Geophysical measurements on sediment cores from North Pond, Mid Atlantic Ridge

Die Porosität ist einer der wichtigsten gesteinsphysikalischen Parameter von Sedimenten. Daher werden in dieser Arbeit die Abhängigkeiten zwischen dem zentralen gesteinsphysikalischen Parameter Porosität und den Parametern Wärmeleitfähigkeit und spezifischer elektrischer Widerstand an Sedimenten von North Pond, eines Sedimentbeckens an der westlichen Flanke des Mittelatlantischen Rückens bei ca. 23°N, qualitativ und empirisch untersucht. Die Messung des spezifischen Widerstands wurde mittels eines miniaturisierten Wenner-Arrays mit einem Zentimeter Elektrodenabstand noch an Bord der FS Maria S. Merian auf der Reise MSM11/1 vom 10. Februar bis 13. März 2009 an Sedimentkernhälften durchgeführt, ebenso wie die Messung der Wärmeleitfähigkeit mit einer Nadelsonde. Die Messung der Gamma-Dichte an einem Multi Sensor Core Logger erfolgte im Rahmen dieser Arbeit und wurde wie die Messung der Porosität an Proben im Marum in Bremen durchgeführt. Die zugrundeliegende und zu untersuchende Beziehung zwischen spezifischem Widerstand und Porosität ist Archie's Law, die untersuchte Beziehung zwischen Wärmeleitfähigkeit und Porosität ist das Modell des geometrischen Mittels der Sedimentkomponenten. Die physikalische Beziehung zwischen der Porosität und den beiden Parametern spezifischer Widerstand und Wärmeleitfähigkeit konnte an den Sedimenten von North Pond bestätigt werden.

Carbon isotopic compositions and concentrations of major fatty acids in the Beggiatoa covered sediment core at the crest of southern Hydrate Ridge

Membrane fatty acids were extracted from a sediment core above marine gas hydrates at Hydrate Ridge, NE Pacific. Anaerobic sediments from this environment are characterized by high sulfate reduction rates driven by the anaerobic oxidation of methane (AOM). The assimilation of methane carbon into bacterial biomass is indicated by carbon isotope values of specific fatty acids as low as -103 per mill. Specific fatty acids released from bacterial membranes include C 16:1 omega 5c , C 17:1 omega 6c , and cyC 17:0 omega 5,6 , all of which have been fully characterized by mass spectrometry. These unusual fatty acids continuously display the lowest d13 C values in all sediment horizons and two of them are detected in high abundance (i.e., C 16:1 omega 5c and cyC 17:0 omega 5,6 ). Combined with microscopic examination by fluorescence in situ hybridization specifically targeting sulfate-reducing bacteria (SRB) of the Desulfosarcina/Desulfococcus group, which are present in the aggregates of AOM consortia in extremely high numbers, these specific fatty acids appear to provide a phenotypic fingerprint indicative for SRB of this group. Correlating depth profiles of specific fatty acid content and aggregate number in combination with pore water sulfate data provide further evidence of this finding. Using mass balance calculations we present a cell-specific fatty acid pattern most likely displaying a very close resemblance to the still uncultured Desulfosarcina/Desulfococcus species involved in AOM.

(Table S1) Molecular analyses and morphological comparisons of deep-sea clams

Large vesicomyid clams are common inhabitants of sulphidic deep-sea habitats such as hydrothermal vents, hydrocarbon seeps and whale-falls. Yet, the species- and genus-level taxonomy of these diverse clams has been unstable due to insufficiencies in sampling and absence of detailed taxonomic studies that would consistently compare molecular and morphological characters. To clarify uncertainties about species-level assignments, we examined DNA sequences from mitochondrial cytochrome-c-oxidase subunit I (COI) in conjunction with morphological characters. New and published COI sequences were used to create a molecular database for 44 unique evolutionary lineages corresponding to species. Overall, the congruence between molecular and morphological characters was good. Several discrepancies due to synonymous species designations were recognized, and acceptable species names were rectified with published COI sequences in cases where morphological specimens were available. We identified seven species with trans-Pacific distributions, and two species with Indo-Pacific distributions. Presently, 27 species have only been documented from one region, which might reflect limited ranges, or insufficient geographical sampling. Vesicomyids exhibit the greatest species diversity along the northwest Pacific ridge systems and in the eastern Pacific, along the western America margin, where depth zonation typically results in segregation of closely related species. The broad distributions of several vesicomyid species suggest that their required chemosynthetic habitats might be more common than previously recognized and occur along most continental margins.