The Ba/Ca ratio in stony corals (Ba/Ca-cor) has been shown in some settings to be a proxy for hydroclimate, specifically river discharge. While this relationship is well-established along the Pacific Coast of Panama, the degree to which temporal variations in Ba/Ca-cor from different regions in the estuary replicate is still an area of uncertainity. Here, we present three near-monthly resolved Porites lobata Ba/Ca-cor time-series from near-shore and off-shore locations in the Gulf of Chiriqu & iacute; to illustrate how different corals can record gulf-wide hydroclimatic conditions. All three records are correlated (r(min) = 0.48, r(max) = 0.92) and replicate one another at monthly, annual average, annual amplitude, wet season average, and dry season average resolutions. By averaging time-matched points, we generated a composite Ba/Ca-cor record that yielded statistically significant river discharge calibrations. The Gulf of Chiriqu & iacute; (GoC) is a prime location for the study of the Ba/Ca-cor- river discharge relationship, as the region is not substantially impacted by seasonal upwelling or temperature variability due to the topographic blocking of the tradewinds and does not appear to be driven by barite formation in the water column. However, Ba originating from marsh sediment or mangrove forests might contribute to the signal recorded in the corals. Our reconstruction extends the instrumental discharge data by similar to 70 years and demonstrates the strong and consistent relationship between El Ni & ntilde;o events and droughts in Panama with implications for understanding the functioning of the Panama Canal. Therefore, replicated Ba/Ca-cor records in the GoC have the potential to not only improve our quantification of past river discharge, but also serve as a tool to supplement our understanding of paleo-ENSO and its impact on regional hydroclimate.

In the South Pacific Convergence Zone (SPCZ), interannual to interdecadal oceanic and atmospheric variability is especially pronounced. The El Niño Southern Oscillation and the Interdecadal Pacific Oscillation significantly influence the SPCZ diagonal axis and salinity front. Regional coral‐based paleo‐environmental reconstructions extend the relatively short and discontinuous instrumental sea surface temperature (SST) and sea surface salinity (SSS) record to elucidate past variability. We present monthly resolved, composite indices of coral skeletal δ 18 O, Sr/Ca, and calculated δ 18 O sw utilizing coral geochemical time‐series from Rotuma, Fiji, Tonga, and Rarotonga, dubbed the SPCZ coral (SPCZ c ) indices. The new indices build upon previous efforts to describe variability and trends in the SPCZ region with expanded coverage due to a new northwestern coral addition from the SPCZ fresh pool. The increased spatial and temporal resolution of the new indices allows for higher‐fidelity sub‐annual reconstructions of SST and SSS in the region dating back to 1848. The results confirm the secular warming trend of 1°C in the SPCZ region and show a 0.4 S p freshening starting in the 1880s. The SPCZ c δ 18 O sw is the first regional reconstruction of δ 18 O sw and provides valuable insights into past SSS variability, including elucidating responses to El Niño and La Niña events, as well as identifying past SPCZ zonal events. The SPCZ c δ 18 O sw reconstruction extends the instrumental records by ∼100 years. The SPCZ c indices prove the utility of the compositing approach in describing regional oceanographic variability with the increased signal‐to‐noise ratio of the obtained coral climatic data.

The Southwest Pacific region is of great importance to global climate variability, but instrumental climate observations before the 1980s lack in numbers and quality. Despite efforts in complementing instrumental records with proxy sea surface temperature (SST) and sea surface salinity (SSS) reconstructions based on coral Sr/Ca and delta 18Osw records, few of them are longer than a century. This study introduces a northwestern extension to the existing records of South Pacific coral study sites with monthly-resolved Sr/Ca, delta 18O, and delta 18Osw reconstructions from Rotuma dating back to 1821. Additionally, we present new monthly-resolved Sr/Ca and reconstructed delta 18Osw from a coral from Tonga dating back to 1848. Results reveal 1.5 degrees C warming in the Western Pacific Warm Pool, while the adjacent coral from Tonga shows 1 degrees C warming over the twentieth century. The Rotuma Sr/Ca record reveals thermal stress events impacting the Sr/Ca-SST relationship in the following months. Coral delta 18Osw results reveal significant freshening of 0.45 Sp (practical salinity unit) in Tonga since the early twentieth century, suggesting the southeastward expansion of the South Pacific Convergence Zone salinity front. The delta 18Osw inferred SSS provides a valuable extension into the past considering the short and inconsistent instrumental records available. This study demonstrates the utility of coral-based reconstructions in capturing long-term and regional climate variations in the Southwest Pacific and the necessity of expanding replicated studies to other underrepresented areas to enhance our understanding of regional climate dynamics.

