“Source-to-sink” dynamic of the eastern south american slope since the last deglaciation

Abstract

The southwestern Atlantic receives large amounts of terrigenous material from eolian and fluvial sources from South America: north of 39°S the main source of fluvial-derived sediments is the Plata Plume Water (PPW); south of 39°S eastern Patagonia provides large amounts of dust. We analyzed major elements obtained from X-ray fluorescence on two sediment cores retrieved from the South American slope: GeoB22735 (643cm, 36.13ºS-52.83ºW, 1400m, 64 samples), offshore Río de la Plata mouth; and AU_Geo02_GC20 (35cm, 45.92ºS-58.5ºW, 2600m, 14 samples), at the Patagonian margin. Age model of both cores was based on 14C AMS datings and δ18O chronology, spanning the last 18 kyr. To investigate how the climate changes occurred since the last deglaciation affected the terrigenous input to the southwestern Atlantic, Fe/Ca and Ti/Ca ratios were analyzed as fluvial-derived sediment proxies; and Ti/Al as eolian input proxy. Core GeoB22735 shows higher Fe/Ca and Ti/Ca ratios during the last deglaciation compared to the Holocene. This implies that the combined effect of low sea-level together with the equatorward shift of the westerly winds (SWW), and the enhanced precipitations over Subtropical South America occurred during the onset of the deglaciation provoked increased and/or more frequent northward intrusions of the PPW, increasing the continental material fluvial-derived on the slope at the Uruguayan margin, as occur nowadays during austral winter. The lower Ti/Al ratios from core AU_Geo02_GC20 confirmed the equatorward shift of the SWW during the last deglaciation compared to the Holocene. During the Holocene, the sea-level rise along with the poleward shift of the SWW and the establishment of the modern circulation patterns associated with the interplay between South American Monsoon System and the SWW, mark the onset of the current continental input conditions: a strong seasonal PPW behavior depending on precipitations over the Rio de La Plata Basin and/or along-shore wind stress.