Oxygen and Carbon Isotopes in Modern and Historic Mussels from the Snake River, Idaho, May Show Modern Rise of Corn Production

Stable carbon and oxygen isotope compositions were analyzed from local mussels ranging in age from 0 to 1000 years before the present to identify any trends and seasonal variability in the oxygen and carbon (18O and 13C values), compare trends and averages in 18O and 13C across different time periods and species of mussel, and finally use 18O to gain insight into how climate conditions might have changed in the past 1000 years. The Western Ridged Mussel (Gonidea angulate) and Western Pearlshell Mussel (Margaritifera falcata) are two species of freshwater mussels found in the Snake River in southern Idaho. Both species seasonally produce a calcium carbonate shell outward as they age. Previous research has shown mussels typically form their shells in isotopic equilibrium with the surrounding water and therefore can be a reliable indicator of environmental conditions such as temperature and seasonality. Outer growth bands were sampled sequentially from mussels dated ~1200 years before present, as well as from modern shells. The powdered samples were analyzed using an isotope ratio mass spectrometer in the Department of Geosciences, Boise State University, to obtain δ18O and δ13C values. Modern shells were found to have an average δ18O value of -16.6‰ (VPDB) and an average δ13C value of -8.8‰ (VPDB). δ18O was nearly constant across the shell, but δ13C increased as the mussel grew. Historic shells had homogeneous δ18O values of -16.4‰ and homogeneous δ13C values of -11.6‰. δ18O values of the two time periods are very similar, suggesting no resolvable changes to climatic conditions using this proxy. Increased δ13C values in modern mussels relative to historic mussels suggest a potentially significant increase of C4 plant contribution to the Snake River. We interpret this enrichment to be due to modern production of corn (a C4 plant) along the Snake River, especially since ~2000 CE

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warmdry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C4/(C4+ C3) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C4/(C4+ C3) was higher than today, and potential drivers of any changes. Tooth enamel δ18O values for Pleistocene Equus, Bison, and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water δ18O values (-16.1 ± 0.8‰) than modern precipitation (-10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (-12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher δ18O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean δ13C values for the Pleistocene grazers (-6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (-9.6 ± 0.4‰) and indicate more consumption of C4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C4 grass taxa currently present in the valley (55-60%). δ13C values in Camelops tooth enamel (-7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C4 shrub that flourishes in regions with hot, dry summers. Lower water δ18O values, lower abundance of C4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C4 grasses. Dietary partitioning, especially when combined with decreased pCO2 levels during the late Pleistocene, can explain the relatively high δ13C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters derived from dietary and floral records may need to be reevaluated in the context of the potential effects of dietary preferences and lower pCO2 levels on the stability of C3 vs. C4 plants

The New Zealand Kauri (Agathis Australis) Research Project: A Radiocarbon Dating Intercomparison of Younger Dryas Wood and Implications for IntCal13

We describe here the New Zealand kauri (Agathis australis) Younger Dryas (YD) research project, which aims to undertake Δ14C analysis of ~140 decadal floating wood samples spanning the time interval ~13.1–11.7 kyr cal BP. We report 14C intercomparison measurements being undertaken by the carbon dating laboratories at University of Waikato (Wk), University of California at Irvine (UCI), and University of Oxford (OxA). The Wk, UCI, and OxA laboratories show very good agreement with an interlaboratory comparison of 12 successive decadal kauri samples (average offsets from consensus values of –7 to +4 14C yr). A University of Waikato/University of Heidelberg (HD) intercomparison involving measurement of the YD-age Swiss larch tree Ollon505, shows a HD/Wk offset of ~10–20 14C yr (HD younger), and strong evidence that the positioning of the Ollon505 series is incorrect, with a recommendation that the 14C analyses be removed from the IntCal calibration database

