| Summary: | Amino acid racemization (AAR) is a geochronological method that uses the ratio of D- to L- configurations in optically active amino acids from carbonate-based fossils to determine the time elapsed since the death of an organism. In well-dated fossil samples, the extent of racemization can be used to calculate post-depositional temperatures (also known as the effective diagenetic temperature). Calculated post-depositional temperatures of bracketed time intervals have uncertainties ranging from ±2 to 4°C with the dominant source of error in the D/L ratios (Kaufman 2003). Here, I aim to reduce these uncertainties using a bleach pretreatment that isolates the intra-crystalline fraction of amino acids in order to reduce the variability in foraminiferal D/L values to improve the precision of environmental paleotemperature estimates. I investigate the effect of this pretreatment method on the D/L ratios in three species of planktic foraminifera (Globorotalia tumida, Pulleniatina obliquiloculata, and Globorotalia truncatulinoides) from Holocene (~4-5 ka) deep sea sediments of similar environmental settings (Ocean Drilling Program Sites 1056, 1059, and 1062) and early Holocene to Pleistocene (~10.5-410 ka) sediments down-core (Ocean Drilling Program Site 1056 and KNR140 JPC-37). Results are reported for aspartic acid (Asp) and glutamic acid (Glu) because they are among the most abundant amino acids in foraminiferal protein and are the best resolved chromatographically. I analyzed 42 samples, each with an average of 9 replicates per sample and 5-10 individual tests per replicate, depending on the pretreatment method. Comparing D/L ratios from bleached versus unbleached samples indicates that bleaching only slightly reduces the variability in D/L values within the same sample (i.e. same species from the same core interval) by, on average, 1.1% and 3.0% for Asp and Glu, respectively. Furthermore, comparison of D/L ratios from the same species found at more than one site does not show statistical differences whether bleached ...
|
|---|