Pore fluid constraints on deep ocean temperature and salinity during the Last Glacial Maximum

Pore water records of δ^(18)O and [Cl] from ODP Site 1063A on the Bermuda Rise constrain the change in seawater δ^(18)O and salinity from the Last Glacial Maximum (LGM) to the Holocene to be 0.75±0.05‰ and 2.5±0.1% respectively. Coupled with a measured benthic foraminiferal δ^(18)O change, this result means that bottom waters were 4.6±0.8°C cooler than the Holocene at the LGM and therefore at or near the seawater freezing point. Coupled δ^(18)O and chlorinity results give an extrapolated mean ocean LGM to Holocene change in δ^(18)O of 0.95±0.09‰. These data also constrain the past southern source deep‐water salinity to be 35.76±0.04 psu, which is within error of the mean deep ocean value for this time

Seasonally resolved stable isotope chronologies from northern Thailand deciduous trees

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 235 (2005): 752-765, doi:10.1016/j.epsl.2005.05.012.Despite the existence of a number of climate proxies, the terrestrial expression of tropical climate variability over the past few centuries remains poorly resolved. We explore the applicability of stable isotope dendroclimatology as a tool for chronology and paleo-hydrology reconstruction on deciduous trees from monsoonal northern Thailand. Analysis of 11 trees coming from 4 different regions of northern Thailand yielded 7 records with varying degrees of δ18O and δ13C seasonality. We develop age models for trees lacking visible rings based on the seasonality of the δ18O and find agreement to within ≤ 3 years with radiocarbon age estimates. We use the isotopic age models to reconstruct estimates of growth rates and find a significant positive correlation between growth and amplitude of the oxygen and carbon seasonal isotopic signals. A comparison of a reconstructed dendro-isotopic index from Pangmapa with regional rainfall records indicates significant correlations consistent with the locally derived patterns but with decreased representation of the variance. Individual isotopic chronologies stemming from different tree species share common trends, which are also consistent with patterns of rainfall variability. We see an increase in the amplitude of the seasonal δ18O cycle along with an increase in δ18Omax over the past few decades suggesting a tracking of the recent drying trend of Thailand's monsoon.This research was supported by NSERC and the Teresa Heinz Scholarship for Environmental Research to PFP and Award #0402425 from the Paleoclimate Program of the Atmospheric Sciences Division of NSF to DPS

Neutralizing Carbonic Acid in Deep Carbonate Strata below the North Atlantic

Our research is aimed at investigating several technical issues associated with carbon dioxide sequestration in calcium carbonate sediments below the sea floor through laboratory experiments and chemical transport modeling. Our goal is to evaluate the basic feasibility of this approach, including an assessment of optimal depths, sediment types, and other issues related to site selection. The results of our modeling efforts were published this past summer in the Proceedings of the National Academy of Sciences. We are expanding on that work through a variety of laboratory and modeling efforts. In the laboratories at Columbia and at Harvard, we are studying the flow of liquid carbon dioxide and carbon dioxide-water mixtures through calcium carbonate sediments to better understand the geomechanical and structural stability of the sediments during and after injection. We are currently preparing the results of these findings for publication. In addition, we are investigating the kinetics of calcium carbonate dissolution in the presence of CO{sub 2}-water fluids, which is a critical feature of the system as it allows for increased permeability during injection. We are also investigating the possibility of carbon dioxide hydrate formation in the pore fluid, which might complicate the injection procedure by reducing sediment permeability but might also provide an upper seal in the sediment-pore fluid system, preventing release of CO{sub 2} into the deep ocean, particularly if depth and temperature at the injection point rule out immediate hydrate formation. This is done by injecting liquid CO{sub 2} into various types of porous media, and then monitoring the changes in permeability. Finally, we are performing an economic analysis to estimate costs of drilling and gas injection, site monitoring as well as the availability of potential disposal sites with particular emphasis on those sites that are within the 200-mile economic zone of the United States. We present some preliminary results from these analyses. A paper discussing the site selection based on data from the Ocean Drilling Program and Deep Sea Drilling Program is currently in preparation

