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811.
Utilizing a sequential extraction technique this study provides the first quantitative analysis on the abundance of sedimentary
phosphorus and its partitioning between chemically distinguishable phases in sediments of the Bering Sea, the Chukchi Sea
and the Mackenzie River Delta in the western Arctic Ocean. Total sedimentary phosphorus (TSP) was fractionated into five operationally
defined phases: (1) adsorbed inorganic and exchangeable organic phosphorus, (2) Fe-bound inorganic phosphorus, (3) authigenic
carbonate fluorapatite, biogenic apatite and calcium carbonate-bound inorganic and organic phosphorus, (4) detrital apatite,
and (5) refractory organic phosphorus. TSP concentrations in surface sediments increased from the Chukchi Sea (18 μmol g−1 of dried sediments) to the Bering Sea (22 μmol g−1) and to the Mackenzie River Delta (29 μmol g−1). Among the five pools, detrital apatite phosphorus of igneous or metamorphic origin represents the largest fraction (~43%)
of TSP. The second largest pool is the authigenic carbonate fluorapatite, biogenic apatite as well as CaCO3 associated phosphorus (~24% of TSP), followed by the Fe-bound inorganic phosphorus, representing ~20% of TSP. The refractory
organic P accounts for ~10% of TSP and the readily exchangeable adsorbed P accounts for only 3.5% of TSP. Inorganic phosphorus
dominates all of phosphorus pools, accounting for an average of 87% of the TSP. Relatively high sedimentary organic carbon
and total nitrogen contents and low δ13C values in the Mackenzie River Delta together with the dominance of detrital apatite in the TSP demonstrate the importance
of riverine inputs in governing the abundance and speciation of sedimentary phosphorus in the Arctic coastal sediments. 相似文献
812.
T. Dale Bishop Harlan L. MillerIII Randal L. Walker Dorset H. Hurley Theron Menken Charles E. Tilburg 《Estuaries and Coasts》2010,33(3):688-698
The blue crab, Callinectes sapidus Rathbun, 1896, represents the second most important fishery for coastal Georgia; yet, little is known about environmental
forces that affect planktonic postlarval settlement in the region. Here, we describe a study to examine the physical mechanisms
responsible for blue crab settlement in the extensive salt marsh system of coastal Georgia. Bottom and surface samplers were
placed at three sites along a salinity gradient from a low-salinity site in the Altamaha River to a high-salinity area of
the Duplin River, Sapelo Island, GA, USA during 2005. Megalopae and juvenile monitoring occurred from July through December.
The majority of both megalopae (86.8%) and juvenile (89.3%) blue crabs were recovered in bottom samplers at the low-salinity
Altamaha River site during August and early September. Few megalopae were collected at the surface of the Altamaha River or
at the two higher-salinity sites in the Duplin and North Rivers. Downwelling winds were unable to explain all settlement events;
however, winds with an onshore component regularly preceded settlement events. The use of a multiple-regression model revealed
a lagged relationship (r = 0.5461, $ lag = 0–2 days $ lag = 0–2 days ) between wind events, temperature, salinity, maximum tidal height, and settlement. 相似文献
813.
Kathryn L. Sobocinski Jeffery R. Cordell Charles A. Simenstad 《Estuaries and Coasts》2010,33(3):699-711
In coastal environments, the supratidal zone bridges marine and terrestrial ecosystems and is important for energy exchange.
However, it is also subject to extensive anthropogenic disturbance, such as armoring of shorelines. Shoreline armoring is
extensive along many coasts, but the impacts on biota are comparatively unknown. Between 2000 and 2002, paired and synoptic
sampling regimes were employed to assess armoring effects on insects and benthic macroinvertebrates in the supratidal zone
of Puget Sound beaches. Paired sampling showed natural beach sites had significantly more deposited wrack. Infauna was dominated
by oligochaetes and nematodes; talitrid amphipods, insects, and collembolans were significantly more numerous at natural beaches,
and crustaceans were more abundant at altered beaches. Insect assemblages were diverse, with taxon richness higher at natural
beach sites. In the synoptic sampling, where sites with higher elevation modifications were used, there were fewer differences
in invertebrate assemblages between armored and nonarmored sites. The results show that, where shoreline armoring lowers the
land–sea interface, benthic infauna and insect assemblages are disrupted. Widespread shoreline modifications may decrease
the availability of prey resources for fish and wildlife and decrease the contribution of organic material entering the nearshore
ecosystem. 相似文献
814.
