Influence of dissolved organic carbon on photochemically mediated cycling of hydrogen peroxide in rainwater

The influence of sunlight and dissolved organic carbon (DOC) on the photochemically mediated cycling of hydrogen peroxide (H₂O₂) was investigated in rainwater samples collected in Wilmington, North Carolina USA. Upon exposure to simulated sunlight 14 of 19 authentic rainwater samples exhibited significant decreases in H₂O₂. The concentration of hydrogen peroxide did not change significantly in organic-free synthetic rainwater spiked with H₂O₂ in the light or in dark controls suggesting that the loss was not due to direct photolysis or dark mediated reactions. There was a significant correlation between pseudo-first order rate constants of H₂O₂ decay and initial H₂O₂ concentrations. There was also a significant correlation between the rate constant and the abundance of DOC suggesting that rainwater organic carbon plays an important role during photolytic decay either via direct reaction or indirectly through production of peroxide reactive species or scavenging of peroxide generating radicals. Several rain samples exhibited an initial increase in H₂O₂ during the first 2 h of irradiation. These increases were generally small and most likely do not represent a significant input of peroxide in precipitation. The photo-induced destruction of H₂O₂ is important because it may partly explain the late afternoon decrease of peroxide concentrations observed in earlier field studies and the substantial under saturation (<10%) of this oxidant in rainwater compared with gas phase concentrations.     

Threatened archaeological,historic, and cultural resources of the Georgia Coast: Identification,prioritization and management using GIS technology

Archaeological sites in beach and estuarine environments are continually threatened by diverse natural marine processes. Shoreline erosion, bluff retreat, and sea level rise all present potential for site destruction. Using historic maps, aerial imagery, and field survey methods in a GIS, 21 potentially significant archaeological sites on Georgia barrier islands were selected for determination of site‐specific rates of shoreline change using a powerful, new, moving‐boundary GIS analysis tool. A prioritized list of sites, based on the order of site loss from erosion, was generated to assist coastal managers in identifying and documenting sites most at risk. From the original selection of 21 sites, 11 sites were eroding, 8 shorelines were stable, and 2 shorelines were accreting. The methodology outlined here produces critical information on archaeological site loss rates and provides a straightforward means of prioritizing sites for detailed documentation. © 2010 Wiley Periodicals, Inc.     

Mid-infrared spectral variability for compositionally similar asteroids: Implications for asteroid particle size distributions

We report an unexpected variability among mid-infrared spectra (IRTF and Spitzer data) of eight S-type asteroids for which all other remote sensing interpretations (e.g. VNIR spectroscopy, albedo) yield similar compositions. Compositional fitting making use of their mid-IR spectra only yields surprising alternative conclusions: (1) these objects are not “compositionally similar” as the inferred abundances of their main surface minerals (olivine and pyroxene) differ from one another by 35% and (2) carbonaceous chondrite and ordinary chondrite meteorites provide an equally good match to each asteroid spectrum.Following the laboratory work of Ramsey and Christensen (Ramsey, M.S., Christensen, P.R. [1998]. J. Geophys. Res. 103, 577-596), we interpret this variability to be physically caused by differences in surface particle size and/or the effect of space weathering processes. Our results suggest that the observed asteroids must be covered with very fine (<5 μm) dust that masks some major and most minor spectral features. We speculate that the compositional analysis may be improved with a spectral library containing a wide variety of well characterized spectra (e.g., olivine, orthopyroxene, feldspar, iron, etc.) obtained from very fine powders. In addition to the grain size effect, space weathering processes may contribute as well to the reduction of the spectral contrast. This can be directly tested via new laboratory irradiation experiments.     

