Preface The expedition ARK XIX/3 with the German icebreaking RV ...

corrected by use of the ROV. The lander was equipped with 2 oxygen, 2 H 2 S, 1
temperature sensor, and 3 potentiometric sensors (Ca 2+ , pH or CO 2- 3 ).
Sediment samples were retrieved with a multicorer, or by an ROV, or taken from the
incubation chambers (Witte). The cores were placed immediately after retrieval in a
water bath of -1 o C. For laboratory measurements 3 microsensors were mounted in
one holder, allowing simultaneous measurements of 3 parameters.
Most microsensors used have been described previously (O 2 , pH, H 2 S, Ca 2+ (Kühl
and Revsbech, 1999)). The total sulfide was calculated from the local H 2 S
concentration and pH using a dissociation constant of 10e-7.05. New is the use of a
carbonate sensor, based on a recently developed ionophore (Choi et al., 2002). The
2-
DIC was calculated from the local CO 3 concentration and pH using dissociation
constants corrected for salinity, temperature and pressure (Zeebe and Wolf-Gladrow,
2001). The pK 1, 2 values used were 6.126734 and 9.420233 for laboratory
measurements (-1 o C, 3.4 % salinity, 1 bar) and 6.099953 and 9.498722 for in situ
profiles (-1 o C, 3.4 % salinity, 140 bar). These constants may need to be corrected.
The 3 segments of the volcano investigated were the central area, the rim where
extensive Beggiatoa fields are found, and the other regions dominated by symbiontic
methane and sulfide oxidising tubeworms (Pogonophora). The worm-fields with their
highly heterogeneous structure and hard chitine tubes are unfavorable for analysis
with fragile microsensors. The center was supposed to have little microbial activity.
We focussed on the Beggiatoa fields, where AOM was found in a thin zone up to 5
cm below the surface.
Results and discussion
A total of 43 cores were measured with 6 different microsensors, 7 lander
deployments were successfully done, each resulting in 9 profiles. The data need
detailed analysis and to be organized. Here follows a summary of the results, with
examples of measurements. The data are not yet absolute, calibrations are still
estimates. Especially the DIC data obtained from pH and carbonate measurements
are still inaccurate, as the equilibrium constants of the carbonate system at this
pressure and depth are uncertain.
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