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Fossiliferous carbonate concretions are commonly found in sediments deposited in the Late Cretaceous Western Interior Seaway. Although concretions are diagenetic features, well-preserved fossils from within them have been instrumental in reconstructing the temperature and δ18O value of Western Interior Seaway seawater, which is essential for accurate reconstruction of Late Cretaceous climate. Here, we constrain formation conditions of Late Campanian and early Maastrichtian carbonate concretions by combining triple oxygen isotope measurements with carbonate clumped isotope paleothermometry on different carbonate phases within the concretions. We measured both fossil skeletal aragonite and sparry calcite infill from cracks and within macrofossil voids to evaluate differences between “primary” and “altered” geochemical signals. Based on the two temperature-sensitive isotope systems of the primary fossil shell aragonite, the temperature of the Western Interior Seaway was between 20 °C and 40 °C and was likely thermally stratified during the Campanian. The reconstructed δ18Oseawater values of ∼−1‰ for Campanian Western Interior Seaway waters are similar to those expected for the open ocean during greenhouse climates, while the Maastrichtian Western Interior Seaway may have been more restricted, with a δ18Oseawater value of ∼2‰, which reflects more evaporative conditions. We reconstructed the diagenetic history of the sparry infill and altered fossils using a fluid-rock mixing model. Alteration temperature, alteration fluid δ18O value, and the initial formation temperature were calculated by applying the fluid-rock mixing model to a particle swarm optimization algorithm. We found a different range of initial formation temperatures between the Campanian (25−38 °C) and Maastrichtian (9−28 °C). We also found that alteration in the presence of light meteoric fluids (δ18O ≈ −10‰) is required to explain both the sparry infill and the altered fossil isotopic values. Based on our results, both lithification and alteration of the carbonates occurred soon after burial, and light meteoric fluids support prior findings that high-topographic relief existed on the western margin of the Western Interior Seaway during the Late Cretaceous. As one of the first studies to apply these techniques in concert and across multiple mineralogical phases within samples, our results provide important constraints on paleoenvironmental conditions in an enigmatic ocean system and will improve interpretations of the overall health of ecosystems leading into the end-Cretaceous mass extinction. 

We combine calculations of pebble accretion and accretion by large and giant impacts to quantify the effects of pebbles on the hafnium-tungsten system during Earth formation. Our models include an early pebble accretion phase lasting 4–6 Myr with a global magma ocean and core segregation, a 20–50 Myr phase of large impacts, and a late giant impact representing the Moon-forming event. We consider various mass additions during each accretion phase, vary the metal-silicate partition coefficient for tungsten over a wide range, and track (180)Hf, (182)Hf, (182)W and (184)W in proto-Earth and impactor models over time using standard chondritic values for these isotopes in the pebbles. We find that an early phase of pebble accretion is compatible with the tungsten anomaly of Earth's early mantle as well as the present-day Hf/W ratio, but under restricted conditions. In particular, the pebble mass of proto-Earth is limited to 0.7 Earth masses or less, the average metal-silicate partition coefficient for tungsten is 30–50, and because the metal-silicate equilibration efficiency for giant impacts is low, the equilibration efficiency must be high for the large impactors. 

