When the fjords take a breath: Influence of wind forcing and Ekman dynamics on deep ventilation in the North Patagonian fjords

Abstract. Climate change directly alters the dissolved oxygen (DO) dynamics in the ocean. Ocean ventilation is critical for redistributing nutrients and gases throughout the water column, supporting essential biogeochemical cycles, and regulating the ocean capacity to absorb carbon dioxide and heat, making it essential for climate regulation. In the northern Patagonian fjords, ventilation events mitigate the impacts of deoxygenation and hypoxia, which are primarily driven by the poleward transport of Equatorial Subsurface Water. However, climate-driven changes such as surface warming and increased stratification may reduce the frequency and intensity of these ventilation events, thereby contributing to long-term deoxygenation. In this study, we examined the physical drivers, frequency, and variability of deep ventilation events in the northern Patagonian fjords from 2016 to 2024. ERA5 reanalysis data, from an oceanographic platform moored at 170 m depth, were used to evaluate wind stress, Ekman transport, pumping, and layer depth, alongside in situ time series of temperature, salinity, density, and DO. The results showed a seasonal increase in DO concentrations, classified as ventilation periods, whereas synoptic-scale oxygen events were identified and quantified as ventilation pulses. In total, 16 ventilation periods and 35 pulses were registered over the time series. Onshore Ekman transport favouring downwelling was identified as the main driver of ventilation periods from the austral winter to spring, accompanied by salinity decreases before and during oxygen increases. Pulses coincided with synoptic events dominated by negative total Ekman transport, driven by northern wind stress, along with concurrent thermohaline changes. Overall, these findings provide novel insights into the mechanisms governing oxygen renewal in the Patagonian fjords and underscore the importance of sustained observation systems in a changing ocean.