Fire-ice, or methane hydrate, is a frozen form of methane and water that is buried under the ocean floor. It is sometimes called fire-ice because it can be ignited when exposed to air. Methane hydrate is estimated to store about one-sixth of the world’s methane, a potent greenhouse gas that contributes to global warming.
Methane hydrate is stable under cold temperatures and high pressure, but it can melt when the ocean warms or the pressure drops. This can release methane into the water and the atmosphere, creating a positive feedback loop that accelerates climate change. Scientists are concerned that this process could happen more frequently and rapidly as the planet heats up.
How climate change can cause methane to be released from the deep ocean
A new study by an international team of researchers led by Newcastle University has shown that climate change can cause methane to be released from the deep ocean, where most of the methane hydrate is located. The study used advanced three-dimensional seismic imaging techniques to examine the portion of the hydrate that melted during past warm periods off the coast of Mauritania in Northwest Africa.
The researchers found that as the frozen methane and ice melted, methane moved from the deepest parts of the continental slope to the edge of the underwater shelf. They even discovered a pocket that had moved 25 miles (40 kilometers). The methane was then released through a field of underwater depressions, known as pockmarks, into the ocean.
The study suggests that this mechanism is triggered by the slowdown of a key ocean current, called the Atlantic Meridional Overturning Current (AMOC). The AMOC is a slow ocean heat pump that moves warm and cold water between the Arctic and the Southern Ocean. It is driven by temperature, density and salinity contrasts. However, the influx of fresh, frigid water from melting Arctic ice, especially the Greenland Ice Sheet, appears to weaken the current, which could warm the ocean at depths of 300 to 1,300 meters. This could destabilize methane hydrate buried 20 to 30 feet deep in the seabed.
What are the implications and challenges of this finding?
The finding of the study has important implications for the future of climate change and its impacts. It shows that much more methane could potentially be vulnerable and released into the atmosphere as a result of climate warming. Methane is a powerful greenhouse gas that has 28 times the warming potential of carbon dioxide over a 100-year period. It also affects the chemistry of the atmosphere and the ocean, altering the levels of ozone and oxygen.
The study also poses significant challenges for the scientific community and the society. It reveals that the release of methane from the hydrate stability zone can travel a long distance towards land, which means that it could affect coastal areas and ecosystems. It also indicates that this process could have happened in the past, during the Eemian Age, about 125,000 years ago, when the global average temperature was about 1 to 2 degrees Celsius warmer than now. This raises the question of how much methane was released then and how it affected the climate and the biosphere.
The study calls for more research and monitoring of the methane hydrate and its dynamics under changing ocean conditions. It also urges for more action and cooperation to mitigate climate change and reduce greenhouse gas emissions. As the lead author of the study, Professor Richard Davies, Pro-Vice-Chancellor, Global and Sustainability, Newcastle University, said: “Our work shows that some of the hydrate is vulnerable to climatic warming, but we have shown that only some of it is. We need to understand how much, how fast and where methane will be released to work out how to manage it.”