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Student Abstracts

Author/s: Erin E. Ray, Paige Lynch, Emily Moes, Keith M. Prufer

Conference: Society for American Archaeology 85th Annual Meeting: Austin, TX

Date: April, 2020


In Mesoamerica, it is clear the advent of agriculture brought unprecedented population expansion. However, as with many questions about this transition, a lack of archaeological remains has made determining the details such as when population growth began and the demographic profile of the population growth difficult to determine. The rockshelter sites of Saki Tzul and Mayahak Cab Pek, located in Southern Belize, provide a unique opportunity to answer certain questions about changes in the demographic composition of a single population during the transition due to a continuous burial assemblage spanning approximately 9,000 years. We propose to use stable isotopes of carbon and oxygen from multiple molars from adults spanning the transition to examine changes in weaning age. By using molars from adults, we can avoid any compounding issues with early illness or complications from weaning too early. There is still debate among researchers about change, if any, to weaning practices between hunter-gatherer and agricultural groups. This study will allow us to examine a relatively continuous population with similar cultural practices to identify if the average weaning age changes and explore the nature of this change and identify if cultural or environmental factors result in changes in weaning practices.

Author/s: Erick J. Cano and Zachary D. Sharp

Conference: International Eclogite Conference, Petrozavodsk, Karelia, Russia

Date: June, 2019


Oxygen isotope ratios (16O/18O) have been used in numerous studies of mantle lithologies to estimate 1) the protolith 2) the source of metasomatizing fluids, 3) temperature of formation, and 4) degree of equilibration between coexisting minerals. The δ18O value of mantle olivine comprises a very restricted range (Mattey et. al., 1994), so that even subtle deviations from this ‘canonical’ value indicate some form of contamination. Eclogites span a range of 2–8‰ and suggest an altered oceanic crust or sediment protolith (MacGregor and Manton, 1986). However, the 18O/16O information alone provide limited information. The addition of the novel 17O/16O ratios provide additional constraints on mantle minerals, expanding the isotope data from a one-dimensional line to a two-dimensional field.

Our preliminary results demonstrate the utility of triple oxygen isotope analyses of mantle materials. OPX and olivine mineral separates from spinel peridotites are generally well-behaved for 17O, with Δ' 17O values (see Sharp, 2013 for nomenclature) of -0.05 ± 0.01‰, the same as presumed mantle olivine. We see that CPX is out of δ18O equilibrium in all cases. The Δ18O values for olivine, garnet, OPX, CPX and phlogopite from a granular garnet peridotite (Kimberley, SA) suggest complete 18O/16O disequilibrium, but the Δ' 17O values of all samples are again typical of that of the average mantle. In contrast, a sheared peridotite from the same location has Δ18O values in equilibrium at ~950 °C, but Δ' 17O values that suggest mixing between a low Δ' 17O – low δ18O and a high Δ' 17O – high δ18O component. One mantle eclogite sample, a grospydite from Smyth and Hatton (1977), has a wide range of Δ' 17O values but δ18O values that appear in equilibrium. It has been suggested that the wide range in δ18O values could suggest an origin for the eclogites from subducted altered oceanic crust (MacGregor and Manton, 1986). We are measuring the triple oxygen isotope values of altered oceanic crust in order to identify potential sources for the 17O isotope disequilibrium seen. The Δ' 17O values of these samples can be used to support such an idea. In general, the Δ' 17O values of altered oceanic crust are higher than typical mantle. Low Δ' 17O values may be indicative of subducted sedimentary material.

