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A long-term record of global mean surface temperature (GMST) provides critical insight into the dynamical limits of Earth’s climate and the complex feedbacks between temperature and the broader Earth system. Here, we present PhanDA, a reconstruction of GMST over the past 485 million years, generated by statistically integrating proxy data with climate model simulations. PhanDA exhibits a large range of GMST, spanning 11° to 36°C. Partitioning the reconstruction into climate states indicates that more time was spent in warmer rather than colder climates and reveals consistent latitudinal temperature gradients within each state. There is a strong correlation between atmospheric carbon dioxide (CO₂) concentrations and GMST, identifying CO₂as the dominant control on variations in Phanerozoic global climate and suggesting an apparent Earth system sensitivity of ~8°C. 

Abstract We present an updated set of Carboniferous Sr, C and O isotope stratigraphies based on the existing literature, given the importance of chemostratigraphy for stratigraphic correlation in the Carboniferous. The Carboniferous⁸⁷Sr/⁸⁶Sr record, constructed using brachiopods and conodonts, exhibits five first-order phases beginning with a rapid decline from a peak value ofc.0.70840 at the Devonian–Carboniferous boundary to a trough (0.70776–0.70771) in the Visean followed by a rise to a plateau (c.0.70827) in the upper Bashkirian. A decline toc.0.70804 follows from the lowermost Gzhelian to the close of the Carboniferous. Contemporaneous carbonate δ¹³C records exhibit considerable variability between materials analysed and by region, although pronounced excursions (e.g. the mid-Tournaisian positive excursion and the end-Kasimovian negative excursion) are present in most records. Bulk carbonate δ¹³C records from South China and Europe, however, are generally consistent with those of brachiopod calcite from North America in terms of both absolute values and trends. Both brachiopod calcite and conodont phosphate δ¹⁸O document large regional variability, confirming that Carboniferous δ¹⁸O records are invalid for precise stratigraphic correlation. Nevertheless, significant positive δ¹⁸O shifts in certain intervals (e.g. mid-Tournaisian and the Mississippian–Pennsylvanian transition) can be used for global correlation. 

Paleosols represent fossil records of paleolandscape processes, paleobiotic interactions with the land surface, and paleoclimate. Paleosol-based reconstructions have figured prominently in the study of significant changes in global climate and terrestrial life, with one of the more highly studied examples being the end-Permian extinction (EPE). The EPE was once thought to consist of synchronous extinctions in the marine realm and the terrestrial realm, with the latter displaying a lower magnitude extinction of vertebrate, insect, and plant life. However, emerging stratigraphic records, anchored by high-precision U–Pb ages, and compilations of fossil taxa indicate that the terrestrial realm on Gondwana experienced an asynchronous extinction record with the marine realm; and, at the global-scale, possibly the lack of a true mass extinction for plant and vertebrate communities. Moreover, paleosol-based interpretations of the EPE on Gondwana typically focus on one depositional basin and extrapolate those finding to assess the potential for global paleoenvironmental/paleoclimatic change. This review compiles observations of paleosols, sedimentology, stratigraphy, and geochemical data across Gondwana during the Late Permian in order to critically assess these interpretations of global change in the lead up to the EPE. 

Paleo-CO2 reconstructions are integral to understanding the evolution of Earth system processes and their interactions given that atmospheric-CO2 concentrations are intrinsically linked to planetary function. In this talk, we use several case studies, spanning the 3 Phanerozoic Eras, to illustrate the potential of paleo-CO2 records to constrain the magnitude and state-dependency of equilibrium climate sensitivity, to advance our understanding of global biogeochemical cycles, to test the sensitivity of Earth System modeled atmospheric and oceanic circulation to PCO2 over a range of climate states, and to interrogate ecosystem—CO2—climate linkages and physiological responses to CO2. Further advances in these areas, however, are dependent on how well we ‘know’ paleo-CO2 estimates. CO2 estimates exist for much of the past half-billion years, but the degree to which the accuracy and precision of these estimates are constrained is quite variable, leading to substantial uncertainty and inconsistency in paleo-CO2 estimates. Potential sources of this uncertainty and inconsistency include an incomplete understanding of how environmental and ecophysiological conditions and processes imprint the CO2 proxy signals we measure, of the sensitivity of the CO2 estimates to this uncertainty, and differences in approaches to assigning uncertainties to CO2 estimates, among other factors. Application of newly established screening criteria, defined as part of an effort to improve our understanding of how atmospheric CO2 has varied through the Cenozoic, illustrates how the majority of pre-Cenozoic estimates are unreliable in their current form. To address these issues and to advance paleo-CO2 reconstruction, we introduce CO2PIP, a new community-scale project that takes a two-step approach to building the next generation Phanerozoic-CO2 record. Collective efforts are modernizing existing terrestrial-based CO2 estimates through additional analyses, measurements and proxy system modeling to constrain critical parameters used to estimate paleo-CO2. A set of forward proxy system models being developed in collaboration with the CO2 community, will provide a quantified representation of proxy sensitivities to environmental and ecophysiological conditions and processes that govern the CO2 signals. Ultimately, statistical inversion analysis of the simulated and modernized proxy datasets will be used to revise individual CO2 records and to build a new integrated model-data-constrained CO2 record for the Phanerozoic. 

