Abstract Modern lake triple oxygen isotopes (17O-excess [Δ′17O], δ18O) can be used to distinguish flow-through from closed-basin systems and to quantitatively model precipitation composition and evaporative loss. Extending this framework to paleolake carbonates enables new hydrologic and climate reconstructions. For example, regional hydrologic models suggest that cold temperatures and reduced evaporation, not increased precipitation, sustained large Last Glacial Maximum (LGM) lakes. But this has not been tested with proxies sensitive to lake hydrology. We quantitatively assessed changing evaporation and temperature conditions at Pleistocene Lake Bonneville (Utah, USA), the LGM counterpart of the Great Salt Lake, using Δ′17O and clumped isotope (Δ47) analyses of modern lake water and lacustrine carbonates. We measured the Δʹ17O, δ18O, and Δ47 of 26–18 ka Lake Bonneville gastropods, tufa, and deep-lake carbonate. Δ47 values consistently indicate paleolake waters 6–12 °C below modern. Δ′17O–δ18O data place Lake Bonneville with modern flow-through lakes and clearly separate it from evaporative systems like the Great Salt Lake. Combined Δ′17O and Δ47 analyses robustly characterize paleolake hydrology and provide new proxy-based support for the lower-temperature, lower-evaporation hypothesis. We find via Δ′17O–based reconstruction of meteoric δ18O that LGM precipitation had higher Δ′17O values than modern. One explanation is that regional LGM moisture was sourced from higher latitudes, as a southward westerlies shift would drive ice-adjacent air masses toward the lake.

The triple oxygen isotope composition of biominerals is a promising recorder of changes in global primary productivity (GPP), as well as environment and animal physiology. However, application is largely unexplored, particularly in many regions of the world where eggshell is a common component of paleontological/archeological sites of the late Cenozoic. Ratites (ostriches and their relatives), as nonobligate drinkers, gain most of their oxygen from atmospheric O2 and leaves, meaning that their eggshell should carry a strong imprint of anomalous 17O in atmospheric O2-which is ultimately related to GPP and CO2 levels. In this study, we analyzed fossil eggshells from different climate states of the late Cenozoic, notably the Middle Miocene, Late Miocene, and Last Glacial Maximum (LGM), as well as modern eggshell from the same region, southern Africa. We interpret our results using an existing animal body water model, which we modify for parameter estimation using Bayesian inverse methods. Our results show that the predominant signal in the triple isotopic composition of biomineral carbonate is that of global carbon cycling (i.e. the ratio of GPP:CO2), meaning that with further refinement, a relatively common material can be used to reconstruct changes in planetary primary productivity for periods beyond the ice core record. During the Middle Miocene, we find that GPP was significantly lower than today, at 95% confidence. Comparison with box-model output of the atmospheric O2 budget shows that Middle Miocene GPP levels dropped to below 60% of modern values, assuming that Middle Miocene CO2 levels were between 441 and 472 ppm (95% confidence). The result is discussed, with potentially important implications for future climate change.

