Large-Scale Mass Transport in the Austral Fjords and Channels of Chile

The southern coast of Chile (41.0 degrees S - 46.5 degrees S) is a unique region with a complex marine system of fjords and channels that receives melted waters from the glaciers of the southern Patagonian ice field. Despite this region is almost uninhabited, it has been affected by harmful algal blooms called red tide, which has increased in frequency, duration, extension and toxicity. Furthermore, recent events of ISA virus have stroked salmon farms that operate on the region, with severe consequences on the Chilean economy. Considering these environmental trends, it is crucial to understand horizontal transport mechanisms that spread both algae and virus in the region. The main objective of this article is to characterize and quantify the dispersion mechanisms that dominate large-scale mass transport in the upper layer of this region. Particularly, the focus is placed on tide dispersion, estuarine dispersion and wind dispersion. For doing this, we modeled the coupled atmospheric-hydrodynamics three-dimensional conditions for the summer of 2011. The atmospheric simulations were carried out with WRF model and the hydrodynamic simulations were conducted with CWR-ELCOM. In order to define which dispersion mechanism dominates the horizontal transport, different scenarios were simulated considering changes in the external forcing, and the horizontal dispersion coefficient of the upper layer was then computed using the simulated flow velocities. It is shown that estuarine dispersion has an important role in the horizontal shear dispersion during the floods, but more important were the combined effects of tide and wind dispersion during the entire simulation. Particularly, the wind counteracts the effects of tide dispersion, showing an increase on the horizontal dispersion when the wind speed is reduced.