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A late Carboniferous to early Permian carbonate and evaporite succession from the Finnmark Platform (southern Barents Sea) contains nodules of anhydrite partially to fully replaced by calcite spar and native sulfur genetically linked to hydrocarbon migration and/or oxidation, analogous to processes observed in salt diapir caprocks in the Gulf of Mexico. In situ U-Pb dating of this calcite spar therefore has the potential to directly date hydrocarbon migration and provide further insight into the geochemical and temperature conditions during this event when coupled with traditional stable and clumped isotope ratios (δ13C, δ18O, and Δ47). Results indicate calcite formed ca. 50-15 Ma, postdating host-rock deposition by 250-285 m.y. Strongly negative δ13C values in the calcite spar (mean = -15‰) are consistent with a major contribution of carbon from hydrocarbons, and Δ47 paleothermometry indicates a mean precipitation temperature of 46 ± 11 °C. These geochemical results are consistent with the local burial history and suggest protracted hydrocarbon migration and/or oxidation and caprock formation spanning ~35 m.y. [ABSTRACT FROM AUTHOR]

Atmospheric CO2 possibly doubled during Oceanic Anoxic Event (OAE) 1a, likely in response to submarine volcanic outgassing. Despite being important for our understanding of the consequences of carbon cycle perturbations, the response of the climate system to this increase in greenhouse forcing is poorly constrained. Here we provide a new sea-surface temperature (SST) record from the mid-latitude proto-North Atlantic based on the organic geochemical TEX86 paleothermometer. Using different calibrations, including the newly developed Bayesian Spatially-varying Regression (BAYSPAR) deep-time analogue approach, we demonstrate that SSTs increased by ∼2-4 °C during OAE 1a and decreased by ∼4-6 °C at its end, both simultaneous with changes in δ13Corg, which we argue reflects changes in pCO2. We demonstrate that a clear latitudinal SST gradient prevailed during OAE 1a, contrary to the generally accepted view that a nearly flat SST gradient existed during OAE 1a and the Early Cretaceous. These results are more consistent with climate model simulations of the Cretaceous that have failed to produce flat SST gradients. [ABSTRACT FROM AUTHOR]

Abrupt and short-lived "impact winter" conditions have commonly been implicated as the main mechanism leading to the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (ca. 66 Ma), marking the end of the reign of the non-avian dinosaurs. However, so far only limited evidence has been available for such a climatic perturbation. Here we perform high-resolution TEX86 organic paleothermometry on three shallow cores from the New Jersey paleoshelf, (northeastern USA) to assess the impact-provoked climatic perturbations immediately following the K-Pg impact and to place these short-term events in the context of long-term climate evolution. We provide evidence of impact-provoked, severe climatic cooling immediately following the K-Pg impact. This so-called "impact winter" occurred superimposed on a long-term cooling trend that followed a warm phase in the latest Cretaceous. [ABSTRACT FROM AUTHOR]

Carbonate clumped isotope paleothermometry is a promising method for paleoclimate reconstructions and understanding diagenetic processes, although clumped isotope compositions (measured as Δ47 values) can be altered by recrystallization and thermal resetting. Several studies have investigated the effects of deep burial and exhumation on Δ47 values; we present Δ47 values of samples from an ~4500-m-long drill core from Andros Island, Bahamas, which represent the spectrum from shallow to deep burial conditions. These limestones and dolomites originally formed under near-surface temperature conditions, which are reflected by ~27 °C Δ47 temperatures in samples buried to <~1.3 km depth. Below this depth, calculated Δ47 temperatures increase by ~10 °C, indicating a shift from preserved near-surface temperatures to diagenetically modified values. Importantly, this shift is not accompanied by a change in δ18O and δ13C values or cathodoluminescence, and non-uniform micrometer-scale crystallization is observed in both Δ47-altered and unaltered rocks. Similar Δ47 temperatures recorded by each carbonate phase suggest that mineral-specific differences are minor. Finegrained dolomites and calcites are viable materials for recording surface temperature conditions, and both are susceptible to alteration of their primary clumped isotope abundances during burial diagenesis. Our results demonstrate that original Δ47 values of fine-grained carbonates can be altered under mild diagenetic conditions. [ABSTRACT FROM AUTHOR]

