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161.
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163.
Analyses were made of a mollusc‐based meta dataset of 859 δ13C and δ18O data of Miocene nearshore settings in the European Paratethys Sea and its descendant Lake Pannon. The observed trends document a strong tie to geodynamics, which are largely decoupled from Miocene open ocean isotope curves. Semi‐ to fully enclosed, initially marine water bodies such as the Paratethys Sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation/precipitation ratio. Two phases of positive deviations of oxygen isotope values of water (relative to the modern ocean value, SMOW) occurred during the Middle Miocene; both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation. With the final disintegration of the Paratethys, the marine isotope signatures vanish. Instead, the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity. The ‘ocean‐derived’ Paratethys Sea may thus act as a key for understanding isotope trends in epicontinental seas. 相似文献
164.
Estimation of low flows in rivers continues to be a vexing problem despite advances in statistical and process‐based hydrological models. We develop a method to estimate minimum streamflow at seasonal to annual timescales from measured streamflow based on regional similarity in the deviations of daily streamflow from minimum streamflow for a period of interest. The method is applied to 1,019 gauged sites in the Western United States for June to December 2015. The gauges were clustered into six regions with distinct timing and magnitude of low flows. A gamma distribution was fit each day to the deviations in specific discharge (daily streamflow divided by drainage area) from minimum specific discharge for gauges in each region. The Kolmogorov–Smirnov test identified days when the gamma distribution was adequate to represent the distribution of deviations in a region. The performance of the gamma distribution was evaluated at gauges by comparing daily estimates of minimum streamflow with estimates from area‐based regression relations for minimum streamflow. Each region had at least 8 days during the period when streamflow measurements would provide better estimates than the regional regression equation, but the number of such days varied by region depending on aridity and homogeneity of streamflow within the region. Synoptic streamflow measurements at ungauged sites have value for estimating minimum streamflow and improving the spatial resolution of hydrological model in regions with streamflow‐gauging networks. 相似文献
165.
Christine A. Ward‐Paige Gregory L. Britten Dana M. Bethea John K. Carlson 《Marine Ecology》2015,36(3):419-431
The successful management of shark populations requires juvenile recruitment success. Thus, conservation initiatives now strive to include the protection of areas used by pre‐adult sharks in order to promote juvenile survivorship. Many shark species use inshore areas for early life stages; however, species often segregate within sites to reduce competition. Using a fisheries‐independent gillnet survey from the Northern Gulf of Mexico (2000–2010) we describe distribution patterns and preferred habitat features of the juveniles of six shark species. Our results suggest that multiple shark species concurrently use the area for early life stages and although they overlap, they exhibit distinct habitat preferences characterized by physical variables. Habitat suitability models suggest that temperature, depth, and salinity are the important factors driving juvenile shark occurrence. Within each site, across the sampled range of physical characteristics, blacktip shark (Carcharhinus limbatus) preferred higher temperature (>30 °C) and mid‐depth (~5.5 m); bonnethead shark (Sphyrna tiburo) preferred higher temperature (>30 °C) and mid‐salinity (30–35 PSU), finetooth shark (Carcharhinus isodon) preferred low salinity (<20 PSU) with mid‐depth (~4 m), scalloped hammerhead shark (Sphyrna lewini) preferred high temperature (>30 °C) and salinity (>35 PSU), Atlantic sharpnose shark (Rhizoprionodon terraenovae) preferred high temperature (>30 °C) and deep water (>6 m), and spinner shark (Carcharhinus brevipinna) preferred deep water (>8 m) and high temperature (>30 °C). The other investigated factors, including year, month, latitude, longitude, bottom type, inlet distance, coastline and human coast were not influential for any species. Combining habitat preferences with the sampled environmental characteristics, we predicted habitat suitability throughout the four sites for which physical characteristics were sampled. Habitat suitability surfaces highlight the differences in habitat use between and within sites. This work provides important insight into the habitat ecology of juvenile shark populations, which can be used to better manage these species and protect critical habitat. 相似文献
166.
Assessment of the historical trace metal contamination of sediments in the Elizabeth River, Virginia
Two sediment cores (Southern Branch, PC-1, and Western Branch, WB-2) were taken from the highly industrialized Elizabeth River, Virginia. The concentrations of trace metals cadmium, cobalt, chromium, copper, nickel, lead and zinc, major elements iron, manganese and aluminum, organic carbon content and the specific surface area of the sediments were determined in each of the cores. Down-core variations in metals varied significantly in each core with maximum contamination events occurring at different times in different portions of the river. In PC-1, maximum metal concentrations were seen after the appearance of (137)Cs. In contrast, the highest levels in WB-2 occurred well before the appearance of (137)Cs. Although stricter environmental regulations have caused a decrease in metal concentrations since the 1980s, the concentrations in the surface sediments of many trace metals were elevated to levels 2-5 times higher than the levels at the bottom of the cores in both the Southern and Western Branches of the river. 相似文献
167.
