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Brachiopod taxa and shell portions reliably recording past ocean environments: Toward establishing a robust paleoceanographic proxy
Author(s) -
Yamamoto Kazuyuki,
Asami Ryuji,
Iryu Yasufumi
Publication year - 2011
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl047134
Subject(s) - proxy (statistics) , geology , oceanography , taxon , paleontology , computer science , machine learning
Fossils of rhynchonelliform brachiopods (marine invertebrates) constitute ∼70% of the samples used for delineating a well‐known Phanerozoic trend in oxygen isotope composition ( δ 18 O) of low‐Mg calcite shells. The trend represents secular variations in temperature and/or δ 18 O of ancient seawater. However, the use of brachiopods as a paleoceanographic proxy is based on the presupposition that the shell calcite is precipitated in isotopic equilibrium with ambient seawater. Here, we show that high‐resolution time series of the shell δ 18 O values along the maximum growth axes of two long‐lived cool‐water brachiopods are identical to, greater than, or less than those of calcite precipitated in isotopic equilibrium with ambient seawater, depending on the difference in shell growth rates. Coupled with δ 18 O data from subtropical and warm‐temperate brachiopod species examined in our previous studies, we provide a sound framework illustrating which taxa and shell portions reliably recorded past ocean environments.