Author/s: Anthony M. Gargano, Zachary D. Sharp, and Charles K. Shearer

Conference: Lunar and Planetary Science Conference, Houston, TX

Date: March, 2019


The Moon is depleted in volatile elements relative to the Earth due in part from vaporization and volatile loss throughout the Lunar Magma Ocean (LMO). Additionally, lunar materials exhibit large ranges in chlorine isotope compositions (δ37Cl) that are not observed on Earth, thought to result from the preferential loss of light isotopes to space (35Cl). It would be expected that high δ37Cl values would be measured in materials with the lowest Cl concentration. Enigmatically, however, apatite geochemistry suggests that the Cl-poor lithologies (typically mare basalts) have the lowest range of δ37Cl values, whereas the Cl-rich lithologies (typically KREEPy) have the highest range in δ37Cl values. Although the Cl isotope compositions are achievable by degassing following Rayleigh fractionation and Graham’s law diffusion, such that the fractionation factor (α) is proportional to the ratios of the isotopologues of interest (i.e. Fe35Cl2/Fe37Cl35Cl) this does not account for why the most Cl-rich lithologies have the highest δ37Cl values. The underlying assumption that is made, however, when discussing the δ37Cl values of lunar materials relative to their Cl concentrations is that all materials had the same initial Cl content. A more appropriate comparison may be the loss of light volatile elements relative to heavy ones of similar geochemical affinity (i.e. Cl/Br and Cl/I). We intend to address why the most Cl-rich lunar lithologies tend to exhibit the largest ranges in δ37Cl values by measuring the halogen contents and Cl isotope compositions of lunar materials.

Author/s: Whiteman JP, Newsome SD, Ben-David M

Conference: International Conference on Bear Research and Management

Date: June, 2016


In some regions of the Arctic, sea ice decline and the resulting loss of foraging opportunities have been associated with recent reductions in polar bear abundance, survival, and reproduction. It is often assumed that during food deprivation lipid reserves (e.g., adipose fat) are the limiting factor to polar bear survival, and the role of protein reserves (e.g., skeletal muscle) is often under appreciated. Structural tissues require a constant input of amino acids for maintenance; to provide these amino acids, fasting bears catabolize endogenous protein, potentially at a greater rate than endogenous lipid. Recent studies with captive vertebrates demonstrated that when feeding, animals may use carbon derived from dietary lipids to synthesize proteins used to build structural tissue. We hypothesize that fasting polar bears use a similar process to transfer carbon from stored adipose fat to stored protein. To test this hypothesis, we are using amino acid carbon isotope (δ13C) analysis, and archived samples from a previous study of nutritional ecology in the Southern Beaufort Sea, to track carbon flux between protein-rich (red blood cells, serum, skeletal muscle) and lipid-rich (adipose) tissues in individual, free-ranging polar bears that exhibit a spectrum of body condition and feeding status. Our preliminary data suggest that a portion of the non-essential amino acids in red blood cells of fasting polar bears were newly synthesized with carbon that had been transferred from endogenous adipose tissue. If carbon movement between lipid and protein is substantial, it will change our understanding of polar bear fasting physiology and endurance, influencing forecasts of how this species will respond to continued ice loss.

Author/s: Elliott Smith EA, Braje BJ, Rick TC, Szpak P, Newsome SD

Conference: IsoEcol

Date: May, 2016


Kelp forests are among the most productive but vulnerable marine ecosystems on earth. These regions serve as biodiversity hotspots and CO2 sinks, but are also highly sensitive to human impacts such as overexploitation and shifting ocean chemistry. Understanding their dynamics is crucial for effective conservation and management. Here, we employ δ13C analysis of individual amino acids from two top marine consumers, sea otters (Enhydra lutris) and sheephead (Semicossyphus pulcher) to evaluate the importance of kelp forests in the late Holocene (~3500 ybp – present). Since only primary producers and microbes synthesize essential amino acids (AAESS), consumers typically directly route them into tissues and thus AAESS are minimally altered as they move up food chains. Moreover, different producers (e.g., phytoplankton and macroalgae) in nearshore marine ecosystems have highly distinct δ13C values and so the δ13C values of AAESS in top consumers can provide a ‘fingerprint’ of the dominant producers in the local foodweb. We analyzed bone collagen from late Holocene sea otters and sheephead from two islands (San Nicolas and San Miguel) off the coast of southern California. We also characterized the baseline amino acid δ13C profiles for modern producer groups: kelp (Laminaria and Nereocystis), green algae (Ulva) and red algae (Neorhodomela). We used mixing models to quantify the contribution of each algal group to ancient sea otter and sheephead AAESS δ13C values. As expected, kelps had significantly higher δ13C values than red and green algae for all amino acids measured. We found remarkable consistency between ancient sea otters and sheephead, both between individuals and among sites. Both top consumers were predominantly feeding in ecosystems driven by kelp production; in some instances, an estimated 99% of consumer essential amino acids were derived from kelp. These findings suggest that at these sites kelp forests may have been more extensive in the late Holocene than they are today. Our study demonstrates the utility of amino acid δ13C analysis in investigating historical ecological problems that hold relevance for modern conservation biology.

