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  • 1
    In: Nature, 2010, Vol.465(7295), p.211
    Description: Over geologic timescales, C[O.sub.2] is emitted from the Earth's interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial. This balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions (1). Changes in this balance have been attributed to changes in topographic relief, where varying rates of continental rock weathering and erosion (1,2) are superimposed on fluctuations in organic carbon burial (3). Geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation (1,2,4). Widespread observations of a recent (0-5-Myr) fourfold increase in global sedimentation rates require a global mechanism to explain them (4-6). Accelerated uplift and global cooling have been given as possible causes (2,4,6,7), but because of the links between rates of erosion and the correlated rate of weathering (8,9), an increase in the drawdown of C[O.sub.2] that is predicted to follow may be the cause of global climate change instead (2). However, globally, rates of uplift cannot increase every where in the way that apparent sedimentation rates do (4,10). Moreover, proxy records of past atmospheric C[O.sub.2] provide no evidence for this large reduction in recent C[O.sub.2] concentrations (11,12). Here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record (13). As evidence, we recast the ocean dissolved [sup.10]Be/[sup.9]Be isotope system as a weathering proxy spanning the past ~12 Myr (ref. 14). This proxy indicates stable weathering fluxes during the late-Cenozoic era. The sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean. We conclude that processes different from an increase in denudation caused Cenozoic global cooling, and that global cooling had no profound effect on spatially and temporally averaged weathering rates.
    Keywords: Atmospheric Carbon Dioxide -- Research ; Erosion (Geology) -- Research ; Global Temperature Changes -- Research;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 2
    Language: English
    In: Earth and Planetary Science Letters, Oct 15, 2012, Vol.351-352, p.295(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2012.07.022 Byline: Friedhelm von Blanckenburg, Julien Bouchez, Hella Wittmann Keywords: Earth surface processes; cosmogenic nuclides; critical zone; river weathering and erosion fluxes; Amazon river Abstract: The isotope ratio of the meteoric cosmogenic nuclide.sup.10Be to the mineral-derived stable isotope.sup.9Be discloses both the Earth surface denudation rate and its weathering intensity. We develop a set of steady state mass balance equations that describes this system from a soil column over the hillslope scale to an entire river basin. The prerequisites making this new approach possible are: (1) the.sup.9Be concentration of parent rock (typically 2.5[+ or -]0.5ppm in granitic and clastic sedimentary lithologies) is known; (2) both Be isotopes equilibrate between the fluids decomposing rock and reactive solids formed during weathering; and (3) a critical spatial scale is exceeded at which the fluxes of both isotopes into and out of the weathering zone are at steady state over the time scale of weathering (typically [approximately equal to]10kyr). For these cases the isotope ratios can be determined in bulk sediment or soil, on leachates from the reactive (adsorbed and pedogenic mineral-bound) phase in sediment or soil, and even on the dissolved phase in river water. The.sup.10Be/.sup.9Be ratio offers substantial advantages over the single-isotope system of meteoric.sup.10Be. The latter system allows to directly determine erosion rates only in the case that.sup.10Be is fully retentive in the weathering zone and that riverine sorting has not introduced grain size-dependent.sup.10Be concentration gradients in sediments. We show the feasibility of the.sup.10Be/.sup.9Be tracer approach at the river scale for sediment and water samples in the Amazon basin, where independent estimates of denudation rates from in situ-produced.sup.10Be exist. We furthermore calculate meaningful denudation rates from a set of published.sup.10Be/.sup.9Be ratios measured in the dissolved load of globally distributed rivers. We conclude that this isotope ratio can be used to reconstruct global paleo-denudation from sedimentary records. Author Affiliation: GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany Article History: Received 23 March 2012; Revised 12 July 2012; Accepted 16 July 2012 Article Note: (miscellaneous) G. Henderson
    Keywords: Rivers ; Tracers (Biology) ; Geomorphology ; Sediments (Geology)
