Dynamics of methane and hydrogen sulphide
in the water column and sediment
of the Namibian shelf
Volker Brüchert 1, Bronwen Currie 2, Kay-Christian Emeis 3, Rudolf Endler 4,
Thomas Leipe 4, Kathleen R. Peard 2, Thomas Vogt 5
1
Max-Planck Institute for Marine Microbiology and Research Center Ocean
Margins, Bremen
2 Ministry of Fisheries and Marine Resources, Namibia
3 Institute of Biogeochemistry and Marine Chemistry, University of Hamburg
4 Institute for Baltic Sea Research, Warnemünde
5 Geoscience Department University of Bremen
The diatomaceous mud belt off central Namibia
Coastal upwelling
high primary productivity
Porosity > 90%
Diatom-rich
Organic-C: > 12 % dry wt
Accumulation rates:
50 – 1000 g/m2/a
Distribution of
diatomaceous mud,
free gas, and
sediment craters
Areal estimates:
Diatomaceous mud: 17900 km2
Gas-filled sediments: 1357 km2
Sea floor with pockmarks
and sediment craters: 380 km2
Emeis et al., 2004
Water column oxygen profiles and bottom water images
Dissolved oxygen (ml/l)
2
4
0
6
0
0
20
20
40
60
80
100
120
GPS: 26 °25.1S 014° 55.1E
No free gas, low hydrogen sulphide
Pressure (dBar)
Pressure (dbar)
0
Dissolved oxygen (ml/l)
2
4
6
40
60
80
100
GPS: 23 °04.8S 014°16.2E
Shallow gas: Bacterial mats of
Beggiatoa and Thiomargarita
Hydrogen sulphide profile in the water column
Concentration (mM)
0
0
Depth (m)
20
50
100
150
200
250
300
350
Sulphide µM
Oxygen µM
Oxygen
40
60
80
Seawater
100
H2S
Methane Sediment
Seismo acoustics
• Parametric sediment
echosounder Parasound –
Paradigma (Frequency: 2-5 kHz)
• Parametric sediment
echosounder SES96 (Frequency:
4-12 kHz )
• Linear sediment echosounder
SEL96 (Frequency: 5-20 kHz)
• Sparker seismics
Outer shelf: Prograding mud and truncated coastal
sands
Central shelf: Disappearance of horizontal
beds and appearance of gas blankings
SEL96-Echogram: Transition from gas-free mud → partially gas-filled
→ crater structures → gas-saturated
< 660m >
Depth range 75 – 95 m
(1m – contour lines)
Ship direction 180°
14°20‘E, 22°51‘S
Efficient anaerobic oxidation of methane by sulfate in areas where
the depth of free gas is greater than than one meter
Sulphate (mM)
Depth (cm)
0
10
Sulphide (mM)
20
30
0
0
0
50
50
100
100
150
150
200
200
250
250
300
300
350
350
400
400
450
450
500
500
0
500
1000
1500
5000 10000 15000 20000
2000
3
CH4 (nmol/cm )
Emeis, Brüchert et al. (2004)
Evidence for gas escape from the sediment
Bubbles tracked by echosounder
Meteor M 57-3
Pore water methane, sulphate, and sulphide in
sediment crater
181 Multicore
181 gravity core
Methane (mM)
Methane (mM)
0
1
2
3
4
5
6
7
8
9
10
2000
4000
1
6000
10
100
1000
10000
0
Methane
100
Sulphide
Depth (cm)
Depth (cm)
0
200
300
400
Methane
500
Sulfate
600
0
5
10
15
Hydrogen sulphide (mM)
20
0
10
20
Sulphate (mM)
30
Rising mud islands and coast-wide fish kills
Lobster kills
Turquoise,
elemental sulfurcontaining surface
water
MODIS satellite imagery:
turquoise discolourations
often coincide with reports
of hydrogen sulphide smell;
measurements indicate
sulphur concentrations
up to 30 mmoles/L.
September 03, 2003, www.noaa.gov
Temporal variability
4
6
0
1
2
3
4
5
6
Periods of whole-water
column depletion
Depth (m)
8
10
12
14
16
18
Dissolved
oxygen (ml/l)
20
12 0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536
-2
Coincident
hydrogen sulphide
mmol m day
-1
10
8
6
4
Diffusive
sulfide flux
2
and
0
0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
2
6
8
10
12
14
May 2004
March 2004
December 2003
July 2003
August 2003
September 2003
March 2003
January 2003
October 2002
November 2002
July 2002
May 2002
March 2002
December 2001
October 2001
August 2001
16
May 2001
June 2001
Depth (cm)
methane pulses
in the sediment
4
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
Methane
(nmol cm-3)
Publications
• Brüchert V., Jørgensen B.B., Neumann K., Riechmann D., Schlösser M.,
and Schulz H. Regulation of bacterial sulfate reduction and hydrogen
sulfide fluxes in the central Namibian coastal upwelling zone. Geochimica
et Cosmochimica Acta, 2003; 67: 4505-4518.
• Brüchert V., Lass U., Endler R., Dübecke A., Julies E., Leipe T., and
Zitzmann S. An integrated assessment of shelf anoxia and water column
hydrogen sulphide in the Benguela coastal upwelling system off Namibia,
In Past and Present Marine Water Column Anoxia, L.N. Neretin, B.B.
Jorgensen, and J.W. Murray, eds.: Kluwer; in press.
Emeis K.-C., Brüchert V., Currie B., Endler R., Ferdelman T.G., Kiessling
A., Leipe T., Noli-Peard K., Struck U., and Vogt T. Shallow gas in shelf
sediments of the Namibian coastal upwelling ecosystem. Continental Shelf
Research, 2004; 24: 627-642.
• Weeks S.J., Currie B., Bakun A., and Peard K.R. Hydrogen sulphide
eruptions in the Atlantic Ocean off southern Africa: implications of a new
view based on SeaWIFS satellite imagery. Deep-Sea Research, 2004; 51:
153-172.