Arctic Ocean Freshwater Content and Its Decadal Memory of Sea‐Level Pressure

• Published in: Geophysical research letters 2018-05, Vol.45 (10), p.4991-5001
• Main Authors: Johnson, Helen L., Cornish, Sam B., Kostov, Yavor, Beer, Emma, Lique, Camille
• Format: Article
• Language: English
• Subjects: adjustment timescales; Arctic circulation; Arctic Ocean; Atlantic Meridional Overturning Circulation (AMOC); Atmospheric circulation; Atmospheric conditions; Atmospheric models; Circulation; Climate; climate change; Climate models; Dynamics; Earth Sciences; Eddies; Exports; Fresh water; Freshwater; Heat transport; Inland water environment; interannual variability; Ocean circulation; Ocean currents; Ocean dynamics; Ocean models; Oceans; Pressure; Pressure variations; Regression models; Sciences of the Universe; Sea level pressure; Sea level variations; Storage; Temperature; Water circulation; Wind; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2017GL076870

Arctic freshwater content (FWC) has increased significantly over the last two decades, with potential future implications for the Atlantic meridional overturning circulation downstream. We investigate the relationship between Arctic FWC and atmospheric circulation in the control run of a coupled climate model. Multiple linear lagged regression is used to extract the response of total Arctic FWC to a hypothetical step increase in the principal components of sea‐level pressure. The results demonstrate that the FWC adjusts on a decadal timescale, consistent with the idea that wind‐driven ocean dynamics and eddies determine the response of Arctic Ocean circulation and properties to a change in surface forcing, as suggested by idealized models and theory. Convolving the response of FWC to a change in sea‐level pressure with historical sea‐level pressure variations reveals that the recent observed increase in Arctic FWC is related to natural variations in sea‐level pressure. Plain Language Summary This paper shows that the Arctic Ocean circulation and freshwater storage in a fully coupled climate model have a long memory of atmospheric conditions, adjusting to a change in sea‐level pressure over more than a decade. This is important because the Arctic Ocean has recently accumulated a large amount of freshwater, which may ultimately be exported to the Atlantic, with implications for the circulation and heat transport there, yet we do not know if or when it will be exported and at what rate. Based on the relationship we deduce between sea‐level pressure and Arctic freshwater content, we estimate changes in Arctic freshwater content over the last century and show that observed changes since 1992 can largely be explained by historical changes in the winds driving the ocean circulation. Our results have implications for the attribution of Arctic variability and change, the interpretation of observational and model data, and the prediction of freshwater export to the North Atlantic. Key Points Arctic Ocean freshwater content in a fully coupled climate model has a memory of at least a decade of previous atmospheric forcing Observed changes in Arctic Ocean freshwater content over recent decades can be explained by sea‐level pressure variations Long memory suggests potential for predictability