Geochemical Perspectives Letters is an internationally peer-reviewed journal of the European Association of Geochemistry,
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Open access
Short (3000 words all inclusive)
Highest-quality articles spanning geochemical sciences

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 Top 10 most viewed articles (cumulative count of HTML views) for the last 60 days.

The composition and weathering of the continents over geologic time

Abstract:
The composition of continental crust records the balance between construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how igneous addition and chemical weathering have modified the continents’ bulk composition are essential for understanding the evolution of geodynamics and climate. Using novel data analytic techniques we have extracted temporal trends in sediments’ protolith composition and weathering intensity from the largest available compilation of sedimentary major element compositions: ∼15,000 samples from 4.0 Ga to the present. We find that the average Archean upper continental crust was silica-rich and had a similar compositional diversity to modern continents. This is consistent with an early Archean, or earlier, onset of plate tectonics. In the Archean, chemical weathering sequestered ∼25 % more CO2 per mass eroded for the same weathering intensity than in subsequent time periods, consistent with carbon mass balance despite higher Archean outgassing rates and more limited continental exposure. Since 2.0 Ga, over long (>0.5 Gyr) timescales, crustal weathering intensity has remained relatively constant. On shorter timescales over the Phanerozoic, weathering intensity is correlated to global climate state, consistent with a weathering feedback acting in response to changes in CO2 sources or sinks.

A.G. Lipp, O. Shorttle, E.A. Sperling, J.J. Brocks, D.B. Cole, P.W. Crockford, L. Del Mouro, K. Dewing, S.Q. Dornbos, J.F. Emmings, U.C. Farrell, A. Jarrett, B.W. Johnson, P. Kabanov, C.B. Keller, M. Kunzmann, A.J. Miller, N.T. Mills, B. O’Connell, S.E. Peters, N.J. Planavsky, S.R. Ritzer, S.D. Schoepfer, P.R. Wilby, J. Yang

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Geochem. Persp. Let. (2021) 17, 21–26 | doi: 10.7185/geochemlet.2109 | Published 2 March 2021

Article views: 2375

Ca isotope systematics of carbonatites: Insights into carbonatite source and evolution

Abstract:
Carbonatite, an unusual carbonate-rich igneous rock, is known to be sourced from the mantle which provides insights into mantle-to-crust carbon transfer. To constrain further the Ca isotopic composition of carbonatites, investigate the behaviour of Ca isotopes during their evolution, and constrain whether recycled carbonates are involved in their source regions, we report δ44/42Ca for 47 worldwide carbonatite and associated silicate rocks using a refined analytical protocol. Our results show that primary carbonatite and associated silicate rocks are rather homogeneous in Ca isotope compositions that are comparable to δ44/42Ca values of basalts, while non-primary carbonatites show detectable δ44/42Ca variations that are correlated to δ13C values. Our finding suggests that Ca isotopes fractionate during late stages of carbonatite evolution, making it a useful tool in the study of carbonatite evolution. The finding also implies that carbonatite is sourced from a mantle source without requiring the involvement of recycled carbonates.

J. Sun, X.-K. Zhu, N.S. Belshaw, W. Chen, A.G. Doroshkevich, W.-J. Luo, W.-L. Song, B.-B. Chen, Z.-G. Cheng, Z.-H. Li, Y. Wang, J. Kynicky, G.M. Henderson

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Geochem. Persp. Let. (2021) 17, 11–15 | doi: 10.7185/geochemlet.2107 | Published 17 February 2021

Article views: 1588

Selenium isotope evidence for pulsed flow of oxidative slab fluids

Abstract:
Isotope systematics of the redox sensitive and chalcophile element selenium (Se) were investigated on exhumed parts of subducted oceanic lithosphere to provide new constraints on slab dehydration conditions during subduction. The samples show increasing δ82/76SeNIST3149 with higher abundances of fluid mobile elements, comprising a larger range (−1.89 to +0.48 ‰) than that of mantle (−0.13 ± 0.12 ‰) and altered ocean crust (−0.35 to −0.07 ‰). Our data point to pronounced, local scale redox variations within the subducting crust, wherein oxidative fluids dissolve sulfides and mobilise oxidised Se species. Subsequently recrystallising sulfides preferentially incorporate isotopically lighter, reduced Se, which shifts evolving fluids and late stage sulfides to higher δ82/76SeNIST3149. Redistribution of Se by repeated cycles of sulfide reworking within the subducted crust can be reconciled with episodes of oxidised fluid pulses from underlying slab mantle in modern subduction zones.

