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Ob­serving the de­vel­op­ment of a deep-sea green­house gas fil­ter

Sep 28, 2018

It takes time to do a thing well, this also and specifically applies to the deep sea. In a long-term study, marine scientists from Bremen for the first time observed the colonization of a deep-sea mud volcano after its eruption. Only slowly, rich life develops around the crater. The first settlers are tiny organisms that eat methane escaping from the volcano. Thereby, they keep this greenhouse gas from reaching the atmosphere. By and by, other microbes and eventually higher organisms settle. The present study describes how the colonization of the mud volcano proceeds and when the tiny methane-munchers get going.

Large quant­it­ies of the green­house gas meth­ane are stored in the seabed. For­tu­nately, only a small frac­tion of the meth­ane reaches the at­mo­sphere, where it acts as a cli­mate-rel­ev­ant gas, as it is largely de­graded within the sed­i­ment. This de­grad­a­tion is car­ried out by a spe­cial­ized com­munity of mi­crobes, which re­moves up to 90 per­cent of the es­cap­ing meth­ane. Thus, these mi­crobes are re­ferred to as the “mi­cro­bial meth­ane fil­ter”. If the green­house gas were to rise through the wa­ter and into the at­mo­sphere, it could have a sig­ni­fic­ant im­pact on our cli­mate.

But not every­where the mi­crobes work so ef­fi­ciently. On sites of the sea­floor that are more tur­bu­lent than most oth­ers – for ex­ample gas seeps or so-called un­der­wa­ter vol­ca­noes -, the mi­crobes re­move just one tenth to one third of the emit­ted meth­ane. Why is that? Emil Ruff and his col­leagues from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy and the Uni­versity of Bre­men aimed to an­swer this ques­tion

Meth­ane con­sump­tion around a mud vol­cano

In the North Sea off Nor­way at 1250 meters wa­ter depth lies the Håkon Mosby mud vol­cano. There, warm mud from deeper lay­ers rises to the sur­face of the sea­floor. In a long-term ex­per­i­ment, Ruff and his col­leagues were able to film the erup­tion of the mud, take samples and ex­am­ine them closely. “We found sig­ni­fic­ant dif­fer­ences in the dif­fer­ent com­munit­ies on-site. In fresh, re­cently erup­ted mud there were hardly any or­gan­isms. The older the mud, the more life it con­tained”, says Ruff. Within a few years after the erup­tion, the num­ber of mi­croor­gan­isms as well as their di­versity in­creased ten­fold. Also, the meta­bolic activ­ity of the mi­cro­bial com­munity in­creased sig­ni­fic­antly over time. While there were meth­ane con­sumers even in the young mud, ef­fi­cient fil­ter­ing of the green­house gas seems to oc­cur only after dec­ades.

 

“This study has given us new in­sights into these unique com­munit­ies," says Ruff. "But it also shows that these hab­it­ats need to be pro­tec­ted. If the meth­ane-munch­ers are to con­tinue to help re­move the meth­ane, then we must not des­troy their hab­it­ats with trawl­ing and deep-sea min­ing. These hab­it­ats are al­most like a rain­forest - they take dec­ades to grow back after a dis­turb­ance. "

View from above onto the surroundings of the Håkon Mosby mud volcano. Freshly erupted muds flowing across consolidated muds that are covered with white mats of sulfur-oxidizing bacteria. In the middle of the picture you can see the long-term observatory LOOME (Long-term observation of mud volcano eruptions), which spent 12 months on the seafloor taking pictures and measurements. (© Woods Hole Oceanographic Institution)
View from above onto the surroundings of the Håkon Mosby mud volcano. Freshly erupted muds flowing across consolidated muds that are covered with white mats of sulfur-oxidizing bacteria. In the middle of the picture you can see the long-term observatory LOOME (Long-term observation of mud volcano eruptions), which spent 12 months on the seafloor taking pictures and measurements. (© Woods Hole Oceanographic Institution)

