In the Colville Foreland Basin of Arctic Alaska, non-skeletal carbonates rarely occur in Mesozoic and Cenozoic strata. However, glendonites and other cold-water authigenic carbonates are found at specific intervals within the basin fill, forming a unique archive of geochemical, environmental, and climatic conditions at the time of precipitation. New discoveries of glendonites in Lower Cretaceous strata (informal pebble shale unit and Kuparuk Formation), with ages constrained by biostratigraphy and/or nearby ash Isotope Dilution Thermal Ionization Mass Spectrometry (ID-TIMS) zircon dates, provide evidence of cold temperatures during an overall hothouse interval. These occurrences are generally coeval with others previously described elsewhere in the Arctic, supporting the ‘cold snap’ model for early Cretaceous paleoclimate. In younger (Oligocene–Miocene) strata at Carter Creek, newly acquired clumped isotope (Δ47 and Δ48) data from glendonites yield cold paleotemperatures (generally 0–6° C), demonstrating that well-preserved specimens can record quantitative environmental information even after the transformation from ikaite to more stable forms of calcium carbonate. Further, Carter Creek glendonites (δ13C values typically -20 to less than -40‰ Vienna Peedee Belemnite standard) also occur in association with isolated pods of authigenic fine-grained carbonate sediments, which contain evidence of a unique macrofauna and are characterized by isotopically light carbon. These deposits are therefore interpreted as being associated with ancient methane seeps, which may be related to warming following the Mi-1 glaciation circa 24 Ma, with glendonite growth taking place during shorter ‘cold snaps’ within this interval. This occurrence adds additional evidence to the previously hypothesized linkages between glendonites and methane and between seep carbonates and deglaciation and potentially documents an active petroleum system in the Miocene of the Alaska North Slope. Thus, the glendonite examples described here and their sedimentary context allow for new aspects of the basin’s history to be ascertained in a way not possible with other types of sedimentary deposits.

The last interglacial (LIG) is the last time global climate was about as warm as today, with global sea-levels several metres higher. The LIG probably had a reduced latitudinal temperature gradient, with warmer poles and cooler tropics than today. Well-constrained records from low latitudes can test this overall model. We used bivalve shells sampled from six localities thought to expose the LIG age Cockburn Town Member of the Grotto Beach Formation on both San Salvador and Great Inagua Islands, The Bahamas. Previous work described two LIG depositional intervals: older 'Reef I' and younger 'Reef II', separated by a disconformity. New amino acid racemisation (AAR) data were used to date each locality in this context and clumped isotope palaeothermometry was used to reconstruct LIG temperatures and the isotopic composition of sea water. AAR data are described from six sites: four with similar AAR values to the well-dated Reef II Cockburn Town site, one Reef I age site on Great Inagua and one distinctly younger outcrop on San Salvador previously thought to be LIG age that may be MIS 5a. All LIG shells record cooler than modern conditions. The Delta(47) thermometry shows that the Reef I-age shell population preserves the warmest mean temperature (25 +/- 2 degrees C) and most positive water delta O-18 values (+0.7 +/- 0.4 parts per thousand) across all sites. This contrasts with cool mean temperatures (similar to 21-23 degrees C) and fresher water delta O-18 values (-0.5 to +0.6 parts per thousand) found from Reef II populations. Regional glacial isostatic adjustment through the LIG would have resulted in peak sea levels that post-dated peak LIG temperatures. It is suggested that apparent cooler temperatures of Reef II do not reflect peak LIG temperatures but instead document the beginning of cooling into MIS 5d. Comparison with Delta(47) data from Bermuda supports a reduced latitudinal gradient throughout the LIG.

