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Clay mineral isotope paleothermometry is fundamental to understanding Earth’s climate system and landscape evolution. Status quo methods, however, assume constant factors, such as formation temperature and water isotopic compositions, and ignore seasonality, soil water evaporation and depth-dependent temperature changes. We propose first-order modifications to address these factors and test them in a modeling framework using published data from various settings. Our forward model reveals that neglecting evaporation and seasonal soil temperature variability may lead to significant underestimations of clay formation temperatures, especially in Mediterranean settings. Our inverse model indicates that high-latitude Eocene clay formation temperatures were ~8 °C warmer than modern, while Eocene river sediments in the Sierra Nevada show evaporation-influenced trends, suggesting that previous paleoelevation estimates were underestimated. Our framework demonstrates that explicit consideration of soil pore water evaporation and temperature variability is necessary when interpreting clay mineral isotope data in the context of temperature, hydroclimate and elevation reconstructions.

Ice cores and offshore sedimentary records demonstrate enhanced ice loss along Antarctic coastal margins during millennial-scale warm intervals within the last glacial termination. However, the distal location and short temporal coverage of these records leads to uncertainty in both the spatial footprint of ice loss, and whether millennial-scale ice response occurs outside of glacial terminations. Here we present a >100kyr archive of periodic transitions in subglacial precipitate mineralogy that are synchronous with Late Pleistocene millennial-scale climate cycles. Geochemical and geochronologic data provide evidence for opal formation during cold periods via cryoconcentration of subglacial brine, and calcite formation during warm periods through the addition of subglacial meltwater originating from the ice sheet interior. These freeze-flush cycles represent cyclic changes in subglacial hydrologic-connectivity driven by ice sheet velocity fluctuations. Our findings imply that oscillating Southern Ocean temperatures drive a dynamic response in the Antarctic ice sheet on millennial timescales, regardless of the background climate state. Piccione et al find evidence for Antarctic ice sheet instability driven by millennial cycles in Southern Ocean temperature, providing clues for the mechanisms that link climate change and rapid Antarctic ice loss events.

The long-term cooling, decline in the partial pressure of carbon dioxide, and the establishment of permanent polar ice sheets during the Neogene period 1 , 2 have frequently been attributed to increased uplift and erosion of mountains and consequent increases in silicate weathering, which removes atmospheric carbon dioxide 3 , 4 . However, geological records of erosion rates are potentially subject to averaging biases 5 , 6 , and the magnitude of the increase in weathering fluxes—and even its existence—remain debated 7 – 9 . Moreover, an increase in weathering scaled to the proposed erosional increase would have removed nearly all carbon from the atmosphere 10 , which has led to suggestions of compensatory carbon fluxes 11 – 13 in order to preserve mass balance in the carbon cycle. Alternatively, an increase in land surface reactivity—resulting from greater fresh-mineral surface area or an increase in the supply of reactive minerals—rather than an increase in the weathering flux, has been proposed to reconcile these disparate views 8 , 9 . Here we use a parsimonious carbon cycle model that tracks two weathering-sensitive isotopic tracers (stable 7 Li/ 6 Li and cosmogenic 10 Be/ 9 Be) to show that an increase in land surface reactivity is necessary to simultaneously decrease atmospheric carbon dioxide, increase seawater 7 Li/ 6 Li and retain constant seawater 10 Be/ 9 Be over the past 16 million years. We find that the global silicate weathering flux remained constant, even as the global silicate weathering intensity—the fraction of the total denudation flux that is derived from silicate weathering—decreased, sustained by an increase in erosion. Long-term cooling during the Neogene thus reflects a change in the partitioning of denudation into weathering and erosion. Variable partitioning of denudation and consequent changes in silicate weathering intensity reconcile marine isotope and erosion records with the need to maintain mass balance in the carbon cycle and without requiring increases in the silicate weathering flux. A carbon cycle model constrained by weathering-sensitive isotopic tracers reveals that long-term cooling in the Neogene period reflects a change in how surface denudation is partitioned into weathering and erosion.

Rock weathering impacts global nutrient cycles but factoring intrinsic properties of bedrock into weathering models remains a challenge. Here we show that two common tracers of silicate weathering—uranium (U) activity ratios and lithium (Li) isotope ratios of river solutes—inform lithology‐specific modes of landscape denudation. A compilation of paired, published (234U/238U)river and δ7Liriver values demonstrates that watersheds dominated by metamorphic, volcanic, and sedimentary rocks have respectively broader (234U/238U)river ranges but overlapping δ7Liriver values, indicating varying associations of sediment comminution and mineral dissolution with clay formation. Reactive transport models illustrate that intrinsic rock properties like grain size and kinetic rates constants mutually modify (234U/238U)river and δ7Liriver values whereas extrinsic forces like fluid infiltration and rock uplift rates mostly impact δ7Liriver values. These results delineate how given rock types denude and highlight the utility of these proxies in building process‐based models of landscape denudation over the Quaternary Period.

