Circulation in the Guafo Mouth: the gateway to northern Patagonia

Circulation and exchange are important factors governing material transport in all coastal areas. One  such area is Northern Chilean Patagonia, a region that boasts one of the largest aquaculture industries (salmon and mussel farming) in the world and provides habitat for several protected marine mammal species. Linkages between coastline shape and forces of hydraulic conditions are thereby important considerations when understanding constituent concentrations related to water quality issues such as harmful algal blooms (HABs), which threaten aquaculture activities and endanger wildlife and humans. The research presented here characterizes circulation patterns and variability in the Guafo Mouth, the primary connection between the Pacific Ocean and the fjords and channels of Northern Chilean Patagonia, to help inform ocean-fjord circulation in this ecologically and economically important area. In situ measurements of current velocities, salinity, temperature, dissolved oxygen, and nutrients have been collected for over two years at point measurements in the channel. These data, along with companion numerical model output and reanalysis data, provide parallel evidence of subtidal flows driven by a combination of barotropic and baroclinic pressure gradients and Coriolis, indicating a geostrophic balance. Depending on the sign of the barotropic pressure gradient, the barotropic flow either augmented (when positive) or opposed (when negative) the gravitational circulation produced by horizontal gradients in density and, in certain cases, produced subtidal outflow throughout the water column. Temporal variability of the current velocities was driven by changes in sea level gradients at ~35 d and ~50 d, linked to coastal trapped waves forced by the Madden Julian Oscillation. This variability has implications for the ocean-fjord exchange of dissolved oxygen and nutrients, which are critical to the health of the Chilean Inland Seas. Near-bottom waters with high nutrient content and low dissolved oxygen are advected in-channel when the crest of a coastal trapped wave is at the coast of Northern Patagonia due to enhanced subtidal inflows. These results highlight the importance of understanding the periodicity and amplitude of remotely forced coastal trapped waves to estimate ocean-fjord exchange through the gateway to northern Patagonia.