Study of the accretionary biomineralised hardparts of organisms (sclerochronology) can make a useful contribution to palaeoclimatology. Ontogenetic sequences of isotopic data (518O and X 47 values) from the shells of marine molluscs are a source of information on seasonal sea-surface temperatures that can be used for detailed and rigorous evaluation of the outputs of numerical climate models. In situations where there is significant seasonality, and where shell preservation is adequate, accurate information about winter and summer surface temperature can be obtained from shallow-water benthic forms (bivalves and gastropods), in particular the early ontogeny of fast-growing species. Accurate information about winter surface temperature can also be obtained from individuals that lived at mid-shelf depths (20-40 m), but summer seafloor values from these need upward adjustment to derive a plausible surface temperature if thermal stratification of the water column occurs in this season. Ontogenetic 5 18 O profiles from planktonic pteropod gastropods are a potential source of insight into seasonal surface temperatures in the ocean basins; these organisms merit investigation for provision of information to complement shelf data. Temperature profiles constructed from shell 5 18 O require an estimate of the 5 18 O value of ambient seawater, which can be derived by back-calculation from the X 47-temperature supplied by the same shell material. Alternatively, through appropriate sampling and data processing, seasonal temperatures can be obtained directly from X 47 profiles. Climate parameters are defined in terms of the mean state over a period of 30 consecutive years, a statistic (e.g., for seasonal temperatures) which can be derived from the long isotopic temperature records obtainable from bivalve species that live for many tens or hundreds of years. Efforts should be made to acquire such records, especially averaged data from crossdated shells, to specify climate parameters for precise times in the past. Information for precise times would be of particular value for icehouse intervals like the late Cenozoic, characterised by high frequency (high amplitude) climate fluctuation. Short records from noncrossdated shells can nevertheless provide useful insights into climate, particularly if a large dataset is obtained, supplying a reliable picture of the mean state and range of variation in climate parameters over the interval represented by the shells.

The clumped isotope paleothermometer (Delta 47) has been used to reconstruct temperatures from various biogenic carbonate archives. Calibration studies demonstrate that some biogenic carbonates precipitate in Delta 47 equilibrium and record growth temperatures accurately (e.g., many bivalve mollusks), while others appear to exhibit disequilibrium, or 'vital', effects and yield isotopically reconstructed temperatures that are biased (e.g., shallowwater corals). These studies have largely excluded marine gastropods, so it is not known whether they tend to precipitate their shells in or out of isotopic equilibrium. In this study, we present seasonal-scale delta 18O and seasonally targeted Delta 47 and Delta 48 measurements from modern marine gastropods representing 8 genera and 10 species, reconstructing apparent growth temperatures and screening for equilibrium precipitation. We find that most marine gastropods appear to precipitate in Delta 47 and Delta 48 equilibrium and faithfully record environmental temperatures, making them suitable for Delta 47-paleothermometry. A few gastropods (Caviturritella/Turritella sp., Campanile symbolicum, Megastraea undosa) appear to precipitate out of Delta 47 equilibrium, though these disequilibrium signatures may partially be explained by differences between actual growth temperatures and instrumental calibration temperatures (Caviturritella/Turritella sp., M. undosa) or differences between inner and outer layer precipitation (C. symbolicum). We present new Delta 47-temperature data for 2 Middle Eocene Campanile giganteum fossils collected from the Paris Basin and discuss how to interpret the results in the context of our modern samples. Finally, in conducting this calibration we demonstrate paired Delta 47/Delta 48 as an effective tool to screen for disequilibrium precipitation in marine gastropods.

The isotopic composition of the outer shell layers (OSL) of fossil bivalves is commonly used to reconstruct paleotemperature and S18O of water. The inner shell layer (ISL) is generally avoided for these purposes because it may be more susceptible to biologically driven isotopic fractionations (BioDIFs). New tools (paired S18O-A47 and A47-A48 measurements) combining biological and geochemical theory can help us gain a deeper understanding of the physiological mechanisms causing these fractionations. Previous research suggests that distinct types of BioDIFs exist among different bivalve genera. However, the variability of BioDIF expression across species within a single genus or across natural environmental gradients has not been examined. We characterize the difference between ISL and OSL isotopic composition (AS18OISL-OSL, AS13CISL-OSL, AA47 ISL-OSL, AA48 ISL-OSL) in modern bivalve genera Dosinia spp. and Mactra spp. We sampled 12 species of genus Dosinia from four geographic regions and five species of genus Mactra (total n 1/4 33) from one of the regions. A47 and A48 values did not differ between shell layers for any species of these two genera, although a wide variety of AS18OISL-OSL and AS13CISL-OSL values were observed. We find that multiple species of the same genus from the same geographic area had the same type of BioDIF, but this can differ among groups from different geographic areas. Overall, these results confirm that BioDIFs are measurable in modern bivalves, show greater diversity than previously documented, and may be subject to a combination of environmental and phylogenetic controls.