Global climate during the Holocene was relatively stable compared to the late Pleistocene. However, evidence from lacustrine records in South America suggests that tropical latitudes experienced significant water balance variability during the Holocene, rather than quiescence. For example, a tight coupling between insolation and carbonate delta 18O records from central Andean lakes (e.g., Lakes Jun & iacute;n, Pumacocha) suggest water balance is tied directly to South American summer monsoon (SASM) strength. However, lake carbonate delta 18O records also incorporate information about temperature and evaporation. To overcome this ambiguity, clumped and triple oxygen isotope records can provide independent constraints on temperature and evaporation. Here, we use clumped and triple oxygen isotopes to develop Holocene temperature and evaporation records from three central Andean lakes, Lakes Jun & iacute;n, Pumacocha, and Mehcocha, to build a more complete picture of regional water balance (P-E). We find that Holocene water temperatures at all three lakes were stable and slightly warmer than during the latest Pleistocene. These results are consistent with global data assimilations and records from the foothills and Amazon basin. In contrast, evaporation was highly variable and tracks SASM intensity. The hydrologic response of each lake to SASM depends greatly on the physical characteristics of the lake basin, but they all record peak evaporation in the early to mid-Holocene (11,700 to 4,200 years BP) when regional insolation was relatively low and the SASM was weak. These results corroborate other central Andean records and suggest synchronous, widespread water stress tracks insolation-paced variability in SASM strength. Lake carbonate Delta ' 17O and Delta 47 constrain lake temperature and water balance histories in ways that delta 18O records alone cannot resolve Carbonate Delta ' 17O records from three Andean lakes indicate that lake hydrology and regional water balance track insolation across the Holocene Low Delta ' 17O for reconstructed lake water indicates that greater evaporative conditions correspond to weakened early and mid-Holocene South American summer monsoon

The stable isotopic composition of pedogenic carbonates is central to many studies of past climate and topography, providing a basis for our understanding of Earth's terrestrial history. A core assumption of many applications of oxygen isotope values (δ18O) of pedogenic carbonate is that they reflect the δ18O value of precipitation (rain/snow). This assumption is violated if soil carbonates form in evaporated soil waters. In this work, we develop a means to identify evaporation in ancient soils using the triple oxygen isotope composition (16O-17O-18O) of pedogenic carbonates. Both theoretical predictions of isotope kinetics during evaporation and studies of triple oxygen isotopes in other geological materials show that the deviation in the relationship between δ17O and δ18O from a reference line, evaluated using the parameter Δ′17O, is sensitive to evaporation. As a first step in developing the use of Δ′17O in ancient pedogenic carbonates, we report Δ′17O values from 47 near-modern pedogenic carbonate samples from globally distributed environments that vary in aridity (hyper-arid to humid). The Δ′17O values of pedogenic carbonate range from −154 to −60 per meg (as CaCO3, measured via O2, VSMOW-SLAP), corresponding to calculated soil water values of −66 to +27 per meg (VSMOW-SLAP) (using a carbonate-water triple oxygen isotope fractionation exponent of 0.5250 and clumped isotope-derived carbonate growth temperatures). The Δ′17O values indicate that evaporative modification of soil water from which pedogenic carbonate forms is common, especially in arid environments. Arid environments host pedogenic carbonates formed from soil waters ranging from highly to minimally evaporated, while humid environments host pedogenic carbonates formed from waters that are only minimally evaporated. The variability in Δ′17O within environments classified by the same aridity may relate to the fact that pedogenic carbonates record soil conditions only during times of carbonate mineralization, which may deviate from annual conditions. Thus, Δ′17O may be useful in understanding the specific circumstances of pedogenic carbonate formation but may not provide incontrovertible evidence of the magnitude of environmental aridity. Evaporative modification of δ18O values of pedogenic carbonates can be detected with Δ′17O, thereby improving estimates of δ18O of unevaporated waters. Our data show that evaporation must be (re)considered for all paleoclimate inferences based on the δ18O of pedogenic carbonate. The addition of Δ′17O will re-energize paleoclimate studies that use (or have avoided using) δ18O of pedogenic carbonate.