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Earth and Planetary Science Letters, Feb 1, 2014, Vol.387, p.34(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2013.11.004 Byline: Friedhelm von Blanckenburg, Julien Bouchez Abstract: The ratio of the meteoric cosmogenic radionuclide.sup.10Be to the stable isotope.sup.9Be is proposed here to be a flux proxy of terrigenous input into the oceans. The oceanE1/4s dissolved.sup.10Be/.sup.9Be is set by (1) the flux of meteoric.sup.10Be produced in the atmosphere; (2) the denudational flux of the rivers discharging into a given ocean basin; (3) the fraction of.sup.9Be that is released from primary minerals during weathering (meaning the.sup.9Be transported by rivers in either the dissolved form or adsorbed onto sedimentary particles and incorporated into secondary oxides); and (4) the fraction of riverine.sup.10Be and.sup.9Be actually released into seawater. Using published.sup.10Be/.sup.9Be data of rivers for which independent denudation rate estimates exist we first find that the global average fraction of.sup.9Be released during weathering into river waters and their particulate load is 20% and does not depend on denudation rate. We then evaluate this quantitative proxy for terrigenous inputs by using published dissolved seawater Be isotope data and a compilation of global river loads. We find that the measured global average oceanic dissolved.sup.10Be/.sup.9Be ratio of about 0.9x10.sup.-7 is satisfied by the mass balance if only about 6% of the dissolved and adsorbed riverine Be is eventually released to the open ocean after escaping the coastal zone. When we establish this mass balance for individual ocean basins good agreement results between.sup.10Be/.sup.9Be ratios predicted from known river basin denudation rates and measured ocean.sup.10Be/.sup.9Be ratios. Only in the South Atlantic and the South Pacific the.sup.10Be/.sup.9Be ratio is dominated by advected Be and in these basins the ratio is a proxy for ocean circulation. As the seawater.sup.10Be/.sup.9Be ratio is faithfully recorded in marine chemical precipitates the.sup.10Be/.sup.9Be ratio extracted from authigenic sediments can now serve to estimate relative changes in terrigenous input into the oceans back through time on a global and on an ocean basin scale. Author Affiliation: (a) Earth Surface Geochemistry, Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Telegraphenberg, 14473 Potsdam, Germany (b) Institute of Geological Sciences, Freie Universitat Berlin, Germany Article History: Received 21 May 2013; Revised 1 October 2013; Accepted 4 November 2013 Article Note: (miscellaneous) Editor: G. Henderson
    Keywords: Seawater ; Ocean Circulation ; Air Pollution ; Terrigenous Sediments
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Science, 03 December 1999, Vol.286(5446), pp.1862-1863
    Keywords: Physical sciences -- Earth sciences -- Hydrology ; Physical sciences -- Earth sciences -- Geography ; Physical sciences -- Physics -- Microphysics ; Physical sciences -- Chemistry -- Chemical properties ; Physical sciences -- Astronomy -- Astronomical objects ; Physical sciences -- Physics -- Mechanics ; Physical sciences -- Chemistry -- Chemical mixtures ; Environmental studies -- Environmental sciences -- Climate change ; Physical sciences -- Earth sciences -- Geology ; Physical sciences -- Earth sciences -- Geology
    ISSN: 00368075
    E-ISSN: 10959203
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  • 5
    Language: English
    In: Nature, July 16, 2009, Vol.460(7253), p.309(1)
    Keywords: Orogeny -- Environmental Aspects ; Carbon Cycle -- Research ; Weathering -- Environmental Aspects ; Weathering -- Research
    ISSN: 0028-0836
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  • 6
    Language: English
    In: Journal of agricultural and food chemistry, 2013, Vol.61(49), pp.11893-11899
    Description: The stable isotopes of iron disclose the metabolic pathways of iron within the human food chain. We have measured with precise multicollector ICP-MS the iron concentrations and stable isotope composition of 60 food products that are representative of the average German diet. We find that vegetables fall within the range typical of strategy I plants (-0.1 to -1.4‰ in δ56Fe), crop products and processed crop foods into the range typical of strategy II plants (-0.6 to +0.4‰), and animal products into the 54Fe-enriched range known for animal tissue and blood (-1.1 to -2.7‰). Weighting these isotope compositions by the average iron dietary sources, we find a representative composition of European vegetarian diet of -0.45‰, whereas that of omnivores is -0.82‰. For human blood, known to be enriched in light iron isotopes, we find fractionation factors for iron absorption of -2.0 and -2.3‰ for vegetarians (female and male, respectively) and -1.3 and -1.5‰ for omnivores (female and male, respectively). Knowing these fractionation factors is a prerequisite for using stable iron isotope ratios in blood as monitors of intestinal iron uptake regulation. ; p. 11893-11899.
