New constrains on Late Glacial pluvial events on the Southern Bolivian Altiplano
Abstract
Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altiplano during the Late Glacial, providing evidence of dramatic changes in low-latitude moisture. It is now apparent that the Tauca (18.1-14.1 ka) and Coipasa (13-11 ka) lake cycles are part of a regional wet interval, the Central Andean Pluvial Event (CAPE). Proposed driving mechanisms for CAPE include changes in: summer solar insolation, Pacific SST gradients (ENSO variability), Atlantic SST gradients (the Younger Dryas and Heinrich I), and moisture levels in the eastern lowlands. The region impacted by CAPE may extend from 10 to 26°S. The Southern Altiplano (18-22°S) is at the center of this region. Regional climate histories, however, highlight existing uncertainties and contradictions about the timing, magnitude, and synchrony of the CAPE both across the region and within Altiplano lake basins. Are differing conclusions about the timing and mechanisms of central Andean climate change related to regional variability, or are these differences, instead, a result of different chronological or proxy methods? An improved understanding of climate history on the Southern Bolivian Altiplano is critical to addressing the cause of the CAPE. The Coipasa lake cycle coincides with the Younger Dryas (12.8-11 ka) and new insight into lake extent is aided by distinct 87Sr/86Sr values for this lake cycle. Carbonate crusts from this lake cycle produce exceptionally precise U-Th ages (some with uncertainties <150 years). Sediments associated with the Tauca and Coipasa lake cycles are clearly separated stratigraphically in some locations, but at the highest and lowest elevations these crusts often superimposed in a manner that is not obviously disconformable. Both field and geochemical evidence now suggest that the Coipasa lake cycle was ~55 meters deep (~33,000 km2) and began to expand at 12.8 ka. Quantitative assessment of the precipitation/evaporation balance necessary to maintain lakes of various sizes constrains the climate conditions responsible for Southern Altiplano paleolakes. Temperature, precipitation, and hydrologic transfer among sub-basins alter the surface area of a lake. We use 87Sr/86Sr values of modern waters and paleolake carbonates to quantify hydrologic connections between sub-basins. Precipitation changes during the CAPE are quantified over a range of temperatures. For the Tauca lake cycle, we are able to simultaneously model lake and glacial expansions. Our precisely dated shoreline record also allows creation of dynamic hydrologic budget models for the transgression and regression of the Tauca lake cycle.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP23B1399P
- Keywords:
-
- 1051 GEOCHEMISTRY / Sedimentary geochemistry;
- 1622 GLOBAL CHANGE / Earth system modeling;
- 1845 HYDROLOGY / Limnology;
- 4942 PALEOCEANOGRAPHY / Limnology