Divergence in climate model projections of future Arctic Ocean stratification and hydrography

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Morven Muilwijk, Aleksi Nummelin, Lars H. Smedsrud, Igor V. Polyakov, Hannah Zanowski, Céline Heuzé 


The Arctic Ocean is strongly stratified by salinity gradients in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water heat, nutrients, and CO2 between intermediate depths and the surface of the Eurasian and Amerasian basins (EB and AB). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening in the AB is linked to a freshening and deepening of the halocline. In the EB, the weakened stratification is linked to advection of saltier halocline waters and is associated with a shoaling of the halocline (Atlantification). Future simulations from a suite of CMIP6 models project that, under a strong greenhouse-gas forcing scenario (ssp585), the overall surface freshening and warming in both basins continue, but there is a spread in hydrographic trends across the models with even opposite trends in certain regions. Within the AB, there is agreement among the models that the upper layers will become more stratified. However, within the EB models diverge regarding future stratification. The divergence is due to different balances between trends in the upper ocean, related to surface freshwater input, and trends at depth, related to fluxes through Fram Strait. From these simulations, one could conclude that Atlantificaton will not spread eastward into the AB; however, we need to improve models to simulate tendencies in a more delicately stratified EB correctly.




Physical Sciences and Mathematics


Arctic, stratification, CMIP6, climate models, ocean circulation


Published: 2022-05-23 16:21


CC BY Attribution 4.0 International

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