The effect of glacial–interglacial cycles on surface weathering rates has been unclear. A beryllium-based proxy for weathering shows minimal variations in the input of silicate weathering products to the oceans for the past two million years. Throughout the Quaternary period, the Earth’s surface has been subject to large changes in temperature and precipitation associated with fluctuations between glacial and interglacial states that have affected biogeochemical cycling 1 , 2 , 3 , 4 . However, the effect of these climate oscillations on weathering is debated, with climate modelling efforts using empirical relationships between measures of climate and weathering 1 , 5 , 6 suggesting minimal changes in global weathering rates between these two climate states 7 , 8 . The ratio of the cosmogenic isotope 10 Be, which is produced in the atmosphere and deposited to the oceans and the land surface, to 9 Be, which is introduced to the oceans by the riverine silicate weathering flux, can be used to track relative weathering fluxes 9 , 10 . Here we apply this proxy to marine sediment beryllium records 11 , 12 , 13 , 14 , 15 , 16 spanning the past two million years, and find no detectable shifts in inputs from global silicate weathering into the oceans. Using climate model simulations of the Last Glacial Maximum 17 along with a model for silicate weathering 18 , we find that there was large regional variability in runoff between glacial and interglacial periods, but that this regional variability was insufficient to shift global weathering fluxes. We suggest that this stability in weathering explains the observation 19 that the removal of CO 2 from the atmosphere by silicate weathering has been in approximate balance with CO 2 degassing over the past 600,000 years.

The timing and magnitude of the early Cenozoic surface uplift of the Tibetan Plateau is controversial due to a scarcity of unaltered terrestrial sediments required for palaeoaltimetry techniques. Such information is critical, however, for constraining the geodynamic and palaeoclimatic evolution of the Indian and Eurasian continents and for interpreting global climate, biodiversity and biogeochemical cycles since the Cenozoic. We find that substantial uplift occurred by 63 to 61 million years ago, before the collision of the Indian and Eurasian continental plates, based on comparison of triple oxygen isotopes of modern meteoric waters with epithermal Ag–Pb–Zn deposit quartz veins from the Palaeocene Gangdese Arc in southern Lhasa. Low δ18O and δ17O quartz values are consistent with precipitation from meteoric waters influenced by a large degree of topographic rainout. We show that by 63 to 61 Ma, the Gangdese Arc reached an elevation of ~3.5 km, suggesting that the Gangdese Arc achieved >60% of its current elevation before continent–continent collision. This uplift was probably caused by crustal shortening in response to low-angle subduction of Neo-Tethyan oceanic lithosphere. This early high palaeoelevation estimate for the Himalaya–Tibetan system challenges previous assumptions that southern Tibet uplift required continent–continent collision to achieve substantial topography.The triple oxygen isotope composition of quartz veins indicates that the southern Tibetan Plateau was already around 3.5 km high by 60 million years ago, showing that substantial surface uplift started before collision of the Eurasian and Indian plates.

Evolutionary events may impact the geological carbon cycle via transient imbalances in silicate weathering, and such events have been implicated as causes of glaciations, mass extinctions, and oceanic anoxia. However, suggested evolutionary causes often substantially predate the environmental effects to which they are linked—problematic when carbon cycle perturbations must be resolved in less than a million years to maintain Earth's habitability. What is more, the geochemical signatures of such perturbations are recorded as they occur in widely distributed marine sedimentary rocks that have been densely sampled for important intervals in Earth history, whereas the fossil record—particularly on land—is governed by the availability of sedimentary basins that are patchy in both space and time, necessitating lags between the origination of an evolutionary lineage and its earliest occurrence in the fossil record. Here, we present a simple model of the impact of preservational filtering on sampling to show that an evolutionary event that causes an environmental perturbation via weathering imbalance should not appear earlier in the rock record than the perturbation itself and, if anything, should appear later rather than simultaneously. The Devonian Hangenberg glaciation provides an example of how evolutionary events might be more fruitfully considered as potential causes of environmental perturbations. Just as the last samplings of species lost in mass extinction are expected to come before the true environmental event, first appearance should be expected to postdate the geological expression of a lineage's environmental impact with important implications for our reading of Earth history.

Even in relatively wet tropical regions, seasonal fluctuations in the water cycle affect the consistent and reliable supply of water for urban, industrial, and agricultural uses. Historic streamflow monitoring datasets are crucial in assessing our ability to model and subsequently plan for future hydrologic changes. In this technical note, we evaluate a new observation-based global product of monthly runoff (GRUN; Ghiggi et al., 2019) for 55 small tropical catchments in the Philippines with at least 10 years of data, extending back to 1946 in some cases. Since GRUN did not use discharge data from the Philippines to train or calibrate their models, the data presented in this study, 11 915 monthly data points, provide an independent evaluation of this product. We demonstrate across all observations a significant but weak correlation (r2=0.372) between the GRUN-predicted values and observed river discharge, as well as somewhat skillful prediction (volumetric efficiency = 0.363 and log(Nash–Sutcliffe efficiency) = 0.453). GRUN performs best among catchments located in climate types III (no pronounced maximum rainfall with short dry season) and IV (evenly distributed rainfall, no dry season). There was a weak negative correlation between volumetric efficiency and catchment area, and there was a positive correlation between volumetric efficiency and mean observed runoff. Further, analysis for individual rivers demonstrates systematic biases (over- and underestimation) of baseflow during the dry season and underprediction of peak flow during some wet months for most catchments. To correct for underprediction during wet months, we applied a log-transform bias correction which greatly improves the nationwide root mean square error between GRUN and the observations by an order of magnitude (2.648 mm d−1 vs. 0.292 mm d−1). This technical note demonstrates the importance of performing such corrections when determining the proportional contribution of smaller catchments or tropical islands such as the Philippines to global tabulations of discharge. These results also demonstrate the potential use of GRUN and future data products of this nature after consideration and correction of systematic biases to (1) assess trends in regional-scale runoff over the past century, (2) validate hydrologic models for unmonitored catchments in the Philippines, and (3) assess the impact of hydrometeorological phenomena to seasonal water supply in this wet but drought-prone archipelago.