NEWS | 28.07.2022

Labor­at­ory ex­per­i­ment iden­ti­fies as­phalt as a source for non-de­grad­able car­bon and sul­fur com­pounds in the ocean

MARUM Pub­lic­a­tion: Nat­ural As­phalt De­pos­its as an En­ergy Source in the Deep Sea

When oil is re­leased into the sea, it is not al­ways the res­ult of an oil spill. There are nat­ur­ally oc­cur­ring hy­dro­car­bon seeps on the ocean­floor where mi­croor­gan­isms use the es­cap­ing oil as a source for en­ergy and food. In a labor­at­ory ex­per­i­ment, re­search­ers from MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity of Bre­men and from the In­sti­tute for Chem­istry and Bio­logy of the Mar­ine En­vir­on­ment (ICBM) at the Uni­versity of Olden­burg, both members of the DAM, have dis­covered what hap­pens to the nat­ur­ally es­cap­ing wa­ter-sol­uble part of the oil. While a por­tion of it serves as a source of en­ergy and food for mi­croor­gan­isms, there are also non-bio­lo­gic­ally de­grad­able com­pon­ents that are re­leased and per­sist in the oceans for thou­sands of years. The team has pub­lished the res­ults of their labor­at­ory ex­per­i­ment in the in­ter­na­tional journal Environmental Science & Technology.

“Half of the oil in the oceans ori­gin­ates from nat­ural seeps. The other half comes from man-made pol­lut­ants. When we un­der­stand how long it takes for the tox­ins in the oil to de­grade and be trans­formed, then we can learn from nature,” ex­plains first au­thor Jo­nas Brünjes. The aim of the team of re­search­ers from MARUM and the Uni­versity of Olden­burg was to identify the wa­ter-sol­uble com­pon­ents of the oil and their mi­cro­bial de­grad­a­tion in the deep sea. When oil is re­leased as a res­ult of hu­man activ­ity, the amounts are of­ten so great that the eco­sys­tem is severely con­tam­in­ated and over­loaded. But at nat­ural seeps, the amounts re­leased are smal­ler, and the time scale much greater, so that the eco­sys­tem in the deep sea is more capabale to break it down. In a labor­at­ory ex­per­i­ment, Brünjes and his col­leagues tested ex­actly what hap­pens dur­ing this pro­cess.

They fo­cused primar­ily on heavy oil, or as­phalt. The ex­ist­ence of an as­phalt vol­cano was first de­scribed in the Gulf of Mex­ico with the dis­cov­ery of the Chapo­pote As­phalt Vol­cano in the south­ern Gulf, and this is where the samples were ob­tained for their labor­at­ory ex­per­i­ment. They were re­trieved dur­ing an ex­ped­i­tion of the RV MET­EOR in 2015.

For the ex­per­i­ment, ma­ter­ial was im­mersed from a wa­ter depth of about 2,500 meters and then stored in ar­ti­fi­cial sea­wa­ter for four weeks. Ar­ti­fi­cial sea­wa­ter was used be­cause it does not con­tain ad­di­tional or­ganic car­bon sources, but has all the nu­tri­ents needed for mi­cro­bial life. The labor­at­ory ex­per­i­ment re­vealed that the as­phalt was used as the sole car­bon source. “In the labor­at­ory, the bac­terial com­munit­ies that live at these kinds of nat­ur­ally toxic sites were able to col­on­ize the as­phalt. They form the base of the food web for higher or­gan­isms in the deep sea,” sum­mar­izes Dr. Florence Schubotz. She was the ini­ti­ator of the pro­ject and also col­lec­ted the samples.

The oil that seeps from the as­phalt vol­ca­noes is com­plex and con­tains com­pounds that are highly toxic for hu­mans. In the wa­ter-sol­uble frac­tion of the ex­per­i­ment, non-de­grad­able sul­fur com­pounds were found as well as black car­bon, which is known to per­sist in sea wa­ter for thou­sands of years. Un­til now, the only known source for these com­pounds was the soot that res­ults, for ex­ample, from forest fires.

This study forms the basis for fur­ther in­vest­ig­a­tions, par­tic­u­larly on the ele­ment cycles in the deep sea that are not yet com­pletely un­der­stood. In ad­di­tion to the purely quant­it­at­ive ap­proach of quan­ti­fy­ing mass budgets, there is also a qual­it­at­ive as­pect to study­ing the fate of hard-to-de­grade ma­ter­ial in the deep sea.

The aim of the sci­ent­ists is to learn from nature. This is why the de­grad­a­tion of heavy oil, among other com­pounds, is be­ing stud­ied at MARUM within the Cluster of Ex­cel­lence “The Ocean Floor – Earth’s Un­charted In­ter­face” un­der an­aer­obic and aer­obic con­di­tions. Jo­nas Brünjes has dealt with the lat­ter ex­per­i­ment­ally in his dis­ser­ta­tion.

Original publiCation

Jo­nas Brün­jes, Mi­cha­el Sei­del, Thors­ten Ditt­mar, Jut­ta Nig­ge­mann, and Flo­rence Schu­botz: Na­tu­ral Asphalt Seeps Are Po­ten­ti­al Sour­ces for Re­cal­cit­rant Ocea­nic Dis­sol­ved Or­ga­nic Sul­fur and Dis­sol­ved Black Car­bon. En­vi­ron­men­tal Sci­ence & Tech­no­lo­gy Ar­ti­cle ASAP. DOI: 10.1021/acs.est.2c01123


Further Information


ContaCt

MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences, Uni­versity of Bre­men
Jo­nas Brün­jes | jo­nas.bru­en­jes@uni-bre­men.de

MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences, Uni­versity of Bre­men
Dr. Flo­rence Schu­botz | fschubotz@marum.de

 


Header-Image: White mi­cro­bial mats settled on the as­phalt pieces in ar­ti­fi­cial sea­wa­ter after only a few days. Photo: MARUM / J. Brünjes

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