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1. Looking upstream with clumped and triple oxygen isotopes of estuarine oyster shells in the early Eocene of California, USA

   https://doi.org/10.1130/G49634.1  

   Kelson, Julia R. ; Petersen, Sierra V. ; Niemi, Nathan A. ; Passey, Benjamin H. ; Curley, Allison N. ( April 2022 , Geology)

   The δ18O of carbonate minerals that formed at Earth’s surface is widely used to investigate paleoclimates and paleo-elevations. However, a multitude of hydrologic processes can affect δ18O values, including mixing, evaporation, distillation of parent waters, and carbonate growth temperatures. We combined traditional carbon and oxygen isotope analyses with clumped (Δ47) and triple oxygen isotopes (Δ′17O) analyses in oyster shells (Acutostrea idriaensis) of the Goler Formation in southern California (USA) to obtain insights into surface temperatures and δ18O values of meteoric waters during the early Eocene hothouse climate. The Δ47-derived temperatures ranged from 9 °C to 20 °C. We found a correlation between the δ18O of growth water (δ18Ogw) (calculated using Δ47 temperatures and δ18O of carbonate) and the δ13C values of shells. The Δ′17O values of shell growth waters (0.006‰–0.013‰ relative to Vienna standard mean ocean water–standard light Antarctic precipitation [VSMOW-SLAP]) calculated from Δ′17O of carbonate (–0.087‰ to –0.078‰ VSMOW-SLAP) were lower than typical meteoric waters. These isotopic compositions are consistent with oyster habitation in an estuary. We present a new triple oxygen isotope mixing model to estimate the δ18O value of freshwater supplying the estuary (δ18Ofw). The reconstructed δ18Ofw of –11.3‰ to –14.7‰ (VSMOW) is significantly lower than the δ18Ogw of –4.4‰ to –9.9‰ that would have been calculated using “only” Δ47 and δ18O values of carbonate. This δ18Ofw estimate supports paleogeographic reconstructions of a Paleogene river fed by high-elevation catchments of the paleo–southern Sierra Nevada. Our study highlights the potential for paired Δ47 and Δ′17O analyses to improve reconstructions of meteoric water δ18O, with implications for understanding ancient climates and elevations. 

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2. The CoralHydro2K Database: a global, actively curated compilation of coral d18O and Sr/Ca proxy records of tropical ocean hydrology and temperature for the Common Era

   Walter, R. M. ( January 2023 , Earth system science data)

   The response of the hydrological cycle to anthropogenic climate change, especially across the tropical oceans, remains poorly understood due to the scarcity of long instrumental temperature and hydrological records. Massive shallow-water corals are ideally suited to reconstructing past oceanic variability as they are widely distributed across the tropics, rapidly deposit calcium carbonate skeletons that continuously record ambient environmental conditions, and can be sampled at monthly to annual resolution. Most coral-based reconstructions utilize stable oxygen isotope composition (δ18O) that tracks the combined change in sea surface temperature (SST) and the oxygen isotopic composition of seawater (δ18Osw), a measure of hydrologic variability. Increasingly, coral δ18O time series are paired with time series of strontium-to-calcium ratios (Sr / Ca), a proxy for SST, from the same coral to quantify temperature and δ18Osw variability through time. To increase the utility of such reconstructions, we present the CoralHydro2k database: a compilation of published, peer-reviewed coral Sr / Ca and δ18O records from the Common Era. The database contains 54 paired Sr / Ca-δ18O records and 125 unpaired Sr / Ca or δ18O records, with 88 % of these records providing data coverage from 1800 CE to present. A quality-controlled set of metadata with standardized vocabulary and units accompanies each record, informing the use of the database. The CoralHydro2k database tracks large-scale temperature and hydrological variability. As such, it is well-suited for investigations of past climate variability, comparisons with climate model simulations including isotope-enabled models – and application in paleo-data assimilation projects.The CoralHydro2k database will be available on the NOAA National Center for Environmental Information’s Paleoclimate data service with serializations in MATLAB, R, Python, and LiPD. 

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3. Dual carbonate clumped isotope (Δ47-Δ48) measurements constrain different sources of kinetic isotope effects and quasi-equilibrium signatures in cave carbonates

   https://doi.org/10.1016/j.gca.2023.11.017  

   Parvez, Zeeshan A. ; El-Shenawy, Mohammed I. ; Lucarelli, Jamie K. ; Kim, Sang-Tae ; Johnson, Kathleen R. ; Wright, Kevin ; Gebregiorgis, Daniel ; Montanez, Isabel P. ; Wortham, Barbara ; Asrat, Asfawossen ; et al ( February 2024 , Geochimica et Cosmochimica Acta)

   Cave carbonate minerals are an important terrestrial paleoclimate archive. A few studies have explored the potential for applying carbonate clumped isotope thermometry to speleothems as a tool for constraining past temperatures. To date, most papers utilizing this method have focused on mass-47 clumped isotope values (Δ47) at a single location and reported that cave carbonate minerals rarely achieve isotopic equilibrium, with kinetic isotope effects (KIEs) attributed to CO2 degassing. More recently, studies have shown that mass-47 and mass-48 CO2 from acid digested carbonate minerals (Δ47 and Δ48) can be used together to assess equilibrium and probe KIEs. Here, we examined 44 natural and synthetic modern cave carbonate mineral samples from 13 localities with varying environmental conditions (ventilation, water level, pCO2, temperature) for (dis)equilibrium using Δ47-Δ48 values, in concert with traditional stable carbon (δ13C) and oxygen (δ18O) isotope ratios. Data showed that 19 of 44 samples exhibited Δ47-Δ48 values indistinguishable from isotopic equilibrium, and 18 (95 %) of these samples yield Δ47-predicted temperatures within error of measured modern temperatures. Conversely, 25 samples exhibited isotopic disequilibria, 13 of which yield erroneous temperature estimates. Within some speleothemsamples, we find Δ47-Δ48 values consistent with CO2 degassing effects, however, the majority of sampleswith KIEs are consistent with other processes being dominant. We hypothesize that these values reflect isotopicbuffering effects on clumped isotopes that can be considerable and cannot be overlooked. Using a Raleigh Distillation Model, we examined carbon and oxygen isotope exchange trajectories and their relationships with dual clumped isotope disequilibria. Carbon isotope exchange is associated with depletion of both Δ47 and Δ48 relative to equilibrium, while oxygen isotope exchange is associated with enrichment of both Δ47 and Δ48 relative to equilibrium. Cave rafts collected from proximate locations in Mexico exhibit the largest averagedepartures from equilibrium (ΔΔ47 = − 0.032 ± 0.007, ΔΔ48 = − 0.104 ± 0.035, where ΔΔi is the measured value – the equilibrium value). This study shows how the Δ47-Δ48 dual carbonate clumped isotope framework can be applied to a variety of tcave carbonate mineral samples, enabling identification of isotopic equilibria and therefore quantitative application of clumped isotope thermometry for paleoclimate reconstruction, or alternatively, constraining the mechanisms of kinetic effects. 

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4. Compilation of a database of Holocene nearshore marine mollusk shell geochemistry from the California Current System

   https://doi.org/10.5194/essd-14-1695-2022  

   Palmer, Hannah M. ; Padilla Vriesman, Veronica ; Banker, Roxanne M. ; Bean, Jessica R. ( January 2022 , Earth System Science Data)

   Abstract. The shells of marine invertebrates can serve as high-resolution records ofoceanographic and atmospheric change through time. In particular, oxygen andcarbon isotope analyses of nearshore marine calcifiers that grow byaccretion over their lifespans provide seasonal records of environmental andoceanographic conditions. Archaeological shell middens generated byIndigenous communities along the northwest coast of North America containshells harvested over multiple seasons for millennia. These shell middens,as well as analyses of archival and modern shells, have the potential toprovide multi-site, seasonal archives of nearshore conditions throughout theHolocene. A significant volume of oxygen and carbon isotope data fromarchaeological shells exist, yet they are separately published in archaeological,geochemical, and paleoceanographic journals and have not been comprehensivelyanalyzed to examine oceanographic change over time. Here, we compiled adatabase of previously published oxygen and carbon isotope data fromarchaeological, archival, and modern marine mollusks from the CaliforniaCurrent System (North American coast of the northeast Pacific, 32 to55∘ N). This database includes oxygen and carbon isotope data from 598modern, archaeological, and sub-fossil shells from 8880 years before present(BP) to the present, from which there are 4917 total δ13C and7366 total δ18O measurements. Shell dating and samplingstrategies vary among studies (1–345 samples per shell, mean 44.7 samplesper shell) and vary significantly by journal discipline. Data are fromvarious bivalves and gastropod species, with Mytilus spp. being the most commonlyanalyzed taxon. This novel database can be used to investigate changes innearshore sea surface conditions including warm–cool oscillations, heatwaves, and upwelling intensity, and it provides nearshore calcium carbonateδ13C and δ18O values that can be compared to thevast collections of offshore foraminiferal calcium carbonate δ13C and δ18O data from marine sediment cores. Byutilizing previously published geochemical data from midden and museumshells rather than sampling new specimens, future scientific research canreduce or omit the alteration or destruction of culturally valued specimensand sites. The dataset is publicly available through PANGAEA athttps://doi.org/10.1594/PANGAEA.941373 (Palmer et al.,2021). 

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5. Data report: Cenozoic and Upper Cretaceous bulk carbonate stable carbon and oxygen isotopes from IODP Expedition 369 Sites U1513, U1514, and U1516 in the southeast Indian Ocean

   https://doi.org/10.14379/iodp.proc.369.206.2022  

   Edgar, K.M. ; MacLeod, K.G. ; Hasegawa, T. ; Hanson, E.M. ; Boomer, I. ; Kirby, N. ( May 2022 , Proceedings of the International Ocean Discovery Program)

   International Ocean Discovery Program (IODP) Expedition 369 recovered pelagic sediments spanning the Albian to Pleistocene at Sites U1513, U1514, and U1516. The cores provide an opportunity to determine paleoclimatic and paleoceanographic dynamics from a hitherto poorly sampled mid-high-latitude location across an ~110 My interval, beginning during the Cretaceous supergreenhouse when eastern Gondwana was still largely assembled and ending during the modern icehouse climate after the final breakup of Gondwana. Here we present ~650 bulk carbonate carbon and oxygen stable isotope data points and plot them alongside shipboard data sets to present a first broad documentation of chemostratigraphic data that reveal the stratigraphic position of key climatic transitions and events at Sites U1513, U1514, and U1516. These records show a pronounced long-term δ13C decrease and δ18O increase from the Albian/Cenomanian through the Pleistocene. Superimposed on this long-term trend are transient δ13C and δ18O events correlated with Oceanic Anoxic Event 2, peak Cretaceous warmth during the Turonian, Santonian to Maastrichtian cooling, the Cretaceous/Paleogene boundary, the Paleocene/Eocene Thermal Maximum, the Early Eocene Climatic Optimum, the Middle Eocene Climatic Optimum, and the Eocene–Oligocene transition. Recognizing these isotopic events confirms and refines shipboard interpretations and, more importantly, demonstrates the suitability of Sites U1513, U1514, and U1516 for future high-resolution paleoceanographic works aimed at illuminating the links between tectonic and oceanographic dynamics and global versus local environmental changes. 

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