S. König, C. Rosca, T. Kurzawa, M.I. Varas-Reus, B. Dragovic, R. Schoenberg, T. John

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Geochem. Persp. Let. (2021) 17, 27–32 | doi: 10.7185/geochemlet.2110 | Published 9 March 2021

Article views: 1134

Molybdenum isotope constraints on the temporal development of sulfidic conditions during Mediterranean sapropel intervals

Abstract:
Mediterranean sapropels represent some of the largest scale deoxygenation events in recent Earth history. Here, we use high resolution Mo isotope data for seven such events (sapropels S3 to S9) to semi-quantitatively constrain past H2S concentrations using a new interpretive framework. Bottom water H2S was present for all studied sapropels, but the extent of redox changes varied considerably between them, the ultimate driver likely being variations in monsoon strength. Near-quantitative removal of Mo (δ98Mo > 2 ‰) during deposition of sapropels S5 and S7 suggests predominantly highly sulfidic conditions with long deep water residence times, comparable to the modern Black Sea, whereas considerably lower δ98Mo values for sapropels S3, S4, S8, and S9 (−0.4 to +0.9 ‰) imply mildly euxinic conditions only (0 < H2S < 11 μmol/L). The high resolution data reveal consistent temporal patterns that track the development of basin restriction and euxinia over several kyr. These observations illustrate how Mo isotopes can provide quantitative constraints on basin wide redox changes on relatively short time scales.

T. Sweere, R. Hennekam, D. Vance, G.-J. Reichart

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Geochem. Persp. Let. (2021) 17, 16–20 | doi: 10.7185/geochemlet.2108 | Published 18 February 2021

Article views: 1109

Microplastics contaminate the deepest part of the world’s ocean

Abstract:
Millions of metric tons of plastics are produced annually and transported from land to the oceans. Finding the fate of the plastic debris will help define the impacts of plastic pollution in the ocean. Here, we report the abundances of microplastic in the deepest part of the world’s ocean. We found that microplastic abundances in hadal bottom waters range from 2.06 to 13.51 pieces per litre, several times higher than those in open ocean subsurface water. Moreover, microplastic abundances in hadal sediments of the Mariana Trench vary from 200 to 2200 pieces per litre, distinctly higher than those in most deep sea sediments. These results suggest that manmade plastics have contaminated the most remote and deepest places on the planet. The hadal zone is likely one of the largest sinks for microplastic debris on Earth, with unknown but potentially damaging impacts on this fragile ecosystem.

X. Peng, M. Chen, S. Chen, S. Dasgupta, H. Xu, K. Ta, M. Du, J. Li, Z. Guo, S. Bai

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Geochem. Persp. Let. (2018) 9, 1–5 | doi: 10.7185/geochemlet.1829 | Published 27 November 2018

Article views: 1035

Diamond forms during low pressure serpentinisation of oceanic lithosphere

Abstract:
Diamond is commonly regarded as an indicator of ultra-high pressure conditions in Earth System Science. This canonical view is challenged by recent data and interpretations that suggest metastable growth of diamond in low pressure environments. One such environment is serpentinisation of oceanic lithosphere, which produces highly reduced CH4-bearing fluids after olivine alteration by reaction with infiltrating fluids. Here we report the first ever observed in situ diamond within olivine-hosted, CH4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samples from the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated in voids below the polished mineral surface forming a typical serpentinisation array, with methane, serpentine and magnetite, providing definitive evidence for its metastable growth upon low temperature and low pressure alteration of oceanic lithosphere and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage at a reference P-T point appropriate for serpentinisation (350 °C and 100 MPa) is consistent with extreme reduction of the fluid to logfO2 (MPa) = −45.3 (ΔlogfO2[Iron-Magnetite] = −6.5). These findings imply that the formation of metastable diamond at low pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioning a generalised ultra-high pressure origin for ophiolitic diamond.

