Organic matter heterogeneities in 2.72 Ga stromatolites: Alteration versus preservation by sulfur incorporation     

Kevin Lepot  Karim Benzerara  Marine Cotte  Gordon E. Brown Jr.  Pascal Philippot 《Geochimica et cosmochimica acta》2009,73(21):6579-47

The stromatolites of the weakly metamorphosed 2.72 Ga Tumbiana Formation present abundant organic globules that resemble in size, shape and distribution the microorganisms observed in modern stromatolites. In order to evaluate the significance of these cell-like organic materials, we characterized organic matter in-situ down to the nanoscale using a combination of Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Raman microspectroscopy, scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM).These analyses revealed the occurrence of two distinct types of organic matter forming μm-scale textural and chemical heterogeneities distributed in distinct mineralogical laminae of the stromatolites. Type A organic matter, which is by far the most abundant, consists of sulfur-poor organic matter that is located in mud-type laminae at grain boundaries, mostly in association with silicate minerals. In contrast, Type B organic matter is rare and preserved as inclusions in the core of calcite grains forming laminates. It occurs as micrometer-sized cell-like globules containing variable amounts of organic sulfur likely in the form of thiophenes.Different scenarios may account for these compositional heterogeneities in the kerogen. Based on textural and compositional analogies with modern stromatolites, it is argued that Type B sulfur-rich globules may represent microbial cells protected by mineral encapsulation and selectively preserved through polymerization by early diagenetic sulfurization. In modern sediments, this reaction is fuelled by bacterial sulfate reduction (BSR). This metabolism has been widely considered as a major driver in modern stromatolites calcification and could thus have played an important role in the formation of the Tumbiana Formation stromatolites. In contrast, Type A sulfur-poor organic matter corresponds to either fossil extracellular polymer substances (EPS) or recondensed kerogen. This pool was likely not sulfurized due to either local and/or timely variations in the concentrations of H₂S or adverse pyritization driven by the availability of iron. Our observations thus show the need to use spatially-resolved techniques to complement organic geochemistry analyses and provide a detailed analysis of the organic carbon pools composing Archean stromatolites.  相似文献   

Rethinking the nature of urban environmental politics: Security, subjectivity, and the non-human     

Kevin Grove 《Geoforum》2009,40(2):207-216

The growing field of urban political ecology (UPE) has greatly advanced understandings of the socio-ecological transformations through which urban economies and environments are produced. However, this field has thus far failed to fully consider subjective (and subject-forming) dimensions of urban environmental struggle. I argue that this can be overcome through bringing urban political ecology into conversation with both post-structural political ecology and critical geopolitics. Bridging these literatures focuses attention on practices of socio-ecological exclusion and attachment through which environmental subjectivities are formed. This argument is drawn out through a case study of the politics of local economic development and conservation within the watershed of the Big Darby Creek near Columbus, Ohio. This struggle was driven by a preservationist movement that coalesced around a shared understanding of socio-ecological hybridity as a source of metaphysical insecurity. Hybridity appears here as a site of political and ethical struggle over social and ecological exclusions produced in the pursuit of security. This case study demonstrates a paradox of environmental politics: the non-human is at once a site of constituent possibilities for identity and subjectivity as well as forces which seek to foreclose this radical openness. Recognizing the paradoxical nature of environmental struggle allows for a more complex and nuanced account of the multifarious forces that shape the formation of environmental subjectivities.  相似文献   

Sand beach ridges record 6000 year history of extreme tropical cyclone activity in northeastern Australia   总被引：1，自引：0，他引：1  

Jonathan Nott  Scott Smithers  Kevin Walsh  Ed Rhodes 《Quaternary Science Reviews》2009,28(15-16):1511-1520

