Towards an aminostratigraphy of foraminifera for Pleistocene sea-level records: testing the intra-crystalline approach to amino acid racemisation dating

Sea-level records of past interglacials are important archives for understanding long term mechanisms of sea-level change, and for informing predictions of future sea-level rise. Linking sea-level records to the global climate record is essential for assessing processes, leads and lags in the climate system. However, these fragmentary deposits are often challenging to date. Amino acid racemisation dating (AAR, also known as amino acid geochronology) is a technique commonly used to date Pleistocene deposits. Recently, improvements in AAR have been made by isolating an ‘intra-crystalline’ fraction of proteins, which in certain biominerals acts a closed system, reducing the variability of AAR results. This thesis aimed to assess whether the intra-crystalline approach improves the reliability of AAR in calcareous foraminifera, and whether this class of biomineral can be used to inform the chronology of Pleistocene sea-level deposits. A combination of oxidative pre-treatment experiments and high-temperature decomposition experiments were therefore carried out on several species of foraminifera commonly preserved in Pleistocene sea-level records.
These experiments found that biomineral protein in the foraminifer species investigated undergoes predictable patterns of breakdown, making these species suitable substrates for AAR. Contrary to observations in several other calcareous biominerals, this work found no substantial differences in performance between the whole-shell and intra-crystalline approaches to AAR. A weak oxidation pre-treatment using H2O2, common in the preparation of foraminifera for AAR, was therefore used in the development of a pilot aminostratigraphy of UK Pleistocene sea-level records. The majority of the AAR results from this pilot study were consistent with the known chronology of the sites, with the exception of samples which showed indications of contamination. These results demonstrate the importance of analysing a large number (≥ 10) of replicate samples where possible, to enable identification of outliers and estimation of reliable mean D/L values for foraminifera from Pleistocene sea-level records.