Mass coral bleaching on the Great Barrier Reef (GBR) in Australia between 2016 and 2024 was driven by high sea surface temperatures (SST)1. The likelihood of temperature-induced bleaching is a key determinant for the future threat status of the GBR2, but the long-term context of recent temperatures in the region is unclear. Here we show that the January-March Coral Sea heat extremes in 2024, 2017 and 2020 (in order of descending mean SST anomalies) were the warmest in 400 years, exceeding the 95th-percentile uncertainty limit of our reconstructed pre-1900 maximum. The 2016, 2004 and 2022 events were the next warmest, exceeding the 90th-percentile limit. Climate model analysis confirms that human influence on the climate system is responsible for the rapid warming in recent decades. This attribution, together with the recent ocean temperature extremes, post-1900 warming trend and observed mass coral bleaching, shows that the existential threat to the GBR ecosystem from anthropogenic climate change is now realized. Without urgent intervention, the iconic GBR is at risk of experiencing temperatures conducive to near-annual coral bleaching3, with negative consequences for biodiversity and ecosystems services. A continuation on the current trajectory would further threaten the ecological function4 and outstanding universal value5 of one of Earth's greatest natural wonders.

Abstract Boron to calcium (B/Ca) records in benthic foraminifera, used for reconstructing the carbonate ion saturation state (ΔCO3) of the deep ocean, suggest that carbon sequestration in the Southern Pacific contributed to lowering atmospheric CO2 during the last glacial interval. However, the spatial and temporal extent of this storage is debated due to limited ΔCO3 records. To increase available ΔCO3 records, we explored using strontium and sulfur to calcium (Sr/Ca, S/Ca) in Planulina wuellerstorfi as additional proxies for ΔCO3 based on comparison with paired B/Ca down‐core records from Pacific Sites U1486 (1,332 m depth) and U1487 (874 m depth) cored during the International Ocean Discovery Program Expedition 363. The Sr/Ca and S/Ca records from P. wuellerstorfi closely covary with the B/Ca‐derived ΔCO3 records. Temperature, reconstructed using Uvigerina peregrina magnesium to calcium (Mg/Ca), has no discernible effect on Sr/Ca, whereas S/Ca also varies with Mg/Ca in both U. peregrina and P. wuellerstorfi, suggesting an additional temperature effect. Mg/Ca records from P. wuellerstorfi are affected by both temperature and ΔCO3. We assess calibrations of Sr/Ca to ΔCO3 for the Atlantic, Pacific, and Indian Oceans and recommend using the down‐core rather than core‐top calibrations as they yield consistent sensitivity, though with offsets, in all ocean basins. Reconstructing Pacific ΔCO3 records from sites U1486, U1487, and DSDP 593, we demonstrate the benefit of using Sr/Ca as an additional ΔCO3 proxy to assess the contribution of the Southern Pacific to the increase of atmospheric CO2 at glacial terminations.

ABSTRACT Accurate biological models are critical to reliably predict vulnerability of marine organisms and ecosystems to rapid environmental changes. Current predictions on the biological impacts of climate change and human-caused disturbances primarily stem from controlled experiments but lack assessments of the mechanisms underlying biotic variations in natural systems. Such information is key to translating experimental models to natural populations, especially for habitat-forming, climate sensitive species with key ecological roles. This study aimed to characterize and quantify spatial patterns of shell biomineralization and biomechanical properties in a key reef-building oyster, Crassostrea virginica , collected from restored reefs along natural estuarine gradients in the Hudson River Estuary (NY, U.S.). We characterized patterns of oyster shell production (i.e., shape and thickness), structure (i.e., abundance of foliated and chalky calcite), mineralogy (i.e., crystal size and density), composition (i.e., organic matrix and Mg/Ca ratios), and mechanical performance (i.e., elastic modulus and hardness) at the macro and micro scale. Our results demonstrate a strong protective capacity of C. virginica for compensatory adjustments in shell biomineralization and biomechanics to maintain shell production and protective functions as a response to biotic and abiotic stressors. We reveal salinity as a key predictor of oyster shell structure, mechanical integrity, and resistance to dissolution, and describe the functional role of chalky calcite in shaping shell mechanical performance. Compensatory adjustments along salinity gradients indicate that oysters produce shells with i ) high mechanical resistance but increased vulnerability to dissolution under marine conditions, and ii ) lower structural integrity but higher protection from dissolution under brackish conditions. Our work illustrates that biomineralization and biomechanical adjustments may act as compensatory mechanisms in eastern oysters to maintain overall performance under heterogeneous estuarine environments, and could represent a cornerstone for calcifying organisms to acclimate and maintain their ecological functions in a rapidly changing climate.

