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As the World Turns and the Oceans Flow

In his lab, Jack Whitehead gets to the essence of complex phenomena

Source: Oceanus Magazine

Our planet is full of fascinating flowing fluids. Jack Whitehead has investigated all sorts of them around the globe—hardly ever leaving his laboratory.

There’s the once-mysterious Alborán Gyre, for example, an unusual swirling current in the Mediterranean Sea that looks like a bulls-eye on maps and acts like a washing machine in the ocean. Or, the relatively fresh water that pours out of the Baltic Sea into the Skaggerat and noses along the south coast of Norway, floating above saltier, heavier North Sea water. Or, the cold, dense masses of water that shrug along the ocean bottom, occasionally hitting a mountainous seafloor “bump,” rising up, and cascading down the other side, like waterfalls within water.

Not all of the fluid environments Whitehead has explored have been made of water. He also demonstrated how plumes of molten rock deep within the planet could rise buoyantly like hot-air balloons to Earth’s surface and erupt to pave the seafloor with new crust and create islands such as Hawaii.

“I explore the basic principles of how fluids move on the dynamic Earth,” said Whitehead, summarizing his four decades of research.

All very fascinating stuff, of course, but … well, it was January in New England and suddenly I felt clammy when he mentioned something about flows with “abrupt transitions” that involve “supercritical points” and “chaos theory.” Would Whitehead, a scientist at Woods Hole Oceanographic Institution (WHOI), start speaking in thermodynamic tongues and scratching out mathematical equations stretching from here to the Berkshires?

But just then, he popped up and turned on a faucet in a sink near his office. “This is real fluid,” he said, his fingers splashing the water.  “You can see it, you get your hands wet, and you know it really happens. It’s not some mathematician’s idea, or a computer model that works fine in the computer, but that often makes a simplified picture of the real world. This is the real thing.”

“I do get to play a lot when I work,” Whitehead said.  “It’s totally fun.” 

Getting down to the fundamentals

Whitehead has always preferred a hands-on approach to solving scientific mysteries. In the Geophysical Fluid Dynamics (GFD) Laboratory at WHOI, he sets up experiments using real materials: water, salt, wax. He puts water-filled plastic containers, representing oceans, on spinning turntables that simulate Earth’s rotation. In some experiments, pieces of plastic function as straits and continental shelves; in others, metal cylinders might serve as lava tubes. He adds heat when called for—not from Earth’s core, but real heat nonetheless—and colorful dyes to make fluid flow visible.

“For me, it starts in the lab, and you use all of your senses, except taste,” Whitehead said.

The experiments effectively distill complicated processes down to the fundamental forces of physics that generate them. The GFD Lab that Whitehead helped establish is still going strong today, used by many scientists to expose phenomena on a small scale that are impossible to observe in the larger real world. 

“Tongue in cheek, I tell people that in order to help them understand the ocean, I just take a different jar off the shelf,” he said.  “One is water and one is oil.”

That’s because the ocean isn’t a big bathtub of homogenous water. It has masses of cold or saltier water that are heavier than warm or fresher water; the former sinks to the depths and the latter stays on the surface. A major force driving ocean circulation is the difference in density between one water mass and another.

Take the case of the strange Alborán Gyre. Scientists could not figure out how and why it formed until Whitehead conducted one of his classic experiments. He re-created the gigantic gyre in the western part of the Mediterranean Sea in miniature in the lab. He used a container of fresh water, partitioned into two basins. He mixed in salt (and black dye) to one side, representing the salty Mediterranean; the fresh, clear water on other side represented the much less salty Atlantic Ocean. The basins were connected by a narrow channel (the Strait of Gibraltar), blocked by a sliding door.

Whitehead rotated the entire apparatus to simulate the force caused by Earth’s rotation, called the Coriolis force. He slid open the door to allow the fresh water to swoosh into the salty stuff. Voila!—a clear ribbon of water spiraled clockwise out of the narrow chute onto the surface of the dark idealized Mediterranean.

The Atlantic and Mediterranean waters don’t mix seamlessly. Fresher, lighter Atlantic water rises up and over saltier, heavier Mediterranean water. The Coriolis effect causes this freshwater ribbon to spin off in a gyre above the denser water below. Similar gyres are found in many areas where freshwater plumes leave bays or inland seas; knowing where and why they form has helped us understand this facet of ocean circulation and, among other things, to track the movements of fish, submarines, and spilled pollutants within them.

What makes Earth’s tectonic plates move?

Whitehead came to WHOI in 1971, attracted partly because it had become a hub for the nascent field of geophysical fluid dynamics. The term “GFD” was coined by a group of scientists and students that began gathering each summer since 1959 at WHOI for a fellowship program to exchange ideas in the different scientific disciplines that deal with the dynamics of fluids in oceans, atmospheres, and the interiors of planet. One way or another, a sizable proportion of the world’s leaders in the field of GFD have come through the program. Whitehead has been a fixture in it for the lion’s share of that history.

Whitehead said the early 1970s “was an incredibly stimulating time.” The theory of plate tectonics was red hot. Scientists had just begun to understand that Earth’s surface was carved up into individual segments, or plates, that moved apart or collided, forming ocean basins and mountain ranges. But what fueled the plates’ movement?

While many scientists got out their pencils and paper to derive complex mathematical equations that would explain plate tectonics, Whitehead ran straight to the lab. He poured fluids with different viscosities into containers that he heated.  He snapped photos of the action. Thin, worm-like streams of less dense fluid rose buoyantly within denser fluid toward the top of the containers—much the way boiled water rises to the top of the pot and hot air rises. The process is called convection.

Near the top of Whitehead’s containers, streams of the less heavy fluid expanded outward like balloons at the end of straws. The experiment demonstrated how less dense material in Earth’s hot mantle forms “mantle plumes” with bulbous heads. The plumes can cause hard ocean crust above them to spread apart, forming a chain of volcanic mountains between diverging tectonic plates. In some instances, plumes can burst through plates to create volcanic island chains like the Hawaiian Islands.
 
WHOI scientist Joe Pedlosky, who wrote what is considered the definitive textbook on geophysical fluid dynamics, said, “The idealized problem of what happens to a fluid when you uniformly heat it from below and it starts to convect and becomes more and more turbulent was an important problem in fluid mechanics and oceanography, and it occupied the attention of lots of people in the early years of the GFD program. Jack’s early experiments in this area are what first made Jack's reputation. He did really beautiful stuff.”

A sixth sense

“Jack’s got this deep—and to many of us who don’t think exactly the same way he does—mysterious intuition of how fluids are going to react,” said Pedlosky, whose office has been next to Whitehead’s for more than 30 years. “Instead of approaching it mathematically, he does it experimentally in the laboratory. He just seems to have some sixth sense about how to set up experiments that will help clarify fluid processes that are really very remarkable.”

Another of Whitehead’s longtime colleagues, WHOI geochemist Stan Hart, said. “Jack’s got extremely good intuition about the physics behind processes, and sometimes he doesn’t even know where this comes from. At first I kind