N. Pujol-Solà, A. Garcia-Casco, J.A. Proenza, J.M. González-Jiménez, A. del Campo, V. Colás, À. Canals, A. Sánchez-Navas, J. Roqué-Rosell

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Geochem. Persp. Let. (2020) 15, 19–24 | doi: 10.7185/geochemlet.2029 | Published 10 September 2020

Article views: 725

Integration of elemental and isotope data supports a Neoproterozoic Adamastor Ocean realm

Abstract:
A robust elemental and isotopic dataset from Neoproterozoic igneous rocks discloses protracted consumption of oceanic lithosphere in the 3,000 km long orogenic system of southeastern South America. Time dependent isotopic variation trends suggest that Tonian-Cryogenian magmatic rocks formed in intra-oceanic supra-subduction settings, followed by Ediacaran magmatic arc building along Andean-type continental margins. Tectonic slices of basic-ultrabasic rocks associated with deep sea and exhalative rocks are interpreted as remnants of obducted oceanic lithosphere. Protracted closure of the oceanic realm resulted in a Himalayas-sized orogenic belt during Ediacaran-Cambrian collision, as recorded by voluminous aluminum-rich syn-collisional granites followed by post-collisional intrusions. The duration and rates of crust forming processes in island arc, continental margins and collisional settings imply that a vast Adamastor oceanic realm was consumed to form western Gondwana.

F.A. Caxito, M. Heilbron, C.M. Valeriano, H. Bruno, A. Pedrosa-Soares, F.F. Alkmim, F. Chemale, L.A. Hartmann, E. Dantas, M.A.S. Basei

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Geochem. Persp. Let. (2021) 17, 6–10 | doi: 10.7185/geochemlet.2106 | Published 11 February 2021

Article views: 576

A genetic metasomatic link between eclogitic and peridotitic diamond inclusions

Abstract:
Diamond inclusions sample the otherwise inaccessible archive of Earth’s deep interior. The geochemical and petrological diversity of diamond inclusions reflects either pre-metasomatic upper mantle heterogeneity or metasomatism coeval with diamond formation. We focus on the origin of lithospheric garnet and clinopyroxene inclusions by simulating metasomatic reactions between eclogitic fluids and mantle peridotites at 5 GPa, 1000 °C, and across a range of redox conditions (logfO2 = −1 to −6 ΔFMQ). Our results demonstrate that fluid-rock interaction can result in the formation of eclogitic, websteritic, and peridotitic silicates from a single fluid during a single diamond-forming metasomatic event. Ergo, the petrogenesis of diamond and their inclusions can be syngenetic, and the petrological diversity of diamond inclusions can reflect metasomatism coeval with diamond formation. Furthermore, during the metasomatism, refractory peridotite can be converted to fertile websterite which could become a pyroxenitic mantle source for oceanic basalts.

S. Mikhail, M. Rinaldi, E.R. Mare, D.A. Sverjensky

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Geochem. Persp. Let. (2021) 17, 33–38 | doi: 10.7185/geochemlet.2111 | Published 24 March 2021

Article views: 573

Morphology dominated rapid oxidation of framboidal pyrite

Abstract:
The rapid oxidation of framboidal pyrite is conventionally attributed to its fine grain size. However, the effect of the crystal facets of the microcrystals in the framboids on the oxidation process has been overlooked. We synthesised pyrite monocrystals of microscopic size with both {100} and {111} facets, which are two major forms of framboidal pyrite crystals, in order to examine the oxidation behaviour of pyrite framboids. The results showed that the oxidation rate of microcrystals with a greater proportion of {111} facets was approximately 2 times higher than that of those with a greater proportion of {100} facets although the latter’s size was smaller. Such a difference makes framboidal pyrite with {111} facets more sensitive to oxidative weathering in geochemical cycles than other forms of pyrite. These findings emphasise the role of crystal anisotropy in controlling the oxidation of framboidal pyrite, thereby suggesting that the shape controlled oxidation of pyrite is a potential indicator of the local redox conditions of the palaeoenvironment where it occurred.

R. Du, H. Xian, X. Wu, J. Zhu, J. Wei, J. Xing, W. Tan, H. He

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Geochem. Persp. Let. (2021) 16, 53–58 | doi: 10.7185/geochemlet.2104 | Published 9 February 2021

Article views: 569

182W evidence for core-mantle interaction in the source of mantle plumes

Abstract:
Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth’s core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182Hf decayed entirely to 182W in the mantle after metal-silicate segregation. Therefore, the 182W isotopic composition of the Earth’s mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Réunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tungsten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle.