    Keywords: Biochemical Pathways ; Dietary Nutrient Sources ; Omnivores ; Vegetables ; Iron Absorption ; Animal Products ; Blood ; Humans ; Iron ; Stable Isotopes ; Foods ; Human Food Chain ; Vegetarian Diet ; Fractionation
    ISSN: 0021-8561
    E-ISSN: 15205118
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  • 7
    Language: English
    In: Science, 15 March 2002, Vol.295(5562), pp.2065-2066
    Description: Isotopic analysis of human blood and liver and muscle tissue indicates that each individual bears a long-term iron (Fe) isotope signature in the blood. Blood and tissue differ slightly in isotopic composition and are depleted by up to 2.6 per mil in 56 Fe relative to 54 Fe when compared to dietary Fe. The 56 Fe/ 54 Fe isotope ratio in the blood of males is, on average, lower by 0.3 per mil than that of females. These results suggest that Fe isotope effects in the blood reflect differences in intestinal Fe absorption between individuals and genotypes.
    Keywords: Physical sciences -- Physics -- Microphysics ; Biological sciences -- Biology -- Physiology ; Physical sciences -- Chemistry -- Chemical elements ; Physical sciences -- Earth sciences -- Geochemistry ; Biological sciences -- Biology -- Anatomy ; Physical sciences -- Chemistry -- Chemical reactions ; Biological sciences -- Biology -- Anatomy ; Health sciences -- Medical conditions -- Diseases ; Linguistics -- Language -- Orthographies ; Applied sciences -- Food science -- Foodstuffs
    ISSN: 00368075
    E-ISSN: 10959203
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  • 8
    Language: English
    In: Geochimica et Cosmochimica Acta, Oct 1, 2013, Vol.118, p.202(29)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.05.006 Byline: Tilak Hewawasam, Friedhelm von Blanckenburg, Julien Bouchez, Jean L. Dixon, Jan A. Schuessler, Ricarda Maekeler Abstract: Silicate weathering - initiated by major mineralogical transformations at the base of ten meters of clay-rich saprolite - generates the exceptionally low weathering flux found in streams draining the crystalline rocks of the mountainous and humid tropical Highlands of Sri Lanka. This conclusion is reached from a thorough investigation of the mineralogical, chemical, and Sr isotope compositions of samples within a regolith profile extending 〉10m from surface soil through the weathering front in charnockite bedrock (a high-grade metamorphic rock), corestones formed at the weathering front, as well as from the chemical composition of the dissolved loads in nearby streams. Weatherable minerals and soluble elements are fully depleted at the top of the profile, showing that the system is supply-limited, such that weathering fluxes are controlled directly by the supply of fresh minerals. We determine the weathering rates using two independent means: (1) in situ-produced cosmogenic nuclides in surface soil and creek sediments in the close vicinity of the regolith combined with immobile element mass balance across the regolith and (2) river dissolved loads. Silicate weathering rates determined from both approaches range from 16 to 36tkm.sup.-2 y.sup.-1, corresponding to a weathering front advance rate of 6-14mmky.sup.-1. These rates agree across the 10.sup.1 to 10.sup.4 ytime scales over which our rate metrics integrate, suggesting that the weathering system operates at steady state. Within error these rates are furthermore compatible with those obtained by modeling the advance rate of the weathering front from chemical gradients and mineral dissolution rates. The silicate weathering flux out of the weathering profile, measured on small creeks, amounts to 84% of the profile's export flux; the remaining 16% is contributed by non-silicate, atmospheric-derived input. The silicate weathering flux, as measured by dissolved loads in large catchments, amounts to ca. 50% of the total dissolved flux; the remainder being contributed by dust, rain, and weathering of local marble bands. Spheroidal weathering is the key processes of converting the fresh bedrock into saprolite at the weathering front. The