The 18O/16O ratios of biominerals have been widely used for reconstructing ecophysiology and climatic settings of modern and extinct animals. However, the 18O/16O ratios of body water, which largely determine the 18O/16O ratios of biominerals, are influenced by a host of competing factors. Regional climate and local hydrology are dominant controls on water isotopic composition before water is consumed by an animal. Behavioral and physiological factors, modified by local climate, also have a strong influence on body water compositions. The addition of a third isotope, 17O (expressed as Δ’17O) potentially allows for further resolution of these factors. Here we construct a generalized triple oxygen isotope mass balance model based on the 18O model of (Kohn 1996) (Geochim. Cosmochim. Acta 60, 4811–4829) and examine the influence on vertebrate animal body water Δ’17O of numerous climatic, ecological, and isotopic variables. We evaluate the model against new and previously published triple oxygen isotope data from modern and fossil animals. The model predicts that animals from arid environments will have wider ranges and lower minimum values of body water Δ’17O than animals living in humid environments. Leaf water consumers are more sensitive to variations in relative humidity and have lower Δ’17O than surface water consumers, which more closely track meteoric water compositions. In this model, factors such as body mass and relative proportions of evaporative versus nonevaporative effluxes from the animal have a lesser influence on animal Δ’17O. If δ18O of meteoric water is invariant, body water isotopic compositions will form approximately linear arrays in Δ’17O versus δ18O space with slopes of ∼0.52. Study of Δ’17O becomes most useful when δ18O of meteoric water is variable or unknown (as is generally the case for fossil animals); in this case Δ’17O of body water responds more strongly to changes in relative humidity, evaporated water inputs, and animal water use efficiency. These predictions are generally supported by observations of Δ’17O for modern animals. This agreement suggests that Δ’17O analysis of animal tissues has great potential as a paleo-aridity proxy in continental environments and as a proxy for learning about the ecology of modern and extinct animals.

Oxygen isotope distributions from lacustrine carbonates provide insights into climate and hydrological change, but it is difficult to isolate the influences of catchment precipitation δ18O, water temperature, and evaporation on lacustrine carbonate δ18O values. Recent work shows the potential for using a combination of clumped (Δ47) and triple oxygen isotope (Δ′17O) measurements to identify the roles of temperature and evaporation on carbonate δ18O values in lakes, allowing precipitation δ18O values to be inferred and facilitating paleoclimate reconstructions. However, modern calibration of this approach has been mostly limited to arid regions with a high ratio of evaporative losses over inputs (XE) and low relative humidity (h<0.7). Developing this tool for paleoclimate and paleoelevation reconstructions requires expanding the modern calibrations to a greater range of climatic and hydrologic conditions. We sampled four lakes in different hydrologic states under a single, high humidity climate regime (h=0.7–0.9) in the Lake Junín region of central Peru. Clumped isotope temperatures from lake carbonates reflect water temperatures during carbonate formation. Lake hydrology is the main control on the Δ′17O values of carbonates and waters: Δ′17O values are lowest in the larger lakes with higher XE when compared to smaller, headwater lakes where evaporation is minimal and Δ′17O is indistinguishable from that of precipitation. Reconstructed unevaporated catchment precipitation δ′18O (δ′18Orucp) values from lake waters rely on accurate characterization of λlake, the triple oxygen isotope evaporation slope. We explore the influence of humidity on λlake using both new observations and modeled data. Accounting for local humidity improves λlake estimates, which allows for more accurate reconstructions of δ′18Orucp. We generate a δ′18Orucp value of −15.2±2.1‰ from modern carbonates and waters (n=15) in the Lake Junín region, which is similar to amount weighted mean annual precipitation −14.1 (±2.2‰). This study illustrates that (1) Δ′17O can be used to differentiate between lakes with differing XE in humid climates, (2) lake carbonate Δ′17O and δ18O values can be used to evaluate the influence of evaporation on lake water δ18O values in a range of climates, and (3) modeling λlake under appropriate humidity conditions improves δ′18Orucp estimates from lake carbonate Δ′17O.

