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961.
Arne Krtzinger Ludger Mintrop Douglas W. R. Wallace Kenneth M. Johnson Craig Neill Bronte Tilbrook Philip Towler Hisayuki Y. Inoue Masao Ishii Gary Shaffer Rodrigo F. Torres Saavedra Eiji Ohtaki Eiji Yamashita Alain Poisson Christian Brunet Bernard Schauer Catherine Goyet Greg Eischeid 《Marine Chemistry》2000,72(2-4)
The ‘International Intercomparison Exercise of fCO2 Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO2) systems, one discrete fCO2 system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO2 measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final fCO2 were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO2 in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO2 measurements can be made in good agreement (±3 μatm) with underway fCO2 data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO2 results. Calculation of fCO2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO2 measurements. 相似文献
962.
S. E. Fitzwater K. S. Johnson R. M. Gordon K. H. Coale W. O. Smith Jr. 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)
Dissolved and particulate trace metal concentrations (dissolved Fe, Zn, Cd, Co, Cu and Ni; particulate Fe, Mn and Al) were measured along two transects in the Ross Sea during austral summer of 1990. Total Fe concentrations in southern Ross Sea and inshore waters were elevated >3.5 times that of northern waters. Dissolved Zn, Cd and Co concentrations were lower by factors of 4.5, 3.5 and 1.6 in southern surface waters relative to northern waters. Dissolved Cu and Ni concentrations were similar in both areas. Elevated Fe concentrations coincided with areas of increased productivity, phytoplankton biomass and nutrient drawdown, indicating that Fe is an important factor controlling the location of phytoplankton blooms in the Ross Sea. Particulate concentrations of Fe, Mn and Al indicate two possible sources of iron to the Ross Sea, resuspension of continental shelf sediments and iron incorporated in annual sea ice and released with meltwaters. 相似文献
963.
Few approaches exist that explicitly use the uncertainty associated with the spread of climate model simulations in assessing climate change impacts. An approach that does so is second-order approximation (SOA). This incorporates quantification of uncertainty to ascertain its impact on the derived response using a Taylor series expansion of the model. This study uses SOA in a statistical downscaling model of monthly streamflow, with a focus on the influence of dependence in the uncertainty of multiple atmospheric variables. Uncertainty is quantified using the square root error variance concept with a new extension that allows the inter-dependence terms among the atmospheric variable uncertainty to be specified. Applying the model to selected point locations in Australia, it is noted that the downscaling results differ considerably from downscaling that ignores uncertainty. However, when the effects of dependence in uncertainty are incorporated, the results differ according to the regional variations in dependence structure. 相似文献
964.
Groundwater, an essential resource, is likely to change with global warming because of changes in the CO2 levels, temperature and precipitation. Here, we combine water isotope geochemistry with climate modelling to examine future groundwater recharge in southwest Ohio, USA. We first establish the stable isotope profiles of oxygen and deuterium in precipitation and groundwater. We then use an isotope mass balance model to determine seasonal groundwater recharge from precipitation. Climate model output is used to project future changes in precipitation and its seasonal distribution under medium and high climate change scenarios. Finally, these results are combined to examine future changes in groundwater recharge. We find that 76% of the groundwater recharge occurs in the cool season. Climate models project precipitation increase in the cool season and decrease in the warm season. The total groundwater recharge is expected to increase by 3.2% (8.8%) under the medium (high) climate change scenarios. 相似文献
965.
966.
967.
P. W. Boyd P. J. Harrison B. D. Johnson 《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12)
This volume of DSR II is dedicated to the Canadian Joint Global Ocean Flux Study (JGOFS) in the NE subarctic Pacific. This oceanic province is one of three High Nitrate Low Chlorophyll (HNLC) regions in the world oceans. Furthermore, this region is characterised by a shallow (ca. 100–120 m) permanent pycnocline during winter, which permits relatively high numbers of phytoplankton and micro-grazers to subsist over winter, which in turn strongly influences pelagic community structure. The 5-year field study encompassed two phases – phase 1 (seven voyages between September 1992 and May 1995), and the intensive phase 2 (six voyages between September 1995 and June 1997). Each voyage transected line P – from the coastal ocean westward to the open ocean. In addition to the JGOFS study, this volume also includes analyses of long time-series (>20 yr) data sets from Ocean Station Papa (OSP; 50°N 145°W) and other stations in the coastal and open ocean. 相似文献
968.
