A warm interglacial episode during oxygen isotope stage 11 in northern Chile

Abstract

Combined paleontological, morphostratigraphic and geochronologic data from emerged Middle Pleistocene coastal deposits in Mejillones Peninsula (23°S), northern Chile, strongly suggest that climatic conditions were particularly warm during the particularly warm during the Oxygen Isotope Stage 11 high seastand episode. An anomalous warm-water molluscan assemblage from localities assigned to that interglaciation included several extralimital species, presently living only north of 6°S (or 14°S), that were not present in the area during subsequent Middle and Late Pleistocene, or Holocene, interglacial episodes. Only two of these extralimital species may be found nowadays at the 23°S latitude, in a protected locality, immediately after the occurrence of strong El Niño events. Many of the species of the thermally anomalous molluscan assemblage (TAMA) are the same as those which lived in a closed shallow lagoon near Santa, north-central Peru (9°S) during a brief mid-Holocene episode. The new findings thus indicate that lagoonal and protected embayments were significantly warmer than the open marine environment ca. 400 ka. Actually, the co-occurrence of cool water fauna in exposed sectors of the coastline at that time suggests that the coastal upwelling activity and the Humboldt Current effects were not strongly reduced. The warm-water conditions prevailing in lagoons and protected bays during the Mid-Brunhes episode may reflect particularly warm air temperatures and distinct ocean-atmosphere relationships than those prevalent nowadays. These data support the hypothesis that the Oxygen Isotope Stage 11 was the warmest interglaciation, at least in the southern hemisphere.