Do fire and ice link up to alter Earth's climate?
The climate-driven rise and fall of sea level during the past million years matches up with valleys and ridges on the seafloor, suggesting ice ages influence underwater volcanic eruptions, two new studies reveal. And because volcanic chains spread across 37,000 miles (59,500 kilometers) on the ocean floor, the eruptions could pump out enough carbon dioxide gas to shift planetary temperatures, the study authors suggest.
"Surprisingly, the deep seafloor matters in the long-term climate cycle," said Maya Tolstoy, lead author of one of the studies and a marine geophysicist at the Lamont-Doherty Earth Observatory in New York.
New oceanic crust is born at underwater volcanic chains called spreading ridges, where molten rock rises to fill the gap between moving tectonic plates. Scientists think that as the plates pull away from spreading ridges, the new crust cools, cracks and sinks, creating gaps between the lines of volcanoes (which are carried away from the ridge with the plate). These parallel volcanic ridges and valleys are some of the most visible features on Earth's ocean floor. [Infographic: Tallest Mountain to Deepest Ocean Trench]
Tolstoy's study at the East Pacific Rise spreading ridge found connections between ice age cycles and these seafloor corrugations that extend back 800,000 years. The bands of thicker and thinner crust correspond to 100,000-year ice age cycles. When glaciers expanded and sea level dropped, more lava oozed from the ridge volcanoes, Tolstoy discovered. The thinnest crust, which formed when eruptions slowed, matches up with eras of higher sea level. The findings were published Thursday in Geophysical Research Letters.
A separate study conducted at the junction between the Australia and Antarctic tectonic plates came up with similar results. For the past million years, when sea level rose, underwater eruptions slowed along the ridge. And when ice sheets expanded and sea level dropped, the lowered ocean pressure boosted volcanic activity, according to a computer model published Thursday in the journal Science. The model indicates that water weight can change how quickly the molten rock wells up at spreading ridges.
"When ice sheets melt and sea level goes up, it has an effect on volcanoes under the sea," said Richard Katz, co-author of the study in Science and a geophysicist at the University of Oxford.
Both studies suggest that there could be a complex feedback loop involving ice ages, sea level changes and bursts of volcanic activity.