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Abstract Model‐based projections of hydroclimate in western North America (wNA) remain uncertain and depend on how Pacific sea surface temperature (SST) will evolve in the future. However, whether climate models can accurately capture Pacific SST changes and its relationship with wNA hydroclimate in the future remains elusive. Here, we use a synthesis of proxy records and idealized model simulations to elucidate the spatiotemporal evolution and the forcings that drive wNA hydroclimate and Pacific SST during the Holocene (past ∼11,000 years), when the boundary conditions are different from the present. We find that wNA hydroclimate and Pacific SST co‐evolved during the Holocene, where wNA became wetter while the eastern equatorial Pacific and the north Pacific became warmer toward the present. We attribute changes in wNA hydroclimate to precession and carbon dioxide changes, but we are unable to attribute Pacific SST changes unambiguously to any forcing. Our analysis offers a framework to understand the relationship between wNA hydroclimate and Pacific SST and provides an empirical assessment of how these two regions are related over time. 

The stable isotopic composition of soil-formed carbonate, and bulk geochemistry of preserved soil matrix, can provide regionally constrained records of hydroclimatic change throughout deep-time. The SK cores, spanning over 10 km of sediment drilled from the Songliao Basin in Northeast China, represent near continuous terrestrial deposition across the late Jurassic to early Paleogene. In this study we analyze SK-1n paleosol core samples spanning late Maastrichtian to early Danian to interpret the regional hydroclimate response to global climate change, concurrent with Deccan Traps volcanism and the Chicxulub impact. Building on numerous paleosol carbonate datasets from the Sifangtai and Mingshui formations, we present ~40 new carbonate clumped isotope measurements at ca. 10 – 20 kyr resolution between 66.3 to 65.5 Ma. We produce a new kernel-smoothed temperature record and estimate the δ18O of soil porewater (δ18Opw), and δ13C of soil CO2 (δ13Cs) from new and previously published datasets. Molecular weathering ratios, derived from bulk geochemistry, are used to reconstruct weathering (CIA-K), clay formation (Al/Si), soil drainage (Ba/Sr), and calculate mean annual precipitation (MAP) via established transfer functions. Preliminary results suggest elevated K-Pg boundary temperatures, averaging ~30 °C, that decline by ~10 °C over the following 500 kyr. Post-impact cooling may contribute to a negative δ18Ocarb excursion (-2.5‰) at ~65.8 Ma. Further, stable subhumid MAP (~1100 mm/yr) across the dataset suggests negligible amount effect influence. Mean δ18Opw (-6.9‰) is largely stable, and does not reflect regional monsoon seasonality. Instead, stable δ18Opw indicates a consistent moisture source, a potential persistent seasonal bias in carbonate formation. Binning all compiled δ18Opw by soil profile depth reveals statistically significant enrichment in the upper 60 cm of soil profiles, and accounts for variability in the δ18Opw (σ = 1.16‰). Soil respiration, modeled from δ13Cs, increases from ca. 700 to 2000 gC/m2/year across the K-Pg boundary, indicating increased productivity despite declining pCO2 and available phosphorus. Future work will expand the temporal range of isotopic measurements (~72 to 65 Ma) and contextualize our latest Cretaceous results within a spatial framework across Asia. 

Abstract The Asian summer monsoon (ASM) is teleconnected to the El Niño Southern Oscillation (ENSO), but this relationship is nonstationary and has shifted significantly in recent decades. Characterizing the drivers of such shifts is crucial for improving ASM prediction and extreme event preparedness. Paleoclimate records indicate a link between ASM strength and solar activity on multidecadal‐to‐centennial timescales, but 20th‐century data are too short to test mechanisms. Here we evaluate how solar irradiance influences the ASM‐ENSO relationship using last‐millennium paleoclimate data assimilation reconstructions and model simulations. We find that high solar irradiance weakens the ENSO‐East Asian summer monsoon (EASM) correlation, but strengthens the ENSO‐South Asian summer monsoon (SASM) correlation. Solar irradiance likely influences the strength of the ENSO‐EASM and ENSO‐SASM teleconnections via changes in the Western Pacific Subtropical High and the amplitude of ENSO events, respectively. We suggest a need for considering solar activity in decadal ASM rainfall predictions under global warming scenarios. 

Most paleoclimate studies of Mainland Southeast Asia hydroclimate focus on the summer monsoon, with few studies investigating rainfall in other seasons. Here, we present a multiproxy stalagmite record (45,000 to 4,000 years) from central Vietnam, a region that receives most of its annual rainfall in autumn (September-November). We find evidence of a prolonged dry period spanning the last glacial maximum that is punctuated by an abrupt shift to wetter conditions during the deglaciation at ~14 ka. Paired with climate model simulations, we show that sea-level change drives autumn monsoon rainfall variability on glacial-orbital timescales. Consistent with the dry signal in the stalagmite record, climate model simulations reveal that lower glacial sea level exposes land in the Gulf of Tonkin and along the South China Shelf, reducing convection and moisture delivery to central Vietnam. When sea level rises and these landmasses flood at ~14 ka, moisture delivery to central Vietnam increases, causing an abrupt shift from dry to wet conditions. On millennial timescales, we find signatures of well-known Heinrich Stadials (HS) (dry conditions) and Dansgaard–Oeschger Events (wet conditions). Model simulations show that during the dry HS, changes in sea surface temperature related to meltwater forcing cause the formation of an anomalous anticyclone in the Western Pacific, which advects dry air across central Vietnam, decreasing autumn rainfall. Notably, sea level modulates the magnitude of millennial-scale dry and wet phases by muting dry events and enhancing wet events during periods of low sea level, highlighting the importance of this mechanism to autumn monsoon variability. 

North Atlantic cooling during Heinrich Stadial 1 triggered an east-west precipitation dipole over the tropical Indian Ocean. 

Abstract Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V JOIDES Resolution Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.