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

TY - JOUR

T1 - Assessing the intra-crystalline approach to amino acid geochronology of Neogloboquadrina pachyderma (sinistral)

AU - Wheeler, Lucy J.

AU - Penkman, Kirsty E.H.

AU - Sejrup, Hans Petter

PY - 2021/2

Y1 - 2021/2

N2 - 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.

AB - 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.

KW - Amino acid racemisation

KW - Closed system

KW - Foraminifera

KW - Geochronology

KW - IcPD

KW - Neogloboquadrina pachyderma

UR - http://www.scopus.com/inward/record.url?scp=85095422456&partnerID=8YFLogxK

U2 - 10.1016/j.quageo.2020.101131

DO - 10.1016/j.quageo.2020.101131

M3 - Article

AN - SCOPUS:85095422456

VL - 61

JO - Quaternary Geochronology

JF - Quaternary Geochronology

SN - 1871-1014

M1 - 101131

ER -