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Mar 20, 2018 · As oxygen penetrates the layers of the dead seagrass, the chemical mix of bacteria changes, releasing carbon that is otherwise stored in sediment. In total that would've equated to the release of around 9 million tonnes of carbon dioxide (CO2) into the atmosphere.
- Overview
- A threat closer to home
- Like a needle in a haystack
Stores of methane and CO2 in the world's seas are in a strange, icy state, and the waters are warming, creating a ticking carbon time bomb.
Scientists are finding hidden climate time bombs—vast reservoirs of carbon dioxide and methane—scattered under the seafloor across the planet.
And the fuses are burning.
Caps of frozen CO2 or methane, called hydrates, contain the potent greenhouse gases, keeping them from escaping into the ocean and atmosphere. But the ocean is warming as carbon emissions continue to rise, and scientists say the temperature of the seawater surrounding some hydrate caps is within a few degrees of dissolving them.
That could be very, very bad. Carbon dioxide is the most common greenhouse gas, responsible for about three-quarters of emissions. It can remain in the atmosphere for thousands of years. Methane, the main component of natural gas, doesn't stay in the atmosphere as long as CO2—about 12 years—but it is at least 84 times more potent over two decades.
The oceans absorb a third of humanity’s carbon dioxide emissions and 90 percent of the excess heat generated by increased greenhouse gas emissions; it’s the largest carbon sink on the planet. If warming seas melt hydrate caps, there’s a danger that the oceans will become big carbon emitters instead, with grave consequences for climate change and sea level rise.
Other scientists are far more concerned about potential climate time bombs much closer to home—methane hydrates that form on the shallower seafloor at the margins of continents.
For one thing, there apparently are a lot of them. Between 2016 and 2018, for instance, researchers at Oregon State University and the National Oceanic and Atmospheric Administration (NOAA) deployed a new sonar technique to discover 1,000 methane seeps off the Pacific Northwest coast of the United States.
In contrast, just 100 had been identified between 2015 and the late 1980s, when scientists first stumbled across methane deposits. There are likely many more to be located, given that as of 2018, researchers only had mapped 38 percent of the seafloor between Washington State and Northern California.
“Because a lot of methane is stored on the continental margins in relatively shallow water, the effects of ocean warming will get to it sooner and potentially destabilize the methane hydrates that are present in the sediment,” says Dave Butterfield, a senior research scientist and hydrothermal vent expert at NOAA’s Pacific Marine Environmental Laboratory in Seattle.
He noted that these methane seeps likely constitute a far larger global reservoir of greenhouse gases than pools of carbon dioxide under the deep ocean floor.
“This idea is that if you destabilize the methane hydrates, that methane would be injected into the atmosphere and cause more extreme global warming,” says Butterfield, who in 2003 was part of an expedition that discovered a hydrate-capped reservoir of liquid CO2 at a hydrothermal system on the Mariana Arc in the Pacific.
Take the hydrate-capped liquid CO2 reservoir found by Butterfield and his colleagues on a volcano in the Pacific. They calculated that the rate that liquid CO2 bubbles were escaping the seafloor equaled 0.1 percent of the carbon dioxide emitted on the entire Mid-Ocean Ridge. That may seem like a small amount, but consider that the CO2 is escaping from a single, small site along a 40,390 mile-long system of submerged volcanoes that rings the planet.
“That's an astonishing number,” says Stott.
Scientists believe such reservoirs can be formed when volcanic magma deep beneath the ocean floor interacts with seawater to produce superheated fluids rich in carbon or methane that rise toward the surface. When that plume collides with cooler water, an ice-like hydrate forms that traps the carbon or methane in subsurface sediments.
The risk the reservoirs pose depends on their location and depth. For example, rising ocean temperatures could in coming years melt a hydrate capping a lake of liquid CO2 in the Okinawa Trough west of Japan, according to Stott. But the absence of upwelling currents there means a mass release of carbon dioxide at a depth of 4,600 feet would likely acidify the surrounding waters but not enter the atmosphere for an extremely long time.
Stott notes that finding CO2 and methane reservoirs in the deep ocean is a “needle and haystack situation.”
But in a paper published in August, scientists from Japan and Indonesia revealed that they had detected five large and previously unknown CO2 or methane gas reservoirs under the seafloor in the Okinawa Trough by analyzing seismic pressure waves generated by an acoustical device. Since those waves travel more slowly through gas than solids under the seafloor, the researchers were able to locate the reservoirs. The data indicates that hydrates are trapping the gas.
Apr 29, 2024 · Ocean warming enhances hurricane activity, bleaches coral reefs and melts Antarctic sea ice. That warming has been off the charts for the past year.
For eons, the world’s oceans have been sucking carbon dioxide out of the atmosphere and releasing it again in a steady inhale and exhale. The ocean takes up carbon dioxide through photosynthesis by plant-like organisms (phytoplankton), as well as by simple chemistry: carbon dioxide dissolves in water.
- Holli Riebeek
- 2008
Apr 25, 2011 · The oceans' vast stores of carbon dioxide can escape into the atmosphere quickly, according to a new study, enhancing the effects of global warming.
- Wendy Zukerman
Mar 25, 2022 · The ocean helps relieve our atmosphere of a lot of the excess carbon dioxide we've pumped into it. Here's how its "twilight zone" makes that happen, and how the impacts of climate change make it...
Sep 6, 2023 · The main source of ocean heat is sunlight. Additionally, clouds, water vapor, and greenhouse gases emit heat that they have absorbed, and some of that heat energy enters the ocean. Waves, tides, and currents constantly mix the ocean, moving heat from warmer to cooler latitudes and to deeper levels.
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related to: Ocean ReleasingYour gift this Ocean Month helps to protect our ocean from complex threats. Make a difference during National Ocean Month. All donations support our incredible ocean.
