Field Testing the Fidelity of δ<sup>18</sup>O and δ<sup>13</sup>C in Reconstructing Upper Ocean Hydrography

Mekik, Figen; Winkelstern, Ian Z.

doi:10.1029/2020pa003880

Cited by 2 publications

(1 citation statement)

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“…If the difference in the Mg/Ca ratio between the crust and lamellar calcite is not due to calcification at different depths in the water column, then what mechanism could be responsible for the variable difference in δ 18 O along the studied transect? We rule out dissolution since this process acts at the population level and affects the average stable isotope ratios of the sedimentary population through preferential dissolution of non-encrusted shells, but does not directly affect the δ 18 O of individual shells (Erez, 1978;Lohmann, 1995;Mekik & Winkelstern, 2020). Dissolution would therefore reduce the proportion of non-encrusted shells in the sediment, but not directly alter their δ 18 O.…”

Section: Crust Effects On G Inflata Geochemistrymentioning

confidence: 99%

Morphotype and Crust Effects on the Geochemistry of Globorotalia inflata

Jonkers

Gopalakrishnan

Weßel

et al. 2021

Paleoceanog and Paleoclimatol

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The chemical composition, in particular the stable oxygen isotope and Mg/Ca ratio, of its shell is often used to reconstruct subsurface ocean conditions (Groeneveld & Chiessi, 2011;Moffa-Sánchez et al., 2014;Santos et al., 2020). The morphospecies G. inflata contains two different genotypes, with type I associated with subtropical waters in both hemispheres and type II restricted to the subpolar waters of the southern hemisphere (Morard et al., 2011). Subtle differences in shell morphology in G. inflata are thought to reflect this genotypic variation (Morard et al., 2016). However, the two morphotypes are not distinguished in paleoceanographic studies despite different ecological preferences, which may affect their seasonal or vertical habitat and hence chemical composition (Morard et al., 2013). It is also possible (or suspected) that biological differences between the types of G. inflata may induce differences in biomineralization and hence cause their geochemical proxy signals to differ, irrespective of their ecology. In other words, it is unknown if grown under the same conditions, genotype I and II would have the same or different chemical composition. There are indications from other species that genotypes may have different seasonal or vertical habitat preferences (Marshall et al., 2015) as well as for genotypical controls on shell composition (Sadekov et al., 2016). However, despite the obvious implications for paleoceanographic reconstructions, no studies exist that investigate the influence of cryptic diversity on the geochemistry of G. inflata.Next to the unresolved issue of a possible effect of cryptic diversity on its geochemistry, G. inflata is a species that forms a crust that often covers most of the lamellar calcite. In many species of foraminifera such crusts may account for a significant proportion of the shell mass and since crusts may have a markedly

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Section: Crust Effects On G Inflata Geochemistrymentioning

confidence: 99%