An absolute reference frame for clumped isotope thermometry

Analysis of multiply substituted isotopologues of molecules (‘clumped isotope geochemistry’) presents special challenges to both precision and accuracy. Previous discussions have focused on mass spectrometric precision for these rare species and intralaboratory reference frames. This discipline has spread, demanding interlaboratory standardization. We present a four-laboratory study of the calibration of mass-47 anomalies (Δ_(47) values) in CO_2 (especially extracted from carbonate). We consider: instrument linearity, source fragmentation/recombination reactions (which vary between mass spectrometers and with time and instrument settings), and differences in methods, materials and conditions for sample preparation. We address these problems by developing a method for standardizing Δ_(47) measurements to an absolute reference frame based on theoretical predictions of the abundances of multiply-substituted isotopologues of gaseous CO_2 that has reached a thermodynamic equilibrium at a known temperature. By analyzing CO_2 gases that have been subjected to established laboratory procedures known to promote isotopic equilibration (i.e., heated gases and water-equilibrated CO_2), and by reference to the statistical thermodynamic predictions of equilibrium isotopic distributions, it is possible to construct an empirical transfer function that can then be applied to CO_2 samples with unknown Δ_(47) values. This reference frame may be unique in that it is based on thermodynamic equilibrium, rather than the isotopic composition of an arbitrary reference material. We describe the protocol necessary to construct such a reference frame, the method for converting gases with unknown clumped isotope compositions to this frame, and suggest a protocol for ensuring that reported Δ_(47) values can be compared among different laboratories, independent of laboratory-specific analytical or methodological artefacts. Application of this approach to measurements of CO_2 extracted from several carbonate reference materials results in interlaboratory agreement on their Δ_(47) values to within est. ±0.01 ‰, 1σ. Finally, we present a revised paleotemperature scale that applies when using the absolute reference frame described here, as opposed to the previous paleotemperature equation based on data from a single laboratory. More generally, this study presents a model for how interlaboratory standardization might be approached for other ‘clumped isotope’ measurements

Überinfusion von Verbrennungsopfern: häufig und schädlich

Zusammenfassung: Hintergrund: Schwerbrandverletzte (mehr als 20% verbrannter Körperoberfläche bei Erwachsenen) weisen in der ersten Phase (8-48h) einen durch das massive Kapillarleck bedingten Verbrennungsschock auf, der einer Infusionstherapie bedarf, um die Hämodynamik wieder herzustellen. Bis in die 80erJahre stellte eine unzureichende Flüssigkeitstherapie (Unterinfusion) die Haupttodesursache von Verbrennungspatienten dar. Seither ist die übermäßige Flüssigkeitstherapie (Überinfusion) zu einer beachtenswerten Quelle von Komplikationen geworden: abdominales Kompartmentsyndrom, Entlastungsschnitte (Escharotomie), Verschlechterung des Gasaustauschs, Verlängerung der künstlichen Beatmung und des Spitalaufenthalts. Die Überinfusion hat Ende der 90erJahre begonnen, wo innerhalb der ersten 24h Flüssigkeitsmengen zugeführt wurden, die weit über den 4ml/kg/%BSA ("burn surface area") der Parkland-Formel lagen. Ziel: Dieser Beitrag analysiert die Faktoren, welche zu einer Überinfusion führen können und zeigt Möglichkeiten, dem durch eine strikte Kontrolle der präklinischen Infusionstherapie sowie durch eine permissive Hypovolämie vorzubeuge

The energy penalty of post-combustion CO2 capture & storage and its implications for retrofitting the U.S. installed base

