Another nuance to the drivers of greenhouse events has been discovered. Perhaps incorporating this will greatly increase the accuracy of climate models.
Creation and destruction of continents by plate tectonics generates oscillation between continental- and island-arc volcanoes. Island arc volcanoes produce much less CO2. Continental volcano magma interacts with sedimentary carbonates, releasing the stored carbon from them.
93.5 million years ago a huge flare-up of volcanism on the North American continent caused a global marine anoxic event and mass extinction, highlighting the driving role of CO2 release as more dominant than solar proximity.
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,'...
"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 and colleagues found that the planet's greenhouse-icehouse oscillations are a natural consequence of plate tectonics. The research showed that tectonic activity drives an episodic flare-up of volcanoes along continental arcs, particularly during periods when oceans are forming and continents are breaking apart. The continental arc volcanoes that arise during these periods are located on the edges of continents, and the magma that rises through the volcanoes releases enormous quantities of carbon dioxide as it passes through layers of carbonates in the continental crust.
Lee said the study breaks with conventional theories about greenhouse and icehouse periods.
"The standard view of the greenhouse state is that you draw carbon dioxide from the deep Earth interior by a combination of more activity along the mid-ocean ridges -- where tectonic plates spread -- and massive breakouts of lava called 'large igneous provinces,'...
... 93.5 million years ago there was a mass extinction of deepwater organisms that coincided with a global marine anoxic event -- that is, the deep oceans became starved of oxygen,... There was a huge flare-up of volcanism along the western margin of North America, and the peak of all this activity was 93 million years ago.
... Lenardic used numerical models that showed the opening and breakup of continents could change the nature of subduction zones, generating oscillations between continental- and island-arc dominated states.
"The length of subduction zones and the number of arc volcanoes globally don't have to change," Lee said. "But the nature of the arcs themselves, whether they are continental or oceanic, does change. It is in the continental-arc stage that CO2 is released from an ever-growing reservoir of carbonates within the continents." [emphasis mine]