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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. 

Abstract An expanded sedimentary section provides an opportunity to elucidate conditions in the nascent Chicxulub crater during the hours to millennia after the Cretaceous‐Paleogene (K‐Pg) boundary impact. The sediments were deposited by tsunami followed by seiche waves as energy in the crater declined, culminating in a thin hemipelagic marlstone unit that contains atmospheric fallout. Seiche deposits are predominantly composed of calcite formed by decarbonation of the target limestone during impact followed by carbonation in the water column. Temperatures recorded by clumped isotopes of these carbonates are in excess of 70°C, with heat likely derived from the central impact melt pool. Yet, despite the turbidity and heat, waters within the nascent crater basin soon became a viable habitat for a remarkably diverse cross section of the food chain. The earliest seiche layers deposited with days or weeks of the impact contain earliest Danian nannoplankton and dinocyst survivors. The hemipelagic marlstone representing the subsequent years to a few millennia contains a nearly monogeneric calcareous dinoflagellate resting cyst assemblage suggesting deteriorating environmental conditions, with one interpretation involving low light levels in the impact aftermath. At the same horizon, microbial fossils indicate a thriving bacterial community and unique phosphatic fossils including appendages of pelagic crustaceans, coprolites and bacteria‐tunneled fish bone, suggesting that this rapid recovery of the base of the food chain may have supported the survival of larger, higher trophic‐level organisms. The extraordinarily diverse fossil assemblage indicates that the crater was a unique habitat in the immediate impact aftermath, possibly as a result of heat and nutrients supplied by hydrothermal activity. 

Abstract Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth‐system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ₄₇) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ⁴⁷and Δ₄₇values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ₄₇(I‐CDES) values for Intercarb‐Carbon Dioxide Equilibrium Scale.