Sheetfloods,sheetwash, sheetflow,or ... ?

Following McGee's (1897) use of the term sheetflood, there developed a variety of conflicting opinions and numerous terminologies relating to this process, many of which are ill-considered and poorly defined. A classification system is devised on both a hydrologic and geomorphic basis which dispenses with many superfluous terms that have been used with respect to sheetfloods. Magnitude of a storm is expressed in terms of the amount of surface runoff generated from a given storm due to the surface conditions.A sheetflood is defined as a sheet of unconfined flood water moving down a slope. The frequency of a sheetflood is relatively low while its magnitude is relatively great. Sheetflow is defined as relatively high-frequency, low-magnitude overland flow occurring in a continuous sheet and is restricted to laminar flow conditions. Sheetwash, a term of geomorphic origin, is considered to be redundant and is superseded by the more meaningful term rainwash defined as the washing action of rain on slopes.     

Transport and sediment accumulation of210Pb and137Cs in two Southeast Alaskan fjords

Sediment profiles of²¹⁰Pb and¹³⁷Cs in cores collected at increasing distances from the heads of Smeaton Bay and Boca de Quadra fjords indicate that watersheds influence the inventories of radioisotopes present and that the steep topographies of the fjords enhance sediment redistribution. Episodic deposition of terrestrially derived sediment was responsible for roughly 50% of the¹³⁷Cs and 45% of the²¹⁰Pb inventories in shallower (less than 180 m) locations in Wilson and Bakewell arms of Smeaton Bay.²¹⁰Pb sedimentation rates at shallower sites when corrected for episodic deposition were less than sedimentation rates obtained in the deep basins of the fjords where sediment focusing and increased primary productivity in the overlying water column occur. Higher fluxes of dissolved Mn from surficial sediments and subsequent reoxidation in the overlying water may have enhanced scavenging of²¹⁰Pb in basin locations, resulting in higher inventories. Episodic events have occurred frequently in Smeaton Bay and Boca de Quadra suggesting that steady-state conditions with respect to sedimenting particles can be achieved only when averaged over long time periods approaching the time over which¹³⁷Cs and²¹⁰Pb are useful.     

In situ U–Pb dating of micro-baddeleyite by secondary ion mass spectrometry

We introduce a technique for U–Pb dating of baddeleyite using secondary ion mass spectrometry (SIMS) in situ analysis of ng-mass crystals that cannot be efficiently extracted by conventional mineral separation techniques. Average ²⁰⁷Pb/²⁰⁶Pb ages for Precambrian baddeleyite crystals are within < 0.3% of the respective isotope dilution thermal ionization mass spectrometry (ID-TIMS) ages. ²⁰⁶Pb/²³⁸U ratios are corrected for instrumental fractionation calibrated through linear regression in a Pb/U relative sensitivity vs. UO₂⁺/U⁺ calibration plot. Calibration is performed on separated baddeleyite crystals (～ 100–200 μm in maximum dimension) mounted in random crystallographic orientation. ²⁰⁶Pb/²³⁸U ages for baddeleyite from Duluth gabbro (FC4b) and Kovdor are accurate within 1–2% when averaging 15–30 individual spot analyses and relative sensitivities calibrated on Phalaborwa baddeleyite. The relative difference of ²⁰⁶Pb/²³⁸U between large crystals and micro-baddeleyite from FC4b is within ～ 1%. Comparison between silicate glass and baddeleyite, as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in Pb/U sensitivity in baddeleyite due to variable crystal orientations. We successfully utilized oxygen flooding and a UO₂⁺/U⁺-based calibration to significantly reduce orientation dependent bias.     

Using simulated hydrologic response to revisit the 1973 Lerida Court landslide

Hydrologically driven mass wasting in the form of landslides on steep slopes is a worldwide occurrence. High-profile events in, for example, Brazil, Chile, the Philippines, Puerto Rico, and Venezuela during the last three decades all clearly illustrate, based upon significant losses of life and property, that hydrologically driven slope instability in developed (urban) areas can be a major geologic/environmental hazard. The focus of this study is the 1973 hydrologically driven Lerida Court landslide in Portola Valley, CA, USA. Physics-based hydrologic-response simulation, with the comprehensive Integrated Hydrology Model, was employed to forensically estimate the spatiotemporal pore pressure distributions for the Lerida Court site. Slope stability, driven by the simulated pore pressure dynamics, was estimated for the Lerida Court site with the infinite slope/Factor of Safety approach. The pore pressure dynamics for the Lerida Court site were reasonably captured by the hydrologic-response simulation. The estimated time of slope failure for the Lerida Court site compares well with field observations. A recommendation is made that hydrologically driven slope stability estimates including variably saturated subsurface flow be standard protocol for development sites in steep urban settings.     

Elevated concentrations of formate, acetate and dissolved organic carbon found at the Lost City hydrothermal field

Fluids from the ultramafic-hosted Lost City hydrothermal field were analyzed for total dissolved organic carbon and dissolved organic acids. Formate (36-158 μmol/kg) and acetate (1-35 μmol/kg) concentrations are higher than in other fluids from unsedimented hydrothermal vents, and are a higher ratio of the total dissolved organic carbon than has been found in most marine geothermal systems. Isotopic evidence is consistent with an abiotic formation mechanism for formate, perhaps during serpentinization processes in the sub-surface. Further support comes from previous studies where the abiological formation of low molecular weight organic acids has been shown to be thermodynamically favorable during hydrothermal alteration of olivine, and laboratory studies in which the reduction of carbon dioxide to formate has been confirmed. As the second most prevalent carbon species after methane, formate may be an important substrate to microbial communities in an environment where dissolved inorganic carbon is limited. Acetate is found in locations where sulfate reduction is believed to be important and is likely to be a microbial by-product, formed either directly by autotrophic metabolic activity or indirectly during the fermentative degradation of larger organic molecules. Given the common occurrence of exposed ultramafic rocks and active serpentinization within the worlds ocean basins, the abiotic formation of formate may be an important process supporting life in these high pH environments and may have critical implications to understanding the organic precursors from which life evolved.     