H. Rizo, D. Andrault, N.R. Bennett, M. Humayun, A. Brandon, I. Vlastelic, B. Moine, A. Poirier, M.A. Bouhifd, D.T. Murphy

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Geochem. Persp. Let. (2019) 11, 6–11 | doi: 10.7185/geochemlet.1917 | Published 20 June 2019

Article views: 558

 Top 10 most viewed articles (cumulative count of HTML views) for all time.

Microplastics contaminate the deepest part of the world’s ocean

Abstract:
Millions of metric tons of plastics are produced annually and transported from land to the oceans. Finding the fate of the plastic debris will help define the impacts of plastic pollution in the ocean. Here, we report the abundances of microplastic in the deepest part of the world’s ocean. We found that microplastic abundances in hadal bottom waters range from 2.06 to 13.51 pieces per litre, several times higher than those in open ocean subsurface water. Moreover, microplastic abundances in hadal sediments of the Mariana Trench vary from 200 to 2200 pieces per litre, distinctly higher than those in most deep sea sediments. These results suggest that manmade plastics have contaminated the most remote and deepest places on the planet. The hadal zone is likely one of the largest sinks for microplastic debris on Earth, with unknown but potentially damaging impacts on this fragile ecosystem.

X. Peng, M. Chen, S. Chen, S. Dasgupta, H. Xu, K. Ta, M. Du, J. Li, Z. Guo, S. Bai

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Geochem. Persp. Let. (2018) 9, 1–5 | doi: 10.7185/geochemlet.1829 | Published 27 November 2018

Article views: 29255

Global climate stabilisation by chemical weathering during the Hirnantian glaciation

Abstract:
Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled “weathering thermostat” has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (δ7Li) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (~445 Ma). We find a positive δ7Li excursion, suggestive of a silicate weathering decline. Using a coupled lithium-carbon model, we show that initiation of the glaciation was likely caused by declining CO2 degassing, which triggered abrupt global cooling, and much lower weathering rates. This lower CO2 drawdown during the glaciation allowed climatic recovery and deglaciation. Combined, the data and model provide support from the geological record for the operation of the weathering thermostat.

P.A.E. Pogge von Strandmann, A. Desrochers, M.J. Murphy, A.J. Finlay, D. Selby, T.M. Lenton

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Geochem. Persp. Let. (2017) 3, 230–237 | doi: 10.7185/geochemlet.1726 | Published 15 June 2017

Article views: 28488

Copper isotope evidence for large-scale sulphide fractionation during Earth’s differentiation

Abstract:
The differentiation of Earth into a metallic core and silicate mantle left its signature on the chemical and isotopic composition of the bulk silicate Earth (BSE). This is seen in the depletion of siderophile (metal-loving) relative to lithophile (rock-loving) elements in Earth’s mantle as well as the silicon isotope offset between primitive meteorites (i.e. bulk Earth) and BSE, which is generally interpreted as a proof that Si is present in Earth’s core. Another putative light element in Earth’s core is sulphur; however, estimates of core S abundance vary significantly and, due to its volatile nature, no unequivocal S isotopic signature for core fractionation has thus far been detected. Here we present new high precision isotopic data for Cu, a chalcophile (sulphur-loving) element, which shows that Earth’s mantle is isotopically fractionated relative to bulk Earth. Results from high pressure equilibration experiments suggest that the sense of Cu isotopic fractionation between BSE and bulk Earth requires that a sulphide-rich liquid segregated from Earth’s mantle during differentiation, which likely entered the core. Such an early-stage removal of a sulphide-rich phase from the mantle presents a possible solution to the long-standing 1st terrestrial lead paradox.

P.S. Savage, F. Moynier, H. Chen, J. Siebert, J. Badro, I.S. Puchtel, G. Shofner

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Geochem. Persp. Let. (2015) 1, 53–64 | doi: 10.7185/geochemlet.1506 | Published 4 June 2015

Article views: 22257

Oxygenation of the mid-Proterozoic atmosphere: clues from chromium isotopes in carbonates