Coral skeletal Ba/Ca (Ba/Cacor) has been found to be highly correlated with river discharge in some coastal settings. However, any hydrologic interpretation of Ba/Cacor time-series requires thorough evaluation of regional climate, even at sites in close proximity to one another. Here we explore how two corals can be used to provide insight into hydroclimate in the Gulf of Chiriqui, Panama (GoC) using Ba/Cacor, a region whose climate is dictated by seasonal and lower frequency shifts in the Intertropical Convergence Zone. The main purpose of this study is to provide a preliminary assessment of Ba/Cacor replication in pursuit of a regional geochemical network. The two corals analyzed in this study (Secas Island, S1 and Coiba, IC4A-2) were collected similar to 74 km apart and grew in different reef settings at vastly different distances from the main river discharge points. Analytical uncertainty prevents complete confidence determining whether a small geochemical offset Ba/Cacor exists between our two records. However, temporal variability in S1 and IC4A-2 are well correlated at all examined temporal scales (r(monthly) = 0.70, r(annual) = 0.65, r(wet season) = 0.67, r(dry season) = 0.55, r(annual) (amplitude) = 0.77). Considering a potential geochemical offset may exist between the two corals, we took a conservative approach and examined S1 and IC4A-2 separately to establish a relationship with river discharge. Both corals, barring IC4A-2 dry season av-erages, are statistically significantly correlated to river discharge, permitting the creation of Reduced Major Axis regressions to quantify the relationship. Ultimately, in regions where river discharge dominates, a network of Ba/ Cacor records may assist in reconstructing regional variability or notable deviations in hydroclimate. With additional and temporally longer Ba/Cacor records, we will be able to apply our framework to more clearly reconstruct river discharge variability throughout the GoC.

Changes in vertical geochemical gradients within the Western Pacific Warm Pool (WPWP) are important indicators of the region's upper ocean response to climate changes and to the oceanographic coupling between the thermocline and surface mixed layer. Here, we reconstruct temperature and delta O-18(sw) at International Ocean Discovery Program Site U1486 (1332 m water depth, 2.22' S, 144. 36' E) located in the Bismarck Sea in the southern sector of the WPWP. A 670-kyr record of Delta delta O-18 between the surface-dwelling foraminifera Globigerinoides ruber sensu stricto and the thermocline-dwelling foraminifera Pulleniatina obliquiloculata and Globorotalia tumida (when combined with Mg/Ca-based temperature and d18Osw estimates) suggests long-term thermocline shoaling and a progressively increasing vertical salinity gradient commencing near 240 ka. Through a detailed comparison to other Pacific records, it becomes clear this is not solely a local phenomenon, as we identify widespread cooling of the thermocline in the low-latitude Pacific after similar to 240 ka. After examining our temperature reconstructions alongside new delta O-18(sw) and constant flux proxy-derived focusing factor records, we potentially also validate previous models which find obliquity-induced strengthening of low-latitude Pacific currents. We extend this to support periods of increased transport of high-salinity thermocline water masses through the South Pacific low-latitude western boundary current system. These results indicate greater variability in thermocline circulation given amplified obliquity and strengthen previous evidence that variability in the WPWP thermocline is independent from the drivers of WPWP surface variability.

In much of the equatorial Pacific, surface nitrate is consistently available due to upwelling of sub-Antarctic Mode Water-derived nitrate from the thermocline. However, in the low-latitude western boundary current (WBC) region, surface nitrate is limited due to reduced upwelling and less nitrate-replete thermocline water masses. In order to explore South Pacific WBC paleoceanography via upper ocean nitrate dynamics, we present a new bulk sediment δ15N record from within this WBC region at International Ocean Discovery Program Site U1486 (2°22′S, 144°36′E) in the Bismarck Sea north of New Guinea. This record spans from 1420 ka to recent – surpassing nearby sediment δ15N reconstructions by over a million years and allowing for direct comparison to low-latitude Pacific sediment core δ15N records of similar length. Core-top and down-core bulk sediment δ15N, TOC/TN and δ13Corg values indicate minimal or no terrestrial influence on the organic fraction at Site U1486, which is consistent with previous studies of modern processes in the region. After comparison, differences in orbital variability and secular trends throughout the Middle and Late Pleistocene suggest that nitrate dynamics along the equator and in the WBCs were relatively disparate. We observe that δ15N at Site U1486 is consistent with patterns of eastern Pacific denitrification, while we suggest increasing δ15N after the mid-Pleistocene Transition (MPT; ∼1250–700 ka) at Sites 806 (0°19′N, 110°30′W) and 849 (0°19′N, 160°E) is linked to increasing Southern Ocean nitrate utilization. Enhanced nitrate utilization is a key indicator of the strengthened biological pump that contributed to a reduction in atmospheric pCO2 during the last glacial. Therefore, a post-MPT increase in nitrate utilization may bolster the role of the Southern Ocean biological pump in driving the deeper and longer glacial periods of the 100-kyr world.

Global mean sea level (GMSL) during intermediate interglacial Marine Isotope Stage 3 (MIS 3) (60–26 ka) has proven difficult to constrain. Paleo‐sea level estimates based on ice margin, modeling, and paleo‐shoreline reconstructions indicate that MIS 3 GMSL was substantially higher than reconstructed from deep‐ocean benthic foraminifera oxygen isotope (δ 18 O) and coral records, implying much smaller ice sheets during MIS 3. Here, we use the δ 18 O and Mg/Ca chemistry of surface and thermocline dwelling foraminifera in the Sulu Sea in the western Pacific margin to estimate relative changes of the influx of South China Sea surface flow through the Sulu Sea over the last 140 ka. We show that this South China Sea throughflow is controlled in part by changes in GMSL modulating the depth of the 36 m deep Karimata Strait at the southern end of the South China Sea. We constrain maximum allowable GMSL at the beginning and end of MIS 3 to −22 ± 6 and −29 ± 5 m, respectively, and minimum allowable GMSL during interglacial stages MIS 5c and 5a (117–72 ka) to range from −3 ± 8 to −8 ± 8 m and −11 ± 7 to −12 ± 7 m, respectively. Our results constrain MIS 3 GMSL, but do not rule out higher MIS 3 ice margin, modeling, and paleo‐shoreline‐based MIS 3 GMSL estimates or lower coral and seawater δ 18 O‐based estimates. Our results favor the highest MIS 5a and 5c GMSL estimates and confirm that the Sunda Shelf served as a land‐bridge for human and megafauna migration during MIS 3 when humans first arrived in Borneo.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

The meridional migration of the bifurcation latitude of the Pacific North Equatorial Current (NEC) in the western boundary of the tropical Pacific modulates the strength of the Kuroshio Current. Using salinity reanalysis data, we show the NEC bifurcation latitude also acts as the dominant control on thermocline salinity of the Sulu Sea, just west of the Philippine archipelago, by regulating influx of western Pacific thermocline water via the Luzon Strait. We used oxygen isotopes (δ18O) and Mg/Ca in the thermocline-dwelling foraminifera Globorotalia tumida from Sulu Sea sediment core MD97-2141 to determine past thermocline δ18Ow and salinity variability spanning ∼20–5 ka with an average sampling interval of ∼50 years and infer past changes in the NEC bifurcation latitude. Our Sulu Sea thermocline reconstruction reveals high salinity from ∼18.8–15.5 ka, ∼12.2–11.5 ka, and from ∼9.5–8.5 ka indicating the NEC bifurcation latitude was shifted north and the Kuroshio was weak at those times. Low Sulu Sea thermocline salinity from ∼13.0–12.4 ka, ∼11.5–10.9 ka, and from ∼8.5 ka until the end of the record at ∼5.6 ka indicates the NEC bifurcation latitude was shifted south and the Kuroshio Current was relatively strong. Comparison to other paleoclimate records suggests the observed northward (southward) shifts of the NEC bifurcation latitude were driven by southward (northward) shifts of the Indo-Pacific ITCZ, consistent with modern mechanisms controlling interannual NEC bifurcation variability. The NEC bifurcation latitude shifts likely modulated northward energy transport via the Kuroshio Current and the mean temperature and salinity of the Indonesian Throughflow.

