South Brazilian Bight mid- to late Holocene hydrographic fluctuations

摘要

Here, we present two high temporal resolution Holocene sea surface temperature (SST) and salinity (SSS) reconstructions for the SW Atlantic. Mg/Ca data together with the oxygen isotopic composition (delta O-18) of a shallow dwelling planktonic foraminifera species (Globigerinoides ruber(pink)). Two marine sediment cores collected at similar to 25 degrees S are used to assess mid- to late Holocene sea surface hydrographic conditions in the continental shelf of the South Brazilian Bight. Our results show multi-centennial-scale changes of up to 2.7 degrees C in SST and 0.8 parts per thousand in ice volume corrected seawater delta O-18 (a proxy for SSS, indicating changes of up to 2 salinity units). In phase, multicentennial-scale negative SST and SSS incursions were interpreted to indicate shelf-break upwelling events and the northward intrusion of the Plata Plume Water (PPW) under a strengthened Brazil Current (BC) flow. The latitudinal SST gradient between our two records (Delta SST7616-7610), applied here as a proxy for the BC strength, supports the existing hypothesis of antiphase between the BC and the North Brazil Current strength during the last 7 ka. Positive Delta SST(7616-7610)values suggest the presence of the PPW at latitudes of up to 25.5 degrees S, while negative Delta SST(7616-7610)values (centred at around 5.4, 4.3, 2.2 and 1.3 cal ka BP) occurring synchronously with cold events in the Northern Hemisphere suggests that the Atlantic Meridional Overturning Circulation played a central role in the SW Atlantic mid- to late Holocene surface hydrographic conditions.