Morphotype and Crust Effects on the Geochemistry of Globorotalia inflata

Lukas Jonkers; Akshat Gopalakrishnan; Lea We?elCristiano M.ChiessiJeroen GroeneveldPatrick MonienDouglas LessaRapha?l Morard

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Morphotype and Crust Effects on the Geochemistry of Globorotalia inflata

机译：Morphotype and Crust Effects on the Geochemistry of Globorotalia inflata

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Sedimentary specimens of the planktonic foraminifera Globorotalia inflata can provide information on subsurface conditions of past oceans.However,interpretation of their geochemical signal is complicated by possible effects of cryptic diversity and encrustation.Here we address these issues using plankton tow and sediment samples from the western South Atlantic,where two genotypes of G.inflata occur.To separate the genotypes,we analyzed shells from the extreme ends of the morphospace of G.inflata.The δ~(18)O and δ~(13)C of encrusted specimens from both morphotypes are indistinguishable.However,we do find a large influence of encrustation on δ~(18)O and Mg/Ca.Whereas crust Mg/Ca ratios are at all locations lower than lamellar calcite,the crust effect on δ~(18)O is less consistent in space.Plankton tows show that encrusted specimens occur at any depth and that even close to the surface crust Mg/Ca ratios are lower than in lamellar calcite.This is inconsistent with formation of the crust at lower temperature at greater depth.Instead we suggest that the difference between the crust and lamellar calcite Mg/Ca ratio is temperature-independent and due to the presence of high Mg/Ca bands only in the lamellar calcite.The variable crust effect on δ~(18)O is more difficult to explain,but the higher incidence of crust-free specimens in warmer waters and the observation that a crust effect is clearest in the confluence zone,hint at the possibility that the difference reflects advective mixing of specimens from warmer and colder areas,rather than vertical migration.

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《Paleoceanography》 |2021年第4期|e2021PA004224-1-e2021PA004224-16|共16页
作者
Lukas Jonkers; Akshat Gopalakrishnan; Lea We?elCristiano M.ChiessiJeroen GroeneveldPatrick MonienDouglas LessaRapha?l Morard;
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作者单位

Department of Geosciences,University of Bremen,Bremen,Germany;

School of Arts,Sciences and Humanities,University of S?o Paulo,S?o Paulo,S?o Paulo,Brazil;

Alfred Wegener Institute,Helmholtz Center for Polar and Marine Research,Potsdam,GermanyPrograma de Pós-Gradua??o em Geoquímica,Federal Fluminense University,Rio de Janeiro,BrazilMARUM Center for Marine Environmental Sciences,University of Bremen,Bremen,Germany;

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正文语种英语
中图分类海洋学;
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Morphotype; Crust Effects; Geochemistry;

Morphotype and Crust Effects on the Geochemistry of Globorotalia inflata

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