HR: 17:15h
AN: B14B-06    [Abstracts]
TI: Annual Variations in Aspartic Acid Content of Coral Skeleton: A new Proxy for Changes in Biological Activity of Coral
AU: * Gupta, L P
EM: lallan.gupta@aist.go.jp
AF: Institute of Geology and Geoinformation, AIST, 1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Suzuki, A
EM: a.suzuki@aist.go.jp
AF: Institute of Geology and Geoinformation, AIST, 1-1, Higashi, Tsukuba, 305-8567 Japan
AU: Kawahata, H
EM: h.kawahata@aist.go.jp
AF: Institute of Geology and Geoinformation, AIST, 1-1, Higashi, Tsukuba, 305-8567 Japan
AB: Biological or metabolic effects have often been invoked to explain abnormal changes in the annual pattern of the stable isotope record of the coral skeleton. However, it is not possible to isolate and quantify the magnitude of these effects from environmental effects controlling the stable isotopes record. Therefore, there is a need to develop a proxy which could be independently linked with the changes in biological activity of the corals. It is well known that amino acids are closely associated with biomineralization of coral skeleton. We examined variations in amino acid composition of coral skeleton by conducting high resolution micro-sampling along the coral growth axis. The samples (ca. 1 mg each) were collected at about 1 mm interval, which corresponded to about 1 month of coral skeletal growth, and hydrolyzed with 6N HCl at 110 deg.C for 22 hours. The results show that relative molar concentration of aspartic acid (Asp) shows the most pronounced annual variation, in comparison to other amino acids, over a wide range of 20 - 35 mole percent. The comparison of Asp mole content with stable oxygen isotope data shows that Asp content is the highest in summers while lowest in winters. The absence of non-protein amino acids in the samples suggests that the amino acids in the skeleton are neither degraded nor of extraneous origin, because in both the cases some amount of non-protein amino acids like beta-alanine and gama-amino butyric acid must be present in samples. Lack of correlation between Asp and stable isotope of carbon is probably due to the fact that isotope data are average values for all carbon-based compounds including carbonate carbon. In contrast, Asp relative mole content is based on only one compound and closely related with the secretion of polypeptides and amino acids by coral. Therefore, variations in Asp content is likely to reflect change in biological activity more directly than carbon isotope. Out of about 8 consecutive years record examined in this study, 5 years Asp data clearly show summer peaks while those for other years suggest some kind of abnormality in the biological activity of the coral.
DE: 3670 Minor and trace element composition
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting