Earth surface erosion and weathering from the 10Be (meteoric)/9Be ratio

Blanckenburg, Friedhelm von; Bouchez, Julien; Wittmann, Hella

doi:10.1016/j.epsl.2012.07.022

Cited by 102 publications

(147 citation statements)

References 47 publications

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“…In support of this explanation we note that rivers of the northern part of the Andes (e.g. Napo river), draining a larger proportion of volcanic and andesitic rocks, display higher W/D ratios than southern tributaries 31,32 . To summarise, as most river sediment contained in the Earth's largest rivers are derived from meta-sedimentary source rocks, weathering intensity cannot increase significantly with residence time, even if this "Critical Zone" has the size of the Amazon Basin.…”

Section: Limitation Of Weathering Intensity By the Meta-sedimentary Ssupporting

confidence: 61%

Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

Bouchez

Gaillardet

Blanckenburg

2014

Procedia Earth and Planetary Science

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Actively eroding mountains supply un-weathered material into large river basins. It is still not known whether these un-weathered minerals undergo significant chemical weathering during storage in continental alluvial deposits within the surrounding lowland areas. Here we use previously reported weathering and erosion fluxes of rivers from the Amazon Basin to assess this effect. We show that the fraction of total denudation (weathering plus erosion) occurring as dissolved export experiences only a slight increase during transfer through the lowlands. The overall low weathering intensity of Andean sediments throughout the Amazon basin is attributed to the fact that source rocks are recycled meta-sedimentary rocks.

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Section: Limitation Of Weathering Intensity By the Meta-sedimentary Ssupporting

confidence: 61%

Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

Bouchez

Gaillardet

Blanckenburg

2014

Procedia Earth and Planetary Science

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“…Although normalizing 10 Be m by 9 Be in the HCl-leachate is proposed as a way to remove 521 the effects of preferential distribution due to grain size differences (Wittmann et al, 2012), we 522 25 find that normalizing 10 Be m activity by 9 Be reduces but does not eliminate grain-size 523 dependencies, with higher ratios in the <63 µm fraction than in other fractions (Figure 6). This 524 suggests that normalizing 10 Be m data by 9 Be may not remove all the effects of preferential 525 adsorption of 10 Be m , particularly among different grain sizes and geologic settings.…”

Section: Effect Of Be Normalization 520mentioning

confidence: 77%

“…The large concentrations 500 24 of Fe leached from the sediments (Figure 5a) suggest that amorphous Fe oxy-hydroxides are a 501 significant component of reactive grain coatings (e.g., Wittmann et al, 2012). With the exception 502 of Mg, the ratio of HCl-extractable materials to bulk composition of samples, and thus grain 503 coating composition, is relatively uniform across all grain sizes (Figure 5c).…”

Section: Control Of Frn Distribution By Hcl-extractable Materials 490mentioning

confidence: 98%

Effects of grain size, mineralogy, and acid-extractable grain coatings on the distribution of the fallout radionuclides 7Be, 10Be, 137Cs, and 210Pb in river sediment

Singleton

Schmidt

Bierman

et al. 2017

Geochimica et Cosmochimica Acta

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Grain-size dependencies in fallout radionuclide activity have been attributed to either increase in specific surface area in finer grain sizes or differing mineralogical abundances in different grain sizes. Here, we consider a third possibility, that the concentration and composition of grain coatings, where fallout radionuclides reside, controls their activity in fluvial sediment. We evaluated these three possible explanations in two experiments: 1) we examined the effect of sediment grain size, lithology, mineralogy, and composition of the acidextractable materials on the distribution of 7Be, 10Be, 137Cs, and unsupported 210Pb in detrital sediment samples collected from rivers in China and the United States, and 2) we periodically monitored 7Be, 137Cs, and 210Pb retention in samples of known composition exposed to natural fallout in Ohio, USA for 294 days.Acid-extractable materials (made up predominately of Fe, Mn, Al, and Ca from secondary minerals and grain coatings produced during pedogenesis) are positively related to the abundance of fallout radionuclides in our sediment samples. Grain-size dependency of fallout radionuclide concentrations was significant in detrital sediment samples, but not in samples exposed to fallout under controlled conditions. Mineralogy had a large effect on 7Be and 210Pb retention in samples exposed to fallout, suggesting that sieving sediments to a single grain size or using specific surface area-based correction terms may not completely control for preferential distribution of these nuclides.We conclude that time-dependent geochemical, pedogenic, and sedimentary processes together result in the observed differences in nuclide distribution between different grain sizes and substrate compositions. These findings likely explain variability of measured nuclide activities in river networks that exceeds the variability introduced by analytical techniques as well as spatial and temporal differences in erosion rates and processes. In short, we suggest that presence and amount of pedogenic grain coatings is more important than either specific surface area or surface charge in setting the distribution of FRNs. Cs, and 210 Pb in river sediment (GCA manuscript GCA-D-16-0143R2).We are again appreciative of the through and thoughtful review from one reviewer who has previously reviewed the manuscript, particularly with respect to measurements of 7 Be in the "natural delivery" experiment. The reviewer has helped us to clarify the main points of that experiment and to better explain the sources of error in those data. We have made minor changes to the manuscript to reflect these concerns.Below we have enclosed a detailed response point by point to each reviewer concern. Reviewer comments are in black and our responses are in blue.The manuscript is now 7,239 words from the introduction through the acknowledgements and includes a 308 word abstract, 8 figures, 1 table, 66 references, and supporting information including text, 13 figures, and 11 tables. This manuscript is not under con...

