The Ocean Methane Paradox
Vast regions of the world’s surface ocean which are richly oxygenated are strangely super-saturated with methane.
Since oxygen rapidly destroys methane the only way for that super-saturation of methane to exist is if there is a steady supply of new methane being produced in those oxygen rich surface waters.
But methane is an anaerobic (oxygen free) process… right… oops wrong!
When one looks at global methane maps the most striking thing is that the oceans are a substantial source. They ought to be next to nothing as methane has been thought of as an anaerobic process, one that takes place in the absence of oxygen, only in the deepest abyss might such methane production occur and it takes millennia for deep ocean water to reach the surface.
A New Ocean Ecology Is Emerging
Some incredible ocean sleuthing has been going on for about 10 years trying to find the answer that might explain the ocean methane paradox. It now becomes clear that ocean pasture phytoplankton ecology under stress favours a new ecology of methanogenic species. This new ocean pasture ecology survives on ocean pastures under productivity stress where life has found a way to survive by scavenging vital nutrients not previously believed to be available. As ocean pastures become more and more depleted the shift to scavenger ecology becomes a potent source of methane. And this becomes a real problem as there is just so much ocean in this condition, perhaps as much as 50% of our blue planet.
In a ocean methane paper in Nature in the November 14, 2016 issue of the journal Nature Geoscience, Repeta and colleagues at the University of Hawaii found that much of the ocean’s dissolved organic matter is made up of novel polysaccharides—long chains of sugar molecules created by photosynthetic bacteria in the upper ocean. Bacteria begin to slowly break these polysaccharides, tearing out pairs of carbon and phosphorus atoms (called C-P bonds) from their molecular structure. In the process, the microbes create methane, ethylene, and propylene gases as byproducts. Most of the methane escapes back into the atmosphere.
“All the pieces of this puzzle were there, but they were in different parts, with different people, in different labs, at different times,” says Dan Repeta of Woods Hole Oceanographic Institute. “This paper unifies a lot of those observations.”
Methane is a potent greenhouse gas, and it is important to understand the various sources of methane in the atmosphere. The research team’s findings describe a totally new pathway for the microbial production of methane in the environment, that is very unlike all other known pathways.
In 2009, one of Repeta’s co-authors, David Karl one of the world’s most famous ocean scientists, found an important clue to the puzzle. In the lab, he added a manmade chemical called methylphosphonate to samples of seawater and the samples immediately started making methane. But this was just a clue as methylphosphonate has never been detected in the ocean.
Repeta and his team reasoned that bacteria in the wild must be finding another natural source of a similar substance. Exactly what that source was, however, remained elusive. Eventually trying many natural substances they added pure polysaccharides isolated from seawater. Once those were in their seawater soup it began bubbling out large amounts of methane.
That made them think it’s a two-part system. You have one species that makes the special nutrient and another species that can make use of that nutrient.
The middle of the ocean is a highly nutrient-limited system, it rarely blooms even more so in this age of dying ocean pastures. To make DNA, RNA, and proteins, you need a thriving ocean pasture ecosystem. Instead of using the commonly known and much studied free-floating nutrients in the water studies have shown that the microbes that thrive on dying ocean pastures must somehow be able to crack into and obtain nutrient resources bound up and thought to be unavailable deep inside organic molecules.
“Think of it like a buffet,” Repeta says. “If you’re a microbe, inorganic nutrients are like fruits and meats and all the tasty stuff that you reach for immediately. Organic nutrients are more like leftover liver. You don’t really want to eat it, but if you’re hungry enough, you will. It takes years for bacteria to get around to eating the organic phosphorus in the upper ocean. We don’t exactly know why, but there’s another really interesting story there if we can figure it out.”
Global Methane Crisis
Scientists have been surprised by the surge, which began just over 10 years ago in 2007 and then was boosted even further in 2014 and 2015. Concentrations of methane in the atmosphere over those two years alone rose by more than 20 parts per billion, bringing the total to 1,830ppb.
This is a cause for alarm among global warming scientists because emissions of the gas warm the planet by more than 20 times as much as similar volumes of carbon dioxide.
The long-term, global trend for atmospheric methane is clear. The concentration of the gas has been shown to be relatively steady for hundreds of thousands of years. It started to increase rapidly around the year 1750. The reason is simple: increasing human populations coinciding with the Industrial Revolution have meant more agriculture, more waste, and more fossil fuel use. Over the same period, emissions from natural sources have stayed about the same.
The Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite offers one satellite-based perspective on the methane in Earth’s atmosphere. The map at the top of this post shows global methane concentrations in January 2016 at a pressure of 400 hectopascals, or roughly 6 kilometers (4 miles) above the surface. Methane concentrations are higher in the northern hemisphere because both natural- and human-caused sources of methane are more abundant there. Since AIRS observed the methane fairly high in the atmosphere, winds may have transported plumes of gas considerable distances from their sources. While many ocean regions show the obligatory presence of low amounts of methane, many regions show it is remarkably high.
Methane makes up just 0.00018 percent of the atmosphere, compared to 0.039 percent for carbon dioxide. (CO2 is roughly 200 times more abundant.) Yet scientists attribute about one-sixth of recent global warming to methane emissions; what methane lacks in volume it makes up for in potency. Over a 20-year period, one ton of methane has a global warming potential that is 84 to 87 times greater than carbon dioxide. Over a century, that warming potential is 28 to 36 times greater. The difference occurs because methane is mostly scrubbed out of the air by chemical reactions within about ten years, while carbon dioxide persists in the atmosphere for much longer than a century.
Yet Another Reason To Restore Ocean Pastures To Historic Health And Abundance
It just works!
Read more at:
Ocean Methane Paradox http://phys.org/news/2016-11-mysterious-source-greenhouse-gas-methane.html#jCp
Methanogenic aerobic bacters http://science.sciencemag.org/content/337/6098/1104
Methane beneath ice http://www.nature.com/nature/journal/v488/n7413/full/nature11374.html