Author/s: Maltsev OV, Ziegler K, Sharp ZD, Agee CB

Conference: Lunar and Planetary Science Conference

Date: March, 2016


The presence of water in martian meteorites provides a unique glimpse into the evolution of water on Mars. Previous studies have shown that the oxygen extracted from water in martian meteorites is generally not in isotopic equilibrium with the bulk silicate rock. By analyzing the isotopic composition of oxygen in the water extracted from a variety of martian meteorites we hope to identify distinct oxygen isotope reservoirs on Mars (mantle, crust and hydrosphere), and attempt to link them to certain geological processes experienced by the different types of martian meteorites. The pioneering work by Karlsson et al. (1992) has thus far been the only systematic study of oxygen isotopic compositions of water extracted from martian meteorites and their data cannot be easily interpreted. A broader and more detailed sampling is the goal of this study. So far we have measured the oxygen isotope composition of water extracted from martian shergottites Tissint and Zagami and are presently working on analyzing other shergottites as well as a variety of nakhlites, chassignites and the basaltic breccia NWA 7034. Water was extracted from samples using stepwise heating and converted to O2 by fluorination. The O2 gas was then purified in a GC column and measured for the triple oxygen isotope value. Δ17O' values of water extracted from Tissint and Zagami are distinctly elevated relative to that of Earth but are lower than the corresponding bulk rock Δ17O' values (0.33‰). This supports the previous observations [2,3] of isotopic disequilibrium (or terrestrial contamination) between the two sites of oxygen (water and bulk rock). Both samples also show a similar trend in the Δ17O' values of the waters released at different temperature steps. The lowest Δ17O' values (<0.1‰) are measured in waters extracted below 150°C. This is likely due to terrestrial contamination of the absorbed water portion. The highest Δ17O' values were measured for water extracted between 200 and 400°C (0.21‰ for Tissint and 0.1‰ for Zagami). At temperatures above 400°C the Δ17O' values of the extracted water begin to get more negative (0.17‰ for Tissint and 0.09 for Zagami). Since both Tissint and Zagami were observed falls, we would not expect extensive terrestrial contamination, although trace amounts of hydration could affect the 'water' data, but not the bulk rock data. The existence of heterogeneity in the Δ17O' values of water extracted at different temperature intervals from Tissint and Zagami supports the possible existence of isotopically distinct reservoirs on Mars. To better understand the origin of the waters in these meteorites, we are currently working on understanding the mineralogical constraints on storage and release of water. The Δ17O' trend observed in water extracted from Tissint and Zagami will be further evaluated as we continue to expand the body of data on the oxygen isotopic composition of water in martian meteorites.

Author/s: Noble JD, Wolf BO, Newsome SD

Conference: American Society of Mammalogy

Date: June, 2015


In a nutrient limited desert ecosystem, Perognathus flavus (PGFV) utilize a variety of foraging strategies to partition these limited resources and maximize fitness. This research (1) quantified resource use within individual PGFV as either generalists or specialists and (2) calculated the density and distribution of these mice across our study area. Mice were trapped monthly from March to October, 2014, pit-tagged, sexed, aged, bled, and reproductive status determined. We used a Bayesian mixing model to estimate the proportion of assimilated carbon that was derived from C3 versus C4 primary production in plasma, offset by a trophic discrimination factor. Differences in δ13C and δ15N values among rodents and plant functional groups (C3 versus C4) were assessed using Tukey post hoc tests to adjust for multiple comparisons. We used Bayesian spatial metrics to quantify isotope variation temporally across the species as measured by standard ellipse areas in δ13C versus δ15N bivariate space. Variation in isotopic space can be linked to individual variation in diet (specialist versus generalist). δ15N values indicate the trophic breadth of the community while δ13C values represent foraging preferences. By analyzing 1,570 plasma samples with >60 individuals that were trapped and processed 4 or more times over the 8 month period, we were able to adequately quantify foraging strategies. Using the MARC mark-recapture program we calculated density and distribution across our study area.