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“…To directly measure relative weathering fluxes over glacial-interglacial variations, we used the 10 Be(meteoric)/ 9 Be ratio 9 . Unlike most isotope systems, the 10 Be/ 9 Be ratio is set by the individual fluxes of the two isotopes into the oceans 10 (see Supplementary Information Sections 1 and 2).…”

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confidence: 99%

Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles

et al. 2015

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Throughout the Quaternary period, the Earth's surface has been subject to large changes in temperature and precipitation associated with fluctuations between glacial and interglacial states that have a ected biogeochemical cycling 1-4 . However, the e ect of these climate oscillations on weathering is debated, with climate modelling e orts using empirical relationships between measures of climate and weathering 1,5,6 suggesting minimal changes in global weathering rates between these two climate states 7,8 . The ratio of the cosmogenic isotope 10 Be, which is produced in the atmosphere and deposited to the oceans and the land surface, to 9 Be, which is introduced to the oceans by the riverine silicate weathering flux, can be used to track relative weathering fluxes 9,10 . Here we apply this proxy to marine sediment beryllium records 11-16 spanning the past two million years, and find no detectable shifts in inputs from global silicate weathering into the oceans. Using climate model simulations of the Last Glacial Maximum 17 along with a model for silicate weathering 18 , we find that there was large regional variability in runo between glacial and interglacial periods, but that this regional variability was insu cient to shift global weathering fluxes. We suggest that this stability in weathering explains the observation 19 that the removal of CO 2 from the atmosphere by silicate weathering has been in approximate balance with CO 2 degassing over the past 600,000 years.During Quaternary interglacial periods the Earth's surface is subjected to warmer temperatures, a shifted and more intense hydrologic cycle 20 , ecosystem change, and higher atmospheric CO 2 concentrations 19 than during glacial periods. Weathering is sensitive to climate 6 , and an increase in weathering flux is thought to follow exposure of glacial debris at glacial terminations 21 . Yet, empirical watershed relationships between measures of climate and weathering 1,5 , combined with global-scale climate simulations that pair runoff distributions with lithology, have suggested small changes in global weathering fluxes 7,8 . A test of these predictions is still pending, as direct evidence regarding global weathering and sediment 2 fluxes over glacial and interglacial timescales is scarce. Only increased weathering in large floodplains over the Holocene has been reported 3 . Further, radiogenic isotopes measured in the ocean sedimentary record show glacial-interglacial shifts 1 , but these proxies may reflect changes in the source and the style of weathering 21,22 , rather than changes in flux.To directly measure relative weathering fluxes over glacial-interglacial variations, we used the 10 Be(meteoric)/ 9 Be ratio 9 . Unlike most isotope systems, the 10 Be/ 9 Be ratio is set by the individual fluxes of the two isotopes into the oceans 10 (see Supplementary Information Sections 1 and 2). Although the flux of meteoric 10 Be to the ocean can be calculated from cosmic ray 0.0 0.5 1.0 1.5 2.0 Pacific South Atlantic− Indian North Atlantic Mediterranean...

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Earth surface erosion and weathering from the 10Be (meteoric)/9Be ratio

Cited by 102 publications

References 47 publications

Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

Effects of grain size, mineralogy, and acid-extractable grain coatings on the distribution of the fallout radionuclides 7Be, 10Be, 137Cs, and 210Pb in river sediment

Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles

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