Abstract The ocean nitrogen cycle is influenced by climatic conditions, which regulate atmospheric greenhouse gases and generate feedback effects. These feedbacks occur through the release of nitrous oxide and alterations in the fixed‐nitrogen inventory, which in turn regulates carbon sequestration. The Arabian Sea hosts an intense oxygen minimum zone, making it a critical region for understanding marine biogeochemical cycling. Understanding past variability in nitrogen cycling offers crucial insights into the relationship between ocean circulation and productivity, which is essential for predicting future biogeochemical changes. Here, we present reconstructions of spatiotemporal variation in water column denitrification and fixation, the influence of oceanic ventilation, and the role of monsoonal variability on nitrogen cycling in the Arabian Sea. Based on our sedimentary nitrogen isotope ( 15 N) records, we found N 2 fixation and denitrification to be concomitantly high during the Last Glacial Maximum (LGM; ∼23–19 ka) in the northern and southeastern Arabian Sea. In contrast, both processes weakened during the deglaciation. The dominance of denitrification, with the decrease in dissolved oxygen as a result of the reduced influx of Antarctic Intermediate Water, appears to have begun in the early Holocene. On millennial timescales, denitrification intensity is mainly controlled by subsurface ventilation by water masses from the Southern Ocean. Despite temporal variations, both processes remained more intense in the northern Arabian Sea. Our findings underscore the sensitivity of the nitrogen cycle in the Arabian Sea to climate change, with continued warming causing denitrification to intensify, providing positive feedback to the climate.
Abstract The giant diatom Ethmodiscus rex exhibited widespread and episodic blooms in tropical and subtropical oceans during the late Quaternary, yet the mechanisms underlying their formation remain uncertain. A previous hypothesis emphasized the role of atmospheric dust input from inland Asia in triggering diatom blooms in the western Pacific. However, this interpretation has largely overlooked the physiological capacities of E. rex , including vertical migration and intracellular nutrient storage. Here, we use geochemical and isotopic analyses of sediment cores from the western North Pacific Gyre to constrain the timing and nitrogen availability of bloom events. Radiocarbon dating reveals that E. rex blooms occurred from the Last Glacial Maximum through the early Holocene, extending the temporal range proposed by earlier studies. Elevated Si/Ti and Ba/Ti ratios, increased biogenic opal concentrations, and higher bulk organic carbon δ 13 C values indicate enhanced primary productivity and rapid consumption of dissolved inorganic carbon during bloom periods. However, limited organic‐matter preservation suggests extensive remineralization during sedimentation. Most notably, a mean depletion of ∼2.4‰ in organic matter δ 15 N relative to background values points to the utilization of isotopically light subsurface nitrate. We infer that upper ocean dynamics such as Rossby waves and internal oscillations intermittently uplifted the deeper nutricline, bringing nitrate‐rich subsurface waters into an effective depth window for E. rex without penetrating the surface mixed layer. Within this window, nutrients could be effectively utilized, facilitating rapid proliferation under oligotrophic surface conditions. This mechanism remains hypothetical and requires further testing through proxy and modeling studies.
Abstract Oxygen (O 2 ) is essential for almost all life on Earth, but O 2 concentrations are rapidly declining in the oceans under global warming, stressing marine ecosystems and biogeochemical cycles. Numerical model simulations suggest greatly expanded North Atlantic Oxygen Minimum Zones (OMZs) under warm Pliocene conditions, but sparse data limit validation and evaluation of mechanistic drivers. Here we use fossil tests of Globorotaloides hexagonus , a rare species of planktonic foraminifera associated with OMZs today, to reconstruct past variability in oxygenation in the Eastern Tropical North Atlantic Ocean (ETNA). Our astronomically resolved records from ODP Site 659 cover the warm Pliocene through intensification of North Hemisphere Glaciation (3.45–2.33 Ma) and the last glacial cycle (150–0 ka). We document deoxygenation of the ETNA during both the warm Late Pliocene and marine isotope stage (MIS) 5, followed by re‐oxygenation upon the introduction of colder conditions associated with intensified Northern Hemisphere Glaciation (∼3 Ma) and MIS4 (∼70 ka) respectively. Under deoxygenated conditions, OMZ‐strength fluctuated, paced by precession. We rule out “top‐down” control on deoxygenation by changes in ETNA sea surface temperature, upper ocean stratification, upwelling strength or ocean productivity. Instead, we infer “bottom up” control by changes in the ventilation of intermediate waters supplied to the ETNA. Mechanistic clues emerge from the sign of the relationship that we document: deoxygenation peaks occur during insolation maxima, when tropical rainbelt expansion freshened the Mediterranean Sea and altered its outflow properties to the Atlantic Ocean. We propose that Mediterranean Outflow variability modulated OMZ strength in the ETNA.
