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New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation.

ABSTRACT: The oceanic magnesium budget is important to our understanding of Earth's carbon cycle, because similar processes control both (e.g., weathering, volcanism, and carbonate precipitation). However, dolomite sedimentation and low-temperature hydrothermal circulation remain enigmatic oceanic Mg sinks. In recent years, magnesium isotopes (?²⁶Mg) have provided new constraints on the Mg cycle, but the lack of data for the low-temperature hydrothermal isotope fractionation has hindered this approach. Here we present new ?²⁶Mg data for low-temperature hydrothermal fluids, demonstrating preferential ²⁶Mg incorporation into the oceanic crust, on average by ?_solid-fluid???1.6‰. These new data, along with the constant seawater ?²⁶Mg over the past ~20?Myr, require a significant dolomitic sink (estimated to be 1.5-2.9?Tmol?yr^-1; 40-60% of the oceanic Mg outputs). This estimate argues strongly against the conventional view that dolomite formation has been negligible in the Neogene and points to the existence of significant hidden dolomite formation.

SUBMITTER: Shalev N

PROVIDER: S-EPMC6906300 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation.

Shalev Netta N Bontognali Tomaso R R TRR Wheat C Geoffrey CG Vance Derek D

Nature communications 20191211 1

The oceanic magnesium budget is important to our understanding of Earth's carbon cycle, because similar processes control both (e.g., weathering, volcanism, and carbonate precipitation). However, dolomite sedimentation and low-temperature hydrothermal circulation remain enigmatic oceanic Mg sinks. In recent years, magnesium isotopes (δ<sup>26</sup>Mg) have provided new constraints on the Mg cycle, but the lack of data for the low-temperature hydrothermal isotope fractionation has hindered this a ...[more]

PMID: 31827091

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Project description:Demand theory can be applied to analyse how a human or animal consumer changes her selection of commodities within a certain budget in response to changes in price of those commodities. This change in consumption assessed over a range of prices is defined as demand elasticity. Previously, income-compensated and income-uncompensated price changes have been investigated using human and animal consumers, as demand theory predicts different elasticities for both conditions. However, in these studies, demand elasticity was only evaluated over the entirety of choices made from a budget. As compensating budgets changes the number of attainable commodities relative to uncompensated conditions, and thus the number of choices, it remained unclear whether budget compensation has a trivial effect on demand elasticity by simply sampling from a different total number of choices or has a direct effect on consumers' sequential choice structure. If the budget context independently changes choices between commodities over and above price effects, this should become apparent when demand elasticity is assessed over choice sets of any reasonable size that are matched in choice opportunities between budget conditions. To gain more detailed insight in the sequential choice dynamics underlying differences in demand elasticity between budget conditions, we trained N=8 rat consumers to spend a daily budget by making a number of nosepokes to obtain two liquid commodities under different price regimes, in sessions with and without budget compensation. We confirmed that demand elasticity for both commodities differed between compensated and uncompensated budget conditions, also when the number of choices considered was matched, and showed that these elasticity differences emerge early in the sessions. These differences in demand elasticity were driven by a higher choice rate and an increased reselection bias for the preferred commodity in compensated compared to uncompensated budget conditions, suggesting a budget context effect on relative valuation.

Dataset Information

New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation.

Publications

New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation.

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