Decadally resolved lateglacial radiocarbon evidence from New Zealand kauri

Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Arizona Board of Regents on behalf of the University of Arizona for personal use, not for redistribution. The definitive version was published in Radiocarbon 58 (2016): 709-733, doi: 10.1017/RDC.2016.86.The Last Glacial-Interglacial Transition (LGIT; 15,000-11,000 cal BP) was characterized by complex spatiotemporal patterns of climate change, with numerous studies requiring accurate chronological control to decipher leads from lags in global paleoclimatic, -environmental and archaeological records. However, close scrutiny of the few available tree-ring chronologies and 14C-dated sequences composing the IntCal13 radiocarbon calibration curve, indicates significant weakness in 14C calibration across key periods of the LGIT. Here, we present a decadally-resolved atmospheric 14C record derived from New Zealand kauri spanning the Lateglacial from ~13,100 - 11,365 cal BP. Two floating kauri 14C time series, curve-matched to IntCal13, serve as a radiocarbon backbone through the Younger Dryas. The floating Northern Hemisphere (NH) 14C datasets derived from the YD-B and Central European Lateglacial Master tree-ring series are matched against the new kauri data, forming a robust NH 14C time series to ~14,200 cal BP. Our results show that IntCal13 is questionable from ~12,200 - 11,900 cal BP and the ~10,400 BP 14C plateau is approximately five decades too short. The new kauri record and re-positioned NH pine 14C series offer a refinement of the international 14C calibration curves IntCal13 and SHCal13, providing increased confidence in the correlation of global paleorecords.This work was part funded by the Foundation for Research, Science and Technology (FRST)—now Ministry for Business, Innovation & Employment (MBIE)-PROP-20224-SFK-UOA), a Royal Society of New Zealand grant, the Australian Research Council (FL100100195 and DP0664898) and the Natural Environment Research Council (NE/H009922/1, NE/I007660/1, NER/A/S/2001/01037 and NE/H007865/1)

Carbonate-hosted microbial communities are prolific and pervasive methane oxidizers at geologically diverse marine methane seep sites

At marine methane seeps, vast quantities of methane move through the shallow subseafloor, where it is largely consumed by microbial communities. This process plays an important role in global methane dynamics, but we have yet to identify all of the methane sinks in the deep sea. Here, we conducted a continental-scale survey of seven geologically diverse seafloor seeps and found that carbonate rocks from all sites host methane-oxidizing microbial communities with substantial methanotrophic potential. In laboratory-based mesocosm incubations, chimney-like carbonates from the newly described Point Dume seep off the coast of Southern California exhibited the highest rates of anaerobic methane oxidation measured to date. After a thorough analysis of physicochemical, electrical, and biological factors, we attribute this substantial metabolic activity largely to higher cell density, mineral composition, kinetic parameters including an elevated Vmax, and the presence of specific microbial lineages. Our data also suggest that other features, such as electrical conductance, rock particle size, and microbial community alpha diversity, may influence a sample's methanotrophic potential, but these factors did not demonstrate clear patterns with respect to methane oxidation rates. Based on the apparent pervasiveness within seep carbonates of microbial communities capable of performing anaerobic oxidation of methane, as well as the frequent occurrence of carbonates at seeps, we suggest that rock-hosted methanotrophy may be an important contributor to marine methane consumption.https://www.pnas.org/content/118/25/e200685711

Punctuated shutdown of Atlantic Meridional Overturning circulation during Greenland Stadial 1

The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runof that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the ‘bipolar seesaw’). Here we exploit sub-fossil New Zealand kauri trees to report the frst securely dated, decadally-resolved atmospheric radiocarbon (¹⁴C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring ¹⁴C records with marine ¹⁴C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric ¹⁴C ofset was close to zero prior to GS-1, before reaching ‘near-modern’ values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our fndings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes

Reconstructing the Mid-Late Triassic Paleoclimate of the Paraña Basin Using Carbon Isotope Analysis of Dental Enamel

The Triassic Period (251 — 199 Ma), best known as the dawn of the dinosaur age, remains in many ways an enigma. Two of the largest known mass extinctions, both arising from drastic changes to the global climate, mark the beginning and end of this Period. This study seeks to constrain the Triassic paleoclimate, specifically the transition from Mid- to Late Triassic, through stable-isotope examination of dinosaur and reptilian dental enamel. A mass spectrometer, based in the Boise State Geoscience lab, was used to analyze twelve samples from Brazil’s fossil-rich Paraña Basin. The analytic results, expressed in terms of their Carbon-13 to Carbon-12 isotope ratio (or δ13C), strongly suggest a significant decrease in Mean Annual Precipitation in the Paraña Basin over this 10-15 million year period. The estimated maximum decrease in MAP is roughly equivalent to the modern-day difference in annual rainfall between Boise, ID and Phoenix, AZ. This study’s results, based on stable-isotope analysis of dental enamel samples from the Triassic period, match (and validate) previous models of this paleoclimatic period in scientific literature

Testing the Validity of Bogus Basin Ponderosa Pines as an Atmospheric CO\u3csub\u3e2\u3c/sub\u3e Climate Proxy

Tree ring growth and 13 C/12 C isotope compositions have frequently been used as a climate proxy to analyze the paleo atmosphere. The effect of carbon dioxide can be seen by analyzing both the tree ring width and the carbon isotope composition (Stuiver & Quay 1984). In this study we test the validity of previous assessments that plants can serve as pCO2 indicators (McCarroll & Loader 2004, Cui & Schubert 2016). This record of change over time will identify the effects anthropogenic climate change can have on the carbon isotope signature of these Bogus Basin trees. Creating a standard for the localized Boise area allows for future isotope analysis of Central Idaho to have a pre-existing record to compare to. Since we are examining atmospheric variability in the Boise Foothills, samples would all be collected from a localized area from Ponderosa Pines at relatively similar elevations

Accuracy and Practical Considerations for Doubly Labeled Water Analysis in Nutrition Studies Using a Laser-Based Isotope Instrument (Off-Axis Integrated Cavity Output Spectroscopy)

Background: Given the utility of the doubly labeled water (DLW) method for determination of energy expenditure, additional techniques for isotope analysis of the samples are welcome. Laser-based instruments are one such new analytical tool, but their accuracy and feasibility for DLW studies are grossly understudied. Objectives: We assessed the accuracy of laser-based isotope ratio measurements as part of the DLW method for estimation of carbon dioxide production rate (rCO2) and total energy expenditure (TEE), in between-group comparison study designs. Methods: Urine samples from a previous study were analyzed with a laser-based instrument [off-axis integrated cavity output spectroscopy (OA-ICOS)]. In that study, participants consumed a high-, moderate-, or low-carbohydrate diet for 20 wk; urine samples were obtained in weeks 18–20 before and after a 2H- and 18O-enriched water dose. Isotope ratios (δ2H and δ18O), rCO2, and TEE calculated by standard methods were compared to results previously obtained with the standard technique of isotope ratio mass spectrometry (IRMS). Bias, SD, and bias ± 1.96SD bands between IRMS and OA-ICOS were computed. Results: The between OA-ICOS and IRMS rCO2 and TEE trends were equivalent (within 1.2% and 4.1%, respectively), in spite of the differences in measured δ18O values at high enrichment levels. The OA-ICOS δ18O values displayed an increasing offset from the IRMS results as the 18O enrichment increased (mean ± SD 4.6–5.7‰ ± 2‰ offset at the time point with highest 18O enrichment, ∼135‰), whereas the hydrogen isotope ratio (δ2H) differed only slightly between the methods (mean offset −4.9‰ for all time points). The between-diet differences in TEE from the previous study were recapitulated with a smaller subset of participants and time points. Conclusions: OA-ICOS analysis is an accurate and feasible technique for the DLW method. Given the δ18O offset observed at high enrichment, validation of each OA-ICOS instrumental setup against established methods (e.g., IRMS) is recommended