The Influence of Submesoscale Motions on Upper-Ocean Chlorophyll: Case of Benguela Current Large Marine Ecosystem (BCLME)

Submesoscale dynamics are critical modulators of upper-ocean biogeochemistry, yet their net influence on chlorophyll concentrations across seasonal to interannual timescales, particularly within productive regions like the Benguela Current Large Marine Ecosystem (BCLME), remains poorly understood. This study quantifies these complex relationships by analyzing 22 years (2001–2022) of physical and biological data. We examined the link between surface chlorophyll (CHL) and key physical drivers: sea level anomaly (SLA) and submesoscale intensity, quantified by the Rossby number (Ro). Using both cross-correlation analysis and Generalized Linear Models (GLMs), our analyses reveal a multi-scale set of spatially dependent and time-lagged biogeochemical responses. At the basin scale, a key finding from cross-correlation is a significant positive correlation where high SLA precedes a rise in CHL by approximately six months, indicating a delayed ecosystem response to large-scale physical forcing. At the event scale, GLMs show the specific impact of eddies is critical: short-lived cyclonic eddies correlate with a significant increase in CHL (~4.6%) in the southern zone, while anticyclonic eddies are associated with a pronounced decrease in CHL (~97.7%) in the central zone during the austral winter. These findings demonstrate that both large-scale preconditions and localized submesoscale features are essential drivers of vertical nutrient transport and the distribution of primary productivity within the BCLME.