Andean drought and glacial retreat tied to Greenland warming during the last glacial period

The research question focuses on understanding the impact of abrupt warming events in the Arctic, specifically Dansgaard-Oeschger (DO) events, on the hydroclimate of the tropical Andes. These DO events, recorded in Greenland ice cores, are known to be associated with changes in the Atlantic Meridional Overturning Circulation (AMOC), which in turn affects the Intertropical Convergence Zone (ITCZ) and the South American Summer Monsoon (SASM). While changes in SASM strength during DO events have been documented in isotopic records from speleothems, the effects on Andean precipitation and glacier mass balance remain less understood. The study's importance lies in the potential implications for densely populated regions of South America, where future accentuated Arctic warming could lead to significant reductions in water availability and negatively impact water resources. The lack of well-dated, continuous records of hydroclimate in the region necessitates the use of alternative methods to analyze the effects of these events and establish a firmer connection between high-latitude climate variability and the Andes.

Previous research has linked large fluctuations in Andean paleolake levels to Heinrich events and the Younger Dryas, correlating them with Andean glacier advances or stillstands. However, the impacts of shorter DO cycles on precipitation and tropical Andean glacier mass balance are less clear. Existing paleoclimatic evidence, often based on speleothem δ¹⁸O variations, shows a weakened SASM during DO events, but the interpretation of these signals is complicated by the interplay of various factors like upstream rainout, which makes isolating local precipitation variations difficult. The study highlights the need for δ¹⁸O-independent records of hydroclimate to better understand the specific impact of abrupt Arctic warming on water availability and glacial mass balance.

The study uses a sediment core from Lake Junín, a high-elevation lake in the central Peruvian Andes, to reconstruct past lake level fluctuations and paleoglacier mass balance. The core, spanning the last ~50 ka, was dated using 79 radiocarbon measurements from terrestrial macrofossils and charcoal. Multiple proxies were analyzed, including: Ti and Si concentrations (XRF) to indicate glacigenic sediment input, total organic carbon (TOC) to reflect changes in organic matter accumulation, and dry bulk density to reflect sediment compaction. Peat layers in the core, representing lower lake stands, were used to infer lake level changes. These proxies were interpreted in relation to the timing of DO events and existing speleothem δ¹⁸O records from nearby locations (Pacupahuain and El Condor caves). The researchers carefully considered the sedimentary context, including the lake setting, the relationship between the lake and adjacent glaciers, and the various processes that contribute to the sediment record. Statistical analyses, including age-depth modeling, were used to integrate and interpret the data.

The Lake Junín sediment record shows a strong correlation between DO events and reduced glacigenic sediment input, reflecting glacial retreat. All but two DO interstadials (4-13) were associated with increased peat accumulation and lower bulk density, indicating reduced lake levels. These findings strongly suggest decreased precipitation during DO events, leading to the near-complete disappearance of glaciers below 4700 m and significant reductions in Lake Junín's level (up to 8 m). The study reveals a strong, albeit not perfectly proportional, correspondence between the Lake Junín record and nearby speleothem δ¹⁸O records, suggesting that regional monsoon strength is a primary control on hydroclimate. However, the magnitude and duration of Lake Junín's response to individual DO events sometimes differ from those observed in the speleothem records, highlighting the influence of additional local factors besides SASM intensity on the δ¹⁸O signal. The early deglaciation in the central Peruvian Andes (~22.5 ka) is linked to two prolonged droughts preceding the onset of high-latitude warming, suggesting that precipitation changes, not just temperature, drove this early retreat. The study indicates that the Junín region is sensitive to precipitation fluctuations, making it more responsive to dry (DO) events compared to wetter (Heinrich) events recorded in Altiplano lake records. The documented hydroclimatic changes in the Junín region might have affected a broad area of the western Amazon Basin, supported by Amazon River discharge records.

The findings demonstrate a clear link between high-latitude warming events (DO events) and significant hydroclimatic changes in the tropical Andes. The strong correlation between reduced glacial sediment flux and lower lake levels during DO events strongly supports the hypothesis that decreased precipitation, driven by a weakened SASM, was the primary factor causing glacial retreat and lake level decline. The comparison with speleothem δ¹⁸O records confirms the regional importance of SASM variations but also highlights the complex interactions between regional and local factors influencing the isotopic signal. The early onset of deglaciation, linked to prolonged droughts before high-latitude warming, challenges previous interpretations and emphasizes the importance of considering precipitation variability in understanding glacial dynamics. The study’s results have significant implications for understanding the climate teleconnections between high and low latitudes and for predicting the impacts of future Arctic warming on water resources in the Andes.

This study provides compelling evidence for the significant impact of Dansgaard-Oeschger events on Andean glacier mass balance and hydroclimate, highlighting the teleconnection between high-latitude warming and tropical South American precipitation. The findings underscore the sensitivity of the Andean region to changes in the South American Summer Monsoon strength and the need to consider both temperature and precipitation changes in predicting future impacts of climate change. Further research should focus on refining the understanding of local versus regional factors controlling isotopic signatures and expanding the investigation to other regions of the Andes to enhance the regional representativeness of the findings.

The study primarily focuses on the Lake Junín region, limiting the generalizability of the findings to other parts of the Andes. The age model relies on radiocarbon dating of terrestrial macrofossils, which might have inherent uncertainties. While the authors acknowledge potential complexities in interpreting the δ¹⁸O signal from speleothems, a more detailed investigation of these complexities could strengthen the conclusions. Finally, future studies could benefit from incorporating additional proxy data to further validate the findings and improve understanding of the mechanisms driving the observed hydroclimatic changes.