Circulation in the Guafo Mouth: The gateway to northern Patagonia

Resumen: Circulation and exchange are important factors governing material transport in all coastal areas, including Chilean Patagonia, a region that boasts one of the largest aquaculture industries in the world and provides habitat for several protected marine mammal species. Linkages between coastline shape and forces of hydraulic conditions, such as tides, wind, sea level gradients, and river discharge are thereby important considerations when understanding constituent concentrations and transport related to water quality issues, which threaten aquaculture activities and endanger wildlife and humans. The primary connection between the Pacific Ocean and the fjords of Chilean Patagonia is through the Guafo Mouth, however the structure and drivers of circulation, and its impact on water quality, has yet to be studied. The research presented here characterizes circulation patterns and variability in the Guafo Mouth to help inform ocean-fjord exchange. Measurements of current velocities, salinity, temperature, dissolved oxygen, and nutrients were collected from 2020 to 2023 in the channel. These measurements, in addition to a numerical model of the study area and reanalysis data, provide parallel evidence of subtidal flows driven by the competition between barotropic and baroclinic pressure gradients. Depending on the sign of the barotropic pressure gradient, the barotropic flow either augments (when negative) or opposes (when positive) the circulation produced by horizontal density gradients. When the near-bottom subtidal inflow enhances, offshore waters with high nutrient content and low dissolved oxygen can be advected in-channel. This occurred at periods between ∼40 and 70 d concurrent with poleward pulses of the Peru-Chile Undercurrent that is known to transport nutrient rich and low dissolved oxygen waters southward off the coast of Chile. These findings imply that ocean-fjord exchange through the Guafo Mouth, which is controlled by water level gradients from the Pacific Ocean to the inner fjords, directly influences the import of dissolved oxygen and nutrients.