Topographic correlations with soil and regolith thickness from shallow‐seismic refraction constraints across upland hillslopes in the Valles Caldera,New Mexico
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How rock is weathered physically and chemically into transportable material is a fundamental question in critical‐zone science. In addition, the distribution of weathered material (soil and intact regolith) across upland landscapes exerts a first‐order control on the hydrology of watersheds. In this paper we present the results of six shallow seismic‐refraction surveys in the Redondo Mountain region of the Valles Caldera, New Mexico. The P‐wave velocities corresponding to soil (≤ 0.6 km s?1) were inferred from a seventh seismic survey where soil‐thickness data were determined by pit excavation. Using multivariable regression, we quantified the relationships among slope gradient, aspect, and topographic wetness index (TWI) on soil and regolith (soil plus intact regolith) thicknesses. Our results show that both soil and regolith thicknesses vary inversely with TWI in all six survey areas while varying directly with slope aspect (i.e. thicker beneath north‐facing slopes) and inversely with slope gradient (i.e. thinner beneath steep slopes) in the majority of the survey areas. An empirical model based on power‐law relationships between regolith thickness and its correlative variables can fit our inferred thicknesses with R2 ‐values up to 0.880 for soil and 0.831 for regolith in areas with significant topographic variations. These results further demonstrate the efficacy of shallow seismic refraction for mapping and determining how soil and regolith variations correlate with topography across upland landscapes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
969.
Timothy C. Johnson Roelof J. Versteeg Frederick D. Day‐Lewis William Major John W. Lane Jr. 《Ground water》2015,53(6):920-932
Biostimulation is increasingly used to accelerate microbial remediation of recalcitrant groundwater contaminants. Effective application of biostimulation requires successful emplacement of amendment in the contaminant target zone. Verification of remediation performance requires postemplacement assessment and contaminant monitoring. Sampling‐based approaches are expensive and provide low‐density spatial and temporal information. Time‐lapse electrical resistivity tomography (ERT) is an effective geophysical method for determining temporal changes in subsurface electrical conductivity. Because remedial amendments and biostimulation‐related biogeochemical processes often change subsurface electrical conductivity, ERT can complement and enhance sampling‐based approaches for assessing emplacement and monitoring biostimulation‐based remediation. Field studies demonstrating the ability of time‐lapse ERT to monitor amendment emplacement and behavior were performed during a biostimulation remediation effort conducted at the Department of Defense Reutilization and Marketing Office (DRMO) Yard, in Brandywine, Maryland, United States. Geochemical fluid sampling was used to calibrate a petrophysical relation in order to predict groundwater indicators of amendment distribution. The petrophysical relations were field validated by comparing predictions to sequestered fluid sample results, thus demonstrating the potential of electrical geophysics for quantitative assessment of amendment‐related geochemical properties. Crosshole radar zero‐offset profile and borehole geophysical logging were also performed to augment the data set and validate interpretation. In addition to delineating amendment transport in the first 10 months after emplacement, the time‐lapse ERT results show later changes in bulk electrical properties interpreted as mineral precipitation. Results support the use of more cost‐effective surface‐based ERT in conjunction with limited field sampling to improve spatial and temporal monitoring of amendment emplacement and remediation performance. 相似文献
970.
Numerical studies of existing buildings demonstrate the effectiveness of nonlinear/inelastic rooftop tuned mass damper frames (NRTMDF) used as a retrofit for reducing seismic response. The technique utilizes a rooftop penthouse as a tuned mass damper with mass incorporated as the roof deck of the penthouse while targeted nonlinearity and energy dissipation are introduced through buckling restrained braces (BRBs) linking the penthouse mass to the structure below. The writers summarize numerical studies of ten existing buildings modified with a specifically tuned NRTMDF. The studies demonstrate the effectiveness of the technique that stems from elastic and transient inelastic period shifts enabled by the damper coupled with targeted energy dissipation in the penthouse BRBs. Numerical simulations using response nonlinear time‐history analysis techniques show that for many structures and sites, the NRTMDF decreases peak transient response and overall seismic demand of the original structure. The technique also reduces seismic demand on nonstructural elements and components, manifested as reductions in floor acceleration spectra. Energy methods show that the approach enables significant reductions in energy demand on the original structure through the complete earthquake acceleration history. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献