Abstract The South Asian summer monsoon is a major component of the global climate system, yet its response to varying boundary conditions remains debated. We present pollen data from IODP Site U1446 (Bay of Bengal), recording vegetation changes in India's Core Monsoon Zone (CMZ) between 260 and 190 ka, spanning Marine Isotopic Stage (MIS) 7. This interglacial complex is marked by exceptionally large changes in obliquity and precession resulting in two glacial terminations (TIII and TIIIa) and two interglacials (MIS 7e and 7c). Pollen data reveal alternations between semi‐arid/open savanna (MIS 8, 7d, 7b) and tropical forest (MIS 7e, 7c, 7a), reflecting orbital‐scale monsoon intensity fluctuations. As observed for other interglacials periods, monsoon rainfall intensifies during MIS 7e and 7a as precession‐driven northern hemisphere summer insolation increases. However, during MIS 7c, the intense humidity peak coincides with maximum obliquity, rather than precession minimum. We propose that under warmer conditions, both precession and high obliquity forcing enhance summer moisture transport in the CMZ. Conversely, reduced precipitation corresponds to periods of higher ice volume and lower CO 2 levels, likely restricting the northward ITCZ migration and atmospheric moisture, although peak aridity coincides with minima in boreal summer insolation. Our results challenge studies attributing monsoon variability solely to precession or ice volume/CO 2 , emphasizing instead the variable interactions of external and internal forcings under differing boundary conditions. Millennial‐scale variability also influenced vegetation and monsoon dynamics during TIII and TIIIa, modulating the monsoon response in South Asia to the forcings acting at the orbital‐scale.
Abstract The early‐middle Miocene was a critical period of climate transition, marked by significant carbon cycle perturbations and dynamic changes in the Antarctic Ice Sheet (AIS). However, relatively quantitative understandings of how pelagic sedimentary systems responded to and participated in these changes remain limited. To address this gap, mass accumulation rates (MARs) for a low‐latitude pelagic sequence recovered at International Ocean Discovery Program Site U1502 were calculated to evaluate sediment erosion, transport, and deposition. Enabled by a robust, high‐resolution age model established here, we quantified interactions between pelagic MARs and sea level through cross‐recurrence analyses. Integrating additional climate proxies such as atmospheric CO 2 and illite crystallinity, our results demonstrate that cryospheric evolution acted as a critical boundary condition in modulating the long‐term climatic response mode of low‐latitude pelagic sedimentation. During the Miocene Climatic Optimum (MCO) and Middle Miocene Climate Transition (MMCT), when the AIS underwent landward retreat, pelagic MARs responded positively to global changes. This means that higher pelagic MARs occurred during warmer and wetter periods, and vice versa. In contrast, during periods of significant AIS expansion before the MCO and after the MMCT, sea‐level fluctuations strongly modulated shelf accommodation, thereby buffering terrigenous inputs and leading to lower pelagic MARs despite warmer, wetter climate conditions. Furthermore, we found that pelagic sedimentation may mitigate positive benthic δ 13 C excursions in the middle Miocene, motivating future broader perspectives on this relationship.
