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951.
Formation rates of Subantarctic mode water and Antarctic intermediate water within the South Pacific 总被引:1,自引:0,他引:1
Corinne A. Hartin Rana A. FineBernadette M. Sloyan Lynne D. TalleyTeresa K. Chereskin James Happell 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):524-534
The formation of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) significantly contributes to the total uptake and storage of anthropogenic gases, such as CO2 and chlorofluorocarbons (CFCs), within the world's oceans. SAMW and AAIW formation rates in the South Pacific are quantified based on CFC-12 inventories using hydrographic data from WOCE, CLIVAR, and data collected in the austral winter of 2005. This study documents the first wintertime observations of CFC-11 and CFC-12 saturations with respect to the 2005 atmosphere in the formation region of the southeast Pacific for SAMW and AAIW. SAMW is 94% and 95% saturated for CFC-11 and CFC-12, respectively, and AAIW is 60% saturated for both CFC-11 and CFC-12. SAMW is defined from the Subantarctic Front to the equator between potential densities 26.80-27.06 kg m−3, and AAIW is defined from the Polar Front to 20°N between potential densities 27.06-27.40 kg m−3. CFC-12 inventories are 16.0×106 moles for SAMW and 8.7×106 moles for AAIW, corresponding to formation rates of 7.3±2.1 Sv for SAMW and 5.8±1.7 Sv for AAIW circulating within the South Pacific. Inter-ocean transports of SAMW from the South Pacific to the South Atlantic are estimated to be 4.4±0.6 Sv. Thus, the total formation of SAMW in the South Pacific is approximately 11.7±2.2 Sv. These formation rates represent the average formation rates over the major period of CFC input, from 1970 to 2005. The CFC-12 inventory maps provide direct evidence for two areas of formation of SAMW, one in the southeast Pacific and one in the central Pacific. Furthermore, eddies in the central Pacific containing high CFC concentrations may contribute to SAMW and to a lesser extent AAIW formation. These CFC-derived rates provide a baseline with which to compare past and future formation rates of SAMW and AAIW. 相似文献
952.
James V. Lambers Margot G. Gerritsen Bradley T. Mallison 《Computational Geosciences》2008,12(3):399-416
We propose a new single-phase local upscaling method that uses spatially varying multipoint transmissibility calculations.
The method is demonstrated on two-dimensional Cartesian and adaptive Cartesian grids. For each cell face in the coarse upscaled
grid, we create a local fine grid region surrounding the face on which we solve two generic local flow problems. The multipoint
stencils used to calculate the fluxes across coarse grid cell faces involve the six neighboring pressure values. They are
required to honor the two generic flow problems. The remaining degrees of freedom are used to maximize compactness and to
ensure that the flux approximation is as close as possible to being two-point. The resulting multipoint flux approximations
are spatially varying (a subset of the six neighbors is adaptively chosen) and reduce to two-point expressions in cases without
full-tensor anisotropy. Numerical tests show that the method significantly improves upscaling accuracy as compared to commonly
used local methods and also compares favorably with a local–global upscaling method. 相似文献
953.
by James E. Landmeyer Paul M. Bradley Donald A. Trego Kevin G. Hale Joseph E. Haas II 《Ground water》2010,48(1):30-41
Groundwater contamination by fuel-related compounds such as the fuel oxygenates methyl tert -butyl ether (MTBE), tert -butyl alcohol (TBA), and tert -amyl methyl ether (TAME) presents a significant issue to managers and consumers of groundwater and surface water that receives groundwater discharge. Four sites were investigated on Long Island, New York, characterized by groundwater contaminated with gasoline and fuel oxygenates that ultimately discharge to fresh, brackish, or saline surface water. For each site, contaminated groundwater discharge zones were delineated using pore water geochemistry data from 15 feet (4.5 m) beneath the bottom of the surface water body in the hyporheic zone and seepage-meter tests were conducted to measure discharge rates. These data when combined indicate that MTBE, TBA, and TAME concentrations in groundwater discharge in a 5-foot (1.5-m) thick section of the hyporheic zone were attenuated between 34% and 95%, in contrast to immeasurable attenuation in the shallow aquifer during contaminant transport between 0.1 and 1.5 miles (0.1 to 2.4 km). The attenuation observed in the hyporheic zone occurred primarily by physical processes such as mixing of groundwater and surface water. Biodegradation also occurred as confirmed in laboratory microcosms by the mineralization of U- 14 C-MTBE and U-14 C-TBA to 14 CO2 and the novel biodegradation of U- 14 C-TAME to 14 CO2 under oxic and anoxic conditions. The implication of fuel oxygenate attenuation observed in diverse hyporheic zones suggests an assessment of the hyporheic zone attenuation potential (HZAP) merits inclusion as part of site assessment strategies associated with monitored or engineered attenuation. 相似文献
954.
Jörg Geldmacher Kaj Hoernle Barry B. Hanan Janne Blichert-Toft F. Hauff James B. Gill Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2011,162(1):21-36
The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent
hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different
mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all
major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), 176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic
Hf isotopic compositions (176Hf/177Hfm up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend
on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately
enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component
of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between
(1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira
trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic.
Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is
believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower
176Hf/177Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat
older recycling ages of ≥1 Ga. 相似文献
955.
