Dominant scales of subtidal variability in coastal hydrography of the Northern Chilean Patagonia

Abstract

Abstract The Chilean Patagonia, on the southeastern Pacific Ocean, is one of the largest fjord systems in the world. Its complex topography harbors an aquaculture industry that is among the top exporters of salmon and mussels worldwide. However, little is known about the scales of environmental variability of this region and how climate-related changes can alter the current conditions. This study provides a baseline understanding of the dominant scales of subtidal variability in meteorological forcing and water properties along and across the region that encompasses northern Patagonia and specifically the Inner Sea of Chiloe (ISC). We examined multiple datasets spanning multiple spatial and temporal scales. Reanalysis wind time series were combined with satellite-derived data (MODIS-Aqua) and in situ hydrographic records from the mussel farming industry as well as from instruments moored at various locations in the ISC. We assessed the influence of large-scale forcing on the variability of local conditions and used the assembled datasets to find modes of variability at interannual, seasonal and intraseasonal scales. The patterns of atmospheric and oceanographic variability along northern Patagonia are heterogeneous both in time and space. Long-term sea surface temperature (SST) averages revealed two areas with colder temperatures and attenuated seasonal variability that can be associated with stronger vertical mixing. These areas have been previously related to hotspots for whale sightings and might be important as bottom-up controls of Patagonian food webs. Northern Patagonia is strongly affected by large-scale processes at the South Pacific basin scale. Long-term wind data show a poleward displacement of the transition between upwelling and downwelling favorable conditions during spring-summer months for the last decade. The intraseasonal time scale was dominated by a band centered at 30 days that can be attributed to atmospheric variability driven by the Baroclinic Annular Mode (BAM), which induces the periodic mixing of the water column, but with substantial interannual variability. Variability in local conditions was found to closely track the large-scale variability, even in the small channels and bays. These findings highlight the strong connection between large-scale processes and the conditions faced by aquaculture in the ISC, and the need to consider such scales of variability - as well as climate trends - in planning and management decisions.