Page path:
  • Press Of­fice
  • 23.08.2016 Di­versity of hab­it­ats at nat­ural oil...

23.08.2016 Di­versity of hab­it­ats at nat­ural oil seeps

Aug 23, 2016
A research team investigates the allegedly inhospitable sea-floor area in the southern Gulf of Mexico - and finds it surprisingly diverse and multifaceted.
 
Based on a marum press release.
Habitats surrounding natural oil seeps on the sea floor are multifaceted and diverse. During an expedition organized by MARUM, an international team of researchers including participants from the Max Planck Institute for Marine Microbiology (MPI Bremen) discovered gas-bubble streams, massive gas hydrates, oil-soaked sediments, and deposits of heavy oil, all closely spaced at a depth of around three kilometers. Each of the different constituents - gas, light oil, and heavy oil congealed to asphalt - is home to its own characteristic group of organisms. The scientists have now published their initial results, along with photos from the remotely operated vehicle MARUM-QUEST, in the journal Biogeosciences.
 
“Re­cent years have seen a minor re­volu­tion in the field of mar­ine re­search,” ex­plains Heiko Sah­ling from MARUM, the Cen­ter for Mar­ine En­vir­on­mental Sci­ences, and the Geosciences De­part­ment of the Uni­versity of Bre­men. Many Ger­man re­search ships have been out­fit­ted with state-of-the-art mult­i­beam echo­sounders. These are of great help in the sys­tem­atic search for nat­ural seeps of oil and gas on the sea floor. “In the past, this was more like the pro­ver­bial search for a needle in a hay­stack”, says Sah­ling. “Now we have dis­covered hab­it­ats on the sea floor that were un­known be­fore.”
 
MARUM - Center for Marine Environmental Sciences
Asphaltstrukturen am Mictlan Knoll in 3100 Meter Tiefe, aufgenommen mit dem Tiefseerobotoer MARUM-QUEST.
Sci­ent­ists use the echo­sounders to de­tect gas bubbles in the wa­ter column. Hy­dro­car­bons leak­ing from the sea­floor amp­lify the acous­tic sig­nal in the wa­ter, and to some ex­tent also within the sea floor. The team of sci­ent­ists from Bre­men, Kiel, Vi­enna (Aus­tria), Mex­ico City (Mex­ico) and Ta­la­hassee (USA) now ap­plied this mod­ern tech­no­logy dur­ing an ex­ped­i­tion to the Bay of Campeche in the south­ern Gulf of Mex­ico. There they dis­covered hun­dreds of gas seeps and in­vest­ig­ated a num­ber of them in de­tail with the sub­mers­ible vehicle MARUM-QUEST. Their goal was to re­veal the ways of hy­dro­car­bon move­ment at nat­ural seeps. In what form are they re­leased? How do they af­fect the local or­gan­isms? How rap­idly does the oil break down? What hap­pens to the re­leased gas?
 

“The gas is partly con­ver­ted to gas hy­drates (an ice-like form of wa­ter and gas), which form small mounds on the sea floor. These are densely pop­u­lated by meter-long tube worms,” ex­plains Sah­ling. “Some­times the mounds are prised, al­low­ing a view into sev­eral-meter-thick gas hy­drates, a very rare ob­ser­va­tion. The gas hy­drates are over­lain by a re­ac­tion zone where mi­cro­bial com­munit­ies con­vert meth­ane, car­bon­ate is pre­cip­it­ated, and dense colon­ies of tube worms de­velop. These keep the mounds to­gether and live on re­duced sul­fur com­pounds. It is truly a re­mark­able hab­itat,” Sah­ling sim­mar­izes.

In ad­di­tion to the gas, also li­quid oil es­capes from the sea floor. It as­cends slowly through small white chim­neys, the drops of oil form­ing elong­ated threads or seep­ing through the sed­i­ments. “For or­gan­isms that are not ad­ap­ted, the oil is harm­ful,” Sah­ling ex­plains. “But the boun­ti­ful life at these sites shows that there are cer­tain or­gan­isms that can thrive even on these hy­dro­car­bons.”

The basis for this life is formed by mi­croor­gan­isms which de­grade the vari­ous com­pon­ents of the oil. They are the fo­cus of re­search at the MPI Bre­men. Many of these mi­croor­gan­isms live an­aer­obic­ally, i.e. without oxy­gen, in the oily sed­i­ments. Gunter We­gener from MPI Bre­men cur­rently in­vest­ig­ates which mi­croor­gan­isms are ac­tu­ally us­ing the as­phalt and its con­stitu­ents „What’s really ex­cit­ing is that very dif­fer­ent mi­croor­gan­isms – namely bac­teria and so-called ar­chaea – join forces to break up the hy­dro­car­bons. We call this a syn­trophy.“ Other bac­teria de­grad­ing hy­dro­car­bons can­not live without oxy­gen. As a res­ult, their part­ner­ships look quite dif­fer­ent: They form sym­bi­oses with in­ver­teb­rates. „We find these bac­terial ten­ants in mus­sels and dif­fer­ent sponges in­hab­it­ing the the oily crusts and blick of gas hy­drates“, says Chris­tian Borowski from MPI Bre­men. „It’s note­worthy that these sym­bionts are closely re­lated to bac­teria that played a ma­jor role in de­grad­ing hy­dro­car­bons in the Gulf of Mex­ico after the Deep-Wa­ter-Ho­ri­zon-Oilspill.“ Re­search­ers at the MPI Bre­men now in­vest­ig­ate, which meta­bolic path­ways the sym­bi­otic bac­teria use, and which role the play fort he host.

While these bac­terial pro­cesses are not ap­par­ent to the eye, the oil seeps do al­low for some spec­tac­u­lar views. Some com­pon­ents of the so-called “heavy oil” dis­sip­ate. What re­mains forms flow struc­tures of as­phalt on the sea floor. “Dur­ing the ex­ped­i­tion we doc­u­mented many of these unique struc­tures,” says Sah­ling. “The as­phalt cov­ers hun­dreds of meters of the sea floor and thus also forms a hab­itat that is col­on­ized by tube worms and bac­terial mats."

 
 
Back to Top