[M-GI28] Drilling Earth Science

[MGI28-P02] Reconstruction of marine primary productivity and production by analysis of sediment cores: Consideration for the degradation and preservation effects

*Ken Sawada^1,2, Kotaro Hoshi² (1.Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, 2.Department of Natural History Sciences, Graduate School of Science, Hokkaido University)

Keywords:Marine primary pruductivity, Sedimentary core, Diagenesis, Mass accumulation rate

For understanding long time-scale biogeochemical cycles and climatic changes, especially related to the greenhouse effect, evaluation of marine primary production (quantitative parameter) and productivity (qualitative parameter) is essential and can promote the reconstruction of atmospheric CO2 concentrations and related analysis for paleothermometry. Basically, marine primary production/productivity at long time-scale have been evaluated by the fossils and chemical materials in marine sediments. The authors have used biogenic organic matter, biomarkers, for the analysis. In paleoclimatic and paleoceanographic studies, paleoproduction data were provided on the basis of export fluxes, through the mass accumulation rates (MARs) in sediments, and paleoproductivity were interpreted by the proxy of biogenic fossils, elements, isotopes, and compounds. In such evaluations, separating degradation /preservation of fossils and chemical materials during diagenesis from productivity is a key question. The proxies for production / productivity must experience microbial degradation, geochemical diagenetic alteration, and modification. Such investigation has been often neglected, resulting in misleading interpretations. Here we suggest the consideration for the degradation and preservation effects in the investigations of marine primary productivity / production as follows.
1) Reconstruction of variation in redox conditions in the same sediments
2) Evaluation of the degree of selective degradation / preservation
3) Development of new proxies for analysis of marine primary productivity / production.