Southern Oscillation Signal in South American Palaeoclimatic Data of the Last 7000 Years

Abstract

During strong El Niño events, rainfall anomalies and changes in wind patterns are observed in different regions of South America. Along the central Brazilian coast, during the 1983 El Niño year, the frontal systems were blocked to the south, provoking a reversal of the longshore sand transport. Long-duration reversals of longshore transport were also recorded in Holocene beach-ridge terraces from the Rio Doce coastal plain. This led to the formulation of a model relating these reversals of longshore transport to El Niño-like conditions. El Niño-like conditions are past average climate situations that generate the same perturbations as the strong El Niño events observed during the last decade. They are likely to correspond to the long-duration low phase of the Southern Oscillation. To confirm this hypothesis we compared the Holocene beach-ridge record with other palaeoenvironmental records from regions where strong El Niño events would have a substancial signal as well: (1) water-level fluctuations of Lake Titicaca, (2) a pollen and sediment record in an eastern Amazonian lake, (3) changes of the Rio Xingu discharge in eastern Amazonia, and (4) variations of sand supply at the Rio Piura and Rio Chira outlets in the Sechura Desert. The occurrences of El Niño-like conditions were numerous before 3900-3600 yr B.P., absent between 39003600 and 2800-2500 yr B.P., and infrequent after 2800-2500 yr B.P.

Pollen-based biome reconstructions for Latin America at 0, 6000 and 18 000 radiocarbon years ago

“…An extended dry season may explain why Araucaria-dominated forest were still restricted in their distribution relative to the modern day, not significantly increasing in range until approximately 3000 14 C yr BP (Behling, 1997a). From our analysis the temporal perspective is missing, hence, we are unable to indicate if the vegetation reflects a stable dry period, or a period where there are alternating periods of dry and humid climates linked for example to El Niño activity (Martin et al, 1993;Sifeddine et al, 2001). A relatively dry phase is also recorded in northwestern Argentina between 7500 and 5800 14 C yr BP (Schäbitz, 1991).…”

Mid- to late-Holocene El Niño-Southern Oscillation dynamics reflected in the subtropical terrestrial realm

“…indicate wetter periods, relative to the prairie. They are likely caused by short periods of increased ENSO intensity as described from beach ridge deposits (43). However, comparing timing and duration of these events with other records is, given the limitations on the available chronologies, difficult and a likely source of confusion.…”

Late Quaternary lake-level changes constrained by radiocarbon and stable isotope studies on sediment cores from Lake Titicaca, South America

“…However, recent evidence from the Palmer Deep, immediately west of the Antarctic Peninsula, indicates that the middle Holocene was a time of significantly increased surface productivity (Domack et al, 2001), perhaps brought about by a strong teleconnection to sustained El Niño-Southern Oscillation (ENSO) warm mode conditions. The MHLS is thought to be a non-linear coupled response to ENSO and insolation (Martin et al, 1993;Rowe et al, 2002), as it is nearly concurrent with the mid-Holocene re-establishment of ENSO conditions in the equatorial Pacific (Sandweiss et al, 2001, and references therein). The shift toward a strengthened SASM (and weakened West African monsoon) occurred between 5000 and 6000 yr BP.…”