Long‐Term Trends and Variability in Arctic Mixed Layer Depth

Abstract

The Arctic surface mixed layer is an important moderator of the transfer of heat, salt, and momentum between the atmosphere and the warmer, more saline water that enter the Arctic Ocean from the North Pacific and North Atlantic oceans. However, prior observational studies of trends in mixed layer depth produce seemingly conflicting results due to limited temporal and spatial coverage. Using reanalyses which are consistent with the climatological mixed layer seasonal cycle, changes in the pan‐Arctic mixed layer depth are assessed from 1980 to 2024. From the 1980s to the most recent decade, there was a shoaling of the winter (Oct–Mar) mixed layer and a slight deepening of the summer (Apr–Sep) mixed layer. Furthermore, time series of winter mixed layer depth anomalies show for the first time that the seemingly conflicting trends of prior studies can be reconciled as a result of significant decadal variability, particularly in the Canadian and Amerasian Basins. The decadal variability is found to be consistent with changes in the thickness of sea ice centered over the Canadian and Amerasian Basins. This work underscores how decadal variability in the sparsely observed Arctic can complicate the interpretation of long‐term trends.