The History of South American Tropical Precipitation for the Past 25,000 Years

Abstract

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.

Hydrology and climatology at Laguna La Gaiba, lowland Bolivia: complex responses to climatic forcings over the last 25 000 years

“…In a record from the Amazon Fan Maslin et al (2000) also report a dry YD, but with a short lived major peak in Amazon discharge around 11,400 BP, which the authors associate with Termination 1B. In contrast, the Botuvera stalagmite record and lake records from the Bolivian Altiplano (Baker et al, 2001) show wet conditions. Ledru et al (2006) suggest that the apparent contrast in conditions in north east Brazil between inland and northern locations (dry YD) and coastal locations (wet YD) might reflect a greater influence of winter precipitation along the coast.…”

Late Quaternary Climate and Hydrology of Tropical South America Inferred from an Isotopic and Chemical Model of Lake Titicaca, Bolivia and Peru

“…The occurrence of an overflow interval between 10,000 and 8,500 cal yr B.P. (Baker et al, 2001) means that this salinity was likely never reached. However, our assumption that inflow chloride concentration remained at the same (modern) value throughout the simulation is conservative; the value may well have risen during the dry period, as it does seasonally today (Carmouze et al, 1992).…”

“…to present, spanning the late-glacial highstand and early-to-middle Holocene lowstand intervals. We ran a 15,000-year simulation with forcing designed to reproduce the major changes in lake level that we have reconstructed based on our studies of piston cores from deep Lago Grande (Cross et al, 2000;Baker et al, 2001), ice-core records from Sajama (Thompson et al, 1998), correlation with the Lago Junin sediment record (Seltzer et al, 2000), and model studies of the central Altiplano (Blodgett et al, 1997). Because the Sajama ice cap is near Lake Titicaca, and because their modern precipitation is similar in δ 18 O, the ice cap probably records the δ 18 O of precipitation that fed Lake Titicaca throughout the past 25,000 years.…”

“…A short-term period of overflow that occurred between 10,000 and 8,500 cal yr B.P. (Baker et al, 2001) was not modeled. The isotopic composition of the inputs was increased by 5‰ to modern values at 11,500 cal yr B.P.…”

The last deglaciation of Peru and Bolivia

“…Whether the deglaciation from last glacial maximum extents was interrupted by a late-glacial advance in the Andes coeval with the Younger Dryas was identified as a key question for resolving the extent to which the North Atlantic forces global climate (Clapperton, 1993;Rodbell, 2000;Rodbell and Seltzer, 2000), and remains unresolved. At the end of the twentieth century, long sedimentary records extracted from basins beyond the glacial limit provided key hydroclimatic proxies that revised earlier interpretations of a dry LGM, and suggested deglaciation was underway between 22 ka and 19.5 ka BP, thousands of years prior to the Northern Hemisphere Baker et al, 2001aBaker et al, , 2001bSeltzer et al, 2002).…”