Joseph F. Whelan

Carbon isotopes in biological carbonates: Respiration and photosynthesis

Respired carbon dioxide is an important constituent in the carbonates of most air breathing animals but is much less important in the carbonates of most aquatic animals. This difference is illustrated using carbon isotope data from freshwater and terrestrial snails, ahermatypic corals, and chemoautotrophic and methanotrophic pelecypods. Literature data from fish otoliths and bird and mammal shell and bone carbonates are also considered. Environmental CO2/O2 ratios appear to be the major controlling variable. Atmospheric CO2/O2 ratios are about thirty times lower than in most natural waters, hence air breathing animals absorb less environmental CO2 in the course of obtaining 02. Tissue CO2 therefore, does not isotopically equilibrate with environmental CO2 as thoroughly in air breathers as in aquatic animals, and this is reflected in skeletal carbonates. Animals having efficient oxygen transport systems, such as vertebrates, also accumulate more respired CO2 in their tissues. Photosynthetic corals calcify mainly during the daytime when photosynthetic CO2 uptake is several times faster than respiratory CO2 release. Photosynthesis, therefore, affects skeletal δ13C more strongly than does respiration. Corals also illustrate how “metabolic” effects on skeletal isotopic composition can be estimated, despite the presence of much larger “kinetic” isotope effects.

Late Quaternary paleohydrologic and paleotemperature change in southern Nevada

Paleo-spring discharge activity in the southern Great Basin responded to changes in recharge, hence climate changes, in high mountain areas during the late Quaternary. In our study, we examined four stratigraphic sections in southern Nevada in order to reconstruct paleohydrologic change spanning the last two major discharge cycles. The largest discharge event in those sections is expressed as extensive wetland deposits (Unit B) that fall beyond the range of radiocarbon dating (>41 ka). We tentatively correlate this event with marine isotope stage 6, which is so conspicuously represented in cores from Death Valley and Owens Lake. Major wetlands were also present during last glacial maximum (Unit D) deposited between 16.4 and 400 ostracode shells vary by ~5‰, and there is no consistent, section-wide, difference in isotopic values between standing water and spring taxa. This pattern strongly suggests short residence times for water in local basins, due to loss of water from basins by outflow as groundwater or overflow, rather than by evaporation. We used the δ 18 O value of fossil ostracodes to place constraints on paleotemperature in the valley bottoms during glacial periods. This analysis entails at least three key assumptions: no vital or evaporation effects during valve formation of the ostracode Cypridopsis vidua, short transit times in the aquifer, and the basic relationship between

Isotopes as Indicators of Environmental Change

Publisher Summary In addition to providing an understanding of processes within a catchment system, isotopic techniques have been instrumental in providing reconstructions of catchment climate and other environmental indicators at various time scales. Many recent changes are a direct consequence of anthropogenic activities. Isotopic analysis serves as a valuable tool for distinguishing between natural variations in long-term climatic patterns and anthropogenic effects, yielding improved understanding of natural feedback mechanisms and the development of realistic remediation strategies. This chapter discusses the examples of isotopic techniques that have been applied to understand several types of ongoing and recent environmental changes, and in paleo-environmental studies. It discusses isotope geochemistry, hydrology, and climatology to look at new ways of applying isotopic tracing techniques to provide information on environmental change. It also gives an overview on how isotopic indicators are being applied in investigations of environmental change in continental settings.

Marine origin of pyritic sulfur in the Lower Bakerstown coal bed, Castleman coal field, Maryland (U.S.A.)

Abstract The amount, kind, distribution, and genesis of pyrite in the Lower Bakerstown coal bed in a 150 × 15 m area of the Bettinger mine, Castleman coal field, Maryland, were studied by various analytical techniques. The mined coal, which had a nonmarine roof rock, contained 1.4–2.8 wt.% total sulfur, generally much lower than the high-sulfur coal (> 3.0 wt.% total S) to the north, which is associated with marine roof rocks. Small-scale systematic and nonsystematic variations in total sulfur and pyrite distribution were found in the mined area. In the column sample, most of the pyrite was found in the upper 9 cm of the 69-cm-thick mined coal and occurred mainly as a pyrite lens containing cell fillings in seed-fern tissue (coal ball). As-bearing pyrite was detected by laser microprobe techniques in the cell walls of this tissue but not elsewhere in the column sample. This may indicate that the As was derived from decomposition of organic matter in the cell walls. The sulfur isotopic composition and distribution of pyrite in the coal are consistent with introduction of marine sulfate shortly after peat deposition, followed by bacterial reduction and pyrite precipitation. Epigenetic cleat pyrite in the coal is isotopically heavy, implying that later aqueous sulfate was 34S-enriched.

UNSATURATED ZONE CALCITE 813C EVIDENCE OF SOUTHERN NEVADA CLIMATES DURING THE PAST 9 MILLION YEARS

Yucca Mountain, Nevada, is presently the object of intense study as a potential permanent repository for the Nations high-level radioactive wastes. The mountain consists of a thick sequence of volcanic tuffs in which the depth to the water table ranges from 500 to 700 meters below the land surface. This thick unsaturated zone (UZ), which would host the projected repository, coupled with the present-day arid to semi-arid environment, is considered a positive argument for the site. Evaluation of the site includes defining the relationship between climate variability, as the input function or driver of site- and regional-scale ground-water flow, and the possible transport and release of radionuclides. Secondary calcite and opal have been deposited in the UZ by meteoric waters that infiltrated through overlying soils and percolated through the tuffs. The oxygen isotopic composition ({delta}{sup 18}O values) of these minerals reflect contemporaneous meteoric waters and the {delta}{sup 13}C values reflect soil organic matter, and hence the resident plant community, at the time of infiltration (Whelan et al., 1994). Recent U/Pb age determinations of opal in these occurrences allows the {delta}{sup 13}C values of associated calcite to be used to reconstruct general climate variations during the past 9 M.y.