Mg/Ca ratios of two Globigerinoides ruber (white) morphotypes

Implications for reconstructing past tropical/subtropical surface water conditions

Stephan Steinke, Han Yi Chiu, Pai Sen Yu, Chuan Chou Shen, Ludvig Löwemark, Horng-Sheng Mii, Min Te Chen

Research output: Contribution to journalArticle

81 Citations (Scopus)

Abstract

Tests of the planktonic foraminifer Globigerinoides ruber(white; d'Orbigny) have become a standard tool for reconstructing past oceanic environments. Paleoceanographers often utilize the Mg/Ca ratios of the foraminiferal tests for reconstructing low-latitude ocean glacial-interglacial changes in sea surface temperatures (SST). We report herein a comparison of Mg/Ca measurements on sample pairs (n = 20) of two G. ruber (white) morphotypes (G. rubersensu stricto (s.s.) and G. ruber sensu lato (s.l.)) from surface and downcore samples of the western Pacific and Indian Oceans. G. rubers.s. refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide, high arched aperture, whereas G. rubers.l. refers to a more compact test with a diminutive final chamber and small aperture. The G. ruber s.s. specimens generally show significantly higher Mg/Ca ratios compared toG. ruber s.l. Our results from the Mg/Ca ratio analysis suggest that G. ruber s.l. specimens precipitated their shells in slightly colder surface waters thanG. rubers.s. specimens. This conclusion is supported by the differences in δ18O and δ13C values between the two morphotypes. Although it is still unclear if these two morphotypes represent phenotypic variants or sibling species, our findings seem to support the hypothesis of depth and/or seasonal allopatry within a single morphospecies.

Original languageEnglish
Article numberQ11005
JournalGeochemistry, Geophysics, Geosystems
Volume6
Issue number11
DOIs
Publication statusPublished - 2005 Nov 1

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morphotype
surface water
Surface waters
allopatry
chambers
apertures
cold surfaces
planktonic foraminifera
cold water
interglacial
Indian Ocean
Pacific Ocean
sea surface temperature
tropical regions
shell
oceans
ocean
Temperature
test

Keywords

  • Globigerinoides ruber (white)
  • Mg/Ca
  • Morphotypes
  • Planktonic foraminifera
  • Sea surface temperature
  • Stable isotopes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Mg/Ca ratios of two Globigerinoides ruber (white) morphotypes : Implications for reconstructing past tropical/subtropical surface water conditions. / Steinke, Stephan; Chiu, Han Yi; Yu, Pai Sen; Shen, Chuan Chou; Löwemark, Ludvig; Mii, Horng-Sheng; Chen, Min Te.

In: Geochemistry, Geophysics, Geosystems, Vol. 6, No. 11, Q11005, 01.11.2005.

Research output: Contribution to journalArticle

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abstract = "Tests of the planktonic foraminifer Globigerinoides ruber(white; d'Orbigny) have become a standard tool for reconstructing past oceanic environments. Paleoceanographers often utilize the Mg/Ca ratios of the foraminiferal tests for reconstructing low-latitude ocean glacial-interglacial changes in sea surface temperatures (SST). We report herein a comparison of Mg/Ca measurements on sample pairs (n = 20) of two G. ruber (white) morphotypes (G. rubersensu stricto (s.s.) and G. ruber sensu lato (s.l.)) from surface and downcore samples of the western Pacific and Indian Oceans. G. rubers.s. refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide, high arched aperture, whereas G. rubers.l. refers to a more compact test with a diminutive final chamber and small aperture. The G. ruber s.s. specimens generally show significantly higher Mg/Ca ratios compared toG. ruber s.l. Our results from the Mg/Ca ratio analysis suggest that G. ruber s.l. specimens precipitated their shells in slightly colder surface waters thanG. rubers.s. specimens. This conclusion is supported by the differences in δ18O and δ13C values between the two morphotypes. Although it is still unclear if these two morphotypes represent phenotypic variants or sibling species, our findings seem to support the hypothesis of depth and/or seasonal allopatry within a single morphospecies.",
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AU - Yu, Pai Sen

AU - Shen, Chuan Chou

AU - Löwemark, Ludvig

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AU - Chen, Min Te

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