Global Warming Periods More Common Than Thought, Deep-Sea Drilling Off Japan Now Demonstrates

The expedition aboard the scientific drill ship “JOIDES Resolution,” which ended in late October, also revealed that vast areas of the Pacific Ocean were low in oxygen for periods of up to a million years each, said Dr. Timothy Bralower. A marine geologist, Bralower is professor and chair of geological sciences at the University of North Carolina at Chapel Hill.

“These ocean-wide anoxic events were some of the most radical environmental changes experienced by Earth in the last several hundred million years,” he said.

Along with Dr. Isabella Premoli-Silva, a micropaleontologist and stratigrapher at the University of Milan, Bralower served as co-chief of the two-month expedition. Drilling took place on Shatsky Rise, an underwater plateau more than 1,000 miles east of Japan. Its purpose was to better document and understand past global warming.

In geologic time, episodes of warming began almost instantaneously -- over a span of about a thousand years, Bralower said.

“Warming bursts may have been triggered by large volcanic eruptions or submarine landslides that released carbon dioxide and methane, both greenhouse gases,” he said. “Besides reducing the ocean’s oxygen-carrying capacity, warming also increased the water’s corrosive characteristics and dissolved shells of surface-dwelling organisms before they could settle to the bottom.”

In some especially striking layers of black, carbon-rich mud, only the remains of algae and bacteria were left, he said.

“The sheer number of cores that reveal the critical warming events found on this expedition -- three from the 125-million-year event and 10 for the 55-million-year Paleocene event -- exceeds the number of cores recovered for these time intervals by all previous ocean drilling expeditions combined,” Bralower said.

“This means that we will be able to reconstruct in far better detail the nature of environmental changes that took place back then than was previously possible,” he said. “We’ll also have a better chance of determining the cause. Already we’ve seen signs in the sediments for other undetected periods of warming, which suggests that they were much more frequent than geologists have thought.”

Among periods of warmth likely caused by methane was one occurring about 55 million years ago, the geologist said. Cores show that 200,000-year-long event killed off 30 percent to 50 percent of deep ocean life while stimulating evolution of new species near the surface.

Twenty-seven scientists from seven countries and 62 crew spent 35 days above Shatsky Rise on the expedition, which is expected to boost understanding of current global warming, he said.

###The Ocean Drilling Program is an international partnership of scientists and research institutions organized to study the evolution and structure of the Earth. ODP is funded principally by the National Science Foundation, with contributions from its international partners.

A consortium of 16 U.S. academic institutions known as the Joint Oceanographic Institutions manages the program. Texas A&M University oversees science operations.

Photos showing life aboard the drill ship during the expedition are available on the web at http://www-odp.tamu.edu/public/life/leg198.html.