Abstract:
Chromium (Cr) isotopes in marine sedimentary rocks can be used as a sensitive proxy for ancient atmospheric oxygen because Cr-isotope fractionation during terrestrial weathering only occurs when pO2 exceeds a threshold value. This is a useful system when applied to rocks of mid-Proterozoic age, where fundamental questions persist about atmospheric pO2 and its relationship to biological innovation. Whereas previous studies have focused on temporally limited iron-rich sedimentary rocks, we present new Cr-isotope data from a suite of mid-Proterozoic marine carbonate rocks. Application of the Cr-isotope proxy to carbonate rocks has the potential to greatly enhance the temporal resolution of Proterozoic palaeo-redox data. Here we report positive δ53Cr values in four carbonate successions, extending the mid-Proterozoic record of Cr-isotope fractionation – and thus pO2 above threshold values – back to ~1.1 Ga. These data suggest that pO2 sufficient for the origin of animals was transiently in place well before their Neoproterozoic appearance, although uncertainty in the pO2 threshold required for Cr-isotope fractionation precludes definitive biological interpretation. This study provides a proof of concept that the Cr-isotopic composition of carbonate rocks can provide important new constraints on the oxygen content of the ancient atmosphere.

G.J. Gilleaudeau, R. Frei, A.J. Kaufman, L.C. Kah, K. Azmy, J.K. Bartley, P. Chernyavskiy, A.H. Knoll

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Geochem. Persp. Let. (2016) 2, 178–187 | doi: 10.7185/geochemlet.1618 | Published 24 May 2016

Article views: 20260

Release of subducted sedimentary nitrogen throughout Earth’s mantle

Abstract:
The dynamic process of subduction represents the principal means to introduce chemical heterogeneities into Earth's interior. In the case of nitrogen (N) - atmosphere's most abundant gas - biological-activity converts N2 into ammonium ions (NH4+), which are chemically-bound within seafloor sediments and altered oceanic crust that comprise the subducting slab. Although some subducted N re-emerges via arc-related volcanism (Sano et al., 1998), the majority likely bypasses sub-arc depths (150-200 km) and supplies the deeper mantle (Li et al., 2007; Mitchell et al., 2010; Johnson and Goldblatt, 2015; Bebout et al., 2016). However, the fate of subducted N remains enigmatic: is it incorporated by the shallow convecting mantle - the source of ridge volcanism, or is the deeper mantle - nominally associated with mantle plumes - its ultimate repository? Here, we present N-He-Ne-Ar isotope data for oceanic basalts from the Central Indian Ridge (CIR)-Réunion plume region to address this issue. All on-axis samples with depleted MORB mantle (DMM) affinities (3He/4He = 8 ± 1 RA; Graham, 2002) have low N-isotopes (mean δ15N = -2.1 ‰), whereas those with plume-like 3He/4He display higher values (mean δ15N = 1.3 ‰). We explain these data within the framework of a new mantle reference model to predict a time-integrated net N regassing flux to the mantle of ~3.4 × 1010 mol/yr, with the plume-source mantle representing the preferential destination by a factor of 2-3. The model has implications for the present-day imbalance between N subducted at trenches and N emitted via arc-related volcanism, the N-content of Earth's early atmosphere, as well as relationships between N2 and the noble gases in mantle reservoirs, including 3He/4He-δ15N relationships in plume-derived lavas.

P.H. Barry, D.R. Hilton

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Geochem. Persp. Let. (2016) 2, 148–159 | doi: 10.7185/geochemlet.1615 | Published 3 May 2016

Article views: 19907

182W evidence for core-mantle interaction in the source of mantle plumes

Abstract:
Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth’s core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182Hf decayed entirely to 182W in the mantle after metal-silicate segregation. Therefore, the 182W isotopic composition of the Earth’s mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Réunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tungsten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle.

H. Rizo, D. Andrault, N.R. Bennett, M. Humayun, A. Brandon, I. Vlastelic, B. Moine, A. Poirier, M.A. Bouhifd, D.T. Murphy

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Geochem. Persp. Let. (2019) 11, 6–11 | doi: 10.7185/geochemlet.1917 | Published 20 June 2019

Article views: 18042

Rapid response of silicate weathering rates to climate change in the Himalaya

Abstract:
Chemical weathering of continental rocks plays a central role in regulating the carbon cycle and the Earth's climate (Walker et al., 1981; Berner et al., 1983), accounting for nearly half the consumption of atmospheric carbon dioxide globally (Beaulieu et al., 2012). However, the role of climate variability on chemical weathering is still strongly debated. Here we focus on the Himalayan range and use the lithium isotopic composition of clays in fluvial terraces to show a tight coupling between climate change and chemical weathering over the past 40 ka. Between 25 and 10 ka ago, weathering rates decrease despite temperature increase and monsoon intensification. This suggests that at this timescale, temperature plays a secondary role compared to runoff and physical erosion, which inhibit chemical weathering by accelerating sediment transport and act as fundamental controls in determining the feedback between chemical weathering and atmospheric carbon dioxide.

