Assessing the intra-crystalline approach to amino acid geochronology of Neogloboquadrina pachyderma (sinistral)

Lucy J. Wheeler*, Kirsty E.H. Penkman, Hans Petter Sejrup

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


While amino acid (AA) geochronology has been widely applied to foraminiferal biomineral proteins, there has been limited assessment of the potential of isolating an ‘intra-crystalline’ fraction of proteins to improve the reliability of AA geochronology for foraminifera. In this study, bleaching experiments were carried out on the foraminifer Neogloboquadrina pachyderma (sinistral) from an independently dated core from the south eastern Norwegian Sea spanning the last 120 ka. Results show that this species contains a bleach-resistant fraction of biomineral proteins, and that this intra-crystalline fraction may behave as a closed system. Racemisation in both the intra-crystalline and whole-protein fractions was found to systematically increase with time. Isoleucine epimerisation showed reliable trends with depth when analysed by ion exchange chromatography (IEC); analysis by reverse-phase liquid chromatography (RP-HPLC) resulted in reliable age-D/L relationships for aspartic acid, glutamic acid and alanine. Isolating the intra-crystalline fraction with a 48 h bleach treatment reduced the influence of contamination in younger material. Therefore, this paper recommends that the intra-crystalline approach is used when analysing Neogloboquadrina pachyderma (sinistral) for AA geochronology, especially for younger samples. Material-specific regression equations developed in this study successfully convert IEC A/I to RP-HPLC D/L values for aspartic acid, glutamic acid and alanine, enabling integration of geochronologies developed using different methods for this class of biomineral.

Original languageEnglish
Article number101131
Number of pages13
JournalQuaternary Geochronology
Early online date23 Oct 2020
Publication statusPublished - Feb 2021


  • Amino acid racemisation
  • Closed system
  • Foraminifera
  • Geochronology
  • IcPD
  • Neogloboquadrina pachyderma

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