Dynamics of methane and hydrogen sulphidein 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, Bremen2 Ministry of Fisheries and Marine Resources, Namibia3 Institute of Biogeochemistry and Marine Chemistry, University of Hamburg4 Institute for Baltic Sea Research, Warnemünde5 Geoscience Department University of Bremen
The diatomaceous mud belt off central Namibia
Porosity > 90%Diatom-richOrganic-C: > 12 % dry wtAccumulation rates: 50 – 1000 g/m2/a
Coastal upwellinghigh primary productivity
Distribution of diatomaceous mud, free gas, andsediment 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
Shallow gas: Bacterial mats ofBeggiatoa and Thiomargarita
Dissolved oxygen (ml/l)
0
20
40
60
80
100
120
0 2 4 6
Pre
ssu
re (
db
ar)
0
20
40
60
80
100
0 2 4 6Dissolved oxygen (ml/l)
Pre
ssu
re (
dB
ar)
GPS: 26 °25.1S 014° 55.1E GPS: 23 °04.8S 014°16.2E
No free gas, low hydrogen sulphide
Hydrogen sulphide profile in the water column
0 50 100 150 200 250 300 350
Concentration (M)
0
20
40
60
80
100
De
pth
(m
)
Sulphide µM
H2S Methane
Oxygen µMOxygen
Sediment
Seawater
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
Depth range 75 – 95 m (1m – contour lines)Ship direction 180° 14°20‘E, 22°51‘S
< 660m >
Efficient anaerobic oxidation of methane by sulfate in areas where the depth of free gas is greater than than one meter
0
50
100
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500
0 10 20 30
CH4 (nmol/cm3)
Dep
th (
cm)
0 500 1000 1500 2000
Sulphate (mM)
0
50
100
150
200
250
300
350
400
450
500
0 5000 10000 15000 20000
Sulphide (M)
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 gravity core
0
100
200
300
400
500
600
1 10 100 1000 10000
Methane (M)
Dep
th (
cm)
0 10 20 30Sulphate (mM)
Methane
Sulfate
181 Multicore
01
23
456
78
910
0 2000 4000 6000
Methane (M)
Dep
th (
cm)
0 5 10 15 20Hydrogen sulphide (mM)
Methane
Sulphide
Rising mud islands and coast-wide fish kills
Lobster kills
Turquoise, elemental sulfur-containing surface water
MODIS satellite imagery:turquoise discolourations often coincide with reportsof hydrogen sulphide smell;measurements indicatesulphur concentrations up to 30 moles/L.
September 03, 2003, www.noaa.gov
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De
pth
(m
)
4
6
8
10
12
14
16
18
20
0 1 2 3 4 5 6
Dissolved oxygen (ml/l)
Methane (nmol cm-3)
0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536
De
pth
(cm
)0
2
4
6
8
10
12
14
16
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
Ma
y 2
00
1Ju
ne
20
01
Oct
ob
er
20
01
De
cem
be
r 2
00
1
Ma
rch
20
02
Ma
y 2
00
2
July
20
02
Oct
ob
er
20
02
No
vem
be
r 2
00
2
Jan
ua
ry 2
00
3
Ma
rch
20
03
July
20
03
Au
gu
st 2
00
3S
ep
tem
be
r 2
00
3
De
cem
be
r 2
00
3
Ma
rch
20
04
Ma
y 2
00
4
Au
gu
st 2
00
1
Diffusive
sulfide flux
0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536m
mol
m-2
day
-10
2
4
6
8
10
12
Temporal variability
Periods of whole-water column depletion
Coincident hydrogen sulphide
and
methane pulses in the sediment
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.