Massive tropical corals represent one of the most important natural archives of modern climate change. Coral based reconstructions give us the possibility to extend the instrumental oceanographic records and observe hydrographic variability on seasonal to interdecadal scales in tropical oceans. South Pacific convergence zone (SPCZ) variability, Interdecadal Pacific Oscillation (IPO) and El Niño-Southern Oscillation (ENSO) events are major drivers of global climate and may exert control on regional CO2 absorption, outgassing and pH variability. Porites sp. corals from Tonga and Rotuma (Fijian dependency) are being analyzed for multi-proxy (e.g. Sr/Ca, δ18O, δ13C, δ11B, B/Ca) reconstructions of sea surface temperature and salinity (SST, SSS) and carbonate chemistry, on a monthly to annual resolution. Preliminary data of the Rotuma Porites sp. coral shows δ18O has been decreasing by 0.004 ‰ per year at the end of the 20th century, suggesting freshening and/or warming of the surface water. In the same period, we observe a δ13C decrease of 0.017 ‰ per year in-line with the anthropogenic CO2 driven Suess effect. Initial results of the δ11B Tonga Porites sp. show high interannual variability, and a strong trend of decrease of -0.0626 ‰ per year in the last five decades of the record (1949-2004) suggesting acidification. The results are in agreement with published coral-based reconstructions from the region. When completed, the new records will facilitate exploring the effects of modern anthropogenic influence on ocean carbonate system and pH variation, and the relationship between them and interannual and decadal-interdecadal climatic fluctuations.

Pacific-wide measurements of nitrate and its isotopic composition have furthered our understanding of modern subsurface circulation and have revealed basin-scale connections between oceanographic and nitrogen cycle processes. From the Eastern Tropical Pacific (ETP), the isotopic signature of denitrification is spread zonally and meridionally via subsurface currents. From the Pacific sector of the Southern Ocean, Subantarctic Mode Water (SAMW) penetrates to the low latitudes, delivering nitrate (and likely its isotopic signature) to equatorial surface waters via upwelling. These two regional processes combine to inform much of the thermocline nitrogen dynamics of the Pacific. Here, we compare a new 1.4-Myr bulk sediment 𝛿15N record from the New Guinea margin (IODP Site U1486) to other Pacific 𝛿15N records to track Pleistocene changes in denitrification and SAMW properties. Our results highlight a dramatic increasing 𝛿15N trend after the mid-Pleistocene Transition (MPT) at equatorial sites that is not observed at the New Guinea and California margin sites. Strong 41-ky forcing at equatorial sites and little detectable influence from denitrification (counter to larger denitrification signals at margin sites) suggests increasing 𝛿15N within upwelled SAMW. Because the New Guinea and California margin sites are not below equatorial upwelling, thermocline nitrate is less influenced by SAMW, but rather tracks denitrification in the ETP.As equatorial Pacific nitrate utilization has not dramatically increased in the late Pleistocene, an increase in subantarctic zone nitrate utilization is proposed. Initiation of increased nitrate utilization appears to commence near the end of the MPT and accelerate near the Mid-Brunhes Event (~430 ka). The observed southward shift of the polar front at this time (associated with increased sea surface temperature), combined with elevated dust/iron flux, may have contributed to greater nitrate utilization and a more efficient biological pump in the subantarctic zone. Through the production (via denitrification) and sequestration (via nitrate utilization) of greenhouse gases, these biogeochemical processes potentially participated in feedbacks associated with both the MPT and the Mid-Brunhes Event. Until reconstructions of subantarctic zone nitrate are extended beyond the last two glacial cycles, this reconstruction of SAMW properties via equatorial Pacific bulk 𝛿15N may provide the best record of long-term changes in nitrogen dynamics in the subantarctic zone.

