40K–40Ca isotopic constraints on the oceanic calcium cycle

Caro, Guillaume; Papanastassiou, D. A.; Wasserburg, G. J.

doi:10.1016/j.epsl.2010.05.001

Cited by 63 publications

(106 citation statements)

References 38 publications

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“…This conclusion is based on a study of radiogenic 40 Ca in marine carbonates showing no appreciable enrichment of this isotope in the oceans over geological time. The implication is that the ocean Ca-cycle is dominated by weathering of sedimentary carbonates and mantle-derived silicate rocks of basaltic composition (Caro et al, 2010). The latter exhibit such a narrow range of d 44/40 Ca values, however, that it must be the carbonate rocks that control secular changes in d T w .…”

Section: The Role Of Sgd In the Global Ca-cyclementioning

confidence: 99%

δ44/40Ca variability in shallow water carbonates and the impact of submarine groundwater discharge on Ca-cycling in marine environments

Holmden

Papanastassiou

Blanchon

et al. 2012

Geochimica et Cosmochimica Acta

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Section: The Role Of Sgd In the Global Ca-cyclementioning

confidence: 99%

δ44/40Ca variability in shallow water carbonates and the impact of submarine groundwater discharge on Ca-cycling in marine environments

Holmden

Papanastassiou

Blanchon

et al. 2012

Geochimica et Cosmochimica Acta

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“…Work in the 1980s using the Finnigan-MAT 262 reported external precisions of ±0.6-1.5 ε-units (2σ) [16][17]. More recently, using a Thermo-Finnigan Triton Thermal Ionization Mass Spectrometer (TIMS) to analyze samples from Archean cratons, Kreissig and Eliott [18] obtained a reproducibility of ±0.5 ε-units (2σ) and Caro et al [15] reported 40 Ca/ 44 Ca data in marine carbonates with external precision of ±0.35 ε-units. This improvement was made possible by i) the measurement of larger ion beams on the Triton (<50V, against <10V using the MAT262), and ii) the implementation of multidynamic acquisition schemes using the "Zoom" optical system of the Triton.…”

Section: Methodsmentioning

confidence: 95%

“…Previous work showed that the 40 Ca budget of seawater is dominated by mantle inputs [15], so that marine carbonates display a homogeneous ε 40 Ca signature indistinguishable from the mantle value (i.e. ε 40 Ca=0).…”

Section: Introductionmentioning

confidence: 99%

“…This study investigates the potential use of the 40 K-40 Ca system as a tracer to better quantify the contributions of silicate and carbonate lithologies in the dissolved load of major Himalayan rivers [13][14][15]. Previous work showed that the 40 Ca budget of seawater is dominated by mantle inputs [15], so that marine carbonates display a homogeneous ε 40 Ca signature indistinguishable from the mantle value (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Tracing Silicate Weathering in the Himalaya Using the 40K-40Ca System: A Reconnaissance Study

Davenport

Caro

France‐Lanord

2014

Procedia Earth and Planetary Science

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This study investigates the potential of the 40 K-40 Ca decay scheme as a tracer of silicate vs. carbonate weathering in the Himalayan erosional system. To this end, we present high precision 40 Ca data on river sediments, dissolved river loads and whole-rock carbonates representative of the main tectonic units of the Himalayas. Our results show that metamorphosed dolomites from the Lesser Himalaya (LH) exhibit no radiogenic 40 Ca excess despite highly variable 87 Sr/ 86 Sr signatures (0.73-0.85). In contrast, silicate material is radiogenic, with ε 40 Ca ranging between +1 in the TSS to +4 ε-units in the LH. Preliminary results obtained from a series of 27 Himalayan rivers show that ε 40 Ca in the dissolved load is significantly influenced by silicate lithologies, with ε 40 Ca ranging from +0.1 to +1.6 ε-units. Our results suggest that the 40 Ca signature of Himalayan rivers primarily reflects the lithological nature of their erosional source, and highlights the potential of the 40 K-40 Ca decay scheme as a tracer of silicate weathering.

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“…Neoproterozoic 87 Sr/ 86 Sr values, for example, are generally lower than for the Phanerozoic (58), which could be partially explained by contemporaneously low levels of seawater [SO 4 ]. Sulfate could also affect the exchange of radiogenic 40 Ca between seawater and the oceanic crust (52).…”

Section: Hydrothermal Ca and Sr Fluxes Through Timementioning

confidence: 99%

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

Antonelli

Pester

Brown

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Variations in the Mg, Ca, Sr, and SO 4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). We present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87 Sr/ 86 Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO 4 in modern seawater. At other times during the last 500 million years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87 Sr/ 86 Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ∼0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ∼1.6 over the Phanerozoic, with minima when seawater Mg and SO 4 are low. This effect provides a modest negative feedback on seawater composition and 87 Sr/ 86 Sr changes. For the mid-Cretaceous, the low 87 Sr/ 86 Sr of seawater requires either exceptionally large amounts of lowtemperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. The model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO 4 could help explain low seawater 87 Sr/ 86 Sr.paleoseawater | Sr isotopes | hydrothermal systems | midocean ridges M idocean ridge (MOR) hydrothermal circulation, fueled by persistent heat from shallow magma reservoirs, is a key component in the long-term regulation of global climate and ocean chemistry (1). Hydrothermal fluids that emerge from these systems, at temperatures up to ∼400°C, are chemically distinct from seawater due to reactions with newly forming oceanic crust. Relative to seawater, fluids emanating from modern MOR hydrothermal systems are enriched in Ca and transition metals, have lower pH and Eh, and have little to no Mg and SO 4 (2-5).Hydrothermal circulation at MOR is dominated by two important chemical reactions: the removal of seawater SO 4 through mineral precipitation with seawater Ca, and the removal of seawater Mg through precipitation of hydroxy-silicate minerals (3, 6, 7). Seawater SO 4 is primarily lost through the formation of anhydrite (CaSO 4 ) early during hydrothermal circulation, as anhydrite precipitation occurs by simply heating seawater >130°C (8). There can also be minor losses of SO 4 through thermochemical sulfate reduction (9, 10) and bacterial processes.Seawater Mg is lost from hydrothermal fluids at both low and high temperatures, by exchange of seawater Mg for basaltic Ca through the transformation of primary igneous minerals to alteration phases such as montmorillonite ...

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40K–40Ca isotopic constraints on the oceanic calcium cycle

Cited by 63 publications

References 38 publications

δ44/40Ca variability in shallow water carbonates and the impact of submarine groundwater discharge on Ca-cycling in marine environments

δ44/40Ca variability in shallow water carbonates and the impact of submarine groundwater discharge on Ca-cycling in marine environments

Tracing Silicate Weathering in the Himalaya Using the 40K-40Ca System: A Reconnaissance Study

Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

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