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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. 

We present oxygen isotope and charcoal accumulation records from two lakes in eastern Washington that have sufficient temporal resolution to quantitatively compare with tree‐ring records and meteorological data. Hydroclimate reconstructions from tree‐rings and lake sediments show close correspondence after accounting for seasonal‐ to centennial‐ scale temporal sensitivities. Carbonate δ¹⁸O measurements from Castor and Round lakes reveal that the Medieval Climate Anomaly (MCA) experienced wetter November‐March conditions than the Little Ice Age (LIA). Charcoal records from Castor, Round, and nearby lakes show elevated fire activity during the LIA compared to the MCA. Increased multidecadal hydroclimate variability after 1250 CE is evident in proxy records throughout western North America. In the Upper Columbia River Basin, multidecadal wet periods during the LIA may have enhanced fuel loads that burned in subsequent dry periods. A notable decline in biomass burning occurred with Euro‐American settlement in the late nineteenth century.