25th International Meeting on Organic Geochemistry IMOG 2011

P-183
Characterization of dissolved organic matter in the
hydrothermally altered sediment of the Guaymas Basin, Gulf of
California
Yu-Shih Lin 1 , Boris Koch 2 , Matthias Witt 3 , Kai-Uwe Hinrichs 1
1 MARUM, University of Bremen, Bremen, Germany, 2 Alfred Wegener Institute for Polar and Marine
Research, Bremerhaven, Germany, 3 Bruker Daltonik GmbH, Bremen, Germany (corresponding
author:yushih@uni-bremen.de)
Guaymas Basin, located in the central part of the
Gulf of California, is part of a rift zone that links the
East Pacific Rise in the south with the San Andreas
Fault leading north. Covered with thick layers of
sediment, the basin is of special biogeochemical
interest because of the hydrothermal activities
inferred from high heat flow values [1]. Sediments are
typically heated to >100°C within the upper 50 cm,
providing excellent material for investigating thermal
alteration of sedimentary organic matter (OM) and the
accompanying heat-adapted microbial communities.
Petroleum, normally generated at great depths at
geological time scales, has been observed in shallow
sediments [2]. Pore waters in the upper 50 cm of
sediment are usually rich in sulfate, providing
sufficient oxidizing power for OM remineralization [3].
Although microbiological data showed the extensive
presence of thermophiles [e.g., 4], microbial activities
in deeper sediments, where the in-situ temperature
should favor these organisms, are relatively low.
When labile organic substrates were added to deeper
sediments, microbial activities could be enhanced [5].
This suggests the role of OM quality as a limiting
factor of thermophilic life in the sediments.
In this study, we seek to improve the understanding
of OM composition of Guaymas Basin sediments by
molecular characterization of dissolved organic matter
(DOM) in pore waters. Samples were retrieved by DV
Alvin at Station 4568 during RV Atlantis ATT15-56
(2009). The temperature was 102°C at 35 cmbsf.
Concentrations of dissolved organic carbon (DOC)
were >80 µM and have a maximum of 330 µM at
16 cmbsf (Table 1). DOM was concentrated by solidphase
extraction and analyzed using Fourier
transform ion cyclotron resonance mass
spectrometry.
Our preliminary results showed notable differences
between the upper three samples (Table 1). While the
(H/C)wa ratios change only slightly, the (O/C)wa ratios
decrease significantly with depth. In all the three
samples, there is only a small fraction of formulas
(