Causal Mechanisms of Rising Sea Level and Increasing Freshwater Content of the Beaufort Sea

Over the last two decades, sea-level across the arctic’s Beaufort Sea has been rising an order of magnitude faster than its global mean. This rapid sea-level rise is mainly a halosteric change, reflecting an increase in Beaufort Sea’s freshwater content. The rising volume of freshwater is greater than that associated with the Great Salinity Anomaly of the 1970s, raising the prospect of future disruptions in large-scale ocean circulation and climate. Here we provide a new perspective of this Beaufort Sea variation using a global data-constrained ocean and sea-ice model of the Estimating the Circulation and Climate of the Ocean (ECCO) consortium. Causal relationships are quantified using the model’s adjoint. Controlling processes are elucidated analyzing property budgets.

The study reveals the multi-decadal variation to be driven jointly by change in wind stress and sea-ice melt. Strengthening anticyclonic winds surrounding the Beaufort Sea intensify the ocean’s lateral Ekman convergence of relatively fresh near-surface waters. The strengthening winds also enhance convergence of sea-ice and ocean heat that increase the amount of Beaufort Sea’s sea-ice melt. Whereas the region’s direct wind-driven kinematic anomalies equilibrate over weeks, sea-ice-melt-driven diabatic changes persist for years owing to Beaufort Sea’s semi-enclosed gyre circulation. The growing disparity between where sea-ice forms and where it melts results in this rare example of melting floating ice causing large-scale sea-level rise. The spin-up difference suggests that, on their own, the sea-ice-melt-driven diabatic change will last much longer than the direct wind-driven kinematic anomaly.

The study highlights the importance of observations and the utility of ECCO’s modeling system. While ocean and sea-ice observations are essential in diagnosing the change, the study also points to a need for expanded observations of the atmosphere, especially the winds that act on the ocean/sea-ice system. ECCO is implementing a novel “point-and-click” interface for analyzing its modeling system, such as conducted here, without requirements for expertise in numerical modeling, and invites exploitation of its new utility (https://ecco-group.org).