Sand beach ridges are considered to be derived either from aeolian processes and/or waves but their deposition by individual or multiple storms has not been investigated in any detail. We use numerical meteorological and oceanographic models to determine the origin of a sequence of 29 shore parallel sand beach ridges in northeastern Australia. The results suggest that the ridges were constructed by waves and that the final form or height of the ridges is a function of high-energy tropical cyclone generated waves plus storm tides. Hence these landforms archive a nearly 6000 year long history of intense tropical cyclones. The record implies that these extreme tempests occur considerably more frequently than that suggested by the short historical record for this region. The genesis of this sand beach ridge plain has implications for the interpretation of similar sequences elsewhere along the northeast coast of Australia and in comparable environments globally. If other similar sand beach ridge plains have also been deposited by like processes it stands to reason that these long-term records of high intensity tropical cyclones can be used to ascertain a regional scale risk assessment from this hazard.  相似文献   

Movement,memory, landscape: an excursion in non-representational thought     

Kevin E. McHugh 《GeoJournal》2009,74(3):209-218

This paper is an excursion in non-representational thought. The primacy of movement charges this creative geography. Movement as sensation, thought, matter and memory crystallizes in ongoing assemblages (effects) we term selves and landscapes. This movement ontology is animated by a stream of thought running through Bergson, Deleuze, and Massumi, and by Ingold’s temporality of landscape. Memory is vital, as past (virtual) and present (actual) coexist, pushing forward in duration, the dynamic continuation of movement and sensation. David Lynch’s film, The Straight Story, offers dramatic illustration of the entanglement of movement, memory, and landscape. Landscape is emergent as relational lines of movement, an ongoing meshwork of practices and movement signatures. Alvin Straight’s paced journey through Iowa on a John Deere lawn mower during autumn harvest is a road to reminiscence and reconciliation, an American sublime. Lynch’s movement-images and soundscapes are sensorial undulations that illumine landscape as movement of incorporation, ‘dwelling’ in the moment to moment, geographies of care. The take-home message is that we are nothing more and nothing less than agents, next selves, ‘passing’ through. The collective trace of our ‘passings’ constitutes the making and remaking of place.

Kevin E. McHughEmail:

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Trace element geochemistry and mineralogy of the Mount Isa Copper ores,Queensland, Australia     

Rowena Duckworth  Frank Santaguida  Kevin Blake  Kimberley Head  Rhonda O'Sullivan 《Journal of Geochemical Exploration》2009

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Polyphase speleogenesis in Lick Creek Cave,Little Belt Mountains,Montana, USA     

Kevin L. Carriere  Hans G. Machel  John C. Hopkins 《Journal of Geochemical Exploration》2009

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Microbial carbon cycling in oligotrophic regional aquifers near the Tono Uranium Mine, Japan as inferred from δC and ΔC values of in situ phospholipid fatty acids and carbon sources     

Christopher T. Mills  Yuki Amano  Gregory F. Slater  Teruki Iwatsuki  Kevin W. Mandernack 《Geochimica et cosmochimica acta》2010,74(13):3785-3805

Microorganisms are ubiquitous in deep subsurface environments, but their role in the global carbon cycle is not well-understood. The natural abundance δ¹³C and Δ¹⁴C values of microbial membrane phospholipid fatty acids (PLFAs) were measured and used to assess the carbon sources of bacteria in sedimentary and granitic groundwaters sampled from three boreholes in the vicinity of the Tono Uranium Mine, Gifu, Japan. Sample storage experiments were performed and drill waters analyzed to characterize potential sources of microbial contamination. The most abundant PLFA structures in all waters sampled were 16:0, 16:1ω7c, cy17:0, and 18:1ω7c. A PLFA biomarker for type II methanotrophs, 18:1ω8c, comprised 3% and 18% of total PLFAs in anoxic sedimentary and granitic waters, respectively, sampled from the KNA-6 borehole. The presence of this biomarker was unexpected given that type II methanotrophs are considered obligate aerobes. However, a bacterium that grows aerobically with CH₄ as the sole energy source and which also produces 56% of its total PLFAs as 18:1ω8c was isolated from both waters, providing additional evidence for the presence of type II methanotrophs. The Δ¹⁴C values determined for type II methanotroph PLFAs in the sedimentary (−861‰) and granite (−867‰) waters were very similar to the Δ¹⁴C values of dissolved inorganic carbon (DIC) in each water (∼−850‰). This suggests that type II methanotrophs ultimately derive all their carbon from inorganic sources, whether directly from DIC and/or from CH₄ produced by the reduction of DIC. In contrast, δ¹³C values of type II PLFAs in the sedimentary (−93‰) and granite (−60‰) waters indicate that these organisms use different carbon assimilation schemes in each environment despite very similar δ¹³C_CH4 values (∼−95‰) for each water. The δ¹³C_PLFA values (−28‰ to −45‰) of non-methanotrophic bacteria in the KNA-6 LTL water do not clearly distinguish between heterotrophic and autotrophic metabolisms, but Δ¹⁴C_PLFA values indicate that >65% of total bacteria filtered from the KNA-6 LTL water are heterotrophs. Ancient Δ¹⁴C values (∼−1000‰) of some PLFAs suggest that many heterotrophs utilize ancient organic matter, perhaps from lignite seams within the sedimentary rocks. The more negative range of δ¹³C_PLFA values determined for the KNA-6 granitic water (−42‰ to −66‰) are likely the result of a microbial ecosystem dominated by chemolithoautotrophy, perhaps fuelled by abiogenic H₂. Results of sample storage experiments showed substantial shifts in microbial community composition and δ¹³C_PLFA values (as much as 5‰) during 2-4 days of dark, refrigerated, aseptic storage. However, water samples collected and immediately filtered back in the lab from freshly drilled MSB-2 borehole appeared to maintain the same relative relationships between δ¹³C_PLFA values for sedimentary and granitic host rocks as observed for samples directly filtered under artesian flow from the KNA-6 borehole of the Tono Uranium Mine.  相似文献   