Invertebrate macrofossils from the shallow, expansive Cretaceous Western Interior Seaway (WIS) of North America preserve a rich archive of climate and environmental information from a past greenhouse climate interval in their shell chemistry. The use of traditional oxygen isotope paleothermometry on WIS fossils has been thwarted by known but unquantified variations in the oxygen isotopic composition (518Ow) and salinity of seaway waters, interannually and also potentially subannually. Here, we present subannual-resolution clumped isotope (Delta 47) sclerochronology records from fossil Exogyra and Pycnodonte specimens (Ostreida) dating to the Cretaceous Thermal Maximum to estimate paleoseasonality in temperature and 518Ow in the mid-latitude WIS during this period of peak warmth. We demonstrate that 518Ocarb -based estimates consistently underestimate the mean annual range in temperature (MART) compared to T Delta 47-based estimates (MART = 2 to 17 degrees C vs. >14 to >23 degrees C) due to co-occurring changes in 518Ow. Subannual changes in 518Ow are positively correlated with subannual changes in temperature. T Delta 47-based estimates of MART are higher than most mid-latitude sites today. High MART estimates, combined with findings of subannual variations in 518Ow may both be the result of seasonal-scale circulation changes in the basin bringing northern vs. southern water masses to the mid-latitude study region. Alternatively, this data may also be explained by seasonal changes in freshwater delivery. Either scenario would likely have been accompanied by sizable salinity fluctuations. These suggestive seasonal water chemistry changes imply niche flexibility for the oysters in this study and may have been a limiting factor on faunal diversity in the seaway for stenohaline organisms.

High sea levels in the Late Cretaceous led to the formation of vast seaways on every continent. These shallow seaways are without modern analogs and many fundamental aspects of their oceanography are poorly understood. In the Campanian (similar to 83-72 Ma), the Western Interior Seaway (WIS) of North America linked the proto-Gulf of Mexico and Arctic Ocean. Given its shallow depth, freshwater inputs to the WIS could have had a greater influence on conditions in the seaway compared to a deeper ocean and would have become increasingly important as the WIS regressed through the Maastrichtian. The isotopic composition of mollusk shells in freshwater facies can help constrain the composition and temperature of these inputs, improving our understanding of surface temperature, hydrological dynamics, and paleoelevation. Here we measure Delta(47) temperature, delta O-18 water , and Sr-87/Sr-86 in late Campanian (similar to 75 Ma) unionid bivalve shells from fluvial and pond deposits near the western shore of the WIS (similar to 42 degrees N-56 degrees N). Sample mean surface water temperatures spanned 22-44 degrees C, with a mean of 30 +/- 2.7 degrees C. The latitudinal temperature gradient across this region is reduced compared to today, at similar to 7 degrees C across these 14 degrees of latitude based on stream sample means. These temperatures are outside the optimal growth conditions of modern unionids in North America, indicating a shift in niche. Following this finding, we recalculate delta O-18 water values from previously published delta O-18 carb values using new Delta(47) temperatures instead of assumed growth temperatures. Our findings support previous observations of a bimodal distribution in freshwater delta O-18 water values in this region although the absolute values shift higher. Spatial patterns of delta O-18 water are consistent with a Campanian Proto-North American Monsoon and the lowest delta O-18 water values we report are consistent with paleoelevation of >3500 m in the Proto-Cordillera. Sr-87/Sr-86 values broadly align with different facies, with more radiogenic values occurring in major trunk rivers draining the highlands and less radiogenic values in streams recharged by low-elevation precipitation. Predominance of a Sr-87/Sr-86 signature consistent with weathering Paleozoic carbonates could be consistent with seasonal increases in rock weathering associated with a monsoon.

