ABSTRACT

This grant supports research generating continuous, centennial to millennial-scale records of mountain glaciation in Peru spanning the Holocene (~12 ka to present) that tests hypotheses concerning the causes of abrupt climate change in the tropics. Radiocarbon and 210Pb dating of glacial flour flux provides precise ages of Holocene ice advances/retreats and records of abrupt climatic transitions, using proglacial lake sediment cores from multiple lakes along the steep East-West moisture gradient across the central Peruvian Andes. The flux of glacial flour is determined based on multiple proxies at a resolution sufficient to enable comparison with existing stable isotope records of paleoclimate variability from the region. Previous work in the tropical Andes demonstrates that the glacial-flour approach can provide a record of glaciation that is both consistent with and far more continuous than radiometrically-dated moraine records. This approach has the potential to resolve several glacial geologic uncertainties, such as the timing of early Holocene glacial advances, and the possible time-transgressive nature of ice margin fluctuations during the neoglacial. The glacial-lacustrine approach is coupled with detailed moraine mapping and the targeted application of cosmogenic radionuclide dating to select Holocene moraines located up-valley from coring localities. The strategic pairing of glacial flour records with dated moraines provides both the timing and magnitude of ice margin changes. Inverse glacier mass balance-ice flow simulations from multiple watersheds in different precipitation regimes provide validation for the dynamical down-scaling of global-scale circulation and paleoclimate models.
Intellectual Merits and Broader Impacts: Relating the changes in tropical glacier mass to climate dynamics is a priority for global climate modeling efforts to predict future changes based on accurately simulating past changes under different greenhouse scenarios. The long-term perspective of temperature and precipitation changes on tropical glacier mass and energy balance is still poorly understood, primarily because of a lack of detailed and continuous glacial records from both the humid and more arid parts of the tropical Andes. This work substantially improves our understanding of the link between alpine glacial variability, water resources and mass and energy fluxes in the tropical "heat engine" of the planet.
These records are needed to better understand the timing, magnitude, and spatial extent of high elevation (5000 - 6000 masl) tropical atmospheric change during the Holocene to evaluate the role of the low latitude hydrologic cycle in abrupt global climatic shifts. This, in turn, will enable testing of the following hypotheses:
(1) Glacier margin fluctuations in the tropical Andes during the Holocene were driven by changes in the strength of the South American Summer Monsoon
(2) A broad regional pattern of Holocene glacial variability was punctuated by periods of rapid ice advances every ~1000 to 1500 years
(3) Abrupt (centennial to millennial-scale) Holocene glacier variations in the southern tropics were nearly synchronous with those in the Northern Hemisphere (i.e. The Little Ice Age)

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