Implications for chloro- and pheopigment synthesis and preservation from combined compound-specific δ13C, δ15N, and Δ14C analysis

[摘要] Chloropigments and their derivative pheopigments preserved in sediments candirectly be linked to photosynthesis. Their carbon and nitrogen stableisotopic compositions have been shown to be a good recorder of recent andpast surface ocean environmental conditions tracing the carbon and nitrogensources and dominant assimilation processes of the phytoplanktoniccommunity. In this study we report results from combined compound-specificradiocarbon and stable carbon and nitrogen isotope analysis to examine thetime-scales of synthesis and fate of chlorophyll-a and its degradationproducts pheophytin-a, pyropheophytin-a, and13²,17³-cyclopheophorbide-a-enol until burial in Black Sea core-topsediments. The pigments are mainly of marine phytoplanktonic origin asimplied by their stable isotopic compositions. Pigment δ¹⁵Nvalues indicate nitrate as the major uptake substrate but ¹⁵N-depletiontowards the open marine setting indicates either contribution fromN₂-fixation or direct uptake of ammonium from deeper waters.Radiocarbon concentrations translate into minimum and maximum pigment agesof approximately 40 to 1200 years. This implies that protective mechanismsagainst decomposition such as association with minerals, storage in deltaicanoxic environments, or eutrophication-induced hypoxia and light limitationare much more efficient than previously thought. Moreover, seasonalvariations of nutrient source, growth period, and habitat and theirassociated isotopic variability are likely at least as strong as long-termtrends. Combined triple isotope analysis of sedimentary chlorophyll and itsprimary derivatives is a powerful tool to delineate biogeochemical anddiagenetic processes in the surface water and sediments, and to assess theirprecise time-scales.

[学科分类] 地球化学与岩石