Triple oxygen isotope geochemistry is a growing field that investigates mass dependent and mass independent fractionation in 17O/16O relative to 18O/16O imparted by geochemical, physical, and biological processes. Many applications require 10 ppm-level precision in measurement of the & UDelta;& PRIME;17O parameter. Such analytical precisions are rarely realized for some materials (e.g. sulfates), and no method presently exists for many organic compounds. We describe a new analytical method that combines the versatility of high-temperature conversion (HTC, also known as Temperature Conversion Elemental Analysis, TC/EA) with the high-precision of the methanation-fluorination method described by Passey et al. (2014). In this method, materials including organics, phosphates, sulfates, nitrates, carbonates, and silicates undergo high-temperature conversion of their oxygen to CO in a glassy carbon reactor at temperatures >1400 degrees C. This CO is then reacted with hydrogen at 560 degrees C over an iron catalyst to transfer CO oxygen to oxygen in H2O (a methanation reaction). This H2O is subsequently fluorinated by CoF3 to yield O2, which is then analyzed by mass spectrometry to determine & delta;17O and & delta;18O. Sample oxygen conversion is quantitative (or nearly so) for most compatible materials, resulting in excellent reproducibility in & UDelta;& PRIME;17O (<10 ppm 1 & sigma;) and no clear evidence of fractionation affecting & UDelta;& PRIME;17O. We report the first (to our knowledge) high-precision & UDelta;& PRIME;17O measurements for organics, including benzoic acid (IAEA-601, IAEA-602), cellulose (IAEA-CH-3), keratin (USGS KHS), and honey (USGS 83). We present results for silver phosphates (NBS 120c, USGS 80, USGS 81, B2207), carbonates (IAEA-603, IAEA-C1, NBS 18), sulfates (IAEA-SO-5, IAEA-SO-6), a silicate (NBS 28), and waters (VSMOW2, SLAP2). We also present results from several in-house reference materials, including a silver nitrate and a phosphate that was equilibrated with isotopically exotic waters. Analysis of carbonates, sulfates, and silicates requires accelerants (e.g., graphite and AgCl or KF) to achieve high yields and ppm-level precision in & UDelta;& PRIME;17O. Waters can be analyzed using the same method during the same analytical sessions as solid materials, making determination of water-mineral fractionation factors straightforward and enabling values to be placed directly on the VSMOW-SLAP scale by concurrent analyses with those reference materials. We find that the method is especially well-suited for organics, sulfates, phosphates, and nitrates, however traditional fluorination methods may be better suited for many silicate minerals.

Speleothem oxygen isotope (delta O-18) records provide key insight into the rate and timing of terrestrial paleoclimate changes during the late Quaternary. However, it can be difficult to deconvolve the delta O-18 signal into individual components, which include processes related to moisture source, moisture transport, temperature, precipitation amount, infiltration, and the cave environment. We developed a framework that uses triple oxygen isotope distributions in speleothems to refine interpretations of delta O-18 speleothem records. This framework identifies the influence of dominant processes on delta O-18 values through time by their characteristic (although not necessarily unique) trends in Delta'O-17 vs. delta'O-18 space, where Delta'O-17 = delta('17O) - 0.528 delta O-'18 and delta('x) O = ln(delta(x) O + 1). Following Guo and Zhou (2019a), we expect that 'cave kinetic' processes (e.g., fast degassing at the drip site, prior calcite precipitation) will drive positive trends between delta'O-18 and Delta'O-17. In contrast, we can identify hydrologic processes from near-horizontal trends that reflect Rayleigh-type meteoric water processes and negative trends driven by changes in evaporation processes at the moisture source region or at the cave site, mineralization temperature, and seasonality in precipitation/infiltration amount. We applied this framework to four western USA speleothems from Cave of the Bells (Arizona), Leviathan Cave (Nevada), and Lehman Caves (Nevada). The Cave of the Bells and Leviathan data have nearhorizontal to negative trends indicating delta O-18 variability was driven largely by changes in Rayleigh distillation of atmospheric moisture and moisture source conditions, supporting prior interpretations. We analyzed two Lehman Caves records because they were likely influenced by non-equilibrium processes and the data show weak to moderate negative trends. For sample LMC-12b, chosen for its extreme 7.5% delta O-18 range, the trend is statistically distinct from the near-horizontal Rayleighprocess trend and most consistent with changes in local evaporation intensity and infiltration seasonality as primary drivers. None of these records displays a positive covariation slope between delta'O-18 O and Delta'O-17, suggesting limited variability in cave kinetic processes through time or unknown limitations to the kinetic model of Guo and Zhou (2019a). Additionally, reconstructed formation waters for all sites fall near the Delta'O-17 vs. delta'O-18 Local Meteoric Water Line, a correlation we suggest as a novel test of the absolute magnitude of isotopic offset due to cave kinetic processes. More broadly, our framework adds context to the only other study of carbonate speleothem triple oxygen isotope composition (Sha et al., 2020). We find that positive to negative Delta'O-17 vs. delta'O-18 trends likely exist in speleothem data that may reasonably be expected from regional climate processes and that, combined with other proxy data, triple oxygen isotope data will be useful in constraining interpretations of delta O-18(speleothem) records. (C) 2021 Elsevier Ltd. All rights reserved.

