Centennial hydroclimatic and anthropogenic processes of South East South America modulate interannual and decadal river discharge

Abstract

The Río de la Plata (RdlP) mud depocenter is an outstanding centennial ultra-high-resolution information source of hydroclimatic variability and terrigenous export because sedimentation attains values of 13 mmyr−1. Thus, our main objective was to inter-compare and correlate the direct hydroclimatic observations to the proxy record from the RdlP mud depocenter. We correlated continental input and marine productivity proxies to the instrumental historical hydroclimatic observations, and determined the associated periodicity and coherences of such environmental processes by means of wavelet analyses. We discuss the results in the context of both natural climate variability and anthropogenic impacts within the RdlP drainage basin. To this end, we performed a 210Pb and 14C mixed age-depth model and μXRF scanning (every 2 mm), and used Ti/Al and Ba/Al as proxies for continental input and marine productivity changes. We incorporated instrumental observations, i.e., rainfall, river discharges and climate variability modes (CVM) such as: El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). The statistical correlation analyses indicated a consistent correspondence between both proxies and rainfall anomalies for the warm season within the lower Paraná drainage basin. Such rainfall anomalies are dominated at inter-annual, decadal and multi-decadal scales by ENSO, PDO and AMO modes of variability, respectively, which together modulated river flow. Thus, centennial hydrological and proxy variability appear to be mainly modulated by the CVM. In this sense the present study is in close agreement and complementary to previous worldwide studies by showing similar results for RdlP drainage basin. We further identified a strong change in the proxy data after 1970s; i.e., the highest continental input and marine productivity record, and we related it to the combined effect of climatic variability and anthropogenic impact. Such a period is related to a dominance of positive ENSO (El Niño events) and PDO, and negative AMO, leading to increased rainfall and runoff over the drainage basin, together with intensified agricultural practices. The strong intensification of agricultural activities, mostly soy beans, together with increasing rainfall and runoff led to increased soil erosion and sediment transport, whose final fate is the RdlP mud depocenter.