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

Beggiatoa site.
The sediments were less soft as those from the center.
Also here some out-gassing occurred and the sediments
were left for several hours to recover. The white Beggiatoa
mats re-colonized the surface quickly. The filaments were
morphologically the same, having a diameter of ca 10 µm.
This may indicate that these areas are occupied by a
single strain.
The profiles in cores from the Beggiatoa site differed from the Central site. The pH
profiles showed a gradual decrease, contrary of what was expected from the AOM
equation. Furthermore, the top is highly sulfidic. At 2 cm depth, sulfide peaks to a
concentration of 12 mM.
Central segment, 28/6/2003
Central segment
O2, H2S (mM)
0.25
7.9
0.2
O2
7.8
pH 0.15
H2S
7.7
0.1
7.6
0.05
7.5
0
7.4
-100 -50 0
-0.05
50 100 150
7.3
depth (mm)
pH
H2S, sulfide (mM)
0.5
0.4
0.3
0.2
0.1
0
-100 -50 -0.1 0 50 100 150
-0.2
depth (mm)
Profiles in a core of 12 hours age. Same area and MUC
deployment.
Oxygen penetrates less than 2 mm. Further measurements in these sediments
confirmed that the pH only very slightly increased with less than 0.05 unit due to
AOM. It is unlikely that this can explain the extensive calcification observed in other
locations. The carbonate sensor is very new and the profiles must be regarded with
caution. However, we have not found significant interferences from compounds
abundant in this type of sediment. To calculate DIC from pH and CO 2- 3 we need very
precisely the pK values of the carbonate system at this low T and Sal. Thus the
profiles presented here are preliminary. The values in the sediments are very high
and need to be checked by porewater analyses. The measurements may have
suffered from an artifact, the core was too narrow to stir well.
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