Seasonal and inter-annual turbidity variability in the Río de la Plata from 15 years of MODIS: El Niño dilution effect

Abstract

Spatio-temporal variability of turbidity in the Río de la Plata (RdP) estuary (Argentina) at seasonal and inter-annual timescales is analyzed from 15 years (2000–2014) of MODIS data and explained in terms of river discharges and the El Niño Southern Oscillation (ENSO). Satellite estimates were first validated using in situ turbidity measurements and then the time series of monthly averages were analyzed to assess the seasonal and inter-annual variability of turbidity. A strong seasonal variability was found in the upper and middle estuary with high turbidity from March to May and low turbidity from June to January. It was found that this variability is highly correlated to the seasonal cycle of the water discharge of the Bermejo river with a one-month delay between its peak and turbidity in the upper RdP estuary. On inter-annual time scales the influence of ENSO shows low turbidity amplitudes in the upper and middle estuary during moderate El Niño years, while the opposite pattern is observed in some La Niña years. A dilution effect during El Niño years is observed given that the main tributaries, which provide ∼92% of the liquid discharge, show water discharge increases due to excess in rain, while the Bermejo river, which provides ∼70% of the solid discharge and only 2% of the liquid discharge to the RdP, does not show this inter-decadal periodicity. In turn, increased turbidities are observed when negative RdP water discharge anomalies occurred, but this is not always related to La Niña events, since these events are not the only predictor for drought in this region.