mineralogical composition of weathering rinds shows that the sequence of mineral decomposition is: pyroxene; plagioclase; biotite; K-feldspar. Observable biotite alteration does not appear to initiate spheroidal weathering within corestones; therefore, we infer that other processes than biotite oxidation, like pyroxene oxidation, clay formation from pyroxene and plagioclase decomposition, the development of secondary porosity by plagioclase dissolution, or even microbiologic processes at depth enable the coupling between slow advance of the weathering front and slow erosion at the surface. The comparison to tectonically more active tropical landscapes lets us conclude that the combination of hard rock with tightly interlocked mineral grains and slow erosion in the absence of tectonically-induced landscape rejuvenation lead to these exceptionally low weathering rates. Article History: Received 3 October 2012; Accepted 3 May 2013 Article Note: (miscellaneous) Associate editor: S. Krishnaswami
    Keywords: Silicates -- Analysis ; Sediments (Geology) -- Analysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 9
    Article
    Article
    In: Nature, 2009, Vol.460(7253), p.309
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 10
    Language: English
    In: Earth and Planetary Science Letters, Oct 15, 2015, Vol.428, p.293(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2015.07.018 Byline: Michael Tatzel, Friedhelm von Blanckenburg, Marcus Oelze, Jan A. Schuessler, Gerhard Bohrmann Abstract: The heavy isotopes of silicon are strongly enriched in some of the youngest, early diagenetically formed porcellanite layers from the Southwest Indian Ridge (Pleistocene) and the Maud Rise (Pliocene). These porcellanite layers are composed of opal-CT and were formed by the conversion of amorphous silica (opal-A) from siliceous sediment via dissolution-reprecipitation. Their bulk [delta]Si30 values range between 1.7 and 2.3a[degrees]. Detritus-poor siliceous sediment surrounding these layers is significantly lower at -0.3 to 1.5a[degrees]. Sequential chemical extractions of bulk siliceous sediment show (i) preferential dissolution of diatoms featuring higher [delta]Si30 than radiolaria and Al-Si components. The detailed investigation of porcellanite layers by micro-scale Si isotope and Al/Si analyses using UV femtosecond laser ablation ICP mass spectrometry show that (ii) precipitation of authigenic aluminum silicates enriched in light Si isotopes drives pore waters to even higher [delta]Si30. We suggest that the same processes redistributed stable silicon isotopes in precursor siliceous sediments of ancient chert. We infer that past environmental conditions can be reconstructed with high fidelity from the stable Si isotope composition of chert when initial seawater Si concentrations were high (such as in the Precambrian). Exchange of Si between layers during phase transformation (from opal-A to opal-CT and from opal-CT to quartz) is impeded when variable amounts of detrital minerals are present, because they control rates of silica phase transformation and hence the timing of dissolution-reprecipitation during burial. Author Affiliation: (a) GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany (b) Department of Earth Sciences, Institute of Geological Sciences, Freie Universitat Berlin, Germany (c) MARUM - Center for Marine Environmental Sciences, Department of Geosciences, University of Bremen, Klagenfurter Str., 28359 Bremen, Germany Article History: Received 7 August 2014; Revised 29 June 2015; Accepted 9 July 2015 Article Note: (miscellaneous) Editor: G.M. Henderson
    Keywords: Seawater – Analysis ; Silicon – Analysis ; Aluminosilicates – Analysis ; Precipitation (Meteorology) – Analysis ; Sediments (Geology) – Analysis ; Mass Spectrometry – Analysis ; Silicates – Analysis ; Mid-Ocean Ridges – Analysis ; Diagenesis (Geology) – Analysis ; Silicon Dioxide – Analysis ; Femtosecond Lasers – Analysis
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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