An adequate understanding of the nature and extent of response to stressors and resources by marine foundation plant species requires study of local adaptation and plasticity in traits. Analyses of variation among genotypes in growth and morphology and genotype × environment interactions are necessary for restoration in, for example, different combinations of tide, soil, and salinity regimes, and for assessing how foundation plant species will respond to global climate change. We conducted a field experiment to assess differences in responses among 86 half-sibling (same maternal tree) seedling families of the red mangrove (Rhizophora mangle) to different environmental conditions of hydrology imposed at low- and high-intertidal settings. At 3 years, Rhizophora survival and growth varied with maternal tree genotype, elevation, and genotype × elevation. This effect was independent of size of propagules at planting. Growth also differed among the five islands planted, a main effect that is a composite of a number of microenvironmental differences stemming from island size and shape, proximity to passes (and thus fetch), and island slope. Significant genotype × island interactions for some response variables further support the hypothesis that seedlings of different maternal genotypes can perform very differently under various suites of environmental conditions. Planted seedlings reproduced at an early age, and at 3 years there were differences in reproductive output among genotypes but not an overall mean difference between plants at low or high elevation. Whether our results show adaptation to local conditions or differences in plasticity among genotypes will require further study as the plants mature further to demonstrate fitness differences. However, either adaptation or plasticity provides a basis for maintenance of Rhizophora dominance over a wider range of environmental conditions and may be important for adaptation to conditions that will vary with global climate change. 相似文献
815.
Joachim Place Marc Diraison Charles Naville Yves Géraud Marc Schaming Chrystel Dezayes 《Comptes Rendus Geoscience》2010,342(7-8):575-586
A contribution to the definition of the structural pattern of the Soultz-sous-Forêts EGS (Enhanced Geothermal System) is presented here. After reprocessing, the PHN84J seismic reflection profile highlights the tilted blocks of the Merkwiller-Péchelbronn oilfield. In the Soultz-sous-Forêts horst, complex fault patterns are observed: the Hermerswiller normal fault flattens at depth and is rooted in decollements occurring in Triassic salt or clay series, while other steep normal faults affect underlying sedimentary formations and basement. Some methods for the exploitation of a seismic diffraction recorded by multi-component Vertical Seismic Profiling (VSP) are also illustrated to locate the diffractor without specific data processing. Polarisation and travel time analysis of a diffraction event recorded in the GPK1 borehole are analysed, and its exploitation combined with seismic reflection helps defining a tilted block geometry. 相似文献
816.
Melissa M. FITTIPALDO Rhian H. JONES Charles K. SHEARER 《Meteoritics & planetary science》2005,40(4):573-589
Abstract— We measured rare earth element (REE) abundances in selected silicate phases in the angrites Angra dos Reis (AdoR) and Lewis Cliff (LEW) 86010 in order to further clarify the thermal history of AdoR. We also carried out a preliminary experimental study designed to examine apparent REE partitioning between silicates (fassaite, olivine, kirschsteinite, and melt) in synthetic analogs of angrites under disequilibrium conditions at liquidus temperatures. Silicates in AdoR are homogeneous with respect to major, minor, and trace elements, which is consistent with the interpretation that AdoR underwent extensive subsolidus equilibration. REE distributions in olivine and kirschsteinite in AdoR are similar to those in LEW 86010 and are consistent with the formation of kirschsteinite by exsolution from olivine during cooling and/or annealing. There is no evidence for a disequilibrium trace element signature that could have been inherited from rapid cooling at liquidus temperatures. This is supported by our petrographic observations of the occurrence of kirschsteinite within olivine aggregates in AdoR. Olivine/kirschsteinite pairs in AdoR record closure temperatures around 600–650 °C. 相似文献
817.
