Dr. Lara-Peña, Carlos

Surface oceanic fronts are regions characterized by high biological activity. Here, Sea Surface Temperature (SST) fronts are analyzed for the period 2003–2019 using the Multi-scale Ultra-high Resolution (MUR) SST product in northern Patagonia, a coastal region with high environmental variability through river discharges and coastal upwelling events. SST gradient magnitudes were maximum off Chiloé Island in summer and fall, coherent with the highest frontal probability in the coastal oceanic area, which would correspond to the formation of a coastal upwelling front in the meridional direction. Increased gradient magnitudes in the Inner Sea of Chiloé (ISC) were found primarily in spring and summer. The frontal probability analysis revealed the highest occurrences were confined to the northern area (north of Desertores Islands) and around the southern border of Boca del Guafo. An Empirical Orthogonal Function analysis was performed to clarify the dominant modes of variability in SST gradient magnitudes. The meridional coastal fronts explained the dominant mode (78% of the variance) off Chiloé Island, which dominates in summer, whereas the SST fronts inside the ISC (second mode; 15.8%) were found to dominate in spring and early summer (October–January). Future efforts are suggested focusing on high frontal probability areas to study the vertical structure and variability of the coastal fronts in the ISC and its adjacent coastal ocean.

Northern Patagonia is characterized by multiple rivers that discharge considerable amounts of freshwater into the coastal ocean, forming large river plumes that influence hydrographic and ecological processes. In this study, we use satellite ocean color data from MODIS (Moderate Resolution Imaging Spectroradiometer) to characterize the seasonal and interannual variability of turbid freshwater plumes in the inner waters of northern Patagonia for the first time, with a focus on the connections to river discharge and large-scale climatic variability. The turbidity signal from the surface reflectance product centered at 645 nm, Rrs(645), correlates well with peaks in river discharge data and surface salinity minima from boat-based profiles and a surface buoy, validating its use for the identification of turbid river plumes in the region. The seasonal climatology of Rrs(645) showed the presence of large river plumes throughout the year, with variability associated mainly to that of river discharge. Analysis of Rrs(645) fields under low and high discharge conditions allowed for the identification of a threshold value to delineate plume fronts and determine the probability of plume occurrence. EOF analysis reveals the dominant modes of plume variability, associated to turbidity differences between the coastal margin and deeper waters and to in-phase variability of large river plumes throughout the study area. The largest plume event occurred in year 2008, during negative (cold) phases of ENSO (La Niña) and PDO but a positive phase of SAM. The severe drought event of 2016 that occurred during positives phase of ENSO (El Niño), PDO and SAM is well captured by the EOF analysis and is characterized by large negative anomalies in the Rrs(645) signal. In general, complex co-variations are observed between monthly anomalies of Rrs(645) and the ENSO, PDO and SAM indices, highlighting the heterogeneity of climatic regulation in the region.

Colored dissolved organic matter (CDOM) is an indicator and optical proxy of terrestrial processes such as land use with allochthonous material fluxes, biogeochemical cycles, and water quality in coastal zones influenced by rivers. However, the role of land use changes on the spatial and temporal availability of CDOM has been poorly explored in Chile. Here, we studied two watersheds with similar climates and contrasting land use patterns in northern Patagonia considering the sampling of CDOM in their estuarine and adjacent coastal ocean. An empirical algorithm with the coefficients adjusted to our study areas to estimate CDOM was applied to Landsat 7 and 8 images to examine temporal variability of CDOMest from 2001 to 2011 and 2013–2020. Our results showed an increasing trend of CDOMest in both areas. Different trends in land use patterns between the two watersheds showed a significant correlation with CDOMest and contrasting associations with environmental variables. Higher humification was found in Yaldad in comparison with Colu. In both areas, allochthonous materials predominated, especially during austral spring according to the low values of the Fluorescence Index (FI). Our results highlight the potential of CDOMest to parameterize biogeochemical cycling models and to further understand the dynamics of CDOM in coastal ecosystems.