Variation in the strontium isotopic composition of seawater (8 Ma to present) : Implications for chemical weathering rates and dissolved fluxes to the oceans

1990 ◽  
Vol 80 (4) ◽  
pp. 291-307 ◽  
Author(s):  
David A. Hodell ◽  
Gregory A. Mead ◽  
Paul A. Mueller
Keyword(s):  
Isotopic Composition ◽  
Chemical Weathering ◽  
Weathering Rates

Mo mobility in lateritic weathering profiles overlying ultramafic rocks of the East Sulawesi Ophiolite, Indonesia

2021 ◽  
Author(s):  
Adrianus Damanik ◽  
Martin Wille ◽  
Martin Grosjean ◽  
Sri Yudawati Cahyarini ◽  
Hendrik Vogel
Keyword(s):  
Isotopic Composition ◽  
Chemical Weathering ◽  
Isotopic Fractionation ◽  
Reduced Form ◽  
Ultramafic Rocks ◽  
Early Earth ◽  
Atmospheric Input ◽  
First Time ◽  
Weathering Process ◽  
Mo Isotopes

<p>Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on samples obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite samples vary between -0.043‰ to -0.161‰ δ<sup>98</sup>Mo<sub>NIST3134</sub>. The overall close to mantle Mo isotopic composition of the laterite samples, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.</p>

The Role of Restricted Basins in Global Biogeochemical Cycles

2020 ◽  
Author(s):  
Alexandra Turchyn
Keyword(s):  
Isotopic Composition ◽  
Chemical Weathering ◽  
Biogeochemical Cycles ◽  
Biogeochemical Cycle ◽  
Global Ocean ◽  
Sulfur Isotopic Composition ◽  
Sediment Biogeochemistry ◽  
Shelf Slope ◽  
Salt Deposits ◽  
Global Biogeochemical Cycles

<p>The formation of restricted basins isolates seawater from the global ocean and allows the formation of salt deposits, often because restricted basins can have minor connectivity to the global ocean and thus can fill and evaporate many times over. The formation of salts removes ions from the global ocean, potentially decreasing their concentration elsewhere and leading to an alteration of their biogeochemical cycle.  The subsequent exposure and chemical weathering of these salt deposits changes the source of these elements back into the global ocean and can influence their biogeochemical cycles for a long time after the formation of the restricted basin.   Sediment biogeochemistry in restricted basins also differs from most global continental shelf, slope, and deep-sea sediments. The formation of sedimentary minerals and their subsequent diagenesis means that the amount and isotopic composition of deposited minerals in restricted basins can differ greatly from those in the global ocean. In this talk I am going to explore how the formation of restricted basins, including epicontinental seas and isolated seas, has influenced the biogeochemical cycle of carbon and sulfur over the course of the last 65 million years.  I am going to use a combination of new measurements on the carbon and sulfur isotopic composition of the ocean over this time to explore how different types of restricted basins influence global biogeochemical cycles in the rest of the ocean. I will argue that the formation of restricted basins has been important in driving changes in the carbon and sulfur isotopic composition of the ocean over time, linking changes in ocean chemistry to tectonics.</p>

scholarly journals Chemical weathering rates and atmospheric/soil CO2 consumption of igneous and metamorphic rocks under tropical climate in southeastern Brazil

2016 ◽  
Vol 443 ◽  
pp. 54-66 ◽  
Author(s):  
Alexandre Martins Fernandes ◽  
Fabiano Tomazini da Conceição ◽  
Eder Paulo Spatti Junior ◽  
Diego de Souza Sardinha ◽  
Jeferson Mortatti
Keyword(s):  
Chemical Weathering ◽  
Tropical Climate ◽  
Southeastern Brazil ◽  
Metamorphic Rocks ◽  
Soil Co2 ◽  
Weathering Rates ◽  
Co2 Consumption

scholarly journals The rate of chemical weathering beneath a quiescent, surge-type, polythermal-based glacier, southern Spitsbergen, Svalbard

1997 ◽  
Vol 24 ◽  
pp. 27-31 ◽  
Author(s):  
J. L. Wadham ◽  
A. J. Hodson ◽  
M. Tranter ◽  
J. A. Dowdeswell
Keyword(s):  
Thermal Regime ◽  
Chemical Weathering ◽  
High Arctic ◽  
Direct Link ◽  
Water Fluxes ◽  
Weathering Rate ◽  
Weathering Rates ◽  
Pertinent Data ◽  
Chemical Weathering Rate ◽  
Annual Discharge

Glacierized basins in the high Arctic are believed to be regions of low chemical weathering rates, despite the lack of pertinent data, because it is believed that water does not flow in significant quantities through subglacial drainage systems. We have calculated chemical weathering rates at Finsterwalderbreen, a polythermal, surge-type glacier in Svalbard. Rates of 320 and 150 meq Σ+ m−1 year−1 were measured in 1994 and 1995, respectively. The corresponding water fluxes were 4.1 × 107 and 1.7 × 107 m3. We estimate that we have measured ~72% of the total annual discharge, hence the true annual chemical weathering rates are ~440 and 210 meq Σ+ m−2 year−1, respectively This gives a mean annual chemical weathering rate of 330 meq Σ+ m−2 year−1, which approximates the continental average of 390 meq Σ+ m−2 year−1 and is intermediate between chemical weathering rates measured on cold-based glaciers (~110–160 meq Σ+ m−2 year−1) and temperate glaciers (450–1000 meq Σ+ m−2 year−1). This suggests that there may be a direct link between chemical weathering rates and thermal regime, and that glacierized basins in the high Arctic cannot necessarily be considered as regions of low chemical weathering and CO2 drawdown.

scholarly journals Reconciling Chemical Weathering Rates Across Scales: Insights from U-Series Isotopes in Volcanic Weathering Clasts from Basse-Terre Island (Guadeloupe)

2020 ◽  
Author(s):  
Lin Ma ◽  
Jiye Guo ◽  
Yvette Pereyra ◽  
Jacqueline Engel ◽  
Jerome Gaillardet ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Weathering Rates

scholarly journals Direct measurement of fungal contribution to silicate weathering rates in soil

Geology ◽  
2021 ◽  
Author(s):  
Bastien Wild ◽  
Gwenaël Imfeld ◽  
Damien Daval
Keyword(s):  
Chemical Weathering ◽  
Silicate Weathering ◽  
Nutrient Fluxes ◽  
Weathering Rates ◽  
Relative Contribution ◽  
Quantitative Estimates ◽  
Fungal Hyphae ◽  
Nanoscale Topography ◽  
Natural Settings

Chemical weathering produces solutes that control groundwater chemistry and supply ecosystems with essential nutrients. Although microbial activity influences silicate weathering rates and associated nutrient fluxes, its relative contribution to silicate weathering in natural settings remains largely unknown. We provide the first quantitative estimates of in situ silicate weathering rates that account for microbially induced dissolution and identify microbial actors associated with weathering. Nanoscale topography measurements showed that fungi colonizing olivine [(Mg,Fe)2SiO4] samples in a Mg-deficient forest soil accounted for up to 16% of the weathering flux after 9 mo of incubation. A local increase in olivine weathering rate was measured and attributed to fungal hyphae of Verticillium sp. Altogether, this approach provides quantitative parameters of bioweathering (i.e., rates and actors) and opens new avenues to improve elemental budgets in natural settings.

Sign in / Sign up

Export Citation Format

Share Document