Stable carbon isotope composition of amino acids in modern and fossil Mercenaria

• Published in: Organic geochemistry Vol. 38; no. 3; pp. 485 - 498
• Main Authors: O’Donnell, Thomas H., Macko, Stephen A., Wehmiller, John F.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2007; Elsevier Science
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Marine; Mercenaria; Florida; United States; Virginia; ASW, USA, Florida; ANW, USA, Virginia; mollusks; diagenesis; Mercenaria; shells; amino acids; degradation; North America; bivalves; isoleucine; contamination; preservation; modern; Bivalvia; glycine; carbon; isotopes; proteins; alanine; diet; Invertebrata; Mollusca
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2006.06.010

Amino acids were extracted from the bivalve shells of modern and fossil Mercenaria and analyzed for δ 13C (PDB). These data were then compared to the expected impacts of diagenesis and contamination on the isotopic composition of fossilized proteins. The δ 13C of l-amino acids from modern specimens had enriched glycine, glutamic acid, and isoleucine relative to leucine, and phenylalanine. The range of δ 13C in amino acids from modern Mercenaria collected from coastal Virginia (−1.6‰ to −29.6‰) and coastal Florida (−11.6‰ to −35.5‰) suggests the preservation of a diet signal. All of the fossil specimens had amino acids with the same δ 13C distribution pattern as modern specimens. Alanine in the fossil specimens however, was always relatively enriched and often had δ 13C values comparable to or more positive than glycine. Fossil specimens commonly contained glycine and glutamic acid with positive δ 13C values. The variation of δ 13C among the different enantiomers was not predictable. In some specimens, the d- and l-amino acids had the same δ 13C values, a feature attributed to the presence of original amino acids. In other specimens, one or more enantiomers had different δ 13C values, suggesting preferential loss of one enantiomer, the formation of secondary amino acids by the degradation of others, a diagenetic affect, or perhaps contamination.