A major advance of tropical Andean glaciers during the Antarctic cold reversal

Abstract

The Younger Dryas stadial, a cold event spanning 12,800 to 11,500 years ago, during the last deglaciation, is thought to coincide with the last major glacial re-advance in the tropical Andes. This interpretation relies mainly on cosmic-ray exposure dating of glacial deposits. Recent studies, however, have established new production rates for cosmogenic (10)Be and (3)He, which make it necessary to update all chronologies in this region and revise our understanding of cryospheric responses to climate variability. Here we present a new (10)Be moraine chronology in Colombia showing that glaciers in the northern tropical Andes expanded to a larger extent during the Antarctic cold reversal (14,500 to 12,900 years ago) than during the Younger Dryas. On the basis of a homogenized chronology of all (10)Be and (3)He moraine ages across the tropical Andes, we show that this behaviour was common to the northern and southern tropical Andes. Transient simulations with a coupled global climate model suggest that the common glacier behaviour was the result of Atlantic meridional overturning circulation variability superimposed on a deglacial increase in the atmospheric carbon dioxide concentration. During the Antarctic cold reversal, glaciers advanced primarily in response to cold sea surface temperatures over much of the Southern Hemisphere. During the Younger Dryas, however, northern tropical Andes glaciers retreated owing to abrupt regional warming in response to reduced precipitation and land-surface feedbacks triggered by a weakened Atlantic meridional overturning circulation. Conversely, glacier retreat during the Younger Dryas in the southern tropical Andes occurred as a result of progressive warming, probably influenced by an increase in atmospheric carbon dioxide. Considered with evidence from mid-latitude Andean glaciers, our results argue for a common glacier response to cold conditions in the Antarctic cold reversal exceeding that of the Younger Dryas.

Across the Arid Diagonal: deglaciation of the western Andean Cordillera in southwest Bolivia and northern Chile

“…A reasonable hypothesis would be that the Arid Diagonal would demarcate the boundary of influence between these hemispheric effects, but reviews of glacial chronologies have remained inconclusive on this matter (Ward et al, 2015), with some workers (e.g., Jomelli et al, 2014) suggesting that the timing of glacial advances in tropical South America indicates an influence of the ACR there. Among the sites considered here, only the two northernmost appear to have late glacial positions that could correspond to either the YD or the ACR.…”

Revisiting the andean tropical glacier behavior during the Antarctic cold reversal

“…In 2014 a paper suggested that tropical glaciers responded very sensitively to the changing climate during the ACR (Jomelli et al, 2014). In this study, we reexamine the conclusions from this study by recalculating previous chronologies based on 226 10 Be and 14 3 He ages respectively, and using the most up-to date production rates for these cosmogenic nuclides in the Tropical Andes.…”

“…In this study, we reexamine the conclusions from this study by recalculating previous chronologies based on 226 10 Be and 14 3 He ages respectively, and using the most up-to date production rates for these cosmogenic nuclides in the Tropical Andes. 53 moraines from 25 glaciers were selected from the previous analysis provided by Jomelli et al (2014) …”

“…However the impacts of the ACR cooling event on glaciers located at lower latitudes of the southern hemisphere remained unclear in particular in the tropics. Recently Jomelli et al (2014) established the chronology of Ritacuba Negro glacier located in the northern tropics of Colombia. The data revealed that the ACR extent of the glacier was larger than during the YD.…”

The deglaciation of the mountains of Mexico and Central America

“…The timing of the post-LLGM minor advances is not known. However, it must be noted that in the Sierra Nevada del Cocuy, Colombia (6.5°N), there is evidence of a glacial advance within the Antarctic Cold Reversal (14.5-12.9 ka), followed by a minor advance or stillstand during the late Younger Dryas, the latter in connection with abrupt regional warming (Jomelli et al, 2014).…”