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Unusual C35 to C38 alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida)
van Soelen, E.E.; Lammers, J.M.; Eglinton, T.I.; Sinninghe Damsté, J.S.; Reichart, G.-J. (2014). Unusual C35 to C38 alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida). Org. Geochem. 70: 20-28. dx.doi.org/10.1016/j.orggeochem.2014.01.021
In: Organic Geochemistry. Elsevier: Oxford; New York. ISSN 0146-6380, more
Peer reviewed article  

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  • van Soelen, E.E., more
  • Lammers, J.M.
  • Eglinton, T.I.
  • Sinninghe Damsté, J.S., more
  • Reichart, G.-J., more

Abstract
    Unusual C-35 to C-38 alkenones were identified in mid-Holocene (8-3.5 kyr BP) sediments from a restricted estuary in southwest Florida (Charlotte Harbor). The distribution was dominated by a C-36 diunsaturated (omega 15,20) ethyl ketone, identical to the one present in Black Sea Unit 2 sediments. Other unusual alkenones were tentatively assigned as a C-35:2 (omega 15,20) methyl ketone, a C-37:2 (omega 17,22) methyl ketone and a C-38:2 (omega 17,22) ethyl ketone. In late Holocene sediments < 3.5 kyr BP, the common C-37 to C-39 alkenones were found. Compound-specific C-14, C-13, and D isotope measurements were used to constrain the possible origin of the alkenones. Conventional radiocarbon ages of alkenones and higher plant-derived long chain n-alcohols indicated no significant difference in age between mid-Holocene alkenones and higher plant n-alcohols. Both alcohols and alkenones were offset vs. calibrated ages of shell fragments in the same sediment core, which suggests they were pre-aged by 500-800 yr, implying resuspension and redistribution of the fine-grained sedimentary particles with which they are associated. The hydrogen isotopic (delta D) composition (-190 parts per thousand to -200 parts per thousand) of the C-37 and C-38 alkenones in the late Holocene sediments is in line with values for coastal haptophytes in brackish water. However, the unusual C-36 and C-38 alkenones from the mid Holocene sediments were enriched in D (by ca. 100 parts per thousand) vs. the late Holocene alkenones. Also, delta C-13 values of mid-Holocene alkenones were consistently offset compared with late Holocene alkenones (-21 parts per thousand to 22 parts per thousand and -22 parts per thousand to -23 parts per thousand, respectively). We suggest that the alkenones in Charlotte Harbor were produced by unknown alkenone-producing haptophyte.

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