Abstract Great Salt Lake (GSL), Utah, USA, is a large hypersaline lake, but during short‐lived (∼10–20 kyr) pluvials, it was an expansive freshwater lake. We update the age model of GLAD1‐GSL00‐4, a 120‐m sediment core recovered by the Global Lakes Drilling (GLAD) project, with new U‐series measurements dating evaporites representing the driest times in lake history and providing a new basal age of 236.3 ka (2 σ uncertainty = 6.7 kyr) during the penultimate interglacial. We measure microbial membrane lipid abundances, dialkyl glycerol diethers and glycerol dialkyl glycerol tetraethers (GDGT), to reconstruct salinity over the last two glacial cycles. High and variable salinity precludes use of GDGTs as a proxy for temperature. The freshwater, deep, expanded lake phases “Bonneville” and “Little Valley,” here dated to 30.3–16.1 ka (2 σ = 1.0–1.4 kyr) and 140.4–134.6 ka (2 σ = 5.5–5.7 kyr) respectively, occur during deglacial pluvials and briefly interrupt the hypersaline conditions which dominate the record. The salinity rise following the last pluvial agrees with water balance reconstructions from well‐dated lacustrine carbonates. However, evaporite (thenardite) deposition dated to 16.1–12.2 ka (2 σ = 0.8–1.0 kyr) contrasts with Holocene timing elsewhere in the basin. After the Little Valley highstand, a salinity increase culminates in halite precipitation. Despite four disparate halite dates spanning 90–160 ka, age model assignment agrees with U‐series dating of Little Valley shoreline tufa. This continuous salinity record provides context for lake expansion/contraction followed by evaporite deposition across two glacial terminations, consistent with regional pluvials.
Abstract The Rio Grande Rise (RGR) is a major submarine feature in the South Atlantic that plays an important role in regional oceanographic dynamics. This study presents new U‐Pb geochronology of sedimentary rocks from the RGR, offering direct age constraints on carbonate and apatite embedded within Fe‐Mn crusts and associated foraminifera fossils. Samples were analyzed using high‐patial resolution geochronological techniques to establish a comprehensive temporal framework from the Eocene to the Miocene. Our results reveal distinct stages of geological evolution of the RGR. In the Eocene (48.1 ± 0.8/1.4 Ma; 2s), the RGR was marked by a shallow carbonate platform with local areas submitted to subaerial exposure and the presence of Larger Benthic Foraminifera (LBF). In the Oligocene (31.5 ± 0.9/1.9 Ma; 2s), carbonate precipitates infilled pores of previously formed Fe‐Mn crusts, possibly during a period of tectonic subsidence. In the late Oligocene‐early Miocene (21.0 ± 2.0/2.0 Ma; 2s), we identified an episode of phosphatization associated with global changes in marine circulation. Finally, in the Miocene (15.6 ± 1.6/3.0 Ma; 2s), the presence of planktic foraminifera indicates pelagic, open‐marine depositional conditions over the RGR, consistent with its regional subsidence history. These findings enhance the understanding of the geological history of the RGR, its role in shaping South Atlantic oceanic circulation, and provide new insights on Fe‐Mn crust formation and phosphatization events in the region.
Abstract This special collection celebrates the 40th anniversary of Paleoceanography and Paleoclimatology and highlights the breadth, impact, and frontiers in paleoenvironmental research. Since the journal's founding in 1986 as Paleoceanography , the field has expanded from its early emphasis on marine sedimentary archives to an increasingly integrated Earth system perspective encompassing the oceans, atmosphere, cryosphere, biosphere, and terrestrial environments. The papers in this collection are selected from the recent archives since the expansion to Paleoceanography and Paleoclimatology in 2018. The topics span timescales from the Cretaceous to the Common Era and showcase advances in reconstructing past climates, understanding Earth system processes, developing innovative analytical and computational methods, and synthesizing observations and testing mechanisms with numerical models. Together, they illustrate how studies of past environmental change provide fundamental insights into climate sensitivity, carbon‐cycle dynamics, ocean circulation, abrupt climate change, and hydroclimate variability. They also demonstrate the importance of past climate for evaluating climate models, contextualizing modern environmental change, and informing projections of Earth's future under continued anthropogenic forcing. This anniversary collection celebrates four decades of scientific discovery, with a curated selection of articles that illustrate recent themes in the journal, from greenhouse to icehouse climates, and cutting‐edge methods, to reveal how the past informs our future.
Abstract Taxonomic identification of marine microfossils such as foraminifera and coccolithophores is essential for reconstructing past oceanographic and climatic conditions. However, this process remains a major bottleneck in paleoclimate research due to its dependence on expert knowledge and time‐consuming manual analysis. Recent advances in deep learning, especially the convolutional neural networks (CNNs), have spurred efforts to automate such process. Yet, standard CNN models tend to produce overconfident predictions for out‐of‐distribution specimens, as they do not explicitly account for epistemic uncertainty. Such overconfidence can lead to misclassifications, undermining the reliability of downstream paleoclimate reconstructions. In this study, we implement and evaluate three uncertainty‐aware deep learning methods, CNN with Monte Carlo Dropout (MCD), Bayesian CNN, and Deep Kernel Learning (DKL) to enhance robustness of microfossil classification. Using a curated data set of modern planktonic foraminifera, we assess the models' ability to produce uncertainty estimates over predictions. Our results show that these methods can flag out‐of‐distribution samples with large inference uncertainty, thereby significantly reducing both false positive and false negative errors in species identification. We suggest that uncertainty‐aware models, particularly when combined in ensembles, can provide a reliable framework for automated microfossil analysis to enable scalable, high‐throughput analysis in paleoceanographic and paleoclimatic research.
Abstract Little is known about long‐term variability in the organic carbon to carbonate carbon export rain ratio, despite its key role in the global carbon cycle. Here, we reconstruct glacial‐interglacial changes in the sedimentary rain ratio over the Southern Ocean, using micropaleontological (coccoliths and foraminifera) and geochemical (CaCO 3 , Total Organic Carbon (TOC), δ 13 C, C/N) records from sediment core MD04‐2718, located in the Polar Front Zone (PFZ, Indian sector), complemented with published data sets from across the Subantarctic Zone (SAZ). We show that sedimentary CaCO 3 primarily reflects the export of biogenic calcium carbonate by calcifying phytoplankton and zooplankton, while TOC captures the export of phytoplankton‐derived organic carbon. The sedimentary TOC/CaCO 3 ratio thus serves as a robust proxy for past variations in the balance between organic and inorganic carbon export and hence, of the export rain ratio. Our results indicate higher rain ratios during glacial periods, driven by enhanced organic carbon export, as colder conditions and intensified iron‐rich dust inputs stimulated diatom productivity. In contrast, lower rain ratios during interglacials reflect strengthened biogenic carbonate export, as warmer conditions and elevated macronutrient supply from reinvigorated Southern Ocean upwelling supported coccolithophore and foraminifera blooms. These shifts reflect an ecological seesaw between silicifying and calcifying phytoplankton modulated by changes in westerly wind intensity and the position of the Polar Front. The negative correlation between rain ratios from the SAZ‐PFZ and atmospheric pCO 2 suggests that enhanced organic carbon export during glacials likely promoted deep‐ocean carbon sequestration, modulating atmospheric CO 2 levels.
Abstract Understanding the long‐term variability of the El Niño‐Southern Oscillation (ENSO) is essential for assessing its response to external forcings, yet instrumental records are too short to capture its full range of behavior. The giant clam ( Tridacna ) has emerged as a promising archive for high‐resolution ENSO reconstructions, but the scarcity of long modern Tridacna δ 18 O records—due to overfishing—has hindered efforts to establish reliable baselines for past variability. Here we develop a pseudo‐proxy baseline approach to quantitatively assess ENSO variability from fossil Tridacna δ 18 O records. To precisely simulate the behavior of Tridacna δ 18 O records, we advance the Tridacna proxy system model (PSM) by integrating ShellChron, a novel algorithm that accurately reconstructs shell growth information at sub‐annual timescales. The improved PSM is validated against the modern Tridacna δ 18 O record and used to generate a pseudo‐δ 18 O ensemble to serve as a modern baseline. This ensemble is driven by modern temperature and salinity data, but mirrors the sampling resolution, analytical error, and growth characteristics of the fossil record. Using this pseudo‐proxy baseline approach, we quantitatively estimate that ENSO variability was 43% (6%–66%, 95% confidence interval) lower in around 3300 BP compared to modern conditions, based on a 38‐year fossil Tridacna record in the northern South China Sea. This result is consistent with central equatorial Pacific coral records and Peruvian bivalve records. Our approach not only establishes a quantitative framework for Tridacna ‐based ENSO reconstructions, but also points to a potential pathway for assessing past climate variability when sufficiently long modern proxy records are unavailable.
Abstract Global Mean Ocean Temperature (GMOT) changes are thought to be both an important consequence and a possible cause of Dansgaard–Oeschger (DO) events, a series of abrupt climate changes during the last glacial. Despite extensive reconstructions of GMOT from ice cores for other periods, no reliable reconstructions exist for Marine Isotope Stage 3, when DO events were most common. We investigate model simulations showing unforced DO‐like oscillations alongside existing proxy reconstructions of Southern Ocean and Antarctic temperatures, which we show to be strongly linked to GMOT in the models though with consistently larger changes in Antarctic temperature than GMOT. We find that the models reproduce DO events following non‐Heinrich stadials well, but that the GMOT changes they show across these events are comparable to the measurement error for ice core GMOT reconstructions and so would be difficult to detect. The simulations we use, which are not forced by Heinrich meltwater, do not capture the larger Southern Ocean and Antarctic warming associated with DO events that follow Heinrich stadials, making extrapolating our results to these events challenging. Additionally, there is a statistically robust disagreement between the proxies and models regarding the relative warming in Antarctica and the Southern Ocean, which adds further uncertainty to our estimates of GMOT warming. Nonetheless, we find that the GMOT changes across these larger DO events in MIS3 would be detectable. Given the importance of GMOT for understanding DO events, these should therefore be priority targets for future efforts to reconstruct GMOT from ice cores.
Abstract Paleo‐CO 2 proxies are crucial for reconstructing past atmospheric CO 2 variations and understanding their impact on Earth's climate, especially in light of anthropogenic climate change. The mechanistic leaf gas exchange model of Franks et al. (2014), https://doi.org/10.1002/2014gl060457 utilizes the relationship between atmospheric CO 2 and chemical and morphological fossil leaf traits for CO 2 reconstructions. While the model has shown promising results, its applicability to different plant groups remains unclear, particularly whether there are consistent offsets in CO 2 estimates among major plant clades. In this study, we evaluate the performance of the model across different phylogenetic groups (ferns, gymnosperms, and angiosperms), with generic input values and recommended adjustments to isotopic measurement values, assimilation rates and the scaling of maximum to operational stomatal conductance, by applying the Franks model to living plants. Results show generally accurate CO 2 estimates, but high interspecies variations with generic values; a clade‐level bias is therefore unlikely. Consequentially, the corrections to isotopic measurement values to remove a phylogenetic effect do not show improvements across the three plant groups. Adjustments to the assimilation rate based on phylogeny, growth form and solar exposure result in a decrease in variation and an improvement in CO 2 estimates. While the minor change in stomatal conductance scaling values for woody angiosperms results in limited improvements in accuracy, precision decreases due to higher measurement uncertainty. Overall, the results of this study suggest that the Franks model has a high potential for accurately reconstructing past atmospheric CO 2 within a multitaxon study, especially with careful choice of assimilation rate values.
Abstract Plant wax hydrogen isotopes (δ 2 H) preserved in lake sediments provide valuable insights into past climatic changes. However, lake catchments often experience local shifts in vegetation type that can yield distinct isotopic signatures in the sediments, potentially obscuring hydroclimatic signals. Here, we compile regional plant wax data and test different approaches to correct for the impact of changes in vegetation type over time to isolate precipitation δ 2 H values (δ 2 H prc ) since the Younger Dryas (12.9–11.7 ka) from a sediment record from Rotsee (central Switzerland). Our method intercomparison shows that n ‐alkane relative abundances produced the most accurate δ 2 H prc estimates, agreeing with an independent speleothem fluid‐inclusion δ 2 H record from Milandre Cave. This indicates that sedimentary plant wax δ 2 H values represent a vegetation‐weighted community signal. Precipitation was 2 H‐depleted during the Younger Dryas (∼−75‰), and then δ 2 H prc values increased sharply into the Holocene. During the early Holocene (∼10 ka), δ 2 H prc values of ∼−55‰ were reached, consistent with maximum summer insolation, followed by a gradual long‐term decline toward the present, reflecting Neoglacial cooling and consistent with modern δ 2 H prc values (∼−67‰). Importantly, while plant wax δ 2 H values declined sharply due to deforestation beginning in the Roman period, this impact is effectively corrected for by using the relative abundance of n ‐alkanes. These findings underscore the need for site‐specific vegetation corrections to produce robust hydroclimate reconstructions from plant‐wax isotopes, especially in lakes with small catchments, thereby enhancing comparability of sedimentary records with climate models and deepening our understanding of past climate–vegetation–human interactions.
Abstract Fish teeth are widely used as paleoceanographic archives for seawater rare earth elements and yttrium (REY) signatures and Sr isotope chronostratigraphy. However, the reliability of this proxy during extreme climatic perturbations, when both seawater chemistry and diagenetic conditions shift, remains poorly constrained. To elucidate these mechanisms, we conducted multiscale analyses on Paleocene‐Eocene Thermal Maximum (PETM) fossil fish teeth from the eastern equatorial Pacific, a key stratigraphic interval characterized by sharp environmental perturbations. Our integrated petrographic‐geochemical approach, incorporating in situ micro‐analyses (Fourier‐transform infrared spectroscopy, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry) shows that primary productivity promoted fish teeth abundance and increased REY enrichment in bulk seafloor sediments by providing phosphorus and REY ions. However, enhanced productivity and diagenetic conditions that elevated bottom nutrient fluxes did not result in REY enrichment in the bioapatite. We find that reaction kinetics‐based lattice substitution dominated REY incorporation into the bioapatite, which was significantly enhanced by elevated paleotemperatures (ΔT ≈ 3–5°C) during the PETM. On the other hand, the Sr isotopic signature of the fossil teeth was decoupled from global seawater Sr trends during the PETM because of diagenesis, which limits the direct application of Sr chronometry for fish teeth deposited during extreme climatic perturbations. Our results highlight that the Sr isotope chronometry of bioapatite can be compromised during hyperthermal events, and that temperature‐driven substitution kinetics must be considered when interpreting REY enrichment in fossil fish teeth as providing a robust paleoceanographic signals.
Abstract Oxygen concentrations in seawater are sensitive to both changes in carbon storage and surface processes that set the preformed oxygen concentrations of different water masses. New and developing oxygen proxies have led to (semi‐)quantitative estimates of glacial oxygen concentrations, which suggest the glacial deep Atlantic had ∼50 μmol/kg lower oxygen than in the Holocene. However, the water depth structure of oxygen concentrations in the past is poorly constrained, and so attribution of oxygen variability to specific water masses and parsing the potential role of preformed variability is difficult. In this study, we present the most highly resolved depth transect of glacial oxygen concentrations, which comes from the western tropical Atlantic at the Demerara Rise (7–9°N, 53–54°W, 350–2,550 m water depth). We use the novel quantitative proxy U/Ba to generate oxygen reconstructions in a setting where the foraminifera needed for Δδ 13 C, the only other feasible proxy, are rare. Glacial oxygen content along the Demerara Rise was consistently lower than modern, with the largest change (∼100 μmol/kg) occurring at 1,500–2,500 m water depth. We combine these new oxygen reconstructions with published data to optimize an endmember mixing model that provides estimates of the preformed δ 13 C and oxygen content of three water masses in the Atlantic Ocean. In contrast to glacial model simulations, our results suggest lower oxygen concentrations throughout the depth range of our cores, which we suggest was predominately driven by lower preformed oxygen in Antarctic Intermediate Water and North Atlantic Deepwater.
