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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

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slide1

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

slide2

The diatomaceous mud belt off central Namibia

Porosity > 90%

Diatom-rich

Organic-C: > 12 % dry wt

Accumulation rates:

50 – 1000 g/m2/a

Coastal upwelling

high primary productivity

slide3

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
Water column oxygen profiles and bottom water images

No free gas, low hydrogen sulphide

Shallow gas: Bacterial mats of

Beggiatoa and Thiomargarita

hydrogen sulphide profile in the water column

0

50

100

150

200

250

300

350

Hydrogen sulphide profile in the water column

Concentration (mM)

0

Sulphide µM

20

Oxygen µM

Oxygen

40

Depth (m)

60

80

Seawater

100

H2S

Sediment

Methane

seismo acoustics
Seismo acoustics
  • Parametric sediment echosounder Parasound – Paradigma (Frequency: 2-5 kHz)
  • Parametric sediment echosounderSES96 (Frequency: 4-12 kHz )
  • Linear sediment echosounderSEL96 (Frequency: 5-20 kHz)
  • Sparker seismics
sel96 echogram transition from gas free mud partially gas filled crater structures gas saturated
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

slide10
Efficient anaerobic oxidation of methane by sulfate in areas where the depth of free gas is greater than than one meter

Emeis, Brüchert et al. (2004)

evidence for gas escape from the sediment
Evidence for gas escape from the sediment

Bubbles tracked by echosounder

Meteor M 57-3

slide14

Lobster kills

Turquoise, elemental sulfur-containing surface water

slide15

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

slide16

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.

Publications