Meeting Documents

Multidecadal variations of the Arctic Ocean CO2 uptake inferred from models and data products

Abstract

Climate change has greatly impacted sea-ice in the Arctic Ocean (AO), causing an evident reduction in the last decades. Sea-ice is a crucial factor for regulating CO2 uptake in the AO due to its direct influence on air-sea gas exchange. Arctic climate change impacted not only the extent of Arctic sea-ice but also sea-surface temperature and stratification, with direct consequences for the phytoplankton primary production in Arctic waters. These changes impact both the solubility and biological carbon pumps at seasonal, interannual, and multidecadal timescales. To shed light on these changes we use an ocean physical-biogeochemical model (ECCO-Darwin, ED) and three data products to not only quantify the potential trends but also to gain mechanistic understanding of the main processes driving the changes in AO CO2 uptake.

During the 1997–2017 period the ED model and the data products show comparable values for the annual CO2 sink ranging from 164 to 190 TgC yr-1; however, they diverge in the long-term trend because the ED model shows a decreasing CO2 uptake (0.35 TgC yr-1) while the data products show an increasing CO2 uptake (from 2.6 to 6.0 TgC yr-1). In our study we also focus on other aspects: (1) the potential trend differences between the Eastern and Western AO, and (2) variations in trends in different seasons. Our comparison shows that in the Western AO the ED model and the data-products mostly agree, specifically in the Chukchi Sea. However, at pan-Arctic scales, the ED model and the data products tend to agree in all the seasons except for the summer where the CO2 uptake in the ED model completely diverges when compared to the data products. During summer both excessive ocean warming and enhanced stratification might cause the strength of biological pump to be reduced in the ED model, which would explain this specific disagreement with all the data products used in this study. We also discuss mechanisms responsible for other seasonal CO2 uptake trends.