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Bacterial profiles in deep sediments of the Alboran Sea, western Mediterranean, Sites 976-978

Cragg, Barry Andrew, Law, K. M., O'Sullivan, G. M. and Parkes, Ronald John 1999. Bacterial profiles in deep sediments of the Alboran Sea, western Mediterranean, Sites 976-978. Proceedings of the Ocean Drilling Program Scientific Results 161 , pp. 433-438. 10.2973/odp.proc.sr.161.267.1999

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Abstract

Sediments from three sites in the Alboran Sea, Western Mediterranean were investigated for the presence of bacteria in deep sediments. A series of 54 x 1-cm3 sediment samples were removed from core sections of Hole 976B between 26.9 and 646.6 mbsf (16 samples), Hole 977A between 0 and 525.8 mbsf (29 samples), and Hole 978A between 346 and 644.6 mbsf (9 samples) for direct microscopic determination of bacteria. Sites 977 and 978 were only 24 km apart,contained similar sedimentary sequences and interstitial water profiles and covered complimentary depth ranges to provide samples from the surface to 644 mbsf, hence these were treated as one site. Significant bacterial populations were present in the deepest samples of both sites 644 and 647 mbsf in site 977/978 and 976 respectively (3.5 x 106 cells/cm3 and 1.62x106 respectively). These bacterial depth distributions correspond very well with previous data from Atlantic and Pacific Ocean sites, but they also extend considerably the previous deepest marine sediment samples that have been analysed for bacteria (514 mbsf) and extend the depth of the bacterial biosphere in this environment. As the rate of decrease in bacterial populations does not change even in these deep samples it is likely that bacteria are present even deeper than 650 mbsf in marine sediments. At site 977/978 a deep brine incursion supplies sulfate below 400 mbsf and absence of methane in this zone suggests active bacterial anaerobic methane oxidation. A similar brine incursion in the Peru Margin was shown to stimulate bacterial activity and increased bacterial viability at depths of 80 mbsf and approximately 1 mya. A similar effect may be occuring at site 977/978. This would explain why the bacterial profile does not decrease with depth in the deeper layers and demonstrates the viability of bacteia in ancient deposits (6 mya).

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Q Science > QR Microbiology
Publisher: Ocean Drilling Program
ISSN: 1096-7451
Last Modified: 12 Jun 2019 02:18
URI: http://orca-mwe.cf.ac.uk/id/eprint/8682

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