Dr. Lara-Peña, Carlos

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.

Coastal upwelling ecosystems support some of the most productive fisheries of the planet together with a large shellfish aquaculture sector that depends on oceanographic processes to deliver planktonic larvae to replenish and feed the farmed stock. Coastal shellfish aquaculture operations in Chile and Perú have experienced large interannual fluctuations in larval supply over the past decade, yet the drivers of such variability remain unidentified. We focused on the effects of environmental variability on larval supply of the farmed Peruvian bay scallop Argopecten purpuratus in a bay in northern Chile (Tongoy Bay, 30∘ S) that accounts for over 90% of countrywide landings. We examined the hypothesis that the environmental processes governing larval supply were shared with wild benthic invertebrates with planktonic larval development and compared time series of larval abundance for the scallop with larval supply rates to benthic populations of two well-studied wild intertidal species: the Chthamalid barnacle Jehlius cirratus and the purple mussel Perumytilus purpuratus. To this end, we examined the cross-correlation of larval supply to environmental variability using MODIS satellite fields of sea surface temperature (SST) chlorophyll-a concentration (chl-a) and fluorescence line height (nFLH), together with three climate indices relevant for the south east Pacific sector: the Southern Oscillation index (SOI), the Pacific Decadal Oscillation (PDO) and the Antarctic Oscillation Index (AAO). Our results showed that over the five-year study period (2009–2013), patterns of larval supply to the scallop population were related to interannual variability in the environmental processes as captured by their Empirical Orthogonal Functions (EOFs), likely to adult condition before spawning. Surprisingly, larval supply for none of the wild species showed a clear association to the EOFs. In contrast, scallops and wild species showed significant association to lower frequency climate variability as captured by the SOI and the PDO, but not the AAO. Results suggest that larval supply patterns to Tongoy Bay may be modulated by regional patterns of climatic variability, particularly of tropical origin. Thus, changes in coastal oceanography associated with ongoing changes in global climate could have strong and lasting effects on the supply of seedstock for wild and cultivated species across this eastern boundary coastal system and argue for the establishment of long-term ocean observing and early warning systems along the region.