Reconstructions of ancient ocean chemistry are largely based on geochemical proxies obtained from epicontinental seas. Mounting evidence suggests that these shallow inland seas were chemically distinct from the nearby open ocean, decoupling epicontinental records from broader ocean conditions. Here we use the isotope-enabled Community Earth System Model to evaluate the extent to which the oxygen isotopic composition of the late Carboniferous epicontinental sea, the North American Midcontinent Sea (NAMS), reflects the chemistry of its open-ocean sources and connect epicontinental isotope variability in the sea to large-scale ocean-atmosphere processes. Model results support estuarine-like circulation patterns demonstrated by past empirical studies and suggest that orographic runoff produced decreases in surface seawater δ18O (δ18Ow) of up to ∼3between the NAMS and the bordering ocean. Simulated sea surface temperatures are relatively constant across the sea and broadly reproduced from proxy-based δ18O paleotemperatures for which model-based values of epicontinental δ18Oware used, indicating that offshore-onshore variability in surface proxy δ18O is primarily influenced by seawater freshening. Simulated bottom water temperatures in the NAMS are also reproduced from biogenic calcite δ18O using model-based values of epicontinental δ18Ow, suggesting that benthic marine fossil δ18O is also influenced by seawater freshening and coastal upwelling. In addition, glacial-interglacial variations in nearshore seawater freshening counteract the effects of temperature on marine biogenic δ18O values, suggesting that salinity effects should be considered in δ18O-based estimates of glacioeustatic sea level change from nearshore regions of the NAMS. Our results emphasize the importance of constraining epicontinental dynamics for interpretations of marine biogenic δ18O as proxies of paleotemperature, salinity, and glacioeustasy. 

In the southwestern United States, California (CA) is one of the most climatically sensitive regions given its low (≤250 mm/year) seasonal precipitation and its inherently variable hydroclimate, subject to large magnitude modulation. To reconstruct past climate change in CA, cave calcite deposits (stalagmites) have been utilized as an archive for environmentally sensitive proxies, such as stable isotope compositions (δ¹⁸O, δ¹³C) and trace element concentrations (e.g., Mg, Ba, Sr). Monitoring the cave and associated surface environments, the chemical evolution of cave drip-water, the calcite precipitated from the drip-water, and the response of these systems to seasonal variability in precipitation and temperature is imperative for interpreting stalagmite proxies. Here we present monitored drip-water and physical parameters at Lilburn Cave, Sequoia Kings Canyon National Park (Southern Sierra Nevada), CA, and measured trace element concentrations (Mg, Sr, Ba, Cu, Fe, Mn) and stable isotopic compositions (δ¹⁸O, δ²H) of drip-water and for calcite (δ¹⁸O) precipitated on glass substrates over a two-year period (November 2018 to February 2021) to better understand how chemical variability at this site is influenced by local and regional precipitation and temperature variability. Despite large variability in surface temperatures and precipitation amount and source region (North Pacific vs. subtropical Pacific), Lilburn Cave exhibits a constant cave environment year-round. At two of the three sites within the cave, drip-water δ¹⁸O and δ²H are influenced seasonally by evaporative enrichment. At a third collection site in the cave, the drip-water δ¹⁸O responds solely to precipitation δ¹⁸O variability. The Mg/Ca, Ba/Ca, and Sr/Ca ratios are seasonally responsive to prior calcite precipitation at all sites but minimally to water-rock interaction. Lastly, we examine the potential of trace metals (e.g., Mn²⁺and Cu²⁺as a geochemical proxy of recharge and find that variability in their concentrations has high potential to denote the onset of the rainy season in the study region. The drip-water composition is recorded in the calcite, demonstrating that stalagmites from Lilburn Cave, and potentially more regionally, could record seasonal variability in weather even during periods of substantially reduced rainfall. 

Fjords are glacially carved estuaries that profoundly influence ice-sheet stability by draining and ablating ice. Although abundant on modern high-latitude continental shelves, fjord-network morphologies have never been identified in Earth’s pre-Cenozoic glacial epochs, hindering our ability to constrain ancient ice-sheet dynamics. We show that U-shaped valleys in northwestern Namibia cut during the late Paleozoic ice age (LPIA, ca. 300 Ma), Earth’s penultimate icehouse, represent intact fjord-network morphologies. This preserved glacial morphology and its sedimentary fill permit a reconstruction of paleo-ice thicknesses, glacial dynamics, and resulting glacio-isostatic adjustment. Glaciation in this region was initially characterized by an acme phase, which saw an extensive ice sheet (1.7 km thick) covering the region, followed by a waning phase characterized by 100-m-thick, topographically constrained outlet glaciers that shrank, leading to glacial demise. Our findings demonstrate that both a large ice sheet and highland glaciers existed over northwestern Namibia at different times during the LPIA. The fjords likely played a pivotal role in glacier dynamics and climate regulation, serving as hotspots for organic carbon sequestration. Aside from the present-day arid climate, northwestern Namibia exhibits a geomorphology virtually unchanged since the LPIA, permitting unique insight into this icehouse.