Extra-tropical Influence on Hydrologic Balance in the High Elevation Andes: Physical Sedimentology Evidence from Lake Junín, Peru during the Last Glacial Period
Abstract
Modeling and proxy studies have established that the primary climatic control on the oxygen isotope values of rainfall for tropical South America is the amount of precipitation associated with the South American Summer Monsoon. There is less agreement over the extent to which isotopic changes recorded in high elevation Andean paleoclimate records are signals inherited from rainfall amount upstream in the Amazon Basin, or if they reflect local hydrologic conditions at the study site. Here we document changes in glacigenic sediment supply over the past 50 ka to Lake Junín, a large (300 km2) lake in the central Peruvian Andes that is currently a seasonally closed basin, to constrain hydrologic behavior during the radiocarbon-dated portion of a longer sedimentary record that spans 700 ka. Monsoon strength in the Junín region drives both glacier mass balance changes, as recorded in glacial flour flux, and also affects the oxygen isotope values of local speleothems. Measurements of clastic flux and elemental ratios (Ti/Al, Ti+K+Si/Al) show millennial-scale variability in glacially-generated detrital input to Lake Junín, which is further supported by variations in bulk density, magnetic susceptibility, gamma density, and elemental abundances (Ti, Si, Al, Ca, etc.). A series of age models were generated for Lake Junín using two Bayesian age-depth modeling packages, Bacon and Bchron, to compare their effects on the timing and uncertainty of the radiocarbon chronology and resultant flux calculations. Comparison of our record to published isotope fluctuations in Greenland ice and in a speleothem from nearby Pacupahuain Cave demonstrate the presence of Dansgaard/Oeschger (D/O) events in the record of clastic sediment input to Lake Junín throughout the past 50 ka. Despite notable differences among age model tests, the most realistic age models confirm a tight matching in the timing and structure of D/O events between North Atlantic isotope records and the tropical Andes. This climate connection, now grounded by physical sedimentology data from Lake Junín, is then confirmed to be an indicator of local hydrologic conditions and not simply an isotopic signal inherited from the Amazon basin.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP21B..08W
- Keywords:
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- 3335 North American Monsoon;
- ATMOSPHERIC PROCESSESDE: 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4938 Interhemispheric phasing;
- PALEOCEANOGRAPHY