Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)     

《Journal of Oceanography》2007,63(6):983-994

A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m⁻³) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m⁻³, with no prominent diatom bloom. Photosynthetic competence in terms of F _v/F _m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.  相似文献   

Research challenges at the land–sea interface     

Drew M. Talley  Elizabeth W. North  Andrew R. Juhl  David A. Timothy  Daniel Conde  Jody F. C. deBrouwer  Cheryl A. Brown  Linda M. Campbell  Tobias Garstecki  Catherine J. Hall  Filip J. R. Meysman  David M. Nemerson  Pedro W. Souza Filho  Robert J. Wood 《Estuarine, Coastal and Shelf Science》2003,58(4):699

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Multi-method study of the characteristic chemical nature of aquatic humic substances isolated from the Han River,Korea   总被引：1，自引：0，他引：1  

《Applied Geochemistry》2006,21(7):1226-1239

Natural organic matter (NOM) from the Han River, Korea was fractionated into humic and non-humic fractions by absorbing onto XAD-7HP, and these fractions were analyzed using UV-absorption, and for dissolved organic C (DOC). The humic fraction (i.e. humic substances; HS) was extracted and its characteristics were compared to commercial humic materials using various spectroscopic methods such as Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and fluorescence spectroscopy. The humic fraction as organic C was 47.0% on the average, however, a rainfall event brought a higher humic fraction into Han River water. The molar ratios of H/C and O/C in the HS from Han River water (HRHS) were 1.40 and 0.76, respectively, and the ratio of aliphatic to aromatic protons in the HS (P_Al/P_Ar ratio) was 5.8. Aromaticity and humification degree (i.e., degree of condensation) of HRHS were relatively lower than those from other humic materials, while the portion of oxygenated functional groups was relatively higher. FT-IR, ¹H-NMR and fluorescence spectroscopy showed distinct differences between HRHS and the commercial humic materials. Commercial humic materials are not representative of HS extracted from Han River water. The fluorescence spectra, relatively simple measurements, were found to be most useful as fingerprints for humic materials from particular sources.  相似文献   

Multiple magnetization events in the Red River carbonates, Williston Basin, Canada: Evidence for fluid-flow?     

Erika Szabo  Maria T. Cioppa   《Journal of Geochemical Exploration》2006,89(1-3):384

Samples collected from the Upper Ordovician Red River carbonates in a well at the centre of the Williston Basin revealed two paleomagnetic components with different inclinations, 60.3 ± 3.9° (k = 70.7, N = 12) and 20.4 ± 3.3° (k = 141.2, N = 8), but similar declination values in individual specimens. Inclination-only analysis indicates two possible scenarios for the age of these two magnetizations: in scenario (a) the timing of magnetization happened sometime between Late Ordovician to Devonian; and in scenario (b) there are two different remagnetizations, one that overlaps Pennsylvanian to Permian time while the other can have either a Late Jurassic or a Tertiary age. Whereas dolomitization and some isotopic data tend to support scenario (a), previous paleomagnetic data from the Williston Basin and from younger units in the same well, the tectonic evolution of the basin, and the hydrocarbon maturation pattern in the Red River carbonates all favour chemical remagnetization(s) driven by orogenic fluids during the Alleghenian and Laramide orogenies.  相似文献   

Lake Sediment Core Records of Sulphur Accumulation and Sulphur Isotopic Composition in Central Ontario, Canada Lakes     

M. Catherine Eimers  Andrew M. Paterson  Peter J. Dillon  Sherry L. Schiff  Brian F. Cumming  Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109

Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~ 20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ ³⁴S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment were relatively low (1.9–5 mg S g⁻¹ dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in δ ³⁴S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally reciprocal depth pattern between total S concentration and δ ³⁴S ratios. While initial shifts in total S and δ ³⁴S were likely due to enhanced SO₄ reduction of newly available anthropogenic SO₄, both the magnitude and pattern of up-core S enrichment and shifts in δ ³⁴S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and δ ³⁴S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S deposition in this region, likely due to redox-related mobility of S in upper sediment.  相似文献   

Sedimentary facies and climate control on formation of vivianite and siderite microconcretions in sediments of Lake Baikal, Siberia     

Tomasz Sapota  Ala Aldahan  Ihsan S. Al-Aasm 《Journal of Paleolimnology》2006,36(3):245-257

