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11.11.2014 More Meth­ane from the Deep Sea

More Meth­ane from the Deep Sea
Mud-vol­ca­noes as meth­ane source
 
More methane from the deep sea
Mud-volcanoes as methane source

The mud-vol­cano Haakon Mosby in the Bar­ents sea near Nor­way emits yearly sev­eral hun­dred tons of meth­ane, a po­tent green­house gas. A re­search team, co­ordin­ated by the Max-Planck-In­sti­tute in Bre­men, re­ports on the res­ults of a long-term ob­ser­vat­ory in NATURE Com­mu­nic­a­tions. They col­lec­ted dur­ing 431 days data on tem­per­at­ure, pres­sure and pH and doc­u­mented us­ing a cam­era 25 erup­tions of mud and gas. Some of these erup­tions were so vi­ol­ent that the seabed to­po­graphy was pro­foundly changed. They cal­cu­lated that the mud-vol­cano may emit 10 times more meth­ane than pre­vi­ously as­sumed.

There are over 1000 ter­restrial mud-vol­canos known, and a grow­ing num­ber is found in the sea, between 200 and 4000 m depth, such as the Haakon Mosby Mud Vol­cano. Sci­ent­ists es­tim­ated that the sub­mar­ine vol­canos emit 27 Mil­lion tons of meth­ane, which is about 5% of the global emis­sion. This may be an un­der­es­tim­a­tion, as not all vol­ca­noes are found and be­cause they are not mon­itored by long term ob­ser­vat­or­ies.

The rhythm of mud-volcanoes
The ques­tion is whether sub­mar­ine mud-vol­ca­noes emit gas and mud con­tinu­ously or if they have now and then an out­burst? In a steady state a con­tinu­ous of gaseous mud flows through the chim­ney from large depth. A part of the gas goes into the sea­wa­ter, and a part is mi­cro­bi­ally con­ver­ted in the sed­i­ments. While as­sum­ing a steady flow sci­ent­ists have cal­cu­lated the emis­sion and con­ver­sion rates. Erup­tions have never been ob­served dur­ing vis­its with re­search ves­sels. To see such rare events, per­man­ent ob­ser­va­tions are needed. Such an in­stru­ment was de­veloped and used by the team of sci­ent­ist led by Dr. Dirk de Beer.
Figure 1: LOOME (Long Term Ob­ser­vat­ory On Mud-vol­cano Erup­tions) made ob­ser­va­tions on the Haakon Mosby Mud Vol­cano dur­ing 431 days. (Source Dirk de Beer, MPI Bre­men).
Figure 2: Scheme of the mud­vol­cano. It has a dia­meter of 1 kilo­meter but an el­ev­a­tion of only 10 meter. The ar­rows in­dic­ate the mud move­ments. The yel­low squares are the sensor po­s­i­tions. The LOOME-ob­ser­vat­ory is in­dic­ated in red. In the middle is the sig­nal of a gas plume vis­ible, that dis­ap­pears 500 meter be­low the sea­s­ur­face. At that depth it dos­solves in the sea­wa­ter and be­comes ac­cess­ible for meth­ane ox­id­iz­ing bac­teria. Source M. Schlösser, MPI Bre­men).
Figure 3: White mats of sul­fur bac­teria (Beg­gia­toa) dom­in­ate the bor­ders oft he mud vol­cano. The video cam­era doc­u­mented the erup­tions. (Source: WHOI)
Figure 4:The heavy temeprat­ure lance traveled 165 meter dur­ing its 431 days de­ploy­ment. (Source Ifre­mer).
A biological methane filter
It is be­lieved that a large part of the meth­ane does not reach the at­mo­sphere, be­cause it is mostly mi­cro­bi­ally con­ver­ted to CO2 in the seabot­tom. This ox­id­a­tion is driven by sulfate, by very slow grow­ing bac­teria that di­vide every 3-6 months. This mi­cro­bial fil­ter is there­fore very sens­it­ive for dis­turb­ances by erup­tions. The mi­cro­bial fil­ter works only ef­fi­ciently when the gas flow is slow and steady. When the gas flows fast, it will simply pass the fil­ter into the wa­ter column. An erup­tion would per­turb the sed­i­ment and the fil­ter gets totally des­troyed.