Abstract Effective fractionation factors ( ε ) relate the δ 2 H of leaf waxes to ambient water and are essential for paleoclimate and paleotopography reconstructions using biomarker isotopes. The δ 2 H of the water used by plants is often poorly constrained and may contribute to producing highly variable estimates of ε . Herein, we compile ∼700 modern water δ 2 H and δ 18 O values from across the Himalaya and Tibetan plateau (TP) to calibrate a new orographic precipitation isotope model that produces precise estimates of long‐term average primary precipitation isotopes. We couple data and precipitation isotope model predictions with ∼200 leaf wax δ 2 H values to calculate ε between leaf wax n ‐alkanes and meteoric water. Our results demonstrate that: (a) modern primary (non‐evaporated) surface water isotopes across the TP and surrounding region can be effectively estimated with less error than existing spatial interpolation models, (b) the precipitation isotope field across this region is dominated by orographic lifting and condensation superimposed on synoptic precipitation patterns, and (c) the effective fractionation between hydrogen isotopes of leaf waxes in soils and meteoric water shows no correlation with elevation, temperature, relative humidity, or vapor pressure deficit and may be constrained by a single ε value of −120.2‰, despite large variations in ecosystem and climate. This new precipitation isotope modeling approach enables reliable prediction of modern primary (non‐evaporated) surface water isotopes (δ 2 H precip and δ 18 O precip ) as well as reconstruction of ancient δ 2 H precip using δ 2 H leaf wax .
The editors of Paleoceanography and Paleoclimatology would like to sincerely thank those who reviewed manuscripts in 2025. We appreciate their scientific expertise and careful attention to reviewing the work of peers which not only elevates the scientific rigor of the individual manuscripts that they review but also influences that of future research in the field. Reviewers' insightful comments often help authors to improve data analysis and presentation, to better contextualize their findings in the wider literature and to evaluate the accessibility, availability, and sufficiency of data and code, ensuring reproducible results and data reuse. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We received 276 submissions in 2025, and 473 reviewers contributed to their evaluation by providing 765 reviews in total. We deeply appreciate their contributions.
The early Permian (Artinskian) deglacial warming represents a significant climate transition with notable ecosystem reorganization within the late Paleozoic icehouse, yet its impact on tropical landscape erosion remains unclear. In this study, we analyze the siliciclastic Liangshan Formation in western South China deposited during this interval using sandstone petrology, mudrock geochemistry, detrital mineral ages, zircon alpha-dose values, and paleogeography as constraints. All lines of evidence, including zircon grains with rounded inherited overgrowths, Zr enrichment, consistently high weathering intensity, major detrital zircon and rutile U-Pb age populations of 700-500 Ma and 1100-900 Ma, and systematically lower zircon alpha-dose relative to the putative sources, indicate a recycled provenance from the pre-Permian Paleozoic sedimentary rocks. DZmix modeling suggests source contributions of ca. 49%, 20% and 29% from the Devonian, Silurian and Cambrian-Ordovician siliciclastic successions in western South China, respectively. These provenance data reveal enhanced physical erosion by deep incision, especially from the Devonian quartzose sandstones, and suggest a sedimentary regime distinctly different from that recorded by the preceding carbonate-dominated successions. Coupling climate model results with stream power law, we attribute this enhanced erosion in South China to increased mean-annual precipitation and associated expansion of fluvial system leading to effective removal of sediments from source to sink. In contrast, coeval rapid erosion in equatorial Pangea is best explained by greater discharge variability and more frequent threshold-exceeding floods under arid conditions. Results of this study provide a comprehensive framework for interpreting sediment flux variations during past global warming events.
