Volcano location could be greenhouse-icehouse key

A new Rice University-led study finds the real estate mantra ''location, location, location'' may also explain one of Earth's enduring climate mysteries. The study suggests that Earth's repeated flip-flopping between greenhouse and icehouse states over the past 500 million years may have been driven by the episodic flare-up of volcanoes at key locations where enormous amounts of carbon dioxide are poised for release into the atmosphere.

''We found that Earth's continents serve as enormous 'carbonate capacitors,' '' said Rice's Cin-Ty Lee, the lead author of the study in this month's online journal GeoSphere. ''Continents store massive amounts of carbon dioxide in sedimentary carbonates like limestone and marble, and it appears that these reservoirs are tapped from time to time by volcanoes, which release large amounts of carbon dioxide into the atmosphere.''

Lee said as much as 44 per cent of carbonates by weight is carbon dioxide. Under most circumstances that carbon stays locked inside Earth's rigid continental crust.

''One process that can release carbon dioxide from these carbonates is interaction with magma,'' he said. ''But that rarely happens on Earth today because most volcanoes are located on island arcs, tectonic plate boundaries that don't contain continental crust.''

Earth's climate continually cycles between greenhouse and icehouse states, which each last on timescales of 10 million to 100 million years. Icehouse states - like the one Earth has been in for the past 50 million years - are marked by ice at the poles and periods of glacial activity.

By contrast, the warmer greenhouse states are marked by increased carbon dioxide in the atmosphere and by an ice-free surface, even at the poles. The last greenhouse period lasted about 50 million to 70 million years and spanned the late Cretaceous, when dinosaurs roamed, and the early Paleogene, when mammals began to diversify.
Carbonate fluctuation diagram