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

O2, CO3-- (mM)
Beggiatoa mats, 30/06/03
0.3
12
O 2
0.25
10
0.2
8
2-0.15
6
CO 3
0.1
4
DIC 0.05
2
0
0
-100 -50 0 50 100 150
depth (mm)
DIC (mM)
pH
pH
Beggiatoa mats, 30/06/03
12
10
8
6
4
2
0
DIC
-100 -50 0 50 100 150
depth (mm)
8.2
8.1
8
7.9
7.8
7.7
DIC (mM)
O2, CO3-- (mM)
Beggiatoa mat, 30/06/03
1.2
7.98
1
7.96
pH
2-
CO
0.8
3 7.94
7.92
0.4
7.88
O 2
7.86
0.2
7.84
0.6
7.9
0
7.82
-100 -50 -0.2 0 50 100 1507.8
depth (mm)
pH
DIC (mM)
Beggiatoa mat, 30/06/03
50
7.98
7.96
pH 40
7.94
7.92
30
DIC 7.9
20
7.88
7.86
10
7.84
7.82
0
7.8
-100 -50 0 50 100 150
depth (mm)
pH
Measured carbonate and calculated DIC profiles in Beggiatoa
dominated sediments.
The DIC values in the water column are higher than expected. Samples have been
extracted and will be analysed soon. However, both the carbonate and DIC profile
show microbial activity in the zone of AOM. The rates of Ci tot will be calculated from
the profiles after cross-check with the porewater profiles. The high DIC concentration
may explain the relatively modest pH effects that accompany the very high microbial
activities: the DIC in the porewater forms a pH buffer
Similar results were obtained in various duplicate cores. The pH gradients were the
most variable in shape.
Some experiments were conducted on the mats. Addition of 200 µM nitrate caused a
further penetration of oxygen, down to 1 cm. Also the sulfide front was pushed
downwards, but maintained its overlap with the oxygen profile. This is an indication
that the Beggiatoa involved do not store nitrate. The Beggiatoa disappeared from the
surface, following the oxic-sulfidic interface.
- 204 -