A 60,000-year record of hydrologic variability in the Central Andes from the hydrogen isotopic composition of leaf waxes in Lake Titicaca sediments

Abstract

A record of the hydrogen isotopic composition of terrestrial leaf waxes (δDwax) in sediment cores from Lake Titicaca provides new insight into the precipitation history of the Central Andes and controls of South American Summer Monsoon (SASM) variability since the last glacial period. Comparison of the δDwax record with a 19-kyr δD record from the nearby Illimani ice core supports the 2 0 1 4 ) 2 interpretation that precipitation δD is the primary control on δDwax with a lesser but significant role for local evapotranspiration and other secondary influences on δDwax. The Titicaca δDwax record confirms overall wetter conditions in the Central Andes during the last glacial period relative to a drier Holocene. During the last deglaciation, abrupt δDwax shifts correspond to millennial-scale events observed in the high-latitude North Atlantic, with dry conditions corresponding to the Bølling-Allerød and early Holocene periods and wetter conditions during late glacial and Younger Dryas intervals. We observe a trend of increasing monsoonal precipitation from the early to the late Holocene, consistent with summer insolation forcing of the SASM, but similar hydrologic variability on precessional timescales is not apparent during the last glacial period. Overall, this study demonstrates the relative importance of high-latitude versus tropical forcing as a dominant control on glacial SASM precipitation variability. , E A R T H A N D P L A N E T A R Y S C I E N C E L E T T E R S 4 0 8 (

Late Quaternary environmental change in the interior South American tropics: new insight from leaf wax stable isotopes

“…While the Central Andes and southern Brazil experienced a relatively wet LGM, a trend towards drier conditions from ~35-21 ka at LLG suggests a reorganization of monsoon circulation under LGM boundary conditions that led to decreased precipitation in the lowland interior tropics. We do not find any strong evidence of precessional orbital forcing at LLG during the last glacial period, consistent with several Central Andes and western Amazon records (Fornace et al, 2014;Cheng et al, 2013;Mosblech et al, 2012;Kanner et al, 2012) and in contrast to the strong precessional signal in southern Brazilian speleothem records (Cruz et al, 2005, Wang et al, 2007. During the Holocene, however, our record, along with most other SASM records, does support hydrologic change driven by precessional changes in insolation.…”

“…Relative drought during the LGM at LLG stands in contrast to clear evidence of wet conditions in the Central Andes (Baker et al, 2001;Fornace et al, 2014) at this time. However, speleothem records from western Amazonia do not show increased SASM intensity during the LGM as would be expected during a period of high austral summer insolation (Mosblech et al, 2012;Cheng et al, 2013).…”

“…Changes in the distribution and intensity of SASM precipitation can alter hydrologic and vegetation patterns across much of the South American continent with potentially significant ramifications for both the global carbon cycle and climate system. An increasingly coherent picture of late Quaternary SASM behavior has begun to emerge from a number of records of SASM precipitation from the Central Andes, western Amazonia and southern Brazil (Cruz et al, 2005;Wang et al, 2007;Mosblech et al, 2012;Kanner et al, 2012;Cheng et al, 2013;Fornace et al, 2014). These records indicate that generally wet conditions prevailed during the Last Glacial Maximum (LGM) and late glacial period, followed by a shift towards drier conditions in the early/mid-Holocene.…”

Late Quaternary climate variability and terrestrial carbon cycling in tropical South America

“…Relative drought during the LGM at LLG stands in contrast to clear evidence of wet conditions in the Central Andes Fornace et al, 2014) at this time. However, speleothem records from western Amazonia do not show increased SASM intensity during the LGM as would be expected during a period of high austral summer insolation Cheng et al, 2013).…”

“…As discussed extensively in Fornace et al (2014) (Chapter 2 of this thesis), the Titicaca catchment has experienced large changes in precipitation since the last glacial period. Multiple lines of evidence point to wetter conditions on the Altiplano during the last glacial maximum (LGM) and late glacial period Fornace et al, 2014) compared to the Holocene.…”