A Satellite-Based Lagrangian Perspective on Atlantic Water Fractionation Between Arctic Gateways

Abstract

Warm Atlantic Water reaches the Arctic Ocean via two gateways: the Barents Sea Opening (BSO) and Fram Strait. Here, we study the near-surface flow of the Atlantic Water in the Nordic Seas and its fractionation between these Arctic gateways, using simulated Lagrangian trajectories based on satellite altimetry for 1994–2018. Lagrangian particles are released in the eastern Nordic Seas, where Atlantic Water flows poleward in two current cores: an inner branch along the Norwegian Continental Slope and an outer sea ward branch. The trajectories toward Fram Strait and the BSO are, in an averaged sense, largely steered by the bottom topography, and on inter-annual timescales we find an anticorrelation in the number of particles that reach the two gateways. Most of the particles released in the inner branch enter the Barents Sea and most of the particles seeded in the outer branch reach Fram Strait. However, there is a significant cross-over of particles from the outer to the inner branch in the Lofoten Basin, and nearly half of the total number of particles entering the BSO originate in the outer branch. This cross-over is accomplished solely by the time-fluctuating part of the velocity field, and it becomes stronger when the eddy kinetic energy in the Lofoten Basin is anomalously high. Thus, the outer branch may, via processes in the Lofoten Basin, be important for Barents Sea climate variability.