@article {2567,
	title = {Implications for chloro- and pheopigment synthesis and preservation from combined compound-specific δ13C, δ15N, and Δ14C analysis},
	journal = {Biogeosciences},
	volume = {7},
	year = {2010},
	month = {Jan-01-2010},
	pages = {4105 - 4118},
	abstract = {Chloropigments and their derivative pheopigments preserved in sediments can directly be linked to photosynthesis. Their carbon and nitrogen stable isotopic compositions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation processes of the phytoplanktonic community. In this study we report results from combined compound-specific radiocarbon and stable carbon and nitrogen isotope analysis to examine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 132,173-cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of marine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment delta15N values indicate nitrate as the major uptake substrate but 15N-depletion towards the open marine setting indicates either contribution from N2-fixation or direct uptake of ammonium from deeper waters. Radiocarbon concentrations translate into minimum and maximum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought. Moreover, seasonal variations of nutrient source, growth period, and habitat and their associated isotopic variability are likely at least as strong as long-term trends. Combined triple isotope analysis of sedimentary chlorophyll and its primary derivatives is a powerful tool to delineate biogeochemical and diagenetic processes in the surface water and sediments, and to assess their precise time-scales. 

},
	doi = {10.5194/bg-7-4105-201010.5194/bg-7-4105-2010-supplement},
	url = {http://www.biogeosciences.net/7/4105/2010},
	author = {Kusch, S. and Kashiyama, Y. and Ogawa, N. O. and Altabet, M. and Butzin, M. and Friedrich, J. and Ohkouchi, N. and Mollenhauer, G.}
}
@article {1932,
	title = {Carbon isotopic constraints on relict organic carbon contributions to Ross Sea sediments},
	journal = {G-cubed},
	volume = {7},
	year = {2006},
	note = {id: 759},
	month = {2006},
	author = {Ohkouchi, N. and Eglinton, T. I.}
}
@article {1977,
	title = {Radiocarbon dating of alkenones from marine sediments: I. Isolation protocol},
	journal = {Radiocarbon},
	volume = {47},
	year = {2005},
	note = {993nkTimes Cited:13
Cited References Count:22
},
	month = {2005},
	pages = {401-412},
	abstract = {The chemical and isotopic compositions of long-chain (C-36-C-39) unsaturated ketones (alkenones), a unique class of algal lipids, encode surface ocean properties useful for paleoceanographic reconstruction. Recently, we have sought to extend the utility of alkenones as oceanic tracers through measurement of their radiocarbon contents. Here. we describe a method for isolation of alkenones from sediments as a compound class based on a sequence of wet chemical techniques. The steps involved, which include silica gel column chromatography, urea adduction, and silver nitrate-silica gel column chromatography, exploit various structural attributes of the alkenones. Amounts of purified alkenones estimated by GC/FID measurements were highly correlated with CO2 yields after sample combustion, indicating purities of greater than 90\% for samples containing >= 100 mu g C. The degree of alkenone unsaturation (U-37(K{\textquoteright})) also varied minimally through the procedure. We also describe a high-performance liquid chromatography (HPLC) method to isolate individual alkenones for molecular-level structural and isotopic determination.},
	keywords = {AMS, carbon, indicators, proxy, records, tool},
	isbn = {0033-8222},
	author = {Ohkouchi, N. and Xu, L. and Reddy, C. M. and Montlucon, D. and Eglinton, T. I.}
}
@article {1978,
	title = {Radiocarbon dating of alkenones from marine sediments-III. Influence of solvent extractions procedures on 14C measurements of foraminifera},
	journal = {Radiocarbon},
	volume = {47},
	year = {2005},
	note = {id: 554},
	month = {2005},
	pages = {425-432},
	author = {Ohkouchi, N. and Eglinton, T. I. and Hughen, K. A. and Roosen, E. and Keigwin, L.}
}
@article {2073,
	title = {Radiocarbon dating of individual fatty acids as a tool for refining Antarctic margin sediment chronologies},
	journal = {Radiocarbon},
	volume = {45},
	year = {2003},
	note = {735tqTimes Cited:25
Cited References Count:29
},
	month = {2003},
	pages = {17-24},
	abstract = {We have measured the radiocarbon contents of individual, solvent-extractable, short-chain (C-14, C-16, and C-18) fatty acids isolated from Ross Sea surface sediments. The corresponding C-14 ages are equivalent to that of the post-bomb dissolved inorganic carbon (DIC) reservoir. Moreover, molecular C-14 variations in surficial (upper 15 cm) sediments indicate that these compounds may prove useful for reconstructing chronologies of Antarctic margin sediments containing uncertain (and potentially variable) quantities of relict organic carbon. A preliminary molecular C-14 chronology suggests that the accumulation rate of relict organic matter has not changed during the last 500 C-14 yr. The focus of this study is to determine the validity of compound-specific C-14 analysis as a technique for reconstructing chronologies of Antarctic margin sediments.},
	keywords = {carbon, ice-sheet, marine-sediments, north-atlantic, organic-matter, ross-sea, southern-ocean},
	isbn = {0033-8222},
	author = {Ohkouchi, N. and Eglinton, T. I. and Hayes, J. M.}
}
@article {700,
	title = {Spatial and temporal offsets between proxy records in a sediment drift},
	journal = {Science},
	volume = {298},
	year = {2002},
	note = {612mqTimes Cited:147Cited References Count:38},
	month = {Nov 8},
	pages = {1224-1227},
	abstract = {Chronologies for Late Quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera. Signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information. A key premise is that microfossils and other indicators within a given sediment horizon are of equal age. We show here that haptophyte-derived alkenones isolated from Bermuda Rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera. This temporal offset, which is apparently due to lateral transport of alkenones on fine-grained particles from the Nova Scotian margin, markedly influences molecular estimates of sea surface temperatures. More broadly, the observation raises questions about both the temporal and the geographic delity of paleoenvironmental records encoded by readily transported components of sediments.},
	issn = {0036-8075},
	doi = {10.1126/science.1075287},
	author = {Ohkouchi, N. and Eglinton, T. I. and Keigwin, L. D. and Hayes, J. M.}
}
