Marine subseafloor sediment Targeted Locus (Loci)

We examine the relationship between subseafloor microbial diversity and paleoceanographic conditions in samples from three sediment cores from the Eastern Mediterranean Sea and the Black Sea. All three cores record dramatic changes in oceanographic/limnic conditions resulting from oscillation between oligotrophic and euxinic condition, yet they also differ remarkably between sites. Our motivation for this study is based on the premise that paleoenvironmental conditions in the overlying water column are intimately linked to the composition of aquatic microbial communities and thus the inoculum for subseafloor communities. Our study will address the long-standing question to what degree the composition of subseafloor microbial communities is linked to paleoenvironmental conditions at time of deposition. The sample set at both Mediterranean sites is composed of carbonate-rich, organic-lean sediments and interspersed so-called sapropels, that is, organic-rich black layers that were deposited during climates that were probably warmer and more humid than today, when the Mediterranean was euxinic. The samples from the discovery basin are influenced by a highly saline brine and thus may select for halophilic sedimentary microbes. The Black Sea sample set is composed of organic-lean coccolith ooze deposited during the recent few thousand years, an organic-rich sapropel deposited during the early Holocene and below of sediment deposited during the late glacial/early Holocene when the Black Sea was still a freshwater lake. We examine both archaeal and bacterial diversity with a 454-based tag sequencing survey. We can address questions relating to the paleoenvironmental history at each site as well as to the relationship of microbial communities in sediments deposited during euxinic conditions at three sites along a salinity gradient remote to each other, in two different ocean basins. The sample set will be accompanied by an in-depth biogeochemical characterization of its sedimentary habitat. Sediment sampling and characterization are performed and mutually integrated on the same cruise (RV Meteor, M84-1, February 9-22, 2011) by the proponents of this proposal.