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961.
Sarah?K.?FortnerEmail author Martyn?Tranter Andrew?Fountain W.?Berry?Lyons Kathleen?A.?Welch 《Aquatic Geochemistry》2005,11(4):391-412
We have investigated the geochemistry of supraglacial streams on the Canada Glacier, Taylor Valley, Antarctica during the
2001–2002 austral summer. Canada Glacier supraglacial streams represent the link between primary precipitation (i.e. glacier
snow) and proglacial Lake Hoare. Canada Glacier supraglacial stream geochemistry is intermediate between glacier snow and
proglacial stream geochemistry with average concentrations of 49.1 μeq L−1 Ca2+, 19.9 μeq L−1 SO42−, and 34.3 μeq L−1 HCO3−. Predominant west to east winds lead to a redistribution of readily soluble salts onto the glacier surface, which is reflected
in the geochemistry of the supraglacial streams. Western Canada Glacier supraglacial streams have average SO42−:HCO3− equivalent ratios of 1.0, while eastern supraglacial streams average 0.5, suggesting more sulfate salts reach and dissolve
in the western supraglacial streams. A graph of HCO3− versus Ca2+ for western and eastern supraglacial streams had slopes of 0.87 and 0.72, respectively with R2 values of 0.84 and 0.83. Low concentrations of reactive silicate (> 10 μmol L−1) in the supraglacial streams suggested that little to no silicate weathering occurred on the glacier surface with the exception
of cryoconite holes (1000 μmol L−1). Therefore, the major geochemical weathering process occurring in the supraglacial streams is believed to be calcite dissolution.
Proglacial stream, Anderson Creek, contains higher concentrations of major ions than supraglacial streams containing 5 times
the Ca2+ and 10 times the SO42−. Canada Glacier proglacial streams also contain higher concentrations (16.6–30.6 μeq L−1) of reactive silicate than supraglacial streams. This suggests that the controls on glacier meltwater geochemistry switch
from calcite and gypsum dissolution to both salt dissolution and silicate mineral weathering as the glacier meltwater evolves.
Our chemical mass balance calculations indicate that of the total discharge into Lake Hoare, the final recipient of Canada
Glacier meltwater, 81.9% is from direct glacier runoff and 19.1% is from proglacial Andersen Creek. Although during a typical,
low melt ablation season Andersen Creek contributes over 40% of the water added to Lake Hoare, its overall chemical importance
is diluted by the direct inputs from Canada Glacier during high flow years. Decadal warming events, such as the 2001–2002
austral summer produce supraglacial streams that are a major source of water to Lake Hoare. 相似文献
962.
Sarah K. Appleby Martin R. Gillespie Colin M. Graham Richard W. Hinton Grahame J. H. Oliver Nigel M. Kelly 《Contributions to Mineralogy and Petrology》2010,160(1):115-132
In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate
predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian
(~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U–Pb and Hf isotope analyses in zircon in order
to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430–400 Ma) I-type
granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting
their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U–Pb data of inherited zircons,
and high mean zircon δ18O values of 9.0 ± 2.7‰ (2SD) and 9.8 ± 2.0‰ for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains
zircons with much lower δ18O values (6.8 ± 2.1‰), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains
low-δ18O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like
δ18O. Mixing trends in plots of δ18O vs. εHf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study
of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with
local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic
evolution involving two or more magma sources. 相似文献
963.
