Abstract

Coccolithophores remain understudied in the Southeast Pacific despite their ecological relevance as calcifying phytoplankton. This study expands regional knowledge by integrating new in situ observations with satellite-based climatologies of particulate inorganic carbon as a proxy for coccolithophore standing stocks. Sampling across seven oceanographic zones, including newly surveyed coastal and shelf waters influenced by the West Wind Drift (similar to 43 degrees S), was used to assess community responses to physical-chemical gradients. Latitudinal variations in temperature, nutrient availability, and upwelling intensity emerged as primary environmental filters structuring coccolithophore communities. Seasonal particulate inorganic carbon peaks occurred in central-southern coastal and shelf waters (35-45 degrees S) during austral spring-summer. The widespread Gephyrocapsa huxleyi moderate calcified (MC) morphotype dominated across zones, while the G. huxleyi hyper-calcified (HC) morphotype was restricted to upwelling centers and the northern West Wind Drift zone. Northern and offshore coccolithophore communities harbored the "over-calcified" G. huxleyi A-CC morphotype alongside G. muellerae, G. ericsonii/parvula, and Calcidiscus leptoporus. Coccolithophore abundance and diversity correlated significantly with east-west Ekman transport, but not with the Finite-Size Lyapunov Exponents-based frontal metrics, suggesting a stronger influence of upwelling-driven processes than submesoscale frontal convergence. Multivariate analyses (PCoA, RDA) discriminated principally between a coastal-southern assemblage and an offshore-northern assemblage. Sea surface temperature was the strongest predictor of community structure, followed by silicate and nitrate concentrations, with the former covarying with salinity and latitude. These findings highlight the role of environmental filtering in shaping biogeographic patterns and emphasize the value of morphotype-level resolution in trait-based approaches to plankton ecology in the Southeast Pacific.