Could Oceanic Crust Solve Global Warming? Geologists Say It Can Store 'Several Centuries Worth Of CO2 Emissions'
Carbon dioxide (CO2) — a major culprit in global warming — could be stored geologically in deep-sea basalts that form the upper igneous lavas of the oceanic crust, geologists said Tuesday. Although the idea of using offshore basalt formations as a "geological storage option" is not new, this one, published in Tuesday's online issue of Geophysical Research Letters, points to massive reservoir capacities — enough, the authors say, to store several centuries worth of CO2 emissions. The geologists pinpointed five zones on the oceanic crust that could provide centuries of storage; the smallest is capable of providing 393 times to 3,650 times the storage of all the CO2 emissions globally in a year, according to lead author, Ph.D. candidate Chiara Marieni at The National Oceanography Centre. Marieni worked with investigators at the University of Southampton in Great Britain to develop the study.
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For a while now, geologists have been considering the lava flows on Iceland and the Columbia River Basalts in the United States as good candidates for the geological reservoirs for CO2 storage. In her article, Marieni ruled out one of the strongest candidates for deep-sea basalt storage, the Juan de Fuca Plate offshore of Washington State. According to Marieni, the Juan de FucaPlate, as well as the one in the eastern equatorial Pacific are too gravitationally unstable. She also ruled out one in the eastern equatorial Pacific Ocean because too-thick sediment covering young oceanic crust resulted in high temperatures that would render the CO2 less dense than seawater. Marieni maintained that other geologists, because they didn't factor in temperature, unwittingly chose locations that would permit the CO2 to escape.
More promising, maintains Marieni, are five large regions of ancient seabed that are stable and would provide sediment buffers 200 to 700 meters thick: reservoirs in the Atlantic Ocean near Bermuda; the Indian Ocean between Indonesia and Australia; in the northwest Pacific Ocean near the east coast of Japan and Russia; close to South Africa and south of the Aleutian Islands. "Using conservative assumptions about the porosity available, the smallest of these regions can store several centuries of anthropogenic CO2 emissions," she wrote.
The storage capacity in each area is between about 13,800 and 127,800 gigtonnes of CO2. "At the current global annual anthropogenic flux of about 35 gigatonnes of CO2 per year, even the smallest identified reservoir could provide sufficient carbon dioxide sequestration capacity for several centuries," Marieni wrote.
In the past 25 years, geologists have come up with a number of creative ideas for trapping CO2 for long-term storage in seafloor basalt. One would be by so-called physical or permeability trapping, whereby the presence of 200-meter thick strata of marine sediments would trap any leakage from the basalt before they could get to the ocean. Another idea is so-called geo-chemical trapping, whereby CO2 and water react with the basalt host rocks to form geologically stable carbonate minerals.
In her paper, Marieni focused on gravitational trapping, with old ocean crust with 200 to 700 meter-thick sediments - an average porosity of no more than 10 percent - being her storage unit of choice. Ancient ocean crust, she wrote, hosts seawater at high pressures and the right temperature; between zero and 30 degrees centigrade — a must because CO2's density decreases dramatically with decreasing pressure and increasing temperature. It provides stability, sediment thickness — low risk of leakage; and, best of all, the ability to retain fluid for more than 500 years.
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