HR: 11:35h
AN: PP32B-06 INVITED    [Abstracts]
TI: Uncovering the Mysteries of Lacustrine Haptophytes Using Fossil DNA
AU: * D'Andrea, W J
EM: William_DAndrea@Brown.edu
AF: Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Theroux, S
EM: Susanna_Theroux@Brown.edu
AF: Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Huang, Y
EM: Yongsong_Huang@Brown.edu
AF: Brown University, 324 Brook St., Providence, RI 02912, United States
AB: Certain haptophyte algae produce alkenones which are indispensable biomarkers used in paleoclimate studies. Sedimentary alkenones record past water temperatures experienced by the algae via the unsaturation index (U^K₃₇), as well as capturing a snapshot of the source water hydrogen isotope composition (used to reconstruct hydrological changes) and carbon isotope composition (used to reconstruct partial pressure of CO₂). In these ways, alkenones have been exploited for paleoclimate reconstructions from ocean sediments. Paleoclimatologists and organic geochemists are now beginning to discover alkenones in sediments from lakes around the globe. However, unlike in the oceans, the exact haptophytes responsible for producing lacustrine alkenones are unknown and may be specific to different lakes. To effectively use alkenones for isotopic and temperature reconstruction from lake sediments, the identity (and potential temporal variability) of the producer organisms must be understood. Using 18S rDNA we have previously shown that the surface sediments of four lakes in southwestern Greenland, as well as 1000 year old sediment from one of these lakes, all depict the presence of the same haptophyte taxa. Here, we report higher-resolution paleogenomic results from the Holocene sediments of Lake E in southwestern Greenland, which indicate that there has not been any discernable change in the haptophyte population (as inferred from 18S rDNA) within the lake after their appearance 5500 years ago. This differs from the significant shifts in haptophyte taxa which have been reported from the sediment record of Ace Lake, Antarctica (likely due to Lake E having had a more stable environmental history than Ace Lake) and validates the application of a single U^K₃₇-temperature calibration to the entire sediment record of Lake E. We also report the results of the first global survey of lacustrine haptophytes. We compare haptophyte 18S rDNA sequences from lake sediments from Greenland, Tibet, Spain, Great Britain, North America, Europe and Antarctica. This approach utilizes sedimentary DNA to answer questions that traditional algal culturing techniques have been unable to address, providing the first phylogenetic map of lacustrine haptophytes and revealing some of the challenges faced in developing lacustrine alkenones as a continental paleoclimate proxy.
DE: 0424 Biosignatures and proxies
DE: 0458 Limnology (1845, 4239, 4942)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4950 Paleoecology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting