Glacial chronologies and past climate change in the tropical-subtropical Central Andes during the last glacial and deglacial periods
Abstract
Because glaciers advance or retreat in response to changes in temperature and precipitation, glacial chronologies derived from well-dated sequences of inset moraines provide insight into the timing and magnitude of past climate change within the terrestrial realm. During the last glacial and deglacial periods, glaciers at high northern latitudes waxed and waned in phase with orbital- and millennial-scale temperature oscillations. Although paleoclimate records suggest strong correlations between high-latitude temperature variability and low-latitude climate change, the timing and cause of glacial fluctuations at low, southern-latitudes remains unclear - limiting our understanding about the global synchronicity of past glaciations, the causes of abrupt climate change, and the relative importance of high- versus low-latitude forcing for developing and transmitting climate signals around the globe.. Here we present a compilation of cosmogenically dated glacial chronologies from the tropical-subtropical Central Andes (~9-24 °S). We demonstrate that episodes of glacial advance in the Central Andes coincide with Northern Hemisphere cold events, increased pole-to-equator sea-surface temperature gradients, and southward displacements of the Intertropical Convergence Zone. Although glacial fluctuations in the Central Andes were synchronous with Northern Hemisphere records, our data suggest strong contrasts in the cause of ice advance between the last glacial and deglacial periods. During the last glacial period, glaciers were at their greatest extent in the humid Northern Central Andes from ~35-19 ka, coeval with insolation-driven reductions in global temperatures and moderately increased southern summer monsoon intensity. Conversely, in the arid Southern Central Andes, there is no record of moraines deposited during the last glacial period, suggesting that, despite the cold temperatures, limited moisture availability in this region inhibited the growth of glaciers, such that the last glacial moraines were subsequently overridden by more extensive stages of deglacial advance. During deglaciation, all records from the Central Andes reveal that ice advance (or re-advance) was coincident with pronounced increases in precipitation and low-latitude warming during Heinrich Stadial 1 (~15-17 ka) and the Younger Drays (~11-14 ka). However, in the Northern Central Andes these deglacial episodes constitute only minor re-advances or standstills, whereas in the Southern Central Andes they represent the most extensive stages of glacial advance. The apparent contrast in the magnitude of ice advance in the Central Andes during the last glacial and deglacial periods supports the contention that glaciers in the humid Northern Central Andes predominantly respond to changes in temperature, whereas in the arid Southern Central Andes glaciers are most sensitive to changes in precipitation. Overall, the data suggest a distinct transition between temperature-driven ice advance during the last glacial period due to orbital-scale forcing, which favors extensive advance in the humid Northern Central Andes, and precipitation-driven stages of re-advance during deglaciation in response to large millennial-scale shifts in the Intertropical Convergence Zone, which favor more pronounced advances within the arid Southern Central Andes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMPP51B2130C
- Keywords:
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- 0720 CRYOSPHERE / Glaciers;
- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change;
- 4926 PALEOCEANOGRAPHY / Glacial;
- 4938 PALEOCEANOGRAPHY / Interhemispheric phasing