Southern westerly winds and paleoceanography of the San Jorge Gulf (SW-Atlantic ocean, Argentina) during the last 14,000 years

Abstract

We use pollen and dinocyst assemblages from three sedimentary sequences of the San Jorge Gulf (SJG) to document the vegetation history of the extra-Andean/eastern Patagonia (Argentina), and the latitudinal variations of the Southern Westerly Wind Belt (SWWB) in relation with ocean changes during the Late Pleistocene and Holocene. Our results suggest that prior to 14 cal ka BP, the vegetation of the SJG was dominated by halophytic taxa probably related to arid conditions in coastal environments. After 14 cal ka BP, pollen data suggest the development of shrub and herb vegetation in the Patagonian steppe then characterized by semi-arid conditions. The 14 cal ka BP transition is marked by increasing Nothofagus pollen abundances, suggesting strong westerlies at the onset of the Antarctic Cold Reversal (ACR). This transition is also marked by the occurrence of marine palynomorphs (dinocysts, organic linings of foraminifers), which relate to sea-level rise. The dinocyst assemblages allowed us to quantitatively estimates changes in summer sea-surface temperature (SST) and annual net primary productivity. Between 14 and 10.8 cal ka BP, which encompasses the glacial termination and the early Holocene, dinocyst assemblages are dominated by Operculodinium centrocarpum (∼82%) and Spiniferites mirabilis (∼8%) that suggest warmer conditions than at present. The transition from early to middle Holocene was marked by high SWWB intensity as suggested by pollen assemblages, and an increase of heterotrophic taxa such as Brigantedinium spp., Echinidinium sp., Dubridinium sp., and the cysts of Polykrikos kofoidii, suggesting increased primary productivity and gradual cooling of surface water. After 4 cal ka BP, pollen data suggest a decrease in the SWWB intensity that correlates with glacier advances in Patagonia and a further decrease in summer SST in the SJG.