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Terrestrial amplification (TA) of land warming relative to oceans is apparent in recent climatic observations. TA results from land-sea coupling of moisture and heat and is therefore important for predicting future warming and water availability. However, the theoretical basis for TA has never been tested outside the short instrumental period, and the spatial pattern and amplitude of TA remain uncertain. Here, we investigate TA during the Last Glacial Maximum (LGM; ~20 thousand years) in the low latitudes, where the theory is most applicable. We find remarkable consistency between paleotemperature proxies, theory, and climate model simulations of both LGM and future climates. Paleoclimate data thus provide crucial new support for TA, refining the range of future low-latitude, low-elevation TA to 1.37 − 0.23 + 0.27 (95% confidence interval), i.e., land warming ~40% more than oceans. The observed data model theory agreement helps reconcile LGM marine and terrestrial paleotemperature proxies, with implications for equilibrium climate sensitivity.

In central California, irrigation seepage perturbs groundwater inorganic carbon chemistry and complicates radiocarbon dating., Groundwater is an important source of drinking and irrigation water. Dating groundwater informs its vulnerability to contamination and aids in calibrating flow models. Here, we report measurements of multiple age tracers (14C, 3H, 39Ar, and 85Kr) and parameters relevant to dissolved inorganic carbon (DIC) from 17 wells in California’s San Joaquin Valley (SJV), an agricultural region that is heavily reliant on groundwater. We find evidence for a major mid-20th century shift in groundwater DIC input from mostly closed- to mostly open-system carbonate dissolution, which we suggest is driven by input of anthropogenic carbonate soil amendments. Crucially, enhanced open-system dissolution, in which DIC equilibrates with soil CO2, fundamentally affects the initial 14C activity of recently recharged groundwater. Conventional 14C dating of deeper SJV groundwater, assuming an open system, substantially overestimates residence time and thereby underestimates susceptibility to modern contamination. Because carbonate soil amendments are ubiquitous, other groundwater-reliant agricultural regions may be similarly affected.

Significance We report the discovery of anomalously high 3He/4He in “cold” geothermal fluids of central Panama, far from any active volcanoes. Combined with independent constraints from lava geochemistry, mantle source geochemical anomalies in Central America require a Galápagos plume contribution that is not derived from hotspot track recycling. Instead, these signals likely originate from large-scale transport of Galápagos plume material at sublithospheric depths. Mantle flow modeling and geophysical observations further indicate these geochemical anomalies could result from a Galápagos plume-influenced asthenospheric “mantle wind” that is actively “blowing” through a slab window beneath central Panama. The lateral transport of plume material represents a potentially widespread yet underappreciated mechanism that scatters enriched geochemical signatures in mantle domains far from plumes., It is well established that mantle plumes are the main conduits for upwelling geochemically enriched material from Earth's deep interior. The fashion and extent to which lateral flow processes at shallow depths may disperse enriched mantle material far (>1,000 km) from vertical plume conduits, however, remain poorly constrained. Here, we report He and C isotope data from 65 hydrothermal fluids from the southern Central America Margin (CAM) which reveal strikingly high 3He/4He (up to 8.9RA) in low-temperature (≤50 °C) geothermal springs of central Panama that are not associated with active volcanism. Following radiogenic correction, these data imply a mantle source 3He/4He >10.3RA (and potentially up to 26RA, similar to Galápagos hotspot lavas) markedly greater than the upper mantle range (8 ± 1RA). Lava geochemistry (Pb isotopes, Nb/U, and Ce/Pb) and geophysical constraints show that high 3He/4He values in central Panama are likely derived from the infiltration of a Galápagos plume–like mantle through a slab window that opened ∼8 Mya. Two potential transport mechanisms can explain the connection between the Galápagos plume and the slab window: 1) sublithospheric transport of Galápagos plume material channeled by lithosphere thinning along the Panama Fracture Zone or 2) active upwelling of Galápagos plume material blown by a “mantle wind” toward the CAM. We present a model of global mantle flow that supports the second mechanism, whereby most of the eastward transport of Galápagos plume material occurs in the shallow asthenosphere. These findings underscore the potential for lateral mantle flow to transport mantle geochemical heterogeneities thousands of kilometers away from plume conduits.

In 2017, fluid and gas samples were collected across the Costa Rican Arc. He and Ne isotopes, C isotopes as well as total organic and inorganic carbon concentrations were measured. The samples (n = 24) from 2017 are accompanied by (n = 17) samples collected in 2008, 2010 and 2012. He-isotopes ranged from arc-like (6.8 RA) to crustal (0.5 RA). Measured dissolved inorganic carbon (DIC) δ13CVPDB values varied from 3.55 to −21.57‰, with dissolved organic carbon (DOC) following the trends of DIC. Gas phase CO2 only occurs within ~20 km of the arc; δ13CVPDB values varied from −0.84 to −5.23‰. Onsite, pH, conductivity, temperature and dissolved oxygen (DO) were measured; pH ranged from 0.9–10.0, conductivity from 200–91,900 μS/cm, temperatures from 23–89 °C and DO from 2–84%. Data were used to develop a model which suggests that ~91 ± 4.0% of carbon released from the slab/mantle beneath the Costa Rican forearc is sequestered within the crust by calcite deposition with an additional 3.3 ± 1.3% incorporated into autotrophic biomass., Measurement(s)temperature of air • pH • Total Organic Carbon • carbon-13 atom • dissolved inorganic carbon content • dissolved organic carbon content • carbon dioxide • helium-3 atom • helium-4 atom • methaneTechnology Type(s)Temperature Probe Device • pH sensor • mass spectrometerFactor Type(s)time • location where data was collectedSample Characteristic - Environmentvolcanic arc • fumarole • hot spring • seepSample Characteristic - LocationCosta Rica Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.10293350