), S2 (ii), and RCP4.5 (iii), and the baseline model run (iv). B) Annual average temperature anomaly in the upper 25m relative to the baseline run (Temp_EXP –Temp_BASE) for S1 (i), S2 (ii), and RCP4.5 (iii). Red colors indicate warmer waters than the baseline run while blue colors indicate cooler waters than the baseline run. B(iv) shows the temperature difference between the S2 and the RCP4.5 experiment (Temp_RCP4.5 –Temp_S2). C) Difference (Prod_EXP–Prod_BASE) in annual average phytoplankton production relative to the baseline model run for experiments S1 (i), S2 (ii) and RCP4.5 (iii). Red colors indicate higher production than the baseline run while blue colors indicate lower production than the baseline run. D) Change to the annual average ocean-atmosphere CO₂ flux relative to the baseline run (Flux_EXP –Flux_BASE). Red shading indicates an increase in CO₂ influx (flux into the ocean), whereas blue shading indicates a reduced influx. All model results presented are an average of the final ten years of the model run (2000-2009).

Gibson, G.A., Weijer, W., Jeffery, N. and Wang, S. (2020). Relative Impact of Sea Ice and Temperature Changes on Arctic Marine Production. JGR Biogeosciences. 125(7). doi:10.1029/2019JG005343