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71.
Elisabeth Bondar-Kunze Stefan Preiner Friedrich Schiemer Gabriele Weigelhofer Thomas Hein 《Aquatic Sciences - Research Across Boundaries》2009,71(4):437-447
This study evaluated the effects of a controlled surface water connectivity scheme on several backwaters in an urban floodplain
within the city limits of Vienna, the Upper Lobau. A phosphorus budget and ecosystem metabolism measurements were used to
assess the reaction of two trophically distinct floodplain backwater sections on changed connectivity conditions. The surface
water connection led to a reduction of the retention times in the backwater system. The water column nutrient concentrations
in the individual backwater sections approached those of the source water body. The significance of these effects, however,
depends on the historical and current trophic situation of the respective water bodies. Generally, the surface water connectivity
introduced particulate phosphorus export up to 30% increase over the influent loading and dissolved phosphorus up to 14% increase
over the influent loading. However, in sections with submersed macrophyte development, which provided enhanced filtering capacities
for particulate matter, sediment and phosphorus accumulation rates were increased. At the same time, water transparency increased
resulting in a positive feedback supporting further macrophyte development. Based on these findings, the evaluation of restoration
measures in urban floodplains needs to consider the spatial and temporal dynamics of nutrients and ecosystem processes such
as gross primary production and community respiration to predict long-term development. 相似文献
72.
V. K. Banakar J. R. Hein R. P. Rajani A. R. Chodankar 《Journal of Earth System Science》2007,116(1):3-13
The major element relationships in ferromanganese (Fe-Mn) crusts from Afanasiy-Nikitin seamount (ANS), eastern equatorial
Indian Ocean, appear to be atypical. High positive correlations (r = 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the
ANS Fe-Mn crusts are distinct from Pacific seamount Fe-Mn crusts, and reflect region-specific chemical characteristics. The
platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe-Mn crusts are derived from seawater and are mainly
of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5–2) and Pt/Ru ratios (7–28) are closely comparable
to ratios in continental basalts, whereas Pd/Ir ratios exhibit values (<2) similar to CI-chondrite (∼1). The chondrite-normalized
PGE patterns are similar to those of igneous rocks, except that Pd is relatively depleted. The water depth of Fe-Mn crust
formation appears to have a first-order control on both major element and PGE enrichments. These relationships are defined
statistically by significant (r > 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE-Au from seawater
during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations (r > 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized
major-element ratios, and with the other PGE (r < 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co
demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on
the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE-Au and their positive association with redox
sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses. 相似文献
73.
Recent increases in the accuracy of climate models have enhanced the possibilities for analyzing the impacts of climate change on society. This paper explores how the local, economic impacts of climate change can be modeled for a specific eco-region, the Western Sahel. The people in the Sahel are highly dependent on their natural resource base, and these resources are highly vulnerable to climate change, in particular to changes in rainfall. Climate models project substantial changes in rainfall in the Sahel in the coming 50 years, with most models predicting a reduction in rainfall. To connect climate change to changes in ecosystem productivity and local income, we construct an ecological–economic model that incorporates rangeland dynamics, grazing and livestock prices. The model shows that decreased rainfall in the Sahel will considerably reduce local incomes, in particular if combined with increases in rainfall variability. Adaptation to these climate change projections is possible if reductions in rainfall are followed by destocking to reach efficient grazing levels. However, while such a strategy is optimal from the perspective of society, the stocking rate is determined by individual pastoralists that face few incentives to destock. 相似文献
74.
Normally, the use of clays as reference materials in chemical provenance studies of ancient ceramics is complicated due to the original clay paste processing. The primary mixing and/or refining of raw materials during pottery production makes a straightforward comparison of archaeological ceramics with extant geological materials difficult if not impossible in many cases. However, in the case of Pliocene clays from Aegina (Greece), which were examined chemically and mineralogically and compared with Bronze Age pottery produced on the island, a successful exception can be presented. The chemical composition of a large group of Aeginetan pottery resembles the chemical composition of clays from a deposit in close vicinity to the main Bronze Age settlement of the island. Clays from specific outcrops exhibit considerable chemical and mineralogical homogeneity, and the suitability of those clays for pottery production apparently made substantial clay paste processing unnecessary. © 2004 Wiley Periodicals, Inc. 相似文献
75.
Laura E. Wasylenki Colin L. Weeks John R. Bargar James R. Hein 《Geochimica et cosmochimica acta》2011,75(17):5019-5031
Fractionation of Mo isotopes during adsorption to manganese oxides is a primary control on the global ocean Mo isotope budget. Previous attempts to explain what drives the surprisingly large isotope effect δ97/95Modissolved-δ97/95Moadsorbed=1.8‰ have not successfully resolved the fractionation mechanism. New evidence from extended X-ray absorption fine structure analysis and density functional theory suggests that Mo forms a polymolybdate complex on the surfaces of experimental and natural samples. Mo in this polynuclear structure is in distorted octahedral coordination, while Mo remaining in solution is predominantly in tetrahedral coordination as . Our results indicate that the difference in coordination environment between dissolved Mo and adsorbed Mo is the cause of isotope fractionation. The molecular mechanism of metal isotope fractionation in this system should enable us to explain and possibly predict metal isotope effects in other systems where transition metals adsorb to mineral surfaces. 相似文献
76.
77.
James R. Hein Ann E. Gibbs David A. Clague Michael Torresan 《Marine Georesources & Geotechnology》2013,31(2):177-203
This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe‐Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ‐MnO2. The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn‐cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and permeability. Precipitation of Mn oxide below the seafloor is indicated by its occurrence as cement, growth textures that show mineralizing fluids were introduced from below, and pervasive replacement of original matrix of clastic rocks. 相似文献
78.
A. Koschinsky P. Halbach J. R. Hein A. Mangini 《International Journal of Earth Sciences》1996,85(3):567-576
Hydrogenetic ferromanganese crusts reflect the chemical conditions of the sewater from which they formed. Fine-scale geochemical
analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes
which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth
influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of
these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a
much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which
probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic
profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts.10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2–5 Ma ago) resulted
in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out
to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the
Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized
crust generation might be as old as approximately 30–40 Ma. 相似文献
79.
Pisces submersible dives within Baffin Island fjords have revealed the common occurrence of pits on the sea floor, at water depths
between 40 and 326 m. The size of these pits are in the decimeter to meter range. Through indirect evidence (by comparison
of morphologic features to pits or gouges of known origin) they are believed to be feeding traces of narwhal, beluga, or bowhead
whales. If so, they are the deepest mammalian feeding traces yet reported. Bioerosion by large foraging mammals may be a more
common sea floor process than previously thought. 相似文献
80.
Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean 总被引:3,自引:0,他引:3
Graldine Sarthou Alex R. Baker Jurjen Kramer Patrick Laan Agathe Laës Simon Ussher Eric P. Achterberg Hein J.W. de Baar Klaas R. Timmermans Stphane Blain 《Marine Chemistry》2007,104(3-4):186-202
Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters. 相似文献