A. Dosseto, N. Vigier, R. Joannes-Boyau, I. Moffat, T. Singh, P. Srivastava

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Geochem. Persp. Let. (2015) 1, 10–19 | doi: 10.7185/geochemlet.1502 | Published 20 February 2015

Article views: 17977

Molecular hydrogen in mantle minerals

Abstract:
Current models assume that hydrogen was delivered to Earth already in oxidised form as water or OH groups in minerals; similarly, it is generally believed that hydrogen is stored in the present mantle mostly as OH. Here we show by experiments at 2-7 GPa and 1100-1300 °C that, under reducing conditions, molecular hydrogen (H2) has an appreciable solubility in various upper mantle minerals. This observation suggests that during the accretion of the Earth, nebular H2 could have been delivered to the growing solid planet by direct dissolution in a magma ocean and subsequent incorporation in silicates. Moreover, the presence of dissolved molecular H2 in the minerals of the lower mantle could explain why magmas sourced in this region are rich in hydrogen, despite the fact that lower mantle minerals contain almost no OH groups.

X. Yang, H. Keppler, Y. Li

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Geochem. Persp. Let. (2016) 2, 160–168 | doi: 10.7185/geochemlet.1616 | Published 18 March 2016

Article views: 18535

Environmental pressure from the 2014–15 eruption of Bárðarbunga volcano, Iceland

Abstract:
The effusive six months long 2014‒2015 Bárðarbunga eruption (31 August‒27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km3 of lava. The total SO2 emission was 11.8 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO2 exceeded the 350 µg m3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H2SO4, HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surface waters, soils, and vegetation of Iceland.

S.R. Gíslason, G. Stefánsdóttir, M.A. Pfeffer, S. Barsotti, Th. Jóhannsson, I. Galeczka, E. Bali, O. Sigmarsson, A. Stefánsson, N.S. Keller, Á. Sigurdsson, B. Bergsson, B. Galle, V.C. Jacobo, S. Arellano, A. Aiuppa, E.B. Jónasdóttir, E.S. Eiríksdóttir, S. Jakobsson, G.H. Guðfinnsson, S.A. Halldórsson, H. Gunnarsson, B. Haddadi, I. Jónsdóttir, Th. Thordarson, M. Riishuus, Th. Högnadóttir, T. Dürig, G.B.M. Pedersen, Á. Höskuldsson, M.T. Gudmundsson

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Geochem. Persp. Let. (2015) 1, 84–93 | doi: 10.7185/geochemlet.1509 | Published 29 June 2015

Article views: 17480

The effect of warming climate on nutrient and solute export from the Greenland Ice Sheet

Abstract:
Glacial meltwater runoff is likely an important source of limiting nutrients for downstream primary producers. This has particular significance for regions surrounding the Greenland Ice Sheet, which discharges >400 km3 of meltwater annually. The Arctic is warming rapidly but the impact of higher discharge on nutrient export is unknown. We present four years of hydrological and geochemical data from a large Greenland Ice Sheet catchment that includes the two highest melt years on record (2010, 2012). Measurements reveal significant variation in dissolved solute (major ion) and estimated dissolved macronutrient (nitrogen, phosphorus and silica) fluxes, with increases in higher melt years. Labile particulate macronutrients dominate nutrient export, accounting for ~50 % of nitrogen and >80 % of both phosphorus and silica. The response of ice sheet nutrient export to enhanced melting is largely controlled by particle bound nutrients, the future supply of which is uncertain. We propose that the Greenland Ice Sheet provides an underappreciated and annually dynamic source of nutrients for the polar oceans, with changes in meltwater discharge likely to impact marine primary productivity in future decades.

J.R. Hawkings, J.L. Wadham, M. Tranter, E. Lawson, A. Sole, T. Cowton, A.J. Tedstone, I. Bartholomew, P. Nienow, D. Chandler, J. Telling

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Geochem. Persp. Let. (2015) 1, 94–104 | doi: 10.7185/geochemlet.1510 | Published 23 June 2015

Article views: 15744