Authigenic vivianite and siderite microconcretions were found, respectively, in hemipelagic and deltaic facies of 600-m-long BDP-98 sediment section from Lake Baikal. Textural investigations of these microconcretions show that they are typically <1 mm in size, irregular in shape and composed of aggregated crystallites. Dissimilar orientation of vivianite and siderite crystallites suggests formation at different depths in the sediment; up to tens of centimeters for vivianite and tens of meters for siderite. Chemical analyses of both the vivianite and the siderite indicate cation composition characterized by minor amounts of Mn, Ca and Mn apart from the dominating Fe. Rather limited and distinctive carbon isotopic composition of the siderite, with δ ¹³C_VPDB values between about +13 and +16‰, implies formation of the mineral in the methanogenic zone of diagenesis. Isotopic composition of oxygen in the siderite (δ ¹⁸O_VPDB values between about −10 and -11‰ ) is consistent with crystallization temperature at about 10–30°C and water δ ¹⁸O_SMOW values between about −10 and -16‰ . The distribution of the authigenic minerals in the section suggests changes in both sedimentary facies and climate, where vivianite formation was controlled by hemipelagic depositional conditions during the Pliocene and Quaternary, whereas siderite reflects impact of deltaic conditions during the Miocene.  相似文献   

Heavy metal concentrations in surficial sediments from accreting and eroding areas along the coast of Guyana   总被引：1，自引：0，他引：1  

V. Lakhan  K. Cabana  P. LaValle 《Environmental Geology》2002,42(1):73-80

. Surficial sediments sampled from accreting and eroding areas along the coast of Guyana were examined for concentrations of heavy metals; aluminum, copper, chromium, iron, nickel, lead, vanadium and zinc. Twenty-four samples were collected, 12 from each of the eroding and accreting areas. For granulometric composition determination, samples were separated into particle-size fractions using sieving and hydrometer procedures. The consideration of three grain-size fractions (4.0, 5.0, and greater than 5.0 phi), plus 24 bulk samples less than 4.0 phi in diameter, required analyzing a total of 96 samples for the presence of heavy metals. The analysis employed was aquaregia digestion, followed by inductively coupled plasma optical emission spectroscopy. The statistical techniques of discriminant analysis, analysis of variance, and correlation and regression were used to analyze all obtained data. Discriminant analysis revealed that metal concentrations were statistically unique to each area. From the analysis of variance, and correlation and regression, it was discovered that the grain size of the sediment had a pronounced effect on the spatial distribution of heavy metals. The accreting area, with finer sediments, accumulated higher concentrations of heavy metals.  相似文献   

Geology, Geochemistry and Tectonic Significance of Mafic-ultramafic Rocks of Mesoproterozoic Phulad Ophiolite Suite of South Delhi Fold Belt, NW Indian Shield     

M. Shamim Khan  T.E. Smith  M. Raza  J. Huang 《Gondwana Research》2005,8(4):553-566

A thick sequence of mafic-ultramafic rocks, occurs along a major shear zone (Phulad lineament), running across the length of Aravalli Mountain Range for about 300 kms. It has been suggested, that this sequence may represent a fragment of ophiolite or a rift related metavolcanic suite made up of basalts and fractionated ultramafics. The geological and tectonic significance of the complex is assessed using field relationships, petrography and geochemistry. Structurally, the lowest part of the complex comprises a discontinuous band of plastically deformed harzburgite (mantle component) followed by layered cumulus gabbroic rocks (crustal component). A complex of non-cumulus rocks comprising hornblende schists, gabbros, sheeted dykes and pillowed basalts structurally overlies layered gabbros. Huge bodies of diorite intrude volcanics.

Geochemical classification suggests that all non-cumulus mafic rocks are sub-alkaline basalts except one variety of dykes which shows mildly alkaline character. The sub-alkaline rocks are tholeiite to calc-alkaline with boninite affinity. Tectono-magmatic variation diagrams and MORB normalised patterns suggest a fore arc tectonic regime for the eruption of these rocks.