The South Pacific Convergence Zone (SPCZ) is a diagonal band of intense rainfall and deep atmospheric convection extending from the equator to the subtropical South Pacific. Displacement of the SPCZ causes variability in rainfall, tropical-cyclone activity and sea level that affects South Pacific island populations and surrounding ecosystems. In this Review, we synthesize recent advances in understanding the physical mechanisms responsible for the SPCZ location and orientation, its interactions with the principal drivers of tropical climate variability, regional and global effects of the SPCZ and its response to anthropogenic climate change. Emerging insight is beginning to provide a coherent description of the character and variability of the SPCZ over synoptic, intraseasonal, interannual and longer timescales. For example, the diagonal orientation of the SPCZ and its natural variability are both the result of a subtle chain of interactions between the tropical and extratropical atmosphere, forced and modulated by the underlying sea surface temperature gradients. However, persistent biases in, and deficiencies of, existing models limit confidence in future projections. Improved climate models and new methods for regional modelling might better constrain future SPCZ projections, aiding climate change adaptation and planning among vulnerable South Pacific communities. The South Pacific Convergence Zone describes a band of heavy precipitation extending south-eastwards from the Solomon Islands to French Polynesia. This Review discusses the mechanisms explaining the diagonal orientation of the South Pacific Convergence Zone, its variability and projected changes under anthropogenic warming.

The modern increase in atmospheric CO2 driven by fossil fuel combustion and land-use change is warming our atmosphere and surface oceans. The absorption of this excess CO2 by the oceans decreases seawater pH in a process known as ocean acidification (OA), which represents a threat to marine ecosystems with adverse impacts on coral health. It is important to understand how modern climate change impacts interannual and interdecadal climatic cycles and atmospheric phenomena which are originating in the Pacific and modulating global climate. There is a scarcity of data necessary to study the impacts of these changes on natural variability on longer timescales. In this study, we present multi-proxy (e.g. Sr/Ca, δ18O, δ13C, B/Ca) reconstructions of sea surface temperature (SST), surface seawater carbonate chemistry, with implications for pH variability of the South Pacific back to preindustrial times. This region of the Pacific is interesting for tracking the development of OA because of the well-constrained interannual to interdecadal SST and SSS variability from existing coral-based reconstructions. Massive corals (Porites sp.) from Rotuma and Tonga will be analyzed to extend the currently available SST reconstructions and expand the spatio-temporal coverage beyond the instrumental records. New monthly-resolved SST records will provide larger analyses exploring the influence of interannual and decadal-interdecadal climatic fluctuations on CO2 absorption and pH variation. We aim to quantify the anthropogenic impact on SST, pH and the ocean carbonate system to achieve a better understanding of the status in the South Pacific under open ocean conditions.

The Great Barrier Reef (GBR) is an internationally recognized and widely studied ecosystem, yet little is known about its sea surface temperature (SST) evolution since the Last Glacial Maximum (LGM) (~20 kyr BP). Here, we present the first paleo‐application of Isopora coral‐derived SST calibrations to a suite of 25 previously published fossil Isopora from the central GBR spanning ~25–11 kyr BP. The resultant multicoral Sr/Ca‐ and δ 18 O‐derived SST anomaly (SSTA) histories are placed within the context of published relative sea level, reef sequence, and coralgal reef assemblage evolution. Our new calculations indicate SSTs were cooler on average by ~5–5.5°C at Noggin Pass (~17°S) and ~7–8°C at Hydrographer's Passage (~20°S) (Sr/Ca‐derived) during the LGM, in line with previous estimates (Felis et al., 2014, https://doi.org/10.1038/ncomms5102 ). We focus on contextualizing the Younger Dryas Chronozone (YDC, ~12.9–11.7 kyr BP), whose Southern Hemisphere expression, in particular in Australia, is elusive and poorly constrained. Our record does not indicate cooling during the YDC with near‐modern temperatures reached during this interval on the GBR, supporting an asymmetric hemispheric presentation of this climate event. Building on a previous study (Felis et al., 2014, https://doi.org10.1038/ncomms5102 ), these fossil Isopora SSTA data from the GBR provide new insights into the deglacial reef response, with near‐modern warming during the YDC, since the LGM.