Climate Change Drives Evolution of Thermohaline Staircases in the Arctic Ocean

Abstract

A thermohaline staircase detection algorithm, applied to mooring and ice-tethered profiler data, systematically assessed the variability of fine-scale, diffusive-convective staircase abundance in the Arctic Ocean thermoclines in 2004–2023. Over that period, staircase occurrence statistically decreased in both the Amerasian and Eurasian basins, with thinner, shallower staircase layers preferentially decreasing over the Eurasian Basin's slope. In stark contrast to the Amerasian Basin, seasonality of detected staircase occurrence was pronounced in the Eurasian Basin and appeared to be increasing. Interannual and long-term variability of detectable staircase abundance and background thermocline density stratification were correlated, negatively so in the Amerasian Basin and positively in the Eurasian Basin, indicating reversed sensitivities of staircase constructive and destructive processes to stratification. Seasonal and long-term staircase variabilities in both basins were consistent with known environmental contrasts and tendencies, including upper freshening of the stronger, thicker Amerasian Basin halocline, the shift toward deeper winter ventilation of the weaker Eurasian Basin halocline, and more near-surface velocity shear over the Eurasian Basin's slope. There is no reason to believe that climate change will stop anytime soon, and we have good cause to believe that the observed tendencies in staircase structure will persist.