Suppl. Fig. 1 Different instruments at the seafloor. A) the large CO2 tank with B) the control panel with valves that could be manipulated by the arm of the ROV, and the white CO2 tube on the right that was connected to the injector pipe (D, middle left, not yet connected). C) the placement of a temperature logger in a transect from the outside towards the CO2 vent (D). E) the positioning of the microsensor
profiler with the ROV arm. B
C
D E A AB
ED
1 2 3 4 5 6
Date
11.05 13.05 15.05 17.05 19.05
T (C)
8.8 9.0 9.2 9.4 9.6 9.8
CO2 Flux (mol s-1 ) 0.00 0.01 0.02 0.03 0.04 1 m
1.4 m 4 m 7 m
Suppl. Fig. 2 Logger data, recorded at indicated distances from the vent, showing irregular heating at a sediment depth of 15 cm upon CO2 injection.
7 8 9 10
Suppl. Fig. 3 Example of a modeled outcome presented in 3D, demonstrating the shape of the
modeled volume and the flame-shaped temperature distribution (at r=0.006m and mass flow=0.0025 mol s-1).
12 13 14 15 16 17 18 19 20 21
Suppl. Fig. 4 showing increasing number of vents with increasing loading rate. With the increase of the flow rate, the CO2 distributes over more vents, thus each vent does not conduct much more CO2
22
23 24
T (C)
7.65 7.70 7.75 7.80 7.85 7.90 7.95 8.00 8.05
depth (m)
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
pH
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 -0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
O2 (mol m-3)
-0.1 0.0 0.1 0.2 0.3 0.4
depth (m)
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
ORP (mV)
-400 -300 -200 -100 0 100 200 300 -0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
Suppl. Fig. 5 The profiles measured at the vent while the CO2 flow rate was 0.0015 mol s-1 show the large variability of the chemistry in and around the venting channel. The data were recorded with 1 sensor for T, 2 sensors for O2, 3 sensors for pH and 2 sensors for ORP in 3 sequential profiling events at the same vent during one deployment. The profiler was lifted up and repositioned on top of the channel before the profiler was restarted.
26 27 28 29 30 31 32
T(C)
7.7 7.8 7.9 8.0 8.1 8.2
depth (m)
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
20m 8m 4m 1m 0m 3m 5m 8m T (C)
7.7 7.8 7.9 8.0 8.1 8.2
depth (m)
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
0m 2m 4m 8m 14m
T (C)
7.7 7.8 7.9 8.0 8.1 8.2
depth (m)
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
0m 8m 4m 2m 1m 0m 0m
T(C)
7.7 7.8 7.9 8.0 8.1 8.2
depth (m)
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
0m 1m 2m 3m 4m 0m 0m 0m Om
T(C)
7.7 7.8 7.9 8.0 8.1 8.2
depth (m)
-0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12
0m 1m 2m 4m 4m 8m 8m
A B
C D
E
Suppl. Fig. 6 Summary of all measured T profiles, at CO2 venting rates of 0, 0.0015, 0.0037, 0.022 and 0.037 mol s-1 (Fig 5 A-E respectively). They were irregular and interfacial T-gradients were much lower than the maximum model outcomes.
33 34 35 36
