Assessing geochemical carbon management

The challenge of reversing rising atmospheric CO₂ concentrations is growing with the continued expansion of CO₂-emitting energy infrastructure throughout the world and with the lack of coordinated, effective measures to manage and reduce emissions. Given this situation, it is prudent for society to explore all potential carbon management options, including those with seemingly low probability for success. Recent initiatives for advancing and enhancing carbon storage options have focused primarily on the physical trapping of CO₂ in underground geologic formations and on the biological uptake of CO₂; less attention has been given to approaches that rely primarily on geochemical reactions that enhance transformation of CO₂ gas into dissolved or solid phase carbon by liberating cations to neutralize carbonic acid. This paper provides a structured review of the technical status of these geochemical approaches, and also presents a simple framework for assessing the potential and limitations of various proposed geochemical approaches to assist prioritizing future research in this area. Despite major limitations, geochemical approaches have unique potential to contribute to CO₂ reductions in ways that neither physical nor biological carbon storage can by allowing for the direct removal of CO₂ from the atmosphere with minimal requirements for integrating with existing infrastructure. Recognizing the severity and urgency of the need for carbon management options, we argue for an increase in research activity related to geochemical approaches to carbon management.     

Seasonal variations of the clear-sky greenhouse effect: the role of changes in atmospheric temperatures and humidities

We present an analysis of the factors which control the seasonal variations of the clear-sky greenhouse effect, based on satellite observations and radiative transfer simulations. The satellite observations include the radiation budget at the top of the atmosphere from the Earth Radiation Budget Experiment and the total column moisture content derived from the Special Sensor Microwave/Imager. The simulations were performed with the SAMSON system described in an earlier paper, using atmospheric temperatures and humidities from operational analyses produced by the European Centre for Medium Range Weather Forecasts. At low latitudes, the magnitude of the clear-sky greenhouse effect is dominated by the strong thermodynamic link between the total column moisture content of the atmosphere and sea surface temperatures, with minimal seasonal variations. In contrast, at middle to high latitudes there are strong seasonal variations, the clear-sky greenhouse effect being largest in winter and smallest in summer. These variations cannot be explained by the seasonal cycle in the total column moisture content, as this is largest in summer and smallest in winter. The variations are controlled instead by the seasonal changes in atmospheric temperatures. The colder atmosphere in winter enhances the temperature differential between the atmosphere and the sea surface, leading to a larger greenhouse effect despite the lower moisture contents. The magnitude of the clear-sky greenhouse effect is thus controlled by atmospheric humidity at low latitudes, but by atmospheric temperature at middle and high latitudes. These controls are illustrated by results from sensitivity experiments with SAMSON and are interpreted in terms of a simple model.     

Parallel optimal choropleth map classification in PySAL

In this article, we report on our experiences with refactoring a spatial analysis library to support parallelization. Python Spatial Analysis Library (PySAL) is a library of spatial analytical functions written in the open-source language, Python. As part of a larger scale effort toward developing cyberinfrastructure of GIScience, we examine the particular case of choropleth map classification through alternative parallel implementations of the Fisher-Jenks optimal classification method using a multi-core, single desktop environment. The implementations rely on three different parallel Python libraries, PyOpenCL, Parallel Python, (PP) and Multiprocessing. Our results point to the dominance of the CPU-based Parallel Python and Multiprocessing implementations over the Graphical Processing Unit (GPU)-based PyOpenCL approach.     

Computed and observed currents,elevations, and salinity in a branching estuary

A one-dimensional, hydrodynamical model of the Tamar Estuary shows good agreement with measured tidal elevations and currents. Computed currents are used to drive a one-dimensional moving-element model of the salt balance. The moving-element model overcomes the numerical difficulties associated with strong tidal advection. Axial distributions of salinity at high water, computed using the moving-element model, compare well with measurements. The modelled and observed high water salinity distributions in this macrotidal estuary show little dependence on tidal range. The major variability in salinity is due to runoff. This strong and rapid dependence on runoff is a consequence of short residence (or flushing) times. Typically, residence times are less than one day throughout the year in the upper 10 km of estuary. The residence times maximize in summer, reaching 14 d for the whole estuary. During high runoff winter periods residence times are less than 5 d. Mixing coefficients for the moving-element salinity model are deduced from salinity measurements. Dispersion coefficients at fixed locations along the estuary are deduced from solutions of the salinity model. The spatially-averaged coefficients at mean spring and neap tides are 180 and 240 m² s^?1, respectively, for average runoff. Therefore, spring-neap variations in dispersion are fairly small and show a negative correlation with tidal range. The spatially-averaged dispersion coefficients at mean tides vary from 150 to 300 m² s^?1 for typical summer and winter runoff, respectively. The increase in dispersion with runoff and the decrease with tidal range implies that buoyancy-driven currents generate an important component of the shear dispersion in this estuary.     

Event monitoring of herbicides with naked and membrane-covered Empore disk integrative passive sampling devices

Subsequent to an initial wet season flood event in the Brisbane River, Australia, both fast (naked disk) and slow (membrane-covered) variants of SDB-RPS Empore disk passive sampling devices were deployed with an automated grab sampling program. A trend increase in the aquatic dissolved concentrations of diuron and simazine was observed over a 10-day period. Kinetic and equilibrium parameters for each sampler were calculated based on the dynamic concentration. Absolute percent difference for duplicate passive samples was <10% in the fast and <25% in the slow samplers. For kinetic sampling, significantly shortened integrative periods are available with the fast compared with the slow variant, with higher sampling rates offering improved detection limits. The study demonstrates a method for determining kinetic parameters of passive samplers in a variable concentration field deployment, and illustrates the differences in quality between active and passive data, in terms of capturing changes in concentration associated with rainfall events.     

