Impacts of Carbonate Buffering on Atmospheric Equilibration of CO2, δ13CDIC, and Δ14CDIC in Rivers and Streams

Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO2) to the atmosphere. However, the sources of this CO2 and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO2 in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO2 and the stable and radio- isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO2 model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically-coupled 5th-order stream network. We find that carbonate buffering reactions contribute \u3e60% of emissions in high-alkalinity, moderate groundwater-CO2 environments. However, atmosphere equilibration timescales of CO2 are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO2 across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO2 and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio- carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate-dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO2 patterns across variable alkalinities

High Temperature Electrochemical Polishing of H(2)S from Coal Gasification Process Streams.

An advanced process for the separation of hydrogen sulfide from coal gasification streams through an electrochemical membrane is being perfected. H{sub 2}S is removed from a synthetic gas stream, split into hydrogen, which enriches the exiting syngas, and sulfur, which is condensed downstream from an inert sweep gas stream. The process allows for continuous removal of H{sub 2}S without cooling the gas stream while allowing negligible pressure loss through the separator. Moreover, the process is economically attractive due to the elimination of the need for a Claus process for sulfur recovery. To this extent the project presents a novel concept for improving utilization of coal for more efficient power generation

The prevalence and nature of unrequited love

Unrequited love (UL) is unreciprocated love that causes yearning for more complete love. Five types of UL are delineated and conceptualized on a continuum from lower to greater levels of interdependence: crush on someone unavailable, crush on someone nearby, pursuing a love object, longing for a past lover, and an unequal love relationship. Study 1a found all types of UL relationships to be less emotionally intense than equal love and 4 times more frequent than equal love during a 2-year period. Study 1b found little evidence for limerent qualities of UL. Study 2 found all types of UL to be less intense than equal love on passion, sacrifice, dependency, commitment, and practical love, but more intense than equal love on turmoil. These results suggest that UL is not a good simulation of true romantic love, but an inferior approximation of that ideal

Aridification of Central Asia and uplift of the Altai and Hangay mountains, Mongolia: stable isotope evidence

Central Asia has become increasingly arid during the Cenozoic, though the mechanisms behind this aridification remain unresolved. Much attention has focused on the influence and uplift history of the Tibetan Plateau. However, the role of ranges linked to India-Asia convergence but well north of the Plateau—including the Altai, Sayan, and Hangay—in creating the arid climate of Central Asia is poorly understood. Today, these ranges create a prominent rain shadow, effectively separating the boreal forest to the north from the deserts of Central Asia. To explore the role of these mountains in modifying climate since the late Eocene, we measured carbon and oxygen stable isotopes in paleosol carbonates from three basins along a 650 km long transect at the northern edge of the Gobi Desert in Mongolia and in the lee of the Altai and Hangay mountains. We combine these data with modern air-parcel back-trajectory modeling to understand regional moisture transport pathways at each basin. In all basins, δ¹³C increases, with the largest increase in western Mongolia. The first δ¹³C increase occurs in central and southwestern Mongolia in the Oligocene. δ¹³C again increases from the upper Miocene to the Quaternary in western and southwestern Mongolia. We use a 1-D soil diffusion model to demonstrate that these δ¹³C increases are linked to declines in soil respiration driven by dramatic increases in aridity. Using modern-day empirical relations between mean annual precipitation and soil respiration, we estimate that precipitation has likely more than halved over the Neogene. Given the importance of the Hangay and Altai in steering moisture in Mongolia, we attribute these changes to differential surface uplift of the Hangay and Altai. Surface uplift in the Hangay began by the early Oligocene, blocking Siberian moisture and aridifying the northern Gobi. In contrast, surface uplift of the Altai began in the late Miocene, blocking moisture from reaching western Mongolia. Thus, the northern Gobi became increasingly arid east to west since the late Eocene, likely driven by orographic development in the Hangay during the Oligocene and the Altai in the late Miocene through Pliocene

Scale-free networks as preasymptotic regimes of superlinear preferential attachment

We study the following paradox associated with networks growing according to superlinear preferential attachment: superlinear preference cannot produce scale-free networks in the thermodynamic limit, but there are superlinearly growing network models that perfectly match the structure of some real scale-free networks, such as the Internet. We obtain an analytic solution, supported by extensive simulations, for the degree distribution in superlinearly growing networks with arbitrary average degree, and confirm that in the true thermodynamic limit these networks are indeed degenerate, i.e., almost all nodes have low degrees. We then show that superlinear growth has vast preasymptotic regimes whose depths depend both on the average degree in the network and on how superlinear the preference kernel is. We demonstrate that a superlinearly growing network model can reproduce, in its preasymptotic regime, the structure of a real network, if the model captures some sufficiently strong structural constraints -- rich-club connectivity, for example. These findings suggest that real scale-free networks of finite size may exist in preasymptotic regimes of network evolution processes that lead to degenerate network formations in the thermodynamic limit

Seismic Test of Solar Models, Solar Neutrinos and Implications for Metal-Rich Accretion

The Sun is believed to have been the recipient of a substantial amount of metal-rich material over the course of its evolution, particularly in the early stages of the Solar System. With a long diffusion timescale, the majority of this accreted matter should still exist in the solar convection zone, enhancing its observed surface abundance, and implying a lower-abundance core. While helioseismology rules out solar models with near-zero metallicity cores, some solar models with enhanced metallicity in the convection zone might be viable, as small perturbations to the standard model. Because of the reduced interior opacity and core temperature, the neutrino flux predicted for such models is lower than that predicted by the standard solar model. This paper examines how compatible inhomogeneous solar models of this kind are with the observed low and intermediate degree p-mode oscillation data, and with the solar neutrino data from the SNO Collaboration. We set an upper limit on how much metal-rich accretion took place during the early evolution of the Sun at about 2 Earth masses of iron (or about 40 Earth masses of meteoric material).Comment: Revision: 23 pages, 8 figures, 3 tables, to be published in ApJ, Sept 2002. Used newer neutrino cross sections, modified text accordingly, other minor revisions as wel