地球物理学家探测海洋的秘密

There are more than 300 research scientists working in scores of specialties at Columbia University’s Lamont-Doherty Earth Observatory in Palisades New York, but few have made as varied and lasting a contribution as Walter Pitman.

Lamont-Doherty Earth Observatory

Today, Pitman is a distinguished professor of geophysics at Columbia University, and the recipient of many of his field’s most coveted honors.

Even though he is now in his 80s, Pitman’s animated manner makes it easy to picture him as the precocious teenager he once was, visiting his father’s workplace at Bell Labs - the pioneering technology research center - and asking the other scientists there about their work.

“I worked there in the summertime sweeping floors but I was in amongst all these people," he recalls. "It was wonderful.”

Pitman earned an undergraduate degree in electrical engineering and physics, and soon took a job with an electronics firm. The work bored him, but one project - doing research on submarines - sparked a passion for oceanography and a return to university.

For his doctoral thesis at Columbia, Pitman headed back to sea on a research vessel. He hoped to gather evidence that all the continents had once been joined, but for hundreds of millions of years had been drifting apart atop giant plates of the earth’s crust, which floated on a layer of volcanic magma. 

“Now when they pull apart, volcanic material comes up and fills that void," Pitman says. "That volcanic material contains a lot of iron. When that volcanic material cools down that iron will become magnetized in the direction of the earth’s field on that place and at that time.”

This chart shows the magnetic patterns at set distances from the Pacific-Antarctic Ridge. During the 1960s, Pitman used the symmetry in the patterns to help prove the theory of plate tectonics and continental drift. (Credit: Lamont-Doherty)

By recording and analyzing the magnetic patterns in the undersea ridge, Pitman helped prove the theory of continental drift, a revolutionary idea at the time.

“It was electrifying. I didn’t imagine ever being involved in something so astonishing and so very, very important to the geological sciences at such a young stage in my career. I was very fortunate to be there when it was happening.”

Pitman says that in addition to explaining how the continents drift around the oceans, the science of plate tectonics explains how they collide and break apart, creating earthquakes and building mountain chains.

Later, Pitman turned his attention to the surface of the ocean, and sea level changes. He and fellow Columbia University geophysicist William Ryan proposed what is known as the Black Sea Deluge Theory. In their 1998 book, “Noah's Flood: the New Scientific Discoveries About The Event That Changed History,” they contend that the Black Sea was once a landlocked freshwater lake. It probably served as a fertile oasis for Neolithic peoples. Then about 7500 years ago, melting glaciers raised water levels in the neighboring Mediterranean Sea. 

“Until it got to the point where it could flow in through the Bosporus, which was at that time was probably at a depth of 15 or 20 meters. You’re talking about a huge mass of water coming in to fill a very small basin.  And that water as it comes through the Bosporus is going to cut the Bosporus deeper. The deeper it cuts, the faster it flows. The faster it flows, the faster it cuts, and so on. There is a feedback mechanism. You start with a trickle and within a short time, it’s a raging, roaring torrent of water flowing in at 50 cubic kilometers a day. We’re very sure that’s what it (the Biblical flood) was.”

For decades, Pitman served as a distinguished professor of oceanography and geophysics at Columbia University. But he decided to stop teaching when he began to have trouble remembering all of his students’ names.

“Thinking about it, I always liked to become sort of an uncle," Pittman says. "Not a professor, but a bit more like an older uncle with the students. I think that made them more free to talk and question and contradict, than if I was ‘Herr Professor.’ These are bright kids - really bright. And you know damn well that a lot of them are going to go on to achieve much more than you have achieved.”

This octogenarian’s thirst for knowledge is undiminished by age. He and several colleagues are currently studying the climate of the Arctic Ocean, and its effects on the world’s water cycles over the past two million years. Their research can help scientists predict the effects of climate change, which is melting the polar ice caps and causing sea levels to rise. But Walter Pitman remains fascinated by whatever falls under his gaze.    

“I’ve had an incredibly good time at this kind of endeavor. There are bad spots, of course. But the science is always fascinating. You might stop reading for the day and say ‘Wow, that is so great. I learned something about how the Earth works.’ That is really pure pleasure.