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2 February 2021

by Harrison Tasoff, University of California – Santa Barbara

Hydrocarbons and petroleum are almost synonymous in environmental science After all, oil reserves represent almost all the hydrocarbons we encounter But the few hydrocarbons that trace their origin to biological sources may play a more important ecological role than scientists originally suspected

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A team of researchers from UC Santa Barbara and the Woods Hole Oceanographic Institution studied this previously neglected oceanographic area for signs of a neglected global cycle.They also tested the impact of its existence on the response. from the ocean to oil spills.

“We have demonstrated that there is a massive and rapid oil cycle occurring in the ocean, and that it is distinct from the capacity of the ocean to respond to petroleum inputs”, said Professor David Valentine, holder of the Norris Presidential Chair in the Department of Earth Sciences at UCSB Research, led by its graduate students Eleanor Arrington and Connor Love, appears in Nature Microbiology

In 2015, an international team led by scientists from the University of Cambridge published a study showing that the pentadecane hydrocarbon was produced by marine cyanobacteria in laboratory cultures Researchers extrapolated that this compound could be important in the ocean The molecule seems to relieve stress in curved membranes, so it's found in things like chloroplasts, where tightly compacted membranes require extreme curvature, explained Valentine. Some cyanobacteria still synthesize the compound, while other ocean microbes easily consume it for energy

Valentine wrote a two-page commentary on the article, with Chris Reddy from Woods Hole, and decided to dig deeper into the subject with Arrington and Love They visited the Gulf of Mexico in 2015, then the western Atlantic in 2017, to collect samples and conduct experiments.

The team sampled seawater in a nutrient-poor region of the Atlantic known as the Sargasso Sea, named after the floating sargassum seaweed carried into the Gulf of Mexico. It’s beautiful water, clear and blue with Bermuda in the middle, said Valentine

Obtenir les échantillons était apparemment une entreprise plutôt délicate Le pentadécane étant un hydrocarbure courant dans le carburant diesel, l’équipe a dû prendre des précautions supplémentaires pour éviter la contamination du navire lui-même. Ils ont demandé au capitaine de mettre le navire au vent pour que l’échappement ne ternisse pas les échantillons et ils ont analysé la signature chimique du diesel pour s’assurer qu’il n’était pas la source du pentadécane qu’ils avaient trouvé.

Moreover, personne ne pouvait fumer, cuisiner ou peindre sur le pont pendant que les chercheurs collectaient de l’eau de mer «C’était un gros problème», said Valentine, «je ne sais pas si vous avez déjà été sur un bateau pendant une période prolongée, mais vous peignez tous les jours C’est comme le Golden Gate Bridge: vous commencez à une extrémité et au moment où vous arrivez à l’autre extrémité, il est temps de recommencer

Les précautions ont fonctionné et l’équipe a récupéré des échantillons d’eau de mer immaculés «Debout devant le chromatographe en phase gazeuse à Woods Hole après l’expédition de 2017, il était clair que les échantillons étaient propres sans aucun signe de diesel», a déclaré le co-auteur principal Love «Le pentadécane était indubitable et montrait déjà des schémas océanographiques clairs, même dans les deux premiers échantillons que [we] avons analysés

En raison de leur grand nombre dans l’océan mondial, a poursuivi Love, “seuls deux types de cyanobactéries marines ajoutent jusqu’à 500 fois plus d’hydrocarbures à l’océan par an que la somme de tous les autres types d’intrants pétroliers dans l’océan, y compris les suintements d’hydrocarbures naturels, les déversements d’hydrocarbures, les déversements de carburant et les écoulements de terre«Ces microbes produisent collectivement 300 at 600 millions de tonnes métriques de pentadécane par an, une quantité qui éclipse le 13 million metric tonnes of oil released from all other sources

Although these quantities are impressive, they are a little misleading The authors point out that the pentadecane cycle covers 40% or more of the Earth's surface and that more than a trillion quadrillion cyanobacterial cells loaded with pentadecane are suspended in the sunny region of the world ocean. However, the life cycle of these cells is usually less than two days As a result, researchers estimate that the ocean contains only about 2 million metric tons of pentadecane at any one time

It's a spinning wheel that spins quickly, explained Valentine, donc la quantité réelle présente à tout moment n’est pas particulièrement importanteTous les deux jours, vous produisez et consommez tout le pentadécane de l’océan”, did he declare

In the future, les chercheurs espèrent relier la génomique des microbes à leur physiologie et écologie L’équipe dispose déjà de séquences génomiques pour des dizaines d’organismes qui se sont multipliés pour consommer le pentadécane dans leurs échantillonsLa quantité d’informations disponibles est incroyable”, said Valentine, “et je pense que cela révèle à quel point nous ne savons pas à quel point nous ne savons pas sur l’écologie de nombreux organismes consommateurs d’hydrocarbures.

