Environmental Engineering Reference
In-Depth Information
2.1 Water Column
During the research cruises with the German vessels and RV Welwitchia,
water column data were obtained with a CTD SBE 911+ with SBE 43 oxygen
sensors, 2-channel Haardt fluorometer, a Datasonics PSA-900 altimeter with
a 300 m range for bottom finding together with a rosette sampler equipped
with 12 five-litre free-flow HydroBios water sample bottles. Attached to the
CTD frame was an Acoustic Doppler Current Profiler (ADCP) consisting of a
coupled upward- and downward-looking Workhorse ADCP 300 kHz in a 3000
dbar pressure case. Water from the HydroBios bottles was directly transferred
to 120 ml Winkler bottles for duplicate determination of dissolved oxygen and
sulphide. Dissolved oxygen and sulphide were determined immediately after
retrieval of the rosette sampler. Dissolved oxygen was determined by Winkler
titration and dissolved sulphide was determined by the method of Cline [12].
The dissolved oxygen concentrations determined by Winkler were used for
calibration of the CTD SBE oxygen probe. The mooring was equipped with an
upward looking 300 kHz Workhorse ADCP, four Seacat SBE 16 recorders and
three Seamon temperature recorders.
2.2 Sediment
Sediments were collected to determine 35 S-sulphate reduction rates, methane
concentrations, fluxes of hydrogen sulphide, and abundances of the large sul-
phur bacteria Beggiatoa and Thiomargarita . At each station, several casts were
made until sufficient material was obtained. Methods are described in detail in
[7, 14]. Fluxes of hydrogen sulphide and methane were calculated from porewa-
ter profiles using the fitting procedure described by Berg et al [3]. Fluxes were
calculated across the sediment-water interface. These procedures are described
in detail in [7]. Distribution maps of sulphate reduction rates, sulphide fluxes,
large sulphur bacteria, and bottom water oxygen and hydrogen sulphide were
created with the Surfer software package using Kriging with linear interpolation
as the gridding method.
Morphology, distribution, and layering of shelf sediments were investigated
using the multibeam echosounder Hydrosweep and the Parasound sub-
bottom profiling system on R/V Meteor. Detailed technical descriptions of the
acoustic systems are given in [4, 36, 42]. A frequency of 4 kHz and a pulse
length of two periods were used during the cruises. Additional measurements
with different frequencies (2.5-5.5 kHz) and pulse durations of 1 to 6 periods
were performed at coring stations in order to study the influence of frequency
and length of the source signal on the reflection pattern. Parasound data
were recorded continuously. High-resolution sub-bottom profiling in shallow
water (up to 400 m) was performed using the parametric sediment echosounder
SES96-Standard in addition to the Parasound device. The parametric SES96
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