The long-term observatory
To see the oc­cur­rence and fre­quency of erup­tions, the sci­ent­ists placed a plat­form with a vari­ety of sensors on the Haakon Mosby Mud Vol­cano at 1200 meter depth. The vol­cano has a dia­meter of 1 kilo­meter and an el­ev­a­tion of only 10 m. While the bot­tom wa­ter is ice-cold, in­side the sed­i­ment the tem­per­at­ure in­creases rap­idly. Dr. Tom Feseker (MARUM cen­ter for mar­ine en­vir­on­mental sci­ences, Uni­versity of Bre­men): „We meas­ured in the cen­ter of the vol­cano at 1 meter depth a tem­per­at­ure of 25 C. The heat is car­ried from large depth by gas-rich flu­ids. “
The sci­ent­ists aimed with the LOOME ob­ser­vat­ory to find out if the gas hy­drates in the seabot­tom could be dis­in­teg­rated by this heat. In 2009 LOOME was de­ployed by the deep sea ro­bot Quest (MARUM). The sensors were placed on the most act­ive area, con­nec­ted by cables to the ob­ser­vat­ory. The ther­mo­met­ers showed sev­eral heat pulses, gas was lib­er­ated and el­ev­ated the seabot­tom in pulses by over 1 meter. The sed­i­ments slipped side­ways over sev­eral hun­derds of meters. After the series of erup­tions, the seabot­tom sub­sided gradu­ally to its ori­ginal el­ev­a­tion.
10 times more methane than thought
Dr. Dirk de Beer from the Max-Planck-In­sti­tute for Mar­ine Mi­cro­bi­o­logy and sci­entific leader of the LOOME pro­ject ex­plains: „The erup­tions are driven by gas that ori­gin­ates from large depths. Also the heat destabil­izes the gas hy­drates in the sur­face of the vol­cano and the meth­ane gets lib­er­ated. The gas reaches fi­nally the wa­ter column. We cal­cu­lated that to drive these erup­tions at least 10 times more gas is emit­ted that pre­vi­ously as­sumed. Most of the gas may not reach the at­mo­sphere, but gets di­luted in the sea­wa­ter where it can be ox­id­ized by aer­obic bac­teria.“

A study of the ba­thy­met­ric maps made since 2003 showed in­deed drastic changes of the seabot­tom to­po­graphy. Re­mark­ably, no signs were ob­served of mud flow­ing out of the vol­cano. That means that the mov­ing mud is re­cycled in­side the vol­cano. The ho­ri­zontal move­ment of the mud could pre­cisely be re­con­struc­ted, as a 20 m long and 2 ton heavy tem­per­at­ure lance moved in the year a dis­tance of 165 m.
An im­port­ant con­clu­sion of the study is that the mi­cro­bial fil­ter is des­troyed reg­u­larly by the erup­tions, and has no time to grow back in between. Prof. Dr. Antje Boe­t­ius, cruise leader dur­ing de­ploy­ment and re­cov­ery, says: „We have learned a lot from the year-long ob­ser­va­tions. As it was the first in its kind, we got unique data on the vol­cano and its in­flu­ence on the en­vir­on­ment. Since erup­tions of such vol­ca­noes can cause large ava­lanches and form sig­ni­fic­ant sources of meth­ane, we should de­ploy more long-term ob­ser­vat­or­ies.“
Manfred Schlösser
Request for information:
Dr. Dirk de Beer, Max-Planck-In­sti­tute for Mar­ine Mi­cro­bi­o­logy, Tel. +49 421 2028 802,
dbeer@mpi-bre­men.de

Dr. Tom Feseker, MARUM-Zen­trum für mar­ine Um­weltwis­senschaften Fachbereich Geowis­senschaften der Uni­versität Bre­men, feseker@uni-bre­men.de

Prof. Dr. Antje Boe­t­ius, Al­fred –We­gener-In­sti­tute and Max-Planck-In­sti­tut for Mar­ine Mi­cro­bi­o­logy, Tel. +49 421 2028 860, antje.boe­t­ius@awi.de

or the PR per­son:
Dr. Man­fred Schloesser, Max-Planck-In­sti­tut for Mar­ine Mi­cro­bi­o­logy, Tel.: 0421 2028704, mschloes@mpi-bre­men.de

Original title:
Erup­tion of a deep-sea mud vol­cano trig­gers rapid sed­i­ment move­ment
To­mas Feseker, Antje Boe­t­ius, Frank Wen­zhöfer, Jerome Blandin, Karine Olu, Dana R. Yo­er­ger, Richard Ca­m­illi, Chris­topher R. Ger­man, Dirk de Beer.
Nature Com­mu­nic­a­tions, Novem­ber 2014,
doi:10.1038/​ncomms6385

Contributing institutes
Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy, 28359 Bre­men, Ger­many
MARUM - Cen­ter for Mar­ine En­vir­on­mental Sci­ences and Fac­ulty of Geosciences, Uni­versity of Bre­men, 28359 Bre­men, Ger­many
GEO­MAR, Helm­holtz Centre for Ocean Re­search Kiel, 24148 Kiel, Ger­many
HGF-MPG Group for Deep Sea Eco­logy and Tech­no­logy, Al­fred We­gener In­sti­tute for Po­lar and Mar­ine Re­search in the Helm­holtz As­so­ci­ation, 27515 Bremer­haven, Ger­many
IFRE­MER, In­sti­tut Carnot EDROME, RDT/ SI2M F-29280 Plouz­ané, France
IFRE­MER, In­sti­tut Carnot EDROME, REM/​EEP, Labor­atoire En­viron­nement Pro­fond, F-29280 Plouz­ané, France
Woods Hole Ocean­o­graphic In­sti­tu­tion, Woods Hole, MA 02543, USA


Links:

http://www.mpi-bremen.de/Forschung_am_Tiefsee-Schlammvulkan_Haakon_Mosby.html

http://www.esonet-emso.org/ (Web­seite Europäis­cher Meeres­boden Ob­ser­vat­orien)


Acknowledgements: LOOME was paid via the EU pro­gram ESONET, the Helm­holtz Found­a­tion, the Max-Planck-So­ci­ety and the Leib­niz-pro­gramm of the DFG.
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