HR: 14:10h
AN: PP53A-03 INVITED    [Abstracts]
TI: Fossil DNA Stratigraphy revealed Multiple Sources of Alkenones in the Holocene Black Sea at the Strain Level: Implications for UK37 Paleothermometry
AU: * Coolen, M J
EM: mcoolen@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543,
AU: Saenz, J P
EM: jsaenz@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543,
AU: Trowbridge, N
EM: ntrowbridge@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543,
AU: Eglinton, T
EM: teglinton@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543,
AB: The fossil distribution of long-chain alkenones is now a widely accepted tool to reconstruct past sea surface temperatures (SST) (i.e. UK37-index). In most studies, the UK37 index is calibrated for the main source of alkenones, the coccolithophorid haptophyte Emiliania huxleyi. Besides temperature, additional factors such as salinity, growth conditions, or different or multiple biological sources seem to influence the level of unsaturation of alkenones and the reliability of the UK37-inferred SST. The Black Sea is an interesting setting to study such factors since unreliable SST were reconstructed from the Holocene sapropel with high concentrations of an unusual "Black Sea" alkenone (C36:2 ethyl ketone) whereas calcium-bearing microfossils (coccoliths) of haptophytes are lacking. To identify Holocene sources for alkenones in the Black Sea at the unprecedented strain-level and to refine paleoenvironmental conditions, we searched for multiple fossil genetic signatures of haptophytes. This revealed that the slow increase in salinity as a result of post-glacial introduction of Mediterranean waters in the paleo lacustrine Black Sea, caused a succession between alkenone-biosynthesizing haptophytes from Isochrysis spp. (which do not produce coccoliths), to a mixture of Isochrysis and E huxleyi strains, then only E. huxleyi strains, and when the salinity reached a threshold of 18 per mille at 3000 years BP, the fossilized calcium-bearing E. huxleyi strain was introduced. At least 11 E. huxleyi strains were identified and the first non-fossilizing strains already colonized the Black Sea 4000 years before the fossilized calcium-bearing strain appeared. Most E. huxleyi strains were likely sources of C36:2 eK but the presence of one fossil "phylotype" coincided with the highest levels of this unusual alkenone ( more than 80 percent of the total alkenone content) and unreliable past SST (varying between 5 and 30 degrees C; 7500-5500 years BP). C36:2 eK was not biosynthesized by the Isochrysis spp. and the co-occurrence of Isochrysis did not play a significant role in the unreliable SST. Perhaps the past trophic status rather than a low salinity caused the single E. huxleyi strain to biosynthesize high levels of C36:2 eK since this unusual alkenone was recently also found in the oligotrophic DYFAMED station in the Ligurian Sea but its source remains to be identified.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4950 Paleoecology
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting