Reply on RC1

Résumé fourni par la source

Abstract. A global inventory of oceanic dissolved oxygen (DO) indicates that only 0.6 % of the ocean's oxygen originates from the atmosphere. This makes the ocean highly sensitive to both natural and anthropogenic disturbances that can disrupt the physical and biogeochemical processes governing oceanic DO dynamics. The impact of ocean deoxygenation has accelerated globally, driven by warming and diminishing deep-water ventilation. Therefore, the primary objective of this work is to quantify, for the first time, the contribution of the dissipation of turbulent kinetic energy and the diapycnal eddy diffusivity (diapycnal mixing) to water ventilation, as evidenced by the occurrence of upward oxygen transport from deep to subsurface layers denoted as positive dissolved oxygen fluxes in the northern Patagonian fjords. A vertical microstructure profiler was used to measure, with high vertical resolution, the dissipation rate of turbulent kinetic energy and the oxygen characteristics of water at approximately 160 stations in the northern Patagonian fjords during seasonal campaigns in 2023. The results showed a range of dissipation between 10-9 and 10-4 W kg-1, and diapycnal mixing values ranging from 10-5 to 10-2 m2 s-1. The highest values of both variables were recorded in the Chiloé Inner Sea, where previously reported intense mixing has been attributed to tidal energy. Regarding oxygen flux records, larger positive fluxes were reported in the surface layer (10-5 and 10-3 µmol L-1s-1). Still, significant events of positive fluxes were recorded subsurface and in the deep layers of the Puyuhuapi Fjord due to intense diapycnal mixing forced by the advection of dense ocean waters. Moreover, intense turbulence contributes to positive oxygen fluxes over more of the water column than just the surface layer, especially in the Chiloé Inner Sea, driven by the interaction between the semidiurnal tides with the complex topography of the region. Moreover, double-diffusive convection appeared to be another mechanism favoring deep-water ventilation. Our results highlight the importance of incorporating turbulence measurements into fjord studies to understand sensitivity to significant oxygen variability.

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