Tracing how free-ranging organisms interact with their environment to maintain water balance is a difficult topic to study for logistical and methodological reasons. We use a novel combination of triple-oxygen stable isotope analyses of water extracted from plasma (δ¹⁶O, δ¹⁷O, δ¹⁸O) and bulk tissue carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes of feathers and blood to estimate the proportional contribution of marine resources, seawater, and metabolic water used by two species of unique songbirds (genusCinclodes) to maintain their water balance in a seasonal coastal environment. We also assessed the physiological adjustments that these birds use to maintain their water balance. In agreement with previous work on these species, δ¹³C and δ¹⁵N data show that the coastal resident and invertivoreC. nigrofumosusconsumes a diet rich in marine resources, while the diet of migratoryC. oustaletishifts seasonally between marine (winter) to freshwater aquatic resources (summer). Triple-oxygen isotope analysis (Δ¹⁷O) of blood plasma, basal metabolic rate (BMR), and total evaporative water loss (TEWL) revealed that ~25% of the body water pool of both species originated from metabolic water, while the rest originated from a mix of seawater and fresh water. Δ¹⁷O measurements suggest that the contribution of metabolic water tends to increase in summer inC. nigrofumosus, which is coupled with a significant increase in BMR and TEWL. The two species had similar BMR and TEWL during the austral winter when they occur sympatrically in coastal environments. We also found a positive and significant association between the use of marine resources as measured by δ¹³C and δ¹⁵N values and the estimated δ¹⁸O values of ingested (pre-formed) water in both species, which indicates that Cinclodes do not directly drink seawater but rather passively ingest when consuming marine invertebrates. Finally, results obtained from physiological parameters and the isotope-based estimates of marine (food and water) resource use are consistent, supporting the use of the triple-oxygen isotopes to quantify the contribution of water sources to the total water balance of free-ranging birds. 

Abstract The origin of the eclogites that reside in cratonic mantle roots has long been debated. In the classic Roberts Victor kimberlite locality in South Africa, the strongly contrasting textural and geochemical features of two types of eclogites have led to different genetic models. We studied a new suite of 63 eclogite xenoliths from the former Roberts Victor Mine. In addition to major- and trace-element compositions for all new samples, we determined 18O/16O for garnet from 34eclogites. Based on geochemical and textural characteristics we identify a large suite of Type I eclogites (n = 53) consistent with previous interpretations that these rocks originate from metamorphosed basaltic-picritic lavas or gabbroic cumulates from oceanic crust, crystallised from melts of depleted mid-ocean ridge basalt (MORB) mantle. We identify a smaller set of Type II eclogites (n = 10) based on geochemical and textural similarity to eclogites in published literature. We infer their range to very low δ18O values combined with their varied, often very low zirconium-hafnium (Zr-Hf) ratios and light rare earth element-depleted nature to indicate a protolith origin via low-pressure clinopyroxene-bearing oceanic cumulates formed from melts that were more depleted in incompatible elements than N-MORB. These compositions are indicative of derivation from a residual mantle source that experienced preferential extraction of incompatible elements and fractionation of Zr/Hf during previous melting. 

Understanding physiological traits and ecological conditions that influence a species reliance on metabolic water is critical to creating accurate physiological models that can assess their ability to adapt to environmental perturbations (e.g., drought) that impact water availability. However, relatively few studies have examined variation in the sources of water animals use to maintain water balance, and even fewer have focused on the role of metabolic water. A key reason is methodological limitations. Here, we applied a new method that measures the triple oxygen isotopic composition of a single blood sample to estimate the contribution of metabolic water to the body water pool of three passerine species. This approach relies on Δ' 17 O, defined as the residual from the tight linear correlation that naturally exists between δ 17 O and δ 18 O values. Importantly, Δ'17O is relatively insensitive to key fractionation processes, such as Rayleigh distillation in the water cycle that have hindered previous isotope-based assessments of animal water balance. We evaluated the effects of changes in metabolic rate and water intake on Δ' 17 O values of captive rufous-collared sparrows ( Zonotrichia capensis ) and two invertivorous passerine species in the genus Cinclodes from the field. As predicted, colder acclimation temperatures induced increases in metabolic rate, decreases in water intake, and increases in the contribution of metabolic water to the body water pool of Z. capensis , causing a consistent change in Δ' 17 O. Measurement of Δ' 17 O also provides an estimate of the δ 18 O composition of ingested pre-formed (drinking/food) water. Estimated δ 18 O values of drinking/food water for captive Z. capensis were ~ −11‰, which is consistent with that of tap water in Santiago, Chile. In contrast, δ 18 O values of drinking/food water ingested by wild-caught Cinclodes were similar to that of seawater, which is consistent with their reliance on marine resources. Our results confirm the utility of this method for quantifying the relative contribution of metabolic versus pre-formed drinking/food water to the body water pool in birds.