In­ter­na­tional deep-sea re­search

Antje Boe­t­ius, co-au­thor of the study, dir­ector of the Al­fred We­gener In­sti­tute Helm­holtz Cen­ter for Po­lar and Mar­ine Re­search (AWI) and head of the re­search group for deep-sea eco­logy and tech­no­logy at the Max Planck In­sti­tute in Bre­men and the AWI, em­phas­izes the im­port­ance of na­tional and in­ter­na­tional re­search  co­oper­a­tions to achieve such re­search res­ults: "This study was only pos­sible through the long-term co­oper­a­tion between the AWI, the MARUM - Cen­ter for En­vir­on­mental Sci­ences of the Uni­versity of Bre­men and the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy with in­ter­na­tional part­ners in Nor­way, France and Bel­gium. Through vari­ous EU pro­jects, we have been able to use unique deep-sea tech­no­lo­gies to study the Håkon Mosby mud vol­cano and its in­hab­it­ants in great de­tail”, says Boe­t­ius.

 

 

The submersible takes samples in the mud around Håkon Mosby mud volcano. With this tube so-called sediment cores can be taken, which allow an insight into the community of organisms on the surface and deeper in the sediment. (© MARUM – Centre for Marine Environmental Sciences, University of Bremen)
The submersible takes samples in the mud around Håkon Mosby mud volcano. With this tube so-called sediment cores can be taken, which allow an insight into the community of organisms on the surface and deeper in the sediment. (© MARUM – Centre for Marine Environmental Sciences, University of Bremen)

Re­lated Links:

Video footage from Håkon Mosby Mud Volcano

Earlier press release on HMMV

Interview with Emil Ruff

Ori­ginal Pub­lic­a­tion:

S. E. Ruff, J. Felden, H. R. Gruber-Vodicka, Y. Mar­con, K. Knit­tel, A. Ramette, A. Boe­t­ius: In situ development of a methanotrophic microbiome in deep-sea sediments. The ISME Journal. Pub­lished on­line 28 Au­gust 2018.

https://www.nature.com/articles/s41396-018-0263-1
https://doi.org/10.1038/s41396-018-0263-1

Håkon Mosby mud volcano

Named after the Nor­we­gian ocea­no­gra­pher Hå­kon Mos­by, this mud vol­cano was dis­covered in 1990 by an in­ter­na­tional team of re­search­ers in the Bar­ents Sea at a depth of 1250 meters. Be­sides wa­ter and mud, also gas emerges from the cen­ter of the vol­cano, which cov­ers ap­prox­im­ately one square kilo­metre. The gas, which rises from about two kilo­metres be­low the sea floor, con­sists of 99 per­cent meth­ane.

Hå­kon Mos­by is a very flat mud vol­cano with a max­imum height of ten meters. Sur­round­ing the crater are three dis­tinct cir­cu­lar zones: the cen­ter, the middle and the outer ring. En­tirely dif­fer­ent com­munit­ies in­habit these three zones, yet they have one thing in com­mon: meth­ane is the main food source of the or­gan­isms on site. Most of the gas is con­sumed in the outer zone, which can be ex­plained as fol­lows: In the cent­ral and middle zone large quant­it­ies of meth­ane are avail­able, however there is a lack of oxy­gen or sulfate re­quired to ox­id­ize the meth­ane. In the outer zone, the situ­ation is dif­fer­ent: Tube­worms, which grow up to 60 cm deep into the sea­floor, act­ively pump sea­wa­ter and thereby sulfate into deeper lay­ers of the sed­i­ment. Thanks to these “liv­ing pumps”, or­gan­isms liv­ing at their “roots” can use meth­ane even in re­gions where that nor­mally would­n’t be pos­sible. There, hardly any gas es­capes to the wa­ter column. This clearly shows how the com­plex in­ter­ac­tion of com­munit­ies on and in the ocean floor is a pre­requis­ite for the de­vel­op­ment of an ef­fi­cient bio­lo­gical fil­ter for a green­house gas.

Please dir­ect your quer­ies to:

Dr. Emil Ruff

Uni­versity of Cal­gary

Email:emil.ruff@ucalgary.ca

Phone: +1 (403) 210-7457

Dr. Fanni Aspetsberger

Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy

Email: presse@mpi-bremen.de

Phone: +49 421 2028 947

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