Tons of Methane Comes from the Ocean's Most Abundant Organism

Massive amounts of methane gas have been coming from the world's oceans, and researchers have finally determined why. Strains of SAR11, the oceans' most abundant organism, can release large amounts of the potent greenhouse gas when starving, according to a recent study.

The study, published in the journal Nature Communications, details how the smallest and most abundant free-living cell known to man (SAR11) is behind what many experts had long called the "marine methane paradox."

According to co-author Angelicque White, it has long been known that some ocean-born methane stems from anaerobic methane biogenesis performed by certain organisms living in areas where oxygen levels are markedly low.

However, "in the vast central gyres of the Pacific and Atlantic oceans, the surface waters have lots of oxygen from mixing with the atmosphere - and yet they also have lots of methane, hence the ... paradox," White said in a statement.

According to White, understanding the ocean's methane production is an important piece of the puzzle that is the Earth's greenhouse gas production. Although methane is roughly 20 times more potent than carbon dioxide as a greenhouse gas, little is known about it. Recent efforts have focused on reducing methane production among livestock, but little is being done and even understood offshore.

To unravel some of the methane mystery, White and his colleagues worked with Steve Giovannoni, who initially discovered SAR11 in 1990 - organisms now identified as the most prevalent creatures in the ocean.

They theorized that if the oceans were producing methane, the most abundant organism must be at-least partially involved. After analyzing samples from the world's largest bank of SAR11 strains, the research team concluded that when starving for phosphorus - a mineral essential to every living organism - SAR11 strains start breaking down methylphosphonic acid instead. This frees up phosphorus for growth, but often leaves methane behind.

This helps researchers better understand Earth's methane cycle, but they are still far from truly predicting future levels as well as the impact of this greenhouse gas.

"We found that some did produce a methane byproduct, and some didn't," White explained. "Just as some humans have a different capacity for breaking down compounds for nutrition than others, so do these organisms."

White now hopes to determine what makes some SAR11 strains produce more methane than others, and just how much of the "methane budget" is from the tiny organisms alone.