Reconstructing water availability in terrestrial ecosystems is key to understanding past climate and landscapes, but there are few proxies for aridity that are available for use at terrestrial site...

The 618O 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 618O values, including mixing, evaporation, distillation of parent waters, and carbonate growth temperatures. We combined traditional carbon and oxygen isotope analyses with clumped (Delta 47) and triple oxygen isotopes (Delta ' 17O) analyses in oyster shells (Acutostrea idriaensis) of the Goler Formation in southern California (USA) to obtain insights into surface temperatures and delta 18O values of meteoric waters during the early Eocene hothouse climate. The Delta 47-derived temperatures ranged from 9 degrees C to 20 degrees C. We found a correlation between the 618O of growth water (delta 18Ogw) (calculated using Delta 47 temperatures and 618O of carbonate) and the 613C values of shells. The Delta ' 17O values of shell growth waters (0.006%0-0.013%0 relative to Vienna standard mean ocean water-standard light Antarctic precipitation [VSMOW-SLAP]) calculated from Delta ' 17O of carbonate (-0.087%0 to -0.078%0 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 618O value of freshwater supplying the estuary (618Ofw). The reconstructed 618Ofw of -11.3%0 to -14.7%0 (VSMOW) is significantly lower than the delta 18Ogw of -4.4%0 to -9.9%0 that would have been calculated using "only" Delta 47 and 618O values of carbonate. This 618Ofw 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 Delta 47 and Delta ' 17O analyses to improve reconstructions of meteoric water 618O, with implications for understanding ancient climates and elevations.

Global gross primary production (GPP) is the rate of carbon fixation by all primary producing organisms globally, and as such is a measure of the vitality of life on Earth. GPP is an important but understudied aspect of the Earth system, with few estimates for time periods earlier than the Pleistocene. However, triple oxygen isotopes offer a new approach for estimating ancient GPP based on empirical evidence [1]. Mass independent photochemical reactions in the stratosphere yield O 2 with a strongly negative triple oxygen isotope anomaly (δ' 17 O O2 ). The magnitude of the anomaly is dependent on three first-order parameters: atmospheric O 2 concentration, CO 2 concentration, and GPP. The relationship between these variables has been extensively modelled [2,3] which enables constraints to be placed on GPP given reconstructed values for δ' 17 O O2 , [CO 2 ], and [O 2 ]. Vertebrate bioapatites record δ' 17 O O2 because they form in equilibrium with body water, which includes the products of respiration [4]. Here we present GPP reconstructions from the Early Eocene Climate Optimum (EECO) informed by δ' 17 O measurements of fossil mammal teeth from the Willwood Formation in Wyoming, USA. We use triple oxygen isotope enabled animal body water models and a multi-taxon approach to constrain the δ' 17 O O2 signal recorded by these animals. With these data and recent estimates of [CO 2 ] from boron isotopes and alkenone proxies [5], we place constraints on GPP during the EECO.