Scientists go back 120 million years in search of paleoclimate cycles
In a two-month stretch, Scripps Institution of Oceanography, UC San Diego paleontologist Richard Norris and his team took off from the St. George’s dock in Bermuda, travelled 120 million years back in time, and arrived safely at the port of St. John’s, Newfoundland.
That was enough time to survey a “meteor plowing into the Yucatan,” “a great ocean suffocation,” and how “Antarctica became the ice continent,” among several other such dramatic events. The ancient events were all visible from the eastern Seaboard – if one knew where to look.
“What a tour of the sweet spots of the ancient world over the last 120 million years,” wrote Norris, the co-chief scientist of Expedition 342, a research cruise featuring about 30 earth scientists and 65 technicians. Norris posted updates of the expedition from on board the research vessel Joint Oceanographic Institutions for Deep Earth Sampling (JOIDES) Resolution that was headed for Newfoundland from St. George’s in Bermuda.
“On land, water and winds wash away evidence of climatic events in the earth’s past, but in the deep sea, the evidence remains preserved undisturbed for a very long time,” said expedition staff scientist and project manager Peter Blum of Texas A&M University.
Using seismic profiles to create images of the seabed, Norris and his team honed in on several thick piles of sediment that had drifted off the coast of Canada over the past tens of millions years and accumulated at a location several nautical miles from the site of the wreck of R.M.S. Titanic. Then they put the Resolution drill rig to work to extract cores from the seafloor sediment. The rig can bore up to 2 kilometers (1.2 miles) vertically into the ocean bed.
“Ocean currents from Greenland have to pass over this sediment pile. Any change in water temperature, chemistry and currents would be recorded here,” said Norris. “We know that about 50 million years ago the Arctic Ocean used to be a lake surrounded by forest and there was no icecap on Greenland. We wanted to find out how the world worked back then to give us clues to how our own warming world will function in the next century or two.We also hoped to find a detailed record of how that ancient warm Earth developed the icy poles it has today,” said Norris.
Using the sediment piles as archives of both global climate and shifting ocean currents over Earth’s geologic past, Norris and his team hoped to recreate the chain of events that took place between 50 and 34 million years ago as Earth transitioned from an ice-free “hothouse” state into a colder “icehouse” world with the eventual formation of northern glaciers and icebergs. That same ice ultimately sank Titanic in the frigid waters of the North Atlantic 100 years ago.
“The first excitement is when the drill brings the mud core on board,” said co-chief scientist Paul Wilson of the National Oceanographic Center in Southampton, England. “It is the first time in millions of years that this mud has ‘seen’ daylight. The feeling is impossible to describe.”
Over two months, the team extracted over 5.4 kilometers (3.4 miles) of deep-sea cores, filled with sediments dating back 120 million years. In collecting them, the team traveled back nearly twice as long as they had intended. The scientists were targeting samples 65 million years old and younger. The cores contained debris from the meteoritic impact on what is now Mexico’s Yucatan peninsula that scientists now agree killed the dinosaurs about 65 million years ago. He found fossil evidence of other periods, between 55 million and 38 million years ago, when Earth’s climate repeatedly experienced hothouse conditions similar to those expected in Earth’s near future.
“We can see the regular cycle of climate as regular dark and light layers of sediment—formed by a sensitive climate process like flipping between two channels with a TV remote,” said Norris. “Sometimes the channel flips to something completely new—like when the poles became ice-covered,” added Norris.
The Arctic glaciation started about the same time that the Antarctic developed its glaciers, indicating a global flip into the “icehouse” world. Though ice can take over continents in less than 100,000 years, transitions between global-scale regimes of hot and cold climate can take up to 6 million years to complete, said Resolution science party member Sandra Kirtland-Turner, a postdoctoral researcher at Scripps.
“We obtained a lovely record of the glaciation of Greenland and the Arctic. The flip into cold climates happens suddenly about 34 million years ago, and the coming of icebergs is heralded by the appearance of bits of sand and grit in the mud,” said Norris.
Back at St. John’s, Norris and his team held pieces of evidence that would be critical to understand how and why the earth transitioned from a hothouse to a cooler climate, but it could take months or even years to complete all the relevant analysis and studies on the cores the party retrieved.
“The events on the ship really made us appreciate how real-time science works,” said Sandra Kirtland-Turner, a recent Ph.D. graduate of Scripps and part of the scientific party on board Resolution. “How a science party has to make cutting edge, split second decisions and how much everyone has to pitch in for that kind of accuracy. Once you are off the ship, there is no way of getting back there,” said Kirtland-Turner.
“We thought we would only recover the Earth’s history until about 65 million years at most. We now have at least 120 million years. This is what is exciting about science. When you get what you expect, it’s not fun. When you get what you expect, you have, at least, proven your ideas. But when you are surprised, that is when the most exciting discoveries happen,” said Norris.
– Atreyee Bhattacharya has a Ph.D. in earth science from Harvard University and is currently working at the Geosciences Research Division at Scripps
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