Gulf of Alaska Coastal Water Transport Pathways and Implications for Ecosystem Response

Abstract

The Alaska subpolar gyre is a high-nutrient, low-chlorophyll system in which offshore productivity depends on exchange with iron- and macronutrient-rich coastal waters. Mesoscale eddies are the primary mechanism for export of nutrient-rich coastal waters offshore, and their formation is strongly linked to large-scale atmospheric forcing associated with the Aleutian Low (AL), which seasonally modulates regional wind stress, circulation, and eddy generation. Recent marine heatwaves, including the 2013–14 Blob, the 2015–16 El Niño, and the 2019 Alaska heatwave, were associated with distinct climate anomalies that altered atmospheric circulation and modulated the AL, raising questions about how coastal export responds to prolonged climate extremes. Here, we examine variability in Gulf of Alaska coastal transport pathways over 1993–2025, using Lagrangian particle tracking in a high-resolution ocean reanalysis product. We identify three dominant pathways: transport along the mean gyre circulation, offshore export via mesoscale eddies, and coastal retention. Variability in these pathways is primarily linked to atmospheric sea level pressure, local wind stress and wind stress curl, and eddy kinetic energy. Despite weakened circulation and reduced eddy formation during the prolonged marine heatwave conditions between 2013 and 2019, offshore export through the eddy pathway persisted and even periodically intensified during El Niño events. In contrast, transport along the mean gyre circulation declined significantly. These findings suggest that the reorganization of ocean transport pathways can act as a dynamic resilience mechanism for ecosystem response during such extreme conditions.