The mafic rocks of Phulad Ophiolite Suite are zoned across the strike in terms of their distribution from west to east. The hornblende schists and basalts are exposed at the westernmost margin followed by gabbros and dykes. The alkaline dyke occurs at the easternmost part. The rocks of Phulad suite are juxtaposed with shallow water sediments in the east followed by platformal sediments and then continental slope sediments in the further east indicating gradual thickening of the crust from west to east and an eastward subduction. The geochemical interpretation presented in this study, together with discussion of lithological association is used to decipher the tectonic evolution of the Mesoproterozoics of NW Indian shield.  相似文献   

A classification of mineral systems,overviews of plate tectonic margins and examples of ore deposits associated with convergent margins     

《Gondwana Research》2016

In this contribution I presents definitions of mineral systems, followed by a proposed classification of mineral deposits. The concept of mineral systems has been tackled by various authors within the framework of genetic models with the aim of improving the targeting of new deposits in green field areas. A mineral system has to be considered taking into account, by and large, space-time patterns or trends of mineralisation at the regional scale, their tectonic controls and related metallogenic belts. This leads to a suggested classification of mineral systems, together with a summary of previous ideas on what is, without doubt, a kind of “mine field”, because if a classification is based on genetic processes, these can be extremely complex due to the fact that ore genesis usually involves a number of interactive processes. The classification presented is based on magmatic, magmatic-hydrothermal, sedimentary-hydrothermal, non-magmatic, and mechanical-residual processes.An overview of plate tectonics (convergent and divergent margins) is discussed next. Convergent plate margins are characterised by a tectonic plate subducting beneath a lower density plate. Convergent plate margins have landward of a deep trench, a subduction–accretion complex, a magmatic arc and a foreland thrust belt. An important feature is the subduction angle: a steep angle of descent, is exemplified by the Mariana, or Tonga–Kermadec subduction systems, conducive to porphyry-high-sulphidation epithermal systems, whereas in an intra-arc rift systems with spreading centres is conducive to the generation of massive sulphide deposits of kuroko affinity. A shallower subduction zone is the domain of large porphyry Cu–Mo and epithermal deposits. The implications of this difference in terms of metallogenesis are extremely important. Continent–continent, arc–continent, arc–arc, amalgamation of drifting microcontinents, and oceanic collision events are considered to be a major factor in uplift, the inception of fold-and-thrust belts and high P metamorphism. Examples are the Alpine–Himalayan orogenic belt formed by the closure of the Tethys oceanic basins and the great Central Asian Orogenic Belt (CAOB), a giant accretionary collage of island arcs and continental fragments. The closing of oceanic basins, and the accretion of allochthonous terranes, result in the emplacement of ophiolites by the obduction process. Divergent plates include mid-ocean ridges, passive margins and various forms of continental rifting. At mid-ocean spreading centres, magma chambers are just below the spreading centre. Once the oceanic crust moves away from the ridge it is either consumed in a subduction zone, or it may be accreted to continental margins, or island arcs. Spreading centres also form in back arc marginal basins. Transform settings include transtensional with a component of tension due to oblique divergence, transform or strike–slip sensu stricto and transpressive with a component of compression due to oblique convergence. Strike–slip faults that form during extensional processes lead to the formation of pull-apart basins.Mineral systems that form at convergent margins, the topic of this special issue, are succinctly introduced in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, as follows: principal geological features of selected mineral systems at convergent plate margins and back-arcs (Table 1); their recognition criteria (Table 2); principal geological features of selected ore deposits of back-arc basins and post-subduction rifting (Table 3) and of subduction-related magmatic arcs (Table 4), their respective recognition criteria (Table 5); accretionary and collisional tectonics and associated mineral systems (Table 6); principal geological features and associated mineral systems of transform faults (Table 7).  相似文献   

Epithermal base-metal vein mineralization in the southern uplands of scotland: Nature and origin of the fluids     

I. M. Samson  D. A. Banks 《Mineralium Deposita》1988,23(1):1-8

The sedimentary sequences of the Southern Uplands of Scotland host numerous lead-zinc-copper-silver vein deposits, the genesis of which has never been adequately explained. Fluid inclusion and stable isotope analysis of vein minerals from these deposits indicate that, for the vein stages studied, the mineralizing fluids were low temperature (< 150°C), high salinity (19 to 30 equiv. wt. % NaCl + CaCl₂) modified meteoric waters. A consideration of the availability of such fluids throughout the geological history of the Southern Uplands suggests a Lower Carboniferous (Dinantian) age for the mineralization.  相似文献