Variability in dissolved organic matter fluorescence and reduced sulfur concentration in coastal marine and estuarine environments 总被引:1,自引:0,他引:1
Sarah G.S. DePalmaW. Ray Arnold James C. McGeerD. George Dixon D. Scott Smith 《Applied Geochemistry》2011,26(3):394-404
Fluorescence characterization of dissolved organic matter (DOM) and measurements of Cr-reducible sulfide (CRS) are presented for 72 coastal marine and estuarine water samples obtained from the USA and Canada. Each sample is identified according to source: terrigenous, autochthonous, wastewater or mixed. Fluorescence data are resolved into contributions from humic, fulvic, tyrosine and tryptophan-like fluorophores. Humic and fulvic-like fluorophores correlate well with dissolved organic C (DOC) (r2 = 0.73 and 0.71, respectively) but tyrosine and tryptophan-like fluorophores show no correlation with DOC. Quality factors are identified by normalization of fluorescence contributions to DOC. Humic and fulvic components show no statistical differences between sources but the amino acid-like fluorescence quality factors show significant variations between source, with highest values for autochthonous sources (0.07 ± 0.01 arbitrary fluorescence units per mg of C) versus low values (0.015 ± 0.005) for terrigenous source waters. CRS concentrations are highly variable from 0.07 ± 0.01 to 7703 ± 98 nM and do no correlate with DOC except when terrigenous source waters (n = 13) are separated out from the total sample set (r2 = 0.55). There is an open question in the literature; does DOC source matter in terms of protective effects towards metal toxicity? Here is shown that DOC molecular-level quality does vary and that this variation is mostly in terms of the contributions of amino acids to total fluorescence. 相似文献
964.
Vanessa J. Banks Peter F. Jones David J. Lowe Jonathan R. Lee Jeremy Rushton Michael A. Ellis 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(1):117-129
This review considers the geological and geomorphological context of tufa barrages that occupy buried valley settings in the Wye catchment, Derbyshire. It describes the potential relationship of the tufa with locations of hypothesised river captures and inception horizon-guided groundwater flow paths. Tufa barrage development is associated with steps in the bedrock, which may be related to knick-point recession during river capture. Broad estimates of valley incision have been calculated from previously dated deposits. These support current interpretations of particularly significant effective base-level lowering during the Anglian and Devensian stages of the Quaternary and have the potential to add to the knowledge of regional uplift histories. 相似文献
965.
The Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post‐Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. © 2003 Wiley Periodicals, Inc. 相似文献
966.
Marissa A. Davies Jim W. Mclaughlin Maara S. Packalen Sarah A. Finkelstein 《第四纪科学杂志》2023,38(1):92-106
The Hudson Bay Lowlands (HBL) stores a significant proportion of the northern peatland carbon pool, and constraints on the factors controlling local-scale variation are needed to better predict soil carbon stocks. We investigated two treed peatland sites, a fen and a bog, to understand how local ecohydrological factors impacted long-term carbon storage. Ecohydrological conditions were reconstructed using quantitative water table depth reconstructions from testate amoebae (TA) and broad peat type classifications. We also linked these factors and carbon storage to changes in TA community structure through the investigation of morphological and functional traits. Both sites have high rates of peat vertical accretion during the warmer Middle Holocene. A shift to a drier, Sphagnum-dominated habitat after 7400 cal a bp at the bog site, however, led to lower apparent carbon accumulation rates (aCARs) than at the fen site. aCARs decreased with the transition to a cooler Late Holocene climate at both sites. Both sites have higher total carbon masses (kg m−2) than other more open and younger HBL localities, demonstrating the potential importance of treed peatlands in regional carbon storage. Shifts in the frequency of TA traits corresponded to changing ecohydrological conditions and provided insights into the role of TA in carbon storage. 相似文献
967.
Thin sections from 44 sherds representing eight prehistoric sites on four islands (Barbuda, Montserrat, Anguilla, St. Martin) in the northern Lesser Antilles (West Indies) were examined using a petrographic microscope. Point counting distinguished three temper associations: (1) exclusively volcanic,(2) volcanic and carbonate, and (3) volcanic, carbonate, and grog. Exclusively volcanic or dominantly volcanic (with low carbonate) temper associations occur in all Saladoid and many post-Saladoid sherds, with plagioclase feld-spar and volcanic rock fragments being most abundant. Thin sections with significant carbonate content or with grog were restricted to post-Saladoid sherds from Barbuda and to a lesser extent Anguilla. the presence of volcanic grains in sherds from the limestone islands of Barbuda and Anguilla indicates that volcanic islands in the region served as sources of pottery (or volcanic temper) for these two islands. 相似文献