Mineral waters in Slovakia — Evaluation of chemical composition stability using both historical records and the most recent data     

Bodiš Dušan  Kordik Jozef  Slaninka Igor  Malík Peter  Liščák Pavel  Panák Daniel  Božíková Jarmila  Marcin Daniel 《Journal of Geochemical Exploration》2010

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Carbon storage of headwater riparian zones in an agricultural landscape     

Richard D Rheinhardt  Mark M Brinson  Gregory F Meyer  Kevin H Miller 《Carbon balance and management》2012,7(1):1-5

Background

In agricultural regions, streamside forests have been reduced in age and extent, or removed entirely to maximize arable cropland. Restoring and reforesting such riparian zones to mature forest, particularly along headwater streams (which constitute 90% of stream network length) would both increase carbon storage and improve water quality. Age and management-related cover/condition classes of headwater stream networks can be used to rapidly inventory carbon storage and sequestration potential if carbon storage capacity of conditions classes and their relative distribution on the landscape are known.

Results

Based on the distribution of riparian zone cover/condition classes in sampled headwater reaches, current and potential carbon storage was extrapolated to the remainder of the North Carolina Coastal Plain stream network. Carbon stored in headwater riparian reaches is only about 40% of its potential capacity, based on 242 MgC/ha stored in sampled mature riparian forest (forest > 50 y old). The carbon deficit along 57,700 km headwater Coastal Plain streams is equivalent to about 25TgC in 30-m-wide riparian buffer zones and 50 TgC in 60-m-wide buffer zones.

Conclusions

Estimating carbon storage in recognizable age-and cover-related condition classes provides a rapid way to better inventory current carbon storage, estimate storage capacity, and calculate the potential for additional storage. In light of the particular importance of buffer zones in headwater reaches in agricultural landscapes in ameliorating nutrient and sediment input to streams, encouraging the restoration of riparian zones to mature forest along headwater reaches worldwide has the potential to not only improve water quality, but also simultaneously reduce atmospheric CO₂.  相似文献   

The 2dF-SDSS LRG and QSO Survey: evolution of the clustering of luminous red galaxies since z= 0.6     

David A. Wake  Ravi K. Sheth  Robert C. Nichol  Carlton M. Baugh  Joss Bland-Hawthorn  Matthew Colless  Warrick J. Couch  Scott M. Croom  Roberto De Propris  Michael J. Drinkwater  Alastair C. Edge  Jon Loveday  Tsz Yan Lam  Kevin A. Pimbblet  Isaac G. Roseboom  Nicholas P. Ross  Donald P. Schneider  Tom Shanks  Robert G. Sharp 《Monthly notices of the Royal Astronomical Society》2008,387(3):1045-1062

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