After confirming the existence and extent of this biohydrocarbon cycle, the team sought to consider whether his presence could prompt the ocean to break down the spilled oil. The key question, Arrington explained, is whether these abundant pentadecane-consuming microorganisms are active in cleaning up oil spills. To study this, they added pentane – a petroleum hydrocarbon similar to pentadecane – seawater sampled at various distances from natural oil seeps in the Gulf of Mexico.

Ils ont mesuré la respiration globale de chaque échantillon pour voir combien de temps il a fallu aux microbes mangeurs de pentane pour se multiplier Les chercheurs ont émis l’hypothèse que, si le cycle du pentadécane amorçait vraiment les microbes à consommer également d’autres hydrocarbures, alors tous les échantillons devraient développer des proliférations à des taux similaires.

Mais ce n’était pas le cas Des échantillons provenant de près des suintements de pétrole ont rapidement développé des fleursEnviron une semaine après l’ajout du pentane, nous avons vu une population abondante se développer”, said Valentine. «Et cela devient de plus en plus lent à mesure que vous vous éloignez, until, when you are in the North Atlantic, you can wait for months and never see a flower”In fact, Arrington had to stay behind after the expedition to the Woods Hole facility, Massachusetts to continue the experiment on samples from the Atlantic because these flowers took so long to appear.

Interesting fact, the team also found evidence that microbes from another area of ​​life, archaea, may also play a role in the pentadecane cycle “We have learned that a group of mysterious and abundant microbes in the world – that have not yet been domesticated in the laboratory – could be powered by pentadecane in the surface ocean”, said co-lead author Arrington.

The results raise questions as to why the presence of a huge pentadecane ring seems to have no effect on the degradation of petrochemical pentane “Petroleum is different from pentadecane”, said Valentine, “and you need to understand what the differences are and what compounds actually make up oil, to understand how microbes in the ocean will react to it.”

Ultimately, the genes commonly used by microbes to consume pentane are different from those used for pentadecane «A microbe living in the clear waters off Bermuda is much less likely to encounter petrochemical pentane than pentadecane produced by cyanobacteria, and is therefore less likely to carry the genes for pentane consumption», said Arrington

Many microbial species can consume pentadecane, but that does not mean that they can also consume other hydrocarbons, continued Valentine, particularly given the diversity of hydrocarbon structures that exist in oil. Marine organisms produce less than a dozen common hydrocarbons, including pentadecane and methane Meanwhile, le pétrole comprend des dizaines de milliers d’hydrocarbures différents De plus, nous constatons maintenant que les organismes capables de décomposer des produits pétroliers complexes ont tendance à vivre en plus grande abondance à proximité de suintements naturels de pétrole.

Valentine appelle ce phénomène «amorçage biogéographique» – lorsque la population microbienne de l’océan est conditionnée à une source d’énergie particulière dans une zone géographique spécifiqueEt ce que nous voyons avec ce travail est une distinction entre le pentadécane et le pétrole”, he said, “qui est importante pour comprendre comment les différentes régions océaniques réagiront aux déversements d’hydrocarbures.

Nutrient poor gyres such as the Sargasso Sea represent 40% of the Earth's surface But, ignoring the earth, that still leaves 30% planet to explore for other biohydrocarbon cycles Valentine believes processes in higher productivity regions will be more complex and possibly provide more priming for oil consumption He also pointed out that the plan for the nature for the organic production of hydrocarbons held promise for efforts to develop the next generation of green energy.

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Research, Hydrocarbons, Océanographie, Ocean, Biology

News – GB – Researchers discover huge hydrocarbon cycle in the global ocean
Associated title :
Researchers discover huge hydrocarbon cycle in the global ocean &

Source: https://phys.org/news/2021-02-immense-hydrocarbon-world-ocean.html

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