The effects of Hurricane Irene and Tropical Storm Lee on the bed sediment geochemistry of U.S. Atlantic coastal rivers

Hurricane Irene and Tropical Storm Lee, both of which made landfall in the U.S. between late August and early September 2011, generated record or near record water discharges in 41 coastal rivers between the North Carolina/South Carolina border and the U.S./Canadian border. Despite the discharge of substantial amounts of suspended sediment from many of these rivers, as well as the probable influx of substantial amounts of eroded material from the surrounding basins, the geochemical effects on the <63‐µm fractions of the bed sediments appear relatively limited [<20% of the constituents determined (256 out of 1394)]. Based on surface area measurements, this lack of change occurred despite substantial alterations in both the grain size distribution and the composition of the bed sediments. The sediment‐associated constituents which display both concentration increases and decreases include: total sulfur (TS), Hg, Ag, total organic carbon (TOC), total nitrogen (TN), Zn, Se, Co, Cu, Pb, As, Cr, and total carbon (TC). As a group, these constituents tend to be associated either with urbanization/elevated population densities and/or wastewater/solid sludge. The limited number of significant sediment‐associated chemical changes that were detected probably resulted from two potential processes: (1) the flushing of in‐stream land‐use affected sediments that were replaced by baseline material more representative of local geology and/or soils (declining concentrations), and/or (2) the inclusion of more heavily affected material as a result of urban nonpoint‐source runoff and/or releases from flooded treatment facilities (increasing concentrations). Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Whewellite and its key role in living systems

Whewellite is the dominant mineral in the plant kingdom, and one of the most important minerals within the surface veneer of our planet. It is intimately associated with the functioning of living systems and plays a significant role in the carbon cycle. The monohydrate form of calcium oxalate, whewellite, commonly occurs along with the less stable dihydrate form (weddellite). These minerals are not restricted to plants—humans may be painfully aware of whewellite as the principal mineral phase of urinary stones. Geologically whewellite is found in diagenetic settings, hydrothermal veins and in meteorites (carbonaceous chondrites), nevertheless the mineral is massively under‐represented in the geological column given its high productivity in the biosphere. Reasons for this are explored, and it is argued that a better understanding of the relationship between whewellite and host organisms will have benefits for agriculture, medicine, and potentially strategies for CO₂ sequestration.     

Concentrations and annual fluxes of sediment‐associated chemical constituents from conterminous US coastal rivers using bed sediment data

Coastal rivers represent a significant pathway for the delivery of natural and anthropogenic sediment‐associated chemical constituents to the Atlantic, Pacific and Gulf of Mexico coasts of the conterminous USA. This study entails an accounting segment using published average annual suspended sediment fluxes with published sediment‐associated chemical constituent concentrations for (1) baseline, (2) land‐use distributions, (3) population density, and (4) worldwide means to estimate concentrations/annual fluxes for trace/major elements and total phosphorus, total organic and inorganic carbon, total nitrogen, and sulphur, for 131 coastal river basins. In addition, it entails a sampling and subsequent chemical analysis segment that provides a level of ‘ground truth’ for the calculated values, as well as generating baselines for sediment‐associated concentrations/fluxes against which future changes can be evaluated. Currently, between 260 and 270 Mt of suspended sediment are discharged annually from the conterminous USA; about 69% is discharged from Gulf rivers (n = 36), about 24% from Pacific rivers (n = 42), and about 7% from Atlantic rivers (n = 54). Elevated sediment‐associated chemical concentrations relative to baseline levels occur in the reverse order of sediment discharges: Atlantic rivers (49%) > Pacific rivers (40%) > Gulf rivers (23%). Elevated trace element concentrations (e.g. Cu, Hg, Pb, Zn) frequently occur in association with present/former industrial areas and/or urban centres, particularly along the northeast Atlantic coast. Elevated carbon and nutrient concentrations occur along both the Atlantic and Gulf coasts but are dominated by rivers in the urban northeast and by southeastern and Gulf coast (Florida) ‘blackwater’ streams. Elevated Ca, Mg, K, and Na distributions tend to reflect local petrology, whereas elevated Ti, S, Fe, and Al concentrations are ubiquitous, possibly because they have substantial natural as well as anthropogenic sources. Almost all the elevated sediment‐associated chemical concentrations found in conterminous US coastal rivers are lower than worldwide averages. Copyright © 2012 John Wiley & Sons, Ltd.     

Laboratory analogues to cosmic dust

A pulsed laser has been used to vaporize olivine, pyroxene, nickel-iron alloy, Al₂O₃, carbon, calcium carbonate, and silicon carbide, as well as mixtures of immiscible phases (Au–Al₂O₃ and Au-olivine) in oxidizing, reducing, and inert atmospheres. The collected condensates usually consist of strings of grains which have a median diameter of 20–30 nm, which is comparable to the calculated sizes of some interstellar and circumstellar dust grains. The silicate minerals vaporized in O₂ as well as calcium carbonate and carbon vaporized in Ar or H₂, are collected as glassy grains while the other materials produced crystalline grains. The systems of immiscible phases when vaporized produced condensates consisting of intermixed 2–50 nm grains of both components. The type of size distribution, crystal structures, and qualitiative elemental analyses of the condensates are given. Possible similarities between the mechanism of grain growth, structure, morphology, and chemistry of laboratory grains compared to interstellar and circumstellar grains, phases in meteorites and extraterrestrial dust collected in the stratosphere are examined. Applications of the experimental technique include the production of grain systems to serve as laboratory analogues for spectral studies of grain materials believed to exist in astronomical environments, and studies of the structure of grains condensed from complex gas mixtures.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978.