Postglacial South Pacific

Abstract

Most available Holocene paleoceanographic data from the South Pacific originate from the margins of the surrounding continents where higher terrigenous sediment supply, combined with enhanced biological productivity, provides a much better potential for studying Holocene paleoenvironmental variability. In terms of postglacial ‘long-term’ trends, sea surface temperature (SST) records from the Chilean margin suggest an early Holocene maximum warming that coincides with warm conditions as recorded in Antarctic ice cores. This early to middle Holocene climate optimum is similar to that observed throughout much of the Northern Hemisphere, but the southern climatic optimum appears to start earlier. The general SST and Antarctic temperature pattern during the Holocene is paralleled by distinct trends in Chilean rainfall, suggesting a latitudinal antiphasing of rainfall and westerly wind strength changes between the core westerlies in southernmost Chile and the northern margin in central Chile. During the early Holocene, the core westerlies were enhanced and the northern margin was reduced, whereas the opposite pattern is observed in the late Holocene. Marine productivity in parts of the Peru–Chile Current (PCC) was lower during the early and middle Holocene and increased afterward, interpreted in terms of latitudinal shifts of the Antarctic Circumpolar Current (ACC) as the main source of nutrients in the PCC system. Taken together, these long-term trends suggest a close coupling of the main oceanographic (the ACC) and atmospheric (the Southern Westerlies) circulation members of the southeast Pacific, at least on orbital timescales. Further north, along the Peruvian continental margin, long-term changes in the El Niño Southern Oscillation (ENSO) system may have played an important role in postglacial paleoceanographic variability. Most of the data suggest reduced ENSO activity during the early and middle Holocene, a pattern that is broadly consistent with open tropical Pacific records that suggest enhanced zonal SST gradients during the middle Holocene, characteristic for a mean La Niña-like state of ENSO. Records available from the continental margins off New Zealand/Australia and Antarctica (Palmer Deep) share some of the main trends found in the eastern Pacific and in the ice cores. At a millennial- to centennial-scale, climate patterns are only documented in a few records in the South Pacific realm, suggesting two dominant bands of variability with cycles of ~900 and ~1500 years.