The Cretaceous-Paleogene (K-Pg) mass extinction has been attributed to the impact of a large bolide at the end of the Cretaceous Period, although other potential causes have also been proposed, most notably climate change caused by Deccan Traps (India) flood volcanism. Reconstructing paleoclimate, particularly in terrestrial settings, has been hindered by a lack of reliable proxies. The recent development of carbonate clumped isotope paleothermometry has contributed to temperature reconstructions using geochemical proxies in terrestrial settings. We employ this method, along with new stratigraphic constraints, in the Hell Creek (Cretaceous) and overlying Fort Union (Paleogene) Formations (Montana, USA) to examine changes in temperature leading to and across the K-Pg boundary. We demonstrate that well-preserved ca. 66 Ma aragonitic bivalves serve as suitable paleoclimate archives. Although there are limitations in the stratigraphic availability of fossil bivalves for clumped isotope analysis, we record an apparent 8 °C decrease in summer temperatures over the last 300 k.y. of the Cretaceous that corresponds broadly with patterns observed in other paleotemperature proxies. This observed decrease plausibly could be explained by an absolute temperature decrease or by other environmental stresses on the organisms, but in either case suggests changing living conditions over the interval. Previously documented declines in vertebrate and invertebrate biodiversity occur over the same stratigraphic interval at this study location. These results are consistent with published models of the end- Cretaceous mass extinction in which destabilized ecosystems become more susceptible to an abrupt event like a bolide impact. [ABSTRACT FROM AUTHOR]

Understanding how global temperature changes with increasing atmospheric greenhouse gas concentrations, or climate sensitivity, is of central importance to climate change research. Climate models provide sensitivity estimates that may not fully incorporate slow, long-term feedbacks such as those involving ice sheets and vegetation. Geological studies, on the other hand, can provide estimates that integrate long- and short-term climate feedbacks to radiative forcing. Because high latitudes are thought to be most sensitive to greenhouse gas forcing owing to, for example, ice-albedo feedbacks, we focus on the tropical Pacific Ocean to derive a minimum value for long-term climate sensitivity. Using Mg/Ca paleothermometry from the planktonic foraminifera Globigerinoides ruber from the past 500 k.y. at Ocean Drilling Pro- gram (ODP) Site 871 in the western Pacific warm pool, we estimate the tropical Pacific climate sensitivity parameter (λ) to be 0.94-1.06 °C (W m-2)-1, higher than that predicted by model simulations of the Last Glacial Maximum or by models of doubled greenhouse gas concentration forcing. This result suggests that models may not yet adequately represent the long- term feedbacks related to ocean circulation, vegetation and associated dust, or the cryosphere, and/or may underestimate the effects of tropical clouds or other short-term feedback processes. [ABSTRACT FROM AUTHOR]

The Arctic region is subject to a great amplitude of climate variability and is currently undergoing large-scale changes due in part to anthropogenic global warming. Accurate projections of future change depend on anticipating the response of the Arctic climate system to forcing, and understanding how the response to human forcing will interact with natural climate variations. The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal- to multidecadal-scale record of summer temperature for the past 1800 yr from lake sediments of Kongressvatnet on West Spitsbergen, Svalbard, based on the fi rst instrumental calibration of the alkenone paleothermometer. The age model for the High Arctic lake sediments is based on 210Pb, plutonium activity, and the fi rst application of tephrochronology to lake sediments in this region. We fi nd that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18th and 19th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent. Our results suggest that increased wintertime precipitation, rather than cold temperatures, was responsible for LIA glaciations on Svalbard and that increased heat transport into the Arctic via the West Spitsbergen Current began ca. A.D. 1600. [ABSTRACT FROM AUTHOR]

Investigates the deep-sea paleotemperature record of extreme warmth during the Cretaceous in the North Atlantic Ocean. Analysis of oxygen isotope of foraminifera; Estimation on the paleotemperature of correlative middle bathyal foraminifera; Comparison between the global bottom-water temperatures and latitudinal thermal gradients.

Examines equatorial sea-surface temperatures during the Maastrichtian. Preservation of metastable carbonate; Paleothermometry; Implications; Sea-floor spreading; Tropical atmospheric and ocean dynamics.