Marine methane: sources and potential adverse effects

Abstract

Recently, there has been an increase in the occurrence of incidents involving spills of oil and natural gas, such as methane. The world experiences at least one major spill in each decade. An illustrative case is the Deepwater Horizon oil disaster in 2010 in the Gulf of Mexico. This catastrophe resulted in the discharge of about 205.8 million gallons of oil and 225,000 metric tons of methane gas into the Gulf of Mexico. More recently, in 2022, the Nord Stream pipeline leak occurred, which was the largest single methane release ever recorded. It released up to 500K tons of methane underwater, a greenhouse gas with a significantly higher potency than carbon dioxide. Due to the Deepwater Horizon incident, mammals, sea turtles, birds, fish, and invertebrates were adversely affected and caused damage to the corals. More than 90 bird species died, and 1300 miles of shoreline became polluted. The fishing industry suffered a significant reduction. This study systematically reviewed the source and impact of methane in the marine environment, utilizing 271 peer-reviewed academic publications, eight non-peer-reviewed sources, and 44 online resources. In the marine environment, methane can come from various sources such as methane hydrate, methane seeps, pockmarks, mud volcanoes, microbial activities, and anthropogenic sources or human-induced activities. Sediment typically contains methane from methane seeps, methane hydrates, mud volcanoes, and microbial activity. In the water column, methane is produced from diffusion from hydrates, seeps, hydrothermal vents, and thermogenic and anthropogenic sources. On the other hand, air-water interface methane comes from the atmospheric exchange or diffusion from the water column or sediment. In marine water, methane undergoes various reactions. Methane reacts with oxygen, producing carbon dioxide in aerobic conditions. Conversely, in anaerobic conditions, methane is anaerobically oxidized, coupling with sulfate reduction mediating by sulfate-reducing bacteria and methanotrophic archaea. These microorganisms, bacteria, and archaea derive the majority of their carbon and energy from methane, and they can proliferate their number where they find excess methane. However, excess methane can create anoxic conditions by reducing oxygen concentration. Invertebrates utilize methane through a symbiotic relationship with methane-consuming microorganisms. Moreover, the marine ecosystem exhibits complex interdependencies among the organisms and methane.