Isoleucine epimerization in Quarternary planktic foraminifera of sediment core GIK12519-2, Sierra Leone Rise

DOI

Panktonic foraminiferal tests of the spinose species Orbulina universa, of the non-spinose Globorotalia tumida-menardii complex, and of a mixed species assemblage (grain size fraction 200-400 µm) were isolated from Sierra Leone Rise core GIK13519-2 and analyzed for free, total, and bound (by difference) amino acids to study the isoleucine epimerization mechanism in fossil foraminiferal tests and to define empirical calibration curves for dating deep-sea sediments over the past 900,000 years.Total isoleucine epimerization curves typically separate into three "linear" segments of decreasing apparents rates with increasing time and exhibit a pronounced „species effect“. The degree of epimerization attained at time is considerably lower in O. universa than in G. tumida-menardii while the mixed species results scatter between the limits delineated by the two monospecific curves. Total allo/iso ratios are closely related to the proportion of free to total isoleucine accumulating in the tests indicating that the rate of hydrolysis of matrix proteins and peptides controls the overall epimerization reaction. The results are consistent with experimental evidenve where upon isoleucine epimerizes at a rapid rate in terminal positions but at slow rates in interior positions as well as in the free state. Notwithstanding free isoleucine exhibits the highest degree of epimerized terminal isoleucine. Species-specific hydrolysis and epimerization rates are maintained until about 50 % of bound isoleucine have been hydrolyzed to the free state corresponding to a total allo/iso ratio of about 0.5. Remaining peptide units appear to be more resistent against hydrolysis and separate species then show the same apparent epimerization rate dominantly controlled by the slow conversion rate in the free state until equilibrium is achieved in Miocene samples under deep-ocean temperature conditions. The degree of epimerization attained at comparable time in separate species will, however, remain different due to different initial rates of hydrolysis.

Supplement to: Müller, Peter J (1984): Isoleucine epimerization in Quaternary planktonic foraminifera: Effects of diagenetic hydrolysis and leaching, and Atlantic-Pacific intercore correlations. Meteor Forschungsergebnisse, Deutsche Forschungsgemeinschaft, Reihe C Geologie und Geophysik, Gebrüder Bornträger, Berlin, Stuttgart, C38, 25-48

Identifier
DOI https://doi.org/10.1594/PANGAEA.548489
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.548489
Provenance
Creator Müller, Peter J
Publisher PANGAEA
Publication Year 1984
Rights Creative Commons Attribution 3.0 Unported; https://creativecommons.org/licenses/by/3.0/
OpenAccess true
Representation
Language English
Resource Type Supplementary Publication Series of Datasets; Collection
Format application/zip
Size 3 datasets
Discipline Geosciences; Natural Sciences
Spatial Coverage (-19.850 LON, 5.658 LAT); Sierra Leone Rise