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

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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
Issue number11
Publication statusPublished - 2005 Nov 1



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

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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