Biogeochemical features along the northern and central Patagonian shelf during a spring cruise: implications for biological productivity

Abstract

The Patagonian fjords, channels, and glacial meltwater plays a key role in shaping the hydrography and biogeochemistry of the Southeastern Pacific Ocean, through substantial exchanges with open ocean waters. However, the continental shelf between 46°S and 48°S remains less explored, leaving critical gaps in our understanding of nutrient dynamics and productivity patterns. This study investigates latitudinal gradients in water column biogeochemistry and productivity in northern and central Chilean Patagonia during the austral spring of 2018. We identified three distinct zones: a northern area (41°S and 46°S) with higher temperature, salinity, dissolved oxygen, and chlorophyll-a concentrations; an exchange zone between Guafo entrance and Moraleda Channel, characterized by elevated inorganic nutrient concentrations; and a southern area (46°S and 48°S) with increased ammonium concentrations and the lowest silicic acid levels. Offshore stations in the northern area exhibited the highest integrated primary production rates (up to 6.3 g C m⁻² d⁻¹), primarily sustained by nitrate uptake (ƒ ratios up to 0.98). In contrast, the southern area showed a preference for ammonium assimilation, with lower ƒ ratios (0.1–0.3). These findings suggest that the northern area supports a high proportion of new primary production, which likely enhances organic matter export and the efficiency of the biological pump, whereas regenerated production in the southern area may limit carbon export potential. Our study provides the first large-scale description of the biogeochemical features of the Patagonian continental shelf, particularly around the Taitao Peninsula, offering a critical baseline for understanding biogeochemical processes in this region and its potential responses to climate change and anthropogenic pressure.