Trapped in
ocean sediments near continents lie ancient reservoirs of methane called methane hydrates.
Not exact matches
To study the movement of vent products, the researchers set up
sediment traps and current meters
near the hydrothermal vents along the East Pacific Rise, an
ocean ridge located about 800 kilometers off the southern coast of Mexico and a mile and a half below sea level.
Surprise find The team's actual mission was to survey
ocean currents
near the Ross Ice Shelf, a slab of ice extending more than 600 miles (970 kilometers) northward from the grounding zone of the West Antarctic Ice Sheet into the Ross Sea, to model the behavior of a drill string, a length of pipe extending to the seafloor which delivers drilling fluids and retrieves
sediment samples.
Eventually, it makes its way back to the surface as the
ocean's bottom water circulates and rises anew
near the equator (although carbon buried in
sediment might stay buried longer).
These
sediments, collected in modern day Iran, were deposited 252 - 246 million years ago in a relatively shallow tropical
ocean near the equator.
The ubiquitous character of certain events further confirms their importance: «the Younger Dryas and a large number of abrupt changes during the last ice age called Dansgaard / Oeschger events (23 abrupt changes into a climate of
near - modern warmth and out again, during the last glacial period) have been corroborated in multiple ice cores from Greenland, Antarctica and tropical mountains, marine
sediments from the North Atlantic
Ocean, the tropical Atlantic, eastern Pacific, and Indian
Oceans, and from various records on land.
These
sediments were deposited 246 - 252 million years ago in a shallow tropical
ocean near the equator.
The principal dataset we use is the temporal variation of the oxygen isotope ratio (δ18O relative to δ16O; figure 1a right - hand scale) in the shells of deep -
ocean - dwelling microscopic shelled animals (foraminifera) in a
near - global compilation of
ocean sediment cores [4].
Warming bottom waters in deeper parts of the
ocean, where surface
sediment is much colder than freezing and the hydrate stability zone is relatively thick, would not thaw hydrates
near the
sediment surface, but downward heat diffusion into the
sediment column would thin the stability zone from below, causing basal hydrates to decompose, releasing gaseous methane.
Since then, atmospheric CO2 declined as the Indian and Atlantic
Oceans have been major depocentres for carbonate and organic
sediments while subduction of carbonate - rich crust has been limited mainly to small regions
near Indonesia and Central America [10], thus allowing CO2 to decline to levels as low as 170 ppm during recent glacial periods [11].