A review of the literature has found a factor of 4 spread in the estimated values of the energy penalty for post-combustion capture and storage of CO2 from pulverized-coal (PC) fired power plants. We elucidate the cause of that spread by deriving an analytic relationship for the energy penalty from thermodynamic principles and by identifying which variables are most difficult to constrain. We define the energy penalty for CCS to be the fraction of fuel that must be dedicated to CCS for a fixed quantity of work output. That penalty can manifest itself as either the additional fuel required to maintain a power plant's output or the loss of output for a constant fuel input. Of the 17 parameters that constitute the energy penalty, only the fraction of available waste heat that is recovered for use and the 2nd-law separation efficiency are poorly constrained. We provide an absolute lower bound for the energy penalty of ~11%, and we demonstrate to what degree increasing the fraction of available-waste-heat recovery can reduce the energy penalty from the higher values reported. It is further argued that an energy penalty of ~40% will be easily achieved while one of ~29% represents a decent target value. Furthermore, we analyze the distribution of PC plants in the U.S. and calculate a distribution for the additional fuel required to operate all these plants with CO2 capture and storage (CCS).Earth and Planetary SciencesEngineering and Applied Science

Biologically Induced Initiation of Neoproterozoic Snowball-Earth Events

The glaciations of the Neoproterozoic Era (1,000 to 542 MyBP) were preceded by dramatically light C isotopic excursions preserved in preglacial deposits. Standard explanations of these excursions involve remineralization of isotopically light organic matter and imply strong enhancement of atmospheric $CO_2$ greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We examine a scenario in which the isotopic signal, as well as the global glaciation, result from enhanced export of organic matter from the upper ocean into anoxic subsurface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate- or iron-reducing bacteria. In both cases, this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric $CO_2$ concentration, possibly plunging Earth into an ice age. This scenario predicts enhanced deposition of calcium carbonate, the formation of siderite, and an increase in ocean pH, all of which are consistent with recent observations. Late Neoproterozoic diversification of marine eukaryotes may have facilitated the episodic enhancement of export of organic matter from the upper ocean, by causing a greater proportion of organic matter to be partitioned as particulate aggregates that can sink more efficiently, via increased cell size, biomineralization or increased C∶N of eukaryotic phytoplankton. The scenario explains isotopic excursions that are correlated or uncorrelated with snowball initiation, and suggests that increasing atmospheric oxygen concentrations and a progressive oxygenation of the subsurface ocean helped to prevent snowball glaciation on the Phanerozoic Earth.Earth and Planetary Science

Uncovering the Neoproterozoic Carbon Cycle

Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter1,2. Neoproterozoic carbonate records contain unusualand large negative isotopic anomalies within long periods (10–100 million years) characterized by d13C in carbonate (d13Ccarb) enriched to more than +5 per mil. Classically, d13Ccarb is interpreted as a metric of the relative fraction of carbon buried as organic matter in marine sediments2–4, which can be linked to oxygen accumulation through the stoichiometry of primary production3,5. If a change in the isotopic composition of marine dissolved inorganic carbon is responsible for these excursions, it is expected that records of d13Ccarb and d13C in organic carbon (d13Corg) will covary, offset by the fractionation imparted by primary production5. The documentation of several Neoproterozoic d13Ccarb excursions that are decoupled from d13Corg, however, indicates that other mechanisms6–8 may account for these excursions. Here we present d13C data from Mongolia, northwest Canada and Namibia that capture multiple large-amplitude (over 10 per mil) negative carbon isotope anomalies, and use these data in a new quantitative mixing model to examine the behaviour of the Neoproterozoic carbon cycle. We find that carbonate and organic carbon isotope data from Mongolia and Canada are tightly coupled through multiple d13Ccarb excursions, quantitatively ruling out previously suggested alternative explanations, such as diagenesis7,8 or the presence and terminal oxidation of a large marine dissolved organic carbon reservoir6. Our data from Namibia, which do not record isotopic covariance, can be explained by simple mixing with a detrital flux of organic matter. We thus interpret d13Ccarb anomalies as recording a primary perturbation to the surface carbon cycle. This interpretation requires the revisiting of models linking drastic isotope excursions to deep ocean oxygenation and the opening of environments capable of supporting animals9–11.Earth and Planetary Science

Longitudinal decline in striatal dopamine transporter binding in Parkinson’s disease: associations with apathy and anhedonia

Background: Motivational symptoms such as apathy and anhedonia are common in Parkinson’s disease (PD), respond poorly to treatment, and are hypothesised to share underlying neural mechanisms. Striatal dopaminergic dysfunction is considered central to motivational symptoms in PD but the association has never been examined longitudinally. We investigated whether progression of dopaminergic dysfunction was associated with emergent apathy and anhedonia symptoms in PD. Methods: Longitudinal cohort study of 412 newly diagnosed patients with PD followed over 5 years as part of the Parkinson’s Progression Markers Initiative cohort. Apathy and anhedonia were measured using a composite score derived from relevant items of the 15-item Geriatric Depression Scale (GDS-15) and part I of the MDS-Unified Parkinson’s Disease Rating Scale. Dopaminergic neurodegeneration was measured using repeated striatal dopamine transporter (DAT) imaging. Results: Linear mixed-effects modelling across all contemporaneous data points identified a significant negative relationship between striatal DAT specific binding ratio (SBR) and apathy/anhedonia symptoms, which emerged as PD progressed (interaction:β=−0.09, 95% CI (−0.15 to 0.03), p=0.002). Appearance and subsequent worsening of apathy/anhedonia symptoms began on average 2 years after diagnosis and below a threshold striatal DAT SBR level. The interaction between striatal DAT SBR and time was specific to apathy/anhedonia symptoms, with no evidence of a similar interaction for general depressive symptoms from the GDS-15 (excluding apathy/anhedonia items) (β=−0.06, 95% CI (−0.13 to 0.01)) or motor symptoms (β=0.20, 95% CI (−0.25 to 0.65)). Conclusions: Our findings support a central role for dopaminergic dysfunction in motivational symptoms in PD. Striatal DAT imaging may be a useful indicator of apathy/anhedonia risk that could inform intervention strategies

Repositioning the Catalytic Triad Aspartic Acid of Haloalkane Dehalogenase: Effects on Stability, Kinetics, and Structure

Haloalkane dehalogenase (DhlA) catalyzes the hydrolysis of haloalkanes via an alkyl-enzyme intermediate. The covalent intermediate, which is formed by nucleophilic substitution with Asp124, is hydrolyzed by a water molecule that is activated by His289. The role of Asp260, which is the third member of the catalytic triad, was studied by site-directed mutagenesis. Mutation of Asp260 to asparagine resulted in a catalytically inactive D260N mutant, which demonstrates that the triad acid Asp260 is essential for dehalogenase activity. Furthermore, Asp260 has an important structural role, since the D260N enzyme accumulated mainly in inclusion bodies during expression, and neither substrate nor product could bind in the active-site cavity. Activity for brominated substrates was restored to D260N by replacing Asn148 with an aspartic or glutamic acid. Both double mutants D260N+N148D and D260N+N148E had a 10-fold reduced kcat and 40-fold higher Km values for 1,2-dibromoethane compared to the wild-type enzyme. Pre-steady-state kinetic analysis of the D260N+N148E double mutant showed that the decrease in kcat was mainly caused by a 220-fold reduction of the rate of carbon-bromine bond cleavage and a 10-fold decrease in the rate of hydrolysis of the alkyl-enzyme intermediate. On the other hand, bromide was released 12-fold faster and via a different pathway than in the wild-type enzyme. Molecular modeling of the mutant showed that Glu148 indeed could take over the interaction with His289 and that there was a change in charge distribution in the tunnel region that connects the active site with the solvent. On the basis of primary structure similarity between DhlA and other α/β-hydrolase fold dehalogenases, we propose that a conserved acidic residue at the equivalent position of Asn148 in DhlA is the third catalytic triad residue in the latter enzymes.