Mysterious source of greenhouse gas methane in ocean explained

For decades, marine chemists have faced an elusive paradox. The surface waters of the world's oceans are supersaturated with the greenhouse gas methane, yet most species of microbes that can generate the gas can't survive in oxygen-rich surface waters. So where exactly does all the methane come from? This longstanding riddle, known as the "marine methane paradox," may have finally been cracked, thanks to a new study. In a paper released 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 gasses as byproducts. Most of the methane escapes back into the atmosphere.