Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition. Stanley, S., M.; Ries, J., B.; and Hardie, L., a. Proceedings of the National Academy of Sciences of the United States of America, 99(24):15323-6, 11, 2002.
Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition. [pdf]Paper  Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition. [link]Website  abstract   bibtex   
Shifts in the MgCa ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 10(8) years. Since Cambrian time, skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates. Here we report on experiments showing that the ambient MgCa ratio actually governs the skeletal mineralogy of some simple organisms. In modern seas, coralline algae produce skeletons of high-Mg calcite (>4 mol % MgCO(3)). We grew three species of these algae in artificial seawaters having three different MgCa ratios. All of the species incorporated amounts of Mg into their skeletons in proportion to the ambient MgCa ratio, mimicking the pattern for nonskeletal precipitation. Thus, the algae calcified as if they were simply inducing precipitation from seawater through their consumption of CO(2) for photosynthesis; presumably organic templates specify the calcite crystal structure of their skeletons. In artificial seawater with the low MgCa ratio of Late Cretaceous seas, the algae in our experiments produced low-Mg calcite (<4 mol % MgCO(3)), the carbonate mineral formed by nonskeletal precipitation in those ancient seas. Our results suggest that many taxa that produce high-Mg calcite today produced low-Mg calcite in Late Cretaceous seas.
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 title = {Low-magnesium calcite produced by coralline algae in seawater of Late Cretaceous composition.},
 type = {article},
 year = {2002},
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 keywords = {Anthozoa,Anthozoa: drug effects,Anthozoa: metabolism,Calcium,Calcium Carbonate,Calcium Carbonate: chemistry,Calcium Carbonate: metabolism,Calcium: chemistry,Calcium: metabolism,Evolution, Molecular,Magnesium,Magnesium: chemistry,Magnesium: metabolism,Paleontology,Seawater,Seawater: chemistry,Solutions,Solutions: pharmacology},
 pages = {15323-6},
 volume = {99},
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 abstract = {Shifts in the MgCa ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 10(8) years. Since Cambrian time, skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates. Here we report on experiments showing that the ambient MgCa ratio actually governs the skeletal mineralogy of some simple organisms. In modern seas, coralline algae produce skeletons of high-Mg calcite (>4 mol % MgCO(3)). We grew three species of these algae in artificial seawaters having three different MgCa ratios. All of the species incorporated amounts of Mg into their skeletons in proportion to the ambient MgCa ratio, mimicking the pattern for nonskeletal precipitation. Thus, the algae calcified as if they were simply inducing precipitation from seawater through their consumption of CO(2) for photosynthesis; presumably organic templates specify the calcite crystal structure of their skeletons. In artificial seawater with the low MgCa ratio of Late Cretaceous seas, the algae in our experiments produced low-Mg calcite (<4 mol % MgCO(3)), the carbonate mineral formed by nonskeletal precipitation in those ancient seas. Our results suggest that many taxa that produce high-Mg calcite today produced low-Mg calcite in Late Cretaceous seas.},
 bibtype = {article},
 author = {Stanley, Steven M and Ries, Justin B and Hardie, Lawrence a},
 journal = {Proceedings of the National Academy of Sciences of the United States of America},
 number = {24}
}
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