Plio-Pleistocene sediments from the southwestern Florida Peninsula contain an extraordinary density and diversity of marine mollusk and vertebrate fossils which, collectively, document major faunal shifts on the Florida Platform through a period of profound environmental change. Systematic study of these fossil assemblages and the environments in which they lived has been limited, however, by: i) a lack of outcrop sections spanning the full PlioPleistocene stratigraphy of the region and ii) major uncertainties in correlation between previous study sites due to extreme lateral variability in coastal paleoenvironments. Here, we describe a new stratigraphic section from Florida Shell Quarry in Charlotte County, Florida, which contains fossil-rich deposits of each major Plio-Pleistocene unit in the area (the Tamiami, Caloosahatchee, Bermont, and Fort Thompson formations). Bulk sediment samples collected from 22 horizons were used to broadly characterize stratigraphic variations in lithology and faunal content. Predation intensity was estimated from drill-hole frequency among populations of the bivalve Chione spp. While all studied formations were mainly deposited under marine conditions, both lithologic and faunal facies shifts within the Caloosahatchee and Bermont units indicate periods of pronounced freshwater influence. Faunal diversity is relatively high in the Tamiami, Caloosahatchee, and Bermont units but declines in the Fort Thompson. Similarly, predation intensity is high in the Caloosahatchee and Bermont units but lower in the Fort Thompson at the sampled sites. In addition to characterizing changes in the local paleoenvironment, we propose a sequence stratigraphic model for the section based on inferred local sea-level fluctuations. We leverage this sequence stratigraphic framework to correlate the Florida Shell section with other studied sections in the Charlotte Harbor area. The development of this new site provides a workable basis for more detailed studies of the long-term paleoecological and paleoenvironmental evolution of southwestern Florida.

∆47 based clumped isotope thermometry has enabled reconstruction of Earth’s surface temperatures independent of the source of oxygen within the carbonate. It has been postulated that carbonate samples can contain contaminants that cause isobaric interferences, compromising measured ∆47 values and reconstructed temperatures. The exact nature of contaminants and isobaric interferents, however, largely remained unidentified. Here, we demonstrate that compromised measurements can be identified through high-precision analysis of ∆48 alongside ∆47. We provide evidence that nitrate constitutes a serious contaminant even if present in the carbonate in sub-wt-% quantities only. During phosphoric acid digestion of carbonates at 90°C, nitrate decomposes to NO2, which, in turn, is not effectively removed during subsequent purification of carbonate-derived CO2 using cryogenic traps and gas chromatography (packed Porapak Q column at -15°C). In dual clumped isotope space, samples affected by variable sub-ppm contributions of NO2 to CO2 plot along a characteristic slope of -0.3, in agreement with theoretical predictions. Nitrate contamination occurs in a synthetic calcite precipitated using Ca(NO3)2, a pedogenic carbonate nodule, a plasma-ashed echinoid spine, ETH-3 (a recently assigned anchor for ∆47 analysis of carbonates) and, presumably, in a bioapatite (Greenland shark dentine). The extent of NO2 generation may depend on analytical setup and additional parameters such as nitrate concentration inside the carbonate, acid digestion temperature, reaction time, filament current and filament age. Sequential bleaching tests reveal that nitrate contaminant can be effectively removed from carbonates if samples are pre-treated overnight with 3 wt-% sodium hypochlorite (NaOCl). Our high-precision long-term ∆47 (CDES 90) values for ETH-1 and ETH-2 (Bernecker et al., 2023) and for bleached ETH-3 exactly confirm recently assigned ∆47-I-CDES values for these standards. Unless independent evidence is given that NO2 contamination is irrelevant for a specific analytical setup we strongly recommend that ETH-3 is bleached with 3 wt-% NaOCl overnight in order to enable accurate projection of raw data to the I-CDES. Moreover, systematic bleaching tests should be carried out on unknown samples in order to avoid any isotopic bias.

