East Australian Current System: Frontal Barrier and Fine‐Scale Control of Chlorophyll‐a Distribution

Abstract

The East Australian Current (EAC), as the western boundary current of the South Pacific Gyre, governs the mesoscale circulation dynamics along the East Coast of Australia. It also exhibits meandering and instabilities that generate fine‐scale structures. Understanding the interplay between these fine‐scale processes and the larger‐scale EAC patterns is crucial in regards to chlorophyll‐a distribution, a key indicator of phytoplankton abundance and an essential component of marine ecosystems. However, the link between fine‐scale and large‐scale variability in the EAC's separation dynamics and its impact on chlorophyll‐a distribution remains poorly understood. In this study, we investigate this relationship using a clustering of high‐frequency radar data near the EAC's coherent jet and separation point, combined with satellite data on chlorophyll‐a concentration, sea surface temperature, and altimetry. Our findings reveal that the EAC acts as a frontal barrier for water‐mass and chlorophyll‐a concentration. The EAC separation enhances shelf‐offshore exchange and off‐shelf chlorophyll‐a concentration. In contrast, the extension of the current is characterized by fine‐scale structures with cyclonic vorticity and elevated strain, consequently contributing to an elevation of chlorophyll‐a levels in the region. In conclusion, the impact of separation dynamics on chlorophyll‐a distribution involves a complex interplay between large‐scale and fine‐scale processes, which may possibly compete under certain scenarios. Considering the implications of our findings in the context of future climate conditions, it becomes evident that purely dynamical changes in the separation latitude of the East Australian Current may hold consequences for chlorophyll‐a concentration distribution off the east coast of Australia.