Pleistocene large-lake episodes in the central Andes (Invited)
Abstract
The connection between global climate and regional climate in the southern hemisphere tropics and subtropics is poorly understood. On the Bolivian Altiplano, a new unified lake history based on evidence from both naturally exposed shoreline deposits and sediment cores is coupled with a hydrologic budget model to yield a record of precipitation changes on the southern Bolivian Altiplano over the last 130 ka. Ten lake cycles and two major trends are apparent in the Altiplano precipitation record: 1) the Altiplano was relatively dry during the global cold interval between 80 and 20 ka; and 2) each of ten precipitation increases coincides with a cold event in the north Atlantic. This long range, high-resolution lake record allows us to test possible links between central Andean climate and global climate events such as: 1) changes over glacial-interglacial cycles; 2) seasonal insolation over land; 3) Pacific sea surface temperature (SST) gradients; and 4) Atlantic thermohaline circulation. Millennial-scale pluvial events on the Bolivian Altiplano are the dominant feature of this record, but are superimposed on a glacial-interglacial trend that is generally dry during global cold intervals, consistent with an Amazon basin that was also more arid over this time. A critical difference between the Altiplano lake record and other long-duration tropical/subtropical records from South American caves is that on the Bolivian Altiplano local insolation cycles exert little or no visible control on moisture balance. Pacific sea- surface temperatures (SSTs) also may contribute to variability across the broad region (10-26°S) impacted by the two most recent lake events. Most notably, the Tauca lake cycle (18-14 ka) coincides not only with H1, but also with evidence for intense upwelling in the central Pacific between 18 and 13 ka (La Niña-like conditions); regional variability in the magnitude of this lake cycle is consistent with modern variability in ENSO impacts. Most significantly, we find that the southern Altiplano lake record clearly demonstrates that ocean circulation in the distant north Atlantic can produce a strong, if not first order, impact on climate in the central Andes. Today the link between central Andean climate and the Atlantic SST gradient is weak relative to the impact of Pacific SST anomalies associated with El Niño/Southern Oscillation. However, cold SST anomalies centered in the north Atlantic dominate the lake record; episodes such as the Younger Dryas and Heinrich events result in significant changes in moisture on the southern Altiplano. The ability of north Atlantic SSTs to strongly and synchronously control lake size in such a distant and continental location points to a strong atmospheric component associated with Atlantic meridional overturning circulation. Part of this link could be a result of changes in the strength and position of the intertropical convergence zone. Recent work also suggests that more widespread changes in atmospheric divergence across southeastern South America may be more directly related to tropical Atlantic sea-surface temperatures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP34B..03P
- Keywords:
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- 1105 GEOCHRONOLOGY / Quaternary geochronology;
- 1605 GLOBAL CHANGE / Abrupt/rapid climate change;
- 1616 GLOBAL CHANGE / Climate variability;
- 1655 GLOBAL CHANGE / Water cycles