818.
T. Shahbaz V. S. Dhillon T. R. Marsh J. Casares C. Zurita P. A. Charles C. A. Haswell R. I. Hynes 《Monthly notices of the Royal Astronomical Society》2005,362(3):975-982
We present 450- and 850-μm maps of R Coronae Australis. We compare the maps with previous surveys of the region, and shed new light on the previously unknown nature of the protostellar sources at the centre of the cloud. We clarify the nature of two millimetre sources previously discovered in lower-resolution data. We identify one new Class 0 protostar, which we label SMM 1B, and we measure the envelope masses of a number of more evolved protostars. We identify two new pre-stellar cores, which we call SMM 1A and SMM 6. 相似文献
819.
Friedrich Hrz David W. Mittlefehldt Thomas H. See Charles Galindo 《Meteoritics & planetary science》2002,37(4):501-531
Abstract— We investigated the ballistically dispersed melts from Meteor Crater, Arizona, USA to determine the stratigraphic extent of its melt zone from the compositional relationship of melts and target rocks. Most melt particles are crystallized, hydrated, and oxidized; pristine glasses are rare. Hydration and oxidation occurred at ambient temperatures long after the impact. The preserved glasses are generally clear and texturally homogeneous, but unlike typical impact melts, they have unusually heterogeneous compositions, both within individual particles and from sample to sample. For example, the average SiO2 for individual particles ranges from 43 to 65%. The projectile content is unusually high and it is distributed bimodally, with specific samples containing either 5–10% or 20–30% FeO. These compositional heterogeneities most likely reflect the high carbonate content of the target rocks and the release of copious CO2 that dispersed the melts, thereby terminating melt flow and mixing. The high projectile content and the CO2 depleted residue of purely sedimentary rocks produced mafic melts that crystallized fine‐grained olivine and pyroxene. The melts fall into three compositional groups reflecting variable proportions of the major target formations, Moenkopi, Kaibab, and Coconino. Least‐square mixing calculations revealed one group to contain 55% Moenkopi, 40% quartz‐rich, upper Kaibab, and 5% meteorite, suggesting a source depth of <30 m from the pre‐impact surface. The other two melt groups have higher contents of meteorite (15–20%) and Kaibab (50–70%) and contain more SiO2 than average Kaibab. The additional quartz may have been derived from Coconino or the upper Kaibab, implying melt depths >90 m or <30 m, respectively. Additional studies, especially hydrocode calculations, are needed to better understand the source depth of these melts and their exceptionally high projectile content. 相似文献
820.
Horton E. Newsom Melissa J. Nelson Charles K. Shearer Burkhard O. Dressler 《Meteoritics & planetary science》2006,41(12):1929-1945
Abstract— The concentrations of the fluid mobile trace elements lithium, beryllium, boron, and barium were measured in samples of the altered matrix of several impactite breccias of the Yaxcopoil‐1 drill core using secondary ion mass spectrometry (SIMS) to determine the extent of transport due to aqueous or hydrothermal processes. Three of the elements, Li, Be, and B, have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3.5, 2.2, and 1.5, respectively. Lithium and B are the most enriched elements up section, and appear to have had the greatest mobility. The similar fractionation of Li and B is consistent with fluid transport and alteration under low‐temperature conditions of less than 150 °C based on published experimental studies. In contrast to Li, Be, and B, the concentration of Ba in the altered matrix materials decreases upward in the section, and the concentration of Ba in the matrix is an order of magnitude less than the bulk concentrations, likely due to the presence of barite. The origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units. A different protolith in the altered matrix is suggested by the Mg‐rich composition of the lower units versus the Al‐rich composition of the upper units, which largely correlates with the mobile element variations. The possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system. However, the mobile elements in the sediments do not have to originate from the underlying impactites. In conclusion, our data suggests that the impactites at this location did not experience extensive high‐temperature hydrothermal processing, and that only limited transport of some elements, including Li, Be, and B, occurred. 相似文献