you're reading...


Enormous Source and Sink of Hydrocarbons Discovered in the Ocean

Citation: Love, C. R., Arrington, E. C., Gosselin, K. M., Reddy, C. M., Van Mooy, B. A. S., Nelson, R. K., & Valentine, D. L. (2021). Microbial production and consumption of hydrocarbons in the global ocean. Nature Microbiology, 6, 489–498. https://doi.org/10.1038/s41564-020-00859-8

Hydrocarbons are organic molecules consisting of purely carbon and hydrogen, and they are the main ingredients in the oil and natural gas that currently power our energy grid. Hydrocarbons are the heated and pressurized remnants of long-dead marine organisms, and as a result, many oil and gas reservoirs are often located below the seafloor. However, extracting subseafloor hydrocarbons is risky, as they can wreak havoc on marine ecosystems if they’re accidentally released into the water.

Currently, known hydrocarbon sources to the ocean are both natural and human-caused, and include natural oil and gas seeps, as well as coastal runoff and oil spills. But in 2015, scientists from the University of Cambridge discovered a potential new source: cyanobacteria, which they found produces a hydrocarbon called pentadecane when cultured in the laboratory.

Figure 1: A ball-and-stick chemical diagram of pentadecane, where black spheres represent carbon atoms (15 in total) and light grey spheres represent hydrogen atoms. (Image Source: Wikimedia Commons)

Pentadecane is a long-chain hydrocarbon (Figure 1), consisting of 15 carbon atoms bonded together in a chain and surrounded (or saturated) with hydrogen atoms. Pentadecane is much longer than the short-chain hydrocarbons more commonly found in oil and gas, such as methane (1 carbon), propane (4 carbons), and pentane (5 carbons). While the 2015 study indicated that pentadecane could be produced by cyanobacteria under idealized laboratory conditions, a research team from the University of California: Santa Barbara (UCSB) and the Woods Hole Oceanographic Institution (WHOI) set out to investigate whether pentadecane was actually being made in the ocean, and if so, how abundant it was.

Probing for Pentadecane

Figure 2: Location of the nutrient-poor Sargasso Sea in the Atlantic Ocean. (Image Source: Wikimedia Commons)

The researchers sampled a nutrient-poor area of the ocean called the Sargasso Sea (Figure 2) to search for pentadecane and the cyanobacteria that might produce it. However, the researchers had to be very careful when collecting their water samples. Pentadecane was a component of the diesel fuel being burned by their research vessel, so the water samples needed to be collected upwind of the exhaust pipes to prevent contamination from the ship itself. Back in the lab, the team found high concentrations of pentadecane in Sargasso Sea water samples, but confirmed that the samples were free of other components of diesel fuel. This verified that the pentadecane they measured had come from the sampled water, rather than the air surrounding the ship.

Based on their measurements of pentadecane in 7 different Sargasso Sea locations, and based on the microorganisms present in those samples, the team discovered that just two types of cyanobacteria – Prochlorococcus and Synecococcus – produce between 300 and 600 million metric tons of pentadecane in our oceans every year. This quantity is 100-500 TIMES larger than all other known hydrocarbon inputs to the ocean combined.

But while 300-600 million metric tons is an enormous number, and appears to dwarf our own contribution as humans, the scientists caution that other microorganisms (like archaea) consume pentadecane almost immediately after it’s produced. Therefore, it doesn’t lead to any overall change in hydrocarbon concentration. This is called a “cryptic” cycle, and might explain how we missed this major hydrocarbon source for so long. Just as water in your shower doesn’t accumulate, but immediately flows out the drain, pentadecane doesn’t accumulate in the ocean.

Implications for Oil Spills?

Given their findings, the research team wondered if the cryptic pentadecane cycle was somehow helping “prime” ocean microorganisms to consume the short-chain hydrocarbons found in oil and natural gas. In other words, was the steady consumption of pentadecane teaching marine microorganisms how to clean up after natural oil seeps or oil spills?

The team returned to the lab to test whether the microorganisms consuming pentadecane in the Sargasso Sea could break down oil as well. They added pentane (a hydrocarbon commonly found in oil) to samples of their original seawater, as well as to other samples retrieved from the Gulf of Mexico, where there’s a lot of natural (and unnatural) oil seepage. After monitoring the growth of microorganisms in each sample, the team found that pentadecane consumers were unable to consume pentane, suggesting that these abilities are entirely separate. Even more interestingly, the speed with which microorganisms in a sample could consume pentane was directly related to how close that sample was collected to an existing oil seep. Growth of pentane-consuming microbes in Gulf of Mexico samples was about 9 times faster than their growth in Sargasso Sea samples, likely because Gulf of Mexico microorganisms have more frequent exposure to oil.

Figure 3: Surface water in the Gulf of Mexico on Day 30 of the Deepwater Horizon oil spill in 2010. (Image Source: Green Fire Productions)

The distinction the researchers discovered between oil consumption and pentadecane consumption is a stark reminder that although the ocean has developed mechanisms to deal with localized, natural hydrocarbon inputs, non-natural inputs are a very critical problem (Figure 3). The study demonstrated that different regions of the ocean respond very differently to oil spills, and while biological remediation is an important tool to have in our arsenal, the best strategy is clearly to prevent hydrocarbon pollution in the first place.


No comments yet.

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com