Yang LIU Christine FLOSS James M. D. DAY Eddy HILL Lawrence A. TAYLOR 《Meteoritics & planetary science》2009,44(2):261-284
Abstract— Miller Range (MIL) 05035 is a low‐Ti mare basalt that consists predominantly of pyroxene (62.3 vol%) and plagioclase (26.4 vol%). Pyroxenes are strongly shocked and complexly zoned from augite (Wo33) and pigeonite (Wo17) cores with Mg# = 50–54 to hedenbergite rims. Coexisting pyroxene core compositions reflect crystallization temperatures of 1000 to 1100 °C. Plagioclase has been completely converted to maskelynite with signs of recrystallization. Maskelynite is relatively uniform in composition (An94Ab6–An91Ab9), except at contacts with late‐stage mesostasis areas (elevated K contents, An82Ab15Or3). Symplectites (intergrowth of Fe‐augite, fayalite, and silica) of different textures and bulk compositions in MIL 05035 suggest formation by decomposition of ferro‐pyroxene during shock‐induced heating, which is supported by the total maskelynitization of plagioclase, melt pockets, and the presence of a relict pyroxferroite grain. Petrography and mineral chemistry imply that crystallization of MIL 05035 occurred in the sequence of Fe‐poor pyroxenes (Mg# = 50–54), followed by plagioclase and Fe‐rich pyroxenes (Mg# = 20–50), and finally hedenbergite, Fe‐Ti oxides, and minor late‐stage phases. Petrography, bulk chemistry, mineral compositions, and the age of MIL 05035 suggest it is possibly source crater‐paired with Asuka (A‐) 881757 and Yamato (Y‐) 793169, and may also be launch‐paired with Meteorite Hills (MET) 01210. MIL 05035 represents an old (?3.8–3.9 Ga), incompatible element‐depleted low‐Ti basalt that was not sampled during the Apollo or Luna missions. The light‐REE depleted nature and lack of Eu anomalies for this meteorite are consistent with an origin distant from the Procellarum KREEP Terrane, and genesis from an early cumulate mantle‐source region generated by extensive differentiation of the Moon. 相似文献
168.
Spatial Variation of Sea-Spray Fluxes over a Mediterranean Coastal Zone Using a Sea-State Model 总被引:1,自引:1,他引:0
Jacques Piazzola Philippe Forget Christine Lafon Serge Despiau 《Boundary-Layer Meteorology》2009,132(1):167-183
We first deal with sea-spray flux estimates for short fetch conditions in coastal Mediterranean areas. To this end, a sea-state
dependent model for the whitecap fraction was included in three different formulations for the sea-spray source function.
A comparison with the sea-spray fluxes, calculated on the basis of aerosol size distributions measured at the island of Porquerolles
located south off the French Riviera, evaluates the predictions of different whitecap dependant flux formulations. Then we
deal with the spatial distribution of the whitecap fraction and the sea-spray fluxes in the study area. To achieve this, a
whitecap dependant flux formulation was forced by a wave numerical model that was implemented in the study area. Experimental
results on wave conditions have been used to adjust the model in the Mediterranean coastal area. Numerical simulations of
wave and whitecap coverage have been carried out during typical regional wind events, and they show a nonhomogeneous distribution
of the sea-surface production over the northern Mediterranean as a consequence of the spatial variation of the sea state.
In particular, we note the occurrence of a narrow band of high sea-surface production following the northern coast and along
the east part of the Gulf of Lions. 相似文献
169.
Bushfire and everyday life: Examining the awareness-action ‘gap’ in changing rural landscapes 总被引:1,自引:0,他引:1
In this paper we use the notion of ‘everyday life’ to critically examine an apparent ‘gap’ between bushfire risk awareness and preparedness amongst diverse landholders in rural landscapes affected by amenity-led in-migration in southeast Australia. Landholders were found to bring their own agency to bushfire preparedness in the relationships between everyday procedures, dilemmas, and tradeoffs. Consequently, regardless of landholders’ awareness levels, attitudes towards bushfire and natural resource management influence if, how, and to what extent landowners prepare for bushfires. We argue that not only is the ‘gap’ complex but also paradoxical in that it is both evident in, and constituted by, landholder attitudes and action and simultaneously dissolved in their practices and decision-making in everyday life. Three dilemmas of everyday life in particular were found to underpin these attitudes: costs (in terms of monetary and time values), gender roles, and priorities. Using a mixed-methods research approach, this simultaneous cultural construction and material nature of bushfire in everyday life is mapped out through landholders’ narratives and actions that embody living with fire on the land. The place of bushfire in landholders’ everyday life has direct relevance to recent international discussions of the vulnerability of the growing number of people living in bushfire-prone rural-urban interface areas. 相似文献
170.