Faraday Rotation Response to Coronal Mass Ejection Structure

We present the results from modeling the coronal mass ejection (CME) properties that have an effect on the Faraday rotation (FR) signatures that may be measured with an imaging radio antenna array such as the Murchison Widefield Array (MWA). These include the magnetic flux rope orientation, handedness, magnetic-field magnitude, velocity, radius, expansion rate, electron density, and the presence of a shock/sheath region. We find that simultaneous multiple radio source observations (FR imaging) can be used to uniquely determine the orientation of the magnetic field in a CME, increase the advance warning time on the geoeffectiveness of a CME by an order of magnitude from the warning time possible from in-situ observations at L ₁, and investigate the extent and structure of the shock/sheath region at the leading edge of fast CMEs. The magnetic field of the heliosphere is largely “invisible” with only a fraction of the interplanetary magnetic-field lines convecting past the Earth; remote sensing the heliospheric magnetic field through FR imaging from the MWA will advance solar physics investigations into CME evolution and dynamics.     

Use of stream response functions to determine impacts of replacing surface-water use with groundwater withdrawals

A regional-scale numerical groundwater model is used to study the impacts of replacing surface-water use with groundwater wells to improve low-flow stream conditions for endangered species within the Bertrand and Fishtrap watersheds, southern British Columbia, Canada and Washington, USA. Stream response functions ranging from 0 to 1.0 were calculated for individual wells placed within a steady-state groundwater flow model at varying distances from the streams to determine the impact that these replacement wells, operating under sustained pumping rates, would have on summer instream flows. Lower response ratios indicate groundwater pumping will have less of an impact on streamflow than taking an equivalent amount of water directly from a surface-water source. Results show that replacing surface-water use with groundwater withdrawals may be a viable alternative for increasing summer streamflows. Assuming combined response factors should be ≤0.5 for irrigators to undergo the expense of installing new wells, ~57% of the land area within 0.8 km of Bertrand Creek would be suitable for replacement wells. Similarly, 70% of the land area within 0.8 km of Fishtrap Creek was found to be appropriate. A visual analysis tool was developed using STELLA to allow stakeholders to quickly evaluate the impact associated with moving their water right.     

Future changes in Central Europe heat waves expected to mostly follow summer mean warming

Daily output from the PRUDENCE ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe is used to show that the increasing intensity of the most damaging summer heat waves over Central Europe is mostly due to higher base summer temperatures. In this context, base temperature is defined as the mean of the seasonal cycle component for those calendar days when regional heat waves occur and is close, albeit not identical, to the mean temperature for July–August. Although 36–47% of future Central Europe July and August days at the end of the twenty-first century are projected to be extreme according to the present day climatology, specific changes in deseasonalized heat wave anomalies are projected to be relatively small. Instead, changes in summer base temperatures appear much larger, clearly identifiable and of the same order of magnitude as changes in the whole magnitude of heat waves. Our results bear important consequences for the predictability of central European heat wave intensity under global warming conditions.     

The impact and rotational light curves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C₃, CH, C₂, NH₂, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400-600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way.     

High resolution profiles of vertical particulate organic matter export off Cape Blanc,Mauritania: Degradation processes and ballasting effects

Vertical carbon fluxes between the surface and 2500 m depth were estimated from in situ profiles of particle size distributions and abundances me/asured off Cape Blanc (Mauritania) related to deep ocean sediment traps. Vertical mass fluxes off Cape Blanc were significantly higher than recent global estimates in the open ocean. The aggregates off Cape Blanc contained high amounts of ballast material due to the presence of coccoliths and fine-grained dust from the Sahara desert, leading to a dominance of small and fast-settling aggregates. The largest changes in vertical fluxes were observed in the surface waters (<250 m), and, thus, showing this site to be the most important zone for aggregate formation and degradation. The degradation length scale (L), i.e. the fractional degradation of aggregates per meter settled, was estimated from vertical fluxes derived from the particle size distribution through the water column. This was compared with fractional remineralization rate of aggregates per meter settled derived from direct ship-board measurements of sinking velocity and small-scale O₂ fluxes to aggregates measured by micro-sensors. Microbial respiration by attached bacteria alone could not explain the degradation of organic matter in the upper ocean. Instead, flux feeding from zooplankton organisms was indicated as the dominant degradation process of aggregated carbon in the surface ocean. Below the surface ocean, microbes became more important for the degradation as zooplankton was rare at these depths.     

Shoreline management in a policy vacuum: A local authority perspective

In Ireland there is no national shoreline management policy. Instead, management involves a series of actions at the local authority (County) level that respond to local demands, politics and economics within only a broad legal framework. Through the COREPOINT project, University of Ulster scientists have been working with local authority officials in Donegal to bring a scientific understanding of coastal processes to bear on practical management. Experience at several sites has shown significant changes in practice as a result of this interaction, compared to the previous situation when rock armouring was the favoured response to coastal erosion. We argue that achieving sustainable approaches to coastal management in a policy vacuum relies on a combination of (i) commitment to these approaches by local officials, (ii) low levels of public pressure for action, and (iii) limited financial resources. A change in any one of these is likely to lead to unsustainable actions. While close co-operation with scientists can help management in the absence of a coherent policy, only a formal regulatory instrument can deliver sustainable shoreline management.     

In-situ hafnium and lead isotope analyses of detrital zircons from the Devonian sedimentary basin of NE Greenland: a record of repeated crustal reworking

An intramontane collapse basin developed within the hanging wall above the large-scale extensional Fjord Regional Detachment of NE Greenland in middle to late Devonian times. The continental clastic sediments within the basin are derived locally from Laurentian source rocks, which makes them well suited for a study of the crustal evolution of the source terrain. This is the first integrated in-situ Pb and Hf isotope study to be presented, and zircon data on a selected sandstone from the basin are combined with Sm-Nd whole-rock data on sand/siltstones. Nd whole-rock ages of two samples of sandstones and a siltstone are 2.0-2.1 Ga. Peak frequencies of zircon ²⁰⁷Pb/²⁰⁶Pb ages at 1,764-1,912 Ma, and ¹⁷⁶Hf/¹⁷⁷Hf values at 0.28142-0.28163 (t_DM=2.47 to 2.06) for the sandstone suggest the generation of a considerable volume of juvenile continental crust in the ultimate zircon provenance at 1.9-2.0 Ga. The Hf isotopic compositions of Archaean zircons in the sandstone are distinct from those of the source materials of Proterozoic protocrust at 1.9-2.0 Ga, but zircons with elevated Hf-t_DM ages of up to 2.47 Ga can be related to a component of Archaean crust or reworked Archaean material in the ultimate zircon source area. Zircon ²⁰⁷Pb/²⁰⁶Pb ages are also recorded at 1,480-1,572, 1,318 and 1,014 Ma (Grenvillian). The Hf isotope compositions of these zircons are consistent with reworking of the Proterozoic protocrust at these times, with little or no juvenile input. The Proterozoic zircons form two distinct groups defined by ¹⁷⁶Yb/¹⁷⁷Hf>0.05055 and ¹⁷⁶Yb/¹⁷⁷Hf<0.03301, and the latter group overlaps with Yb-Hf isotope data on the Archaean zircons. The two groups may represent zircons derived from evolved granites and intermediate to mildly felsic rocks, respectively. The repeated reworking of the continental crust also comprised erosion and deposition of sediments in the Proterozoic (the Krummedal sequence and the Eleonore Bay Supergroup, EBS) and intrusion of Caledonian anatectic granites in the EBS, which both represent provenance components to the Devonian sediments. No discrete Caledonian Pb-Pb zircon ages are recorded, but Caledonian magmatism may be represented by strongly discordant zircons which form arrays with a lower intercept age at ca. 400 Ma and an upper intercept at 1,600-2,000 Ma. One undated zircon records a ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282218, higher than that of the Proterozoic protocrust in Caledonian/late-Caledonian times (380-450 Ma) which may represent a Caledonian mantle contribution.