Coral Transplantation: A Useful Management Tool or Misguided Meddling?

The primary objectives of coral transplantation are to improve reef ‘quality' in terms of live coral cover, biodiversity and topographic complexity. Stated reasons for transplanting corals have been to: (1) accelerate reef recovery after ship groundings, (2) replace corals killed by sewage, thermal effluents or other pollutants, (3) save coral communities or locally rare species threatened by pollution, land reclamation or pier construction, (4) accelerate recovery of reefs after damage by Crown-of-thorns starfish or red tides, (5) aid recovery of reefs following dynamite fishing or coral quarrying, (6) mitigate damage caused by tourists engaged in water-based recreational activities, and (7) enhance the attractiveness of underwater habitat in tourism areas. Whether coral transplantation is likely to be effective from a biological standpoint depends on, among other factors, the water quality, exposure, and degree of substrate consolidation of the receiving area. Whether it is necessary (apart from cases related to reason 3 above), depends primarily on whether the receiving area is failing to recruit naturally.

The potential benefits and dis-benefits of coral transplantation are examined in the light of the results of research on both coral transplantation and recruitment with particular reference to a 4.5 year study in the Maldives. We suggest that in general, unless receiving areas are failing to recruit juvenile corals, natural recovery processes are likely to be sufficient in the medium to long term and that transplantation should be viewed as a tool of last resort. We argue that there has been too much focus on transplanting fast-growing branching corals, which in general naturally recruit well but tend to survive transplantation and re-location relatively poorly, to create short-term increases in live coral cover, at the expense of slow-growing massive corals, which generally survive transplantation well but often recruit slowly. In those cases where transplantation is justified, we advocate that a reversed stance, which focuses on early addition of slowly recruiting massive species to the recovering community, rather than a short-term and sometimes short-lived increase in coral cover, may be more appropriate in many cases.     

Replacing carbon lost from forests: an assessment of insurance, reserves, and expiring credits

Concern over the “non-permanence” or reversibility of carbon sequestration projects has been prominent in discussions over how to develop guidelines for forest project investments under the Clean Development Mechanism (CDM) of the UNFCCC Kyoto Protocol. Accordingly, a number of approaches have been proposed that aim to help ensure that parties do not receive credit for carbon that is lost before project obligations are fulfilled. These approaches include forest carbon insurance, land reserves, and issuance of expiring credits. The potential costs of each of these different approaches are evaluated using a range of assumptions about project length, risk and discount rate, and a comparison of costs is ventured based on the estimated reduction in value of these credits compared with uninsured, and permanent credits. Obstacles to participation in the different approaches are discussed related to problems of long-term commitments, project scale, rising replacement costs, and low credit value. It is concluded that a system of expiring credits, which could be coupled with insurance or reserves, could guarantee obligations that span time-scales longer than that of conventional insurance policies while maintaining incentives for long-term sequestration.     

Impact of the Montreal protocol and its amendments on the rate of change of global radiative forcing

Increases in chlorinated and brominated halocarbons are believed to be responsible for the depletion of stratospheric ozone observed over much of the globe in the past decade or so. Ozone depletion is in turn believed to lead to a negative radiative forcing, tending to cool the stratosphere and the surface. We show that the increasing atmospheric concentrations of ozone-depleting halocarbons and onset of related ozone depletion likely led to a negative forcing of the climate system in the 1980s that slowed significantly the rate of change of total anthropogenic radiative forcing due to the combined effect of all greenhouse gases over that decade. Within the next decade, emissions of these halocarbons are expected to rapidly decrease, with corresponding impacts on ozone and radiative forcing. As the emissions of ozone-depleting gases are reduced and eventually phased out, the rate of ozone depletion is expected to decrease and eventually reverse. All other things being equal, we show that the change from deepening ozone depletion in the 1980s to ozone increases in the future should lead to a pronounced increase in the decadal rate of change of anthropogenic greenhouse forcing of the next few decades, perhaps to levels unprecedented in this century.     

Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core

This work presents the refractory black carbon(rBC)results of a snow and firn core drilled in West Antarctica(79°55'34.6"S,94°21'13.3"W)during the 2014?15 austral summer,collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse.The core was drilled to a depth of 20 m,and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling.The core was analyzed at the Department of Geological Sciences,Central Washington University(CWU),WA,USA,using a single particle soot photometer(SP2)coupled to a CETAC Marin-5 nebulizer.The continuous melting system was recently assembled at CWU and these are its first results.We also present experimental results regarding SP2 reproducibility,indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations,like those found in the Antarctic core.Dating was carried out using mainly the rBC variation and sulfur,sodium and strontium as secondary parameters,giving the core 17 years(1998?2014).The data show a well-defined seasonality of rBC concentrations for these first meters,with geometric mean summer/fall concentrations of 0.016μg L^?1 and geometric mean winter/spring concentrations of 0.063μg L^?1.The annual rBC concentration geometric mean was 0.029μg L^?1(the lowest of all rBC cores in Antarctica referenced in this work),while the annual rBC flux was 6.1μg m^?2 yr^?1(the lowest flux in West Antarctica records so far).