The islands of Bermuda preserve carbonates from several glacial and interglacial intervals with demonstrated potential for reconstructing past North Atlantic climate. Here, we describe new clumped and conventional stable isotope data from Dendostrea (oyster) shells collected from a Last Interglacial / Marine Isotope Stage 5e (MIS 5e) deposit. Interpretation of these and past data is supported by new amino acid racemization age dating results from nine localities around Bermuda.We find that the fossil oyster population on Verrill Island (within the present Great Sound of Bermuda) records MIS 5e temperatures and water δ18O values that are similar to modern. These data contrast with the much cooler temperatures and lighter reconstructed water δ18O values reconstructed for sites on the southern shore. This contrast may in part be due to timing, with the Verrill Island deposit plausibly representing an earlier and warmer portion of MIS 5e. The data also reflect meaningful, highly local differences in environment, with modern Great Sound shells perhaps living in partially restricted waters buffered from cooler and groundwater-influenced conditions along the South Shore. The mobility of Cittarium pica marine snails used in previous work likely also introduces exaggerated variability in those cases. Critically, incorporation of clumped isotope data across multiple sites and genera enables an understanding of Bermudian MIS 5e climate that would be meaningfully different if given data from only one site. We seek to illustrate both the complexities and potential of working with clumped isotope paleoclimate data from coastal deposits.

Since the mid-1970s, groundwater resources in Bermuda have been explored to supplement growing potable water demand on the island. Much of this work has focused on modeling the shape and size of freshwater lenses beneath the island’s surface, mainly the Devonshire Lens. Less attention has been paid to how these freshwater lenses interact with surrounding coastal seawater, a process that may grow in importance as sea levels rise. Due to isotopic differences between aquifer water and seawater, these interactions can be tracked using the oxygen isotopic composition of water (δ18Ow) samples collected from coastal and subterranean areas. A pilot study found more temporal variation in coastal seawater δ18Ow along Bermuda’s South Shore (the section of the coast closest to the Devonshire Lens) compared to elsewhere around the island and suggested that freshwater was discharging into coastal seawater from the Devonshire Lens in significant quantities. However, this study was limited by its small dataset so could not quantify the full spatial and temporal variability of δ18Ow in this area. Here, we present salinity and δ18Ow measurements from seawater samples collected around Bermuda and in wells tapping the Devonshire Lens on timescales ranging from hourly to monthly to better visualize the dynamic interaction between coastal seawater and aquifer-sourced freshwater. We find tight correlation between salinity and δ18Ow in well waters, indicating a simple linear mixing relationship between seawater and aquifer water in the subsurface. We confirm previous findings of larger variability in δ18Ow along the South Shore compared to elsewhere and relate observed changes to tidal height on hourly to monthly timescales. Surprisingly, South Shore seawater salinity does not vary in accordance with δ18Ow, implying additional mechanisms, such as the addition of salt spray, must be acting to mute salinity changes. These findings also demonstrate the potential in using δ18Ow to study submarine groundwater discharge, as salinity measurements alone did not detect as much variability. As sea levels rise and interactions between ocean and aquifer waters change, coastal and well water δ18Ow measurements may be helpful in tracking these processes, and in particular, changes in aquifer size.

Turritellid gastropods are aragonitic marine mollusks that are particularly abundant and widespread in the fossil record. With fast growth rates and a shallow coastal habitat, the oxygen isotopic composition of their shells has the potential to be an excellent recorder of ancient subannual climate variation. To date, tests of the reliability of oxygen isotope paleothermometry in this family of gastropods have been restricted to a few localities. We produce 15 new high-resolution oxygen isotope profiles of modern turritellid shells, and combine these with 28 other published profiles from a range of latitudes and locations in order to investigate generalizable relationships between shell S18Ocarb and local climate data including temperature, precipitation, salinity, and S18Osw. We find that turritellids accurately record mean SST values using existing temperature-S18Ocarb relationships, but seasonal ranges in SST are frequently overestimated. Modern climate data from our study sites show correlations that can explain this overestimation through the following proposed mechanism: seasonal increases/decreases in rainfall lead to decreases/increases in local salinity and, by inference, S18Osw,amplifying the seasonal signal in S18Ocarb. We find that ignoring these seasonal variations in S18Oswcan significantly bias the calculation of seasonal temperature ranges from S18Ocarb profiles derived from turritellids. Similar processes may also affect sclerochronological records from other nearshore, shallow-water marine calcifiers.