13C/12C and 18O/16O ratios of aragonite shells of modern land snails from the southern Great Plains of North America were measured for samples from twelve localities in a narrow east-west corridor that extended from the Flint Hills in North Central Oklahoma to the foothills of the Sangre de Cristo Mountains in Northern New Mexico, USA. Across the study area, shell δ18O values (PDB scale) ranged from −4.1‰ to 1.2‰, while δ13C values ranged from −13.2‰ to 0.0‰. δ18O values of the shell aragonite were predicted with a published, steady state, evaporative flux balance model. The predicted values differed (with one exception) by less than 1‰ from locality averages of measured δ18O values. This similarity suggests that relative humidity at the time of snail activity is an important control on the δ18O values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells. Correlated δ13C values of coexisting Vallonia and Gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern Great Plains plant ecology. Although there is considerable scatter, multispecies, transect average δ13C values of the modern aragonite shells are related to variations in the type of photosynthesis (i.e., C3, C4) in the local plant communities. The results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals, species, etc., and thus better represent the “neighborhood” scale temporal and/or spatial environmental variations of interest in studies of modern and ancient systems. 相似文献
956.
Abstract The Late Oligocene-Early Miocene Nabae Sub-belt of the Shimanto Accretionary Prism was created coevally (ca 25-15 Ma) with the opening of the Shikoku back-arc basin, located to the south of the southwest Japan convergent margin. The detailed geology of the sub-belt has been controversial and the interaction of the Shimanto accretionary prism and the opening of the Shikoku Basin has been ambiguous. New structural analysis of the sub-belt has led to a new perception of its structural framework and has significant bearing on the interpretation of the Neogene tectonics of southwest Japan. The sub-belt is divided into three units: the Nabae Complex; the Shijujiyama Formation; and the Maruyama Intrusive Suite. The Nabae Complex comprises coherent units and mélange, all of which show polyphase deformation. The first phase of deformation appears to have involved landward vergent thrusting of coherent units over the mélange terrane. The second phase of deformation involved continued landward vergent shortening. The Shijujiyama Formation, composed mainly of mafic volcanics and massive sandstone, is interpreted as a slope basin deposited upon the Nabae Complex during the second phase of deformation. The youngest deformational pulse involved regional flexing and accompanying pervasive faulting. During this event, mafic rocks of the Maruyama Intrusive Suite intruded the sub-belt. Fossil evidence in the Nabae Complex and radiometric dates on the intrusive rocks indicate that this tectonic scheme was imprinted upon the sub-belt between ~23 and ~14 Ma. The timing of accretion and deformation of the sub-belt coincides with the opening of the Shikoku Basin; hence, subduction and spreading operated simultaneously. Accretion of the Nabae Sub-belt was anomalous, involving landward vergent thrusting, magmatism in newly accreted strata and regional flexing. It is proposed that this complex and anomalous structural history is largely related to the subduction of the active Shikoku Basin spreading ridge and associated seamounts. 相似文献
957.
A simple and fast treatment of hydrogeologic features with irregularly shaped boundaries in two‐dimensional analytic element groundwater flow models is presented. The star domain shapes of the features are restricted to closed shapes represented as smooth and continuous single‐valued functions of distance from a focus point, . The element can be used to treat a variety of boundary and continuity conditions, including those of irregularly shaped lakes or heterogeneities in hydraulic conductivity. The new element is demonstrated via some simple illustrative test cases and shown to be efficient, accurate, and much simpler to implement than existing solutions for irregular shapes. 相似文献
958.
Pichel WG Veenstra TS Churnside JH Arabini E Friedman KS Foley DG Brainard RE Kiefer D Ogle S Clemente-Colón P Li X 《Marine pollution bulletin》2012,65(1-3):28-41
Marine debris, particularly debris that is composed of lost or abandoned fishing gear, is recognized as a serious threat to marine life, vessels, and coral reefs. The goal of the GhostNet project is the detection of derelict nets at sea through the use of weather and ocean models, drifting buoys and satellite imagery to locate convergent areas where nets are likely to collect, followed by airborne surveys with trained observers and remote sensing instruments to spot individual derelict nets. These components of GhostNet were first tested together in the field during a 14-day marine debris survey of the Gulf of Alaska in July and August 2003. Model, buoy, and satellite data were used in flight planning. A manned aircraft survey with visible and IR cameras and a LIDAR instrument located debris in the targeted locations, including 102 individual pieces of debris of anthropogenic or terrestrial origin. 相似文献
959.
960.
Viet-Ha Nhu Khabat Khosravi James R. Cooper Mahshid Karimi Ozgur Kisi Binh Thai Pham 《水文科学杂志》2020,65(12):2116-2127
ABSTRACT The predictive capability of a new artificial intelligence method, random subspace (RS), for the prediction of suspended sediment load in rivers was compared with commonly used methods: random forest (RF) and two support vector machine (SVM) models using a radial basis function kernel (SVM-RBF) and a normalized polynomial kernel (SVM-NPK). Using river discharge, rainfall and river stage data from the Haraz River, Iran, the results revealed: (a) the RS model provided a superior predictive accuracy (NSE = 0.83) to SVM-RBF (NSE = 0.80), SVM-NPK (NSE = 0.78) and RF (NSE = 0.68), corresponding to very good, good, satisfactory and unsatisfactory accuracies in load prediction; (b) the RBF kernel outperformed the NPK kernel; (c) the predictive capability was most sensitive to gamma and epsilon in SVM models, maximum depth of a tree and the number of features in RF models, classifier type, number of trees and subspace size in RS models; and (d) suspended sediment loads were most closely correlated with river discharge (PCC = 0.76). Overall, the results show that RS models have great potential in data poor watersheds, such as that studied here, to produce strong predictions of suspended load based on monthly records of river discharge, rainfall depth and river stage alone. 相似文献