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Abstract The South American monsoon is central to the continent’s water and energy cycles, however, the relationships between the monsoon, regional water balance, and global climate change is poorly understood. Sediment records at Lake Junín (11°S, 76°W) provide an opportunity to explore these connections over the last 650 ka. Here, we focus on two interglacials, the Holocene (11.7–0 ka) and MIS 15 (621–563 ka), when sediment proxies suggest rapid regional hydroclimate fluctuations occurred. Clumped isotope distributions of lake carbonates reveal that interglacial water temperatures were similar to present, though analytical limitations preclude detecting the small temperature differences expected in the tropics (<2 °C). Combining the reconstructed water temperatures with carbonate oxygen (δ18O) and triple oxygen (Δ′17O) isotope values, we reconstruct precipitation δ18O values and lake water Δ′17O values. Precipitation δ18O values, a proxy of monsoon strength, range from -18.6 to -12.3 ‰ with lower values reflecting a stronger monsoon. Lake water Δ′17O values are -14 to 43 per meg and indicate the extent of lake water evaporation; lower values reflect a higher proportion of evaporation to inputs (i.e., more negative P-E). The precipitation δ18O and lake water Δ′17O values from both interglacials vary with the pacing of local summertime insolation, which follows an orbital pacing. These data document the close connection between Andean water balance, the South American monsoon, and global climate. Further, we analyze the relationship between precipitation δ18O and insolation, and we find that the relationship is consistent among interglacials, suggesting a similar response of the monsoon to orbital forcings over time. In contrast, while lake water Δ′17O and insolation are also correlated during both interglacials, water balance was overall more positive during MIS 15 than the Holocene. This suggests that either other global forcings or local basin dynamics can also contribute to water balance at Lake Junín. Together, these data provide new evidence of the connections between global climate, monsoon strength, and regional water balance. 

Continuous archives of the El Niño Southern Oscillation (ENSO) spanning multiple millennia are rare, as few geologic records faithfully preserve evidence of sub-decadal climate variability over long timescales. Different proxy archive types –such as lake sediments, foraminifera, tree-rings, and corals—have their own unique sensitivities to the climate system and can thus be difficult to intercompare. The sedimentary sequence from Laguna Pallcacocha, Ecuador, represents one of the most widely cited Holocene-scale ENSO reconstructions. Hundreds of mineral-rich flood laminae result from eastern Pacific El Niño events, when convective rainstorms drive erosion and terrigenous sediment transport in the Laguna Pallcacocha watershed. This reconstruction, however, is tangibly different from other ENSO proxy records as well as flood stratigraphies from proximal lakes. The watersheds of these nearby lakes have markedly different landscape characteristics, suggesting that the intensity of storms which generate flood deposits differ between each watershed. Thus, an integrated analysis of these three separate records helps constrain the frequency of paleo-ENSO events of different magnitudes. While moderate El Niño events may have been most frequent approximately 1000 years BP, particularly intense El Niño’s occur more frequently during the subsequent Little Ice Age (1450-1850 CE), consistent with tree-ring based reconstructions of ENSO amplitude and foraminiferal records of high-intensity eastern Pacific warming. A widely reported minima in El Niño frequency between approximately 7-4 kyr BP is a prominent feature in Laguna Pallcacocha record. This minima is not present, however, in the high-intensity flood stratigraphies from the other two lakes, which align more closely with ENSO amplitude records derived from speleothems and corals. These findings highlight the value of integrating evidence from multiple paleoclimate archives in ENSO reconstructions.