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

C. 2 Geochemical and hydrodynamic investigations at the sediment-water
interface
Sauter, E., Baumann, L., Wegner, J., Delius, J.
In close interdisciplinary co-operation with the benthos biology and geology group the
geochemical investigations of the sedimentary and near-bottom environments at the
“Hausgarten” area west of Svålbard were performed. Scientific aim is the description
of gradients in geochemical parameters close above and below the sediment/water
interface. Those gradients are planed to be interpreted in close comparison to benthic
habitat properties (e.g. species distribution and abundances) and the geological
setting (e.g. sediment stratification).
For this purpose the central “Hausgarten” station at 2500 m water depth amongst the
stations along the east-west depth transect from 1200 to 5500 m depth as well as of
the north-south transect at about 2500 m depth have been sampled by multi corer and
bottom water sampler. In addition, having the opportunity for targeted sampling and in
situ measurements by means of “Victor 6000”, the focus was laid on micro profile
measurements and high precision acoustic current measurements.
Vertical gradients of nutrients, C org content, C/N ratio, porosity and other geochemical
parameters will be determined from sediment samples taken at the stations indicated
in Tab. C2-1 in order to characterize the geochemical milieu in which the organisms,
analysed by the biology group, live. The oxygen concentration was determined by
Winkler titration, immediately after sampling of the supernatant bottom water and the
bottom water sampler, respectively (Tab. C2-1). Nutrient gradients will also be
analysed from the bottom water samples in order to quantify interfacial solute fluxes
and rates metabolism.
Special emphasis was laid on the exact measurement of oxygen micro gradients
below the sediment/water interface. For this purpose a deep-sea micro profiler (MIC)
has been modified to fit into the shuttle lander and to be operated by the ROV at the
seafloor (Fig. C2-1). A switch operated by the ROV allows keeping the system down
at the sea floor for several individual measurements. Due to its small dimensions MIC
can be placed precisely by the ROV. Thus, the system was deployed at one of the
disclusion experiment sites, where the sediment was covered by a cage for 4 years.
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