Abstract

The coastal region off Chilean Patagonia has been poorly studied due to the lack ofavailable observations. Here we analyzed, by the very first time, biogeochemical (BGC)data to elucidate the role that biological and physical processes play on nitrate, oxygen,pH and hydrographic variables, along a salinity gradient off central Patagonia. Argo floatprofiles covering the upper ocean from December 2015 to July 2019 reveal that offshorewaters are characterized by low temperatures and high salinities related to high oxygenand medium-high values of pH and nitrate. As the Argo float drifted onshore, freshwaterinfluences the upper 50–100 m with low salinity and high temperature. Waters under theinfluence of the continental runoff were characterized by medium-to-high oxygen andpH levels, and the lowest nitrate concentrations. Interestingly, oxygen-deficient waterslocated beneath the freshwater-modified layer showed the lowest pH and highest nitrate.A comprehensive analysis of the temporal and vertical variability of the oxygen:nitrateratio, in conjunction with biological-related and physical parameters, indicates that theBGC variability seems to be the result of a synergistic interaction between physical andbiological processes, where the stratification sets up the environment and promotes thebiological response that, in turn, is auto-regulated by modifying the chemical compositionin the freshwater-influenced zone. The arrival of future floats with additional sensors(Chlorophyll/Fluorescence, Photosynthetically Active Radiation, Backscatter, etc.) willadd new BGC properties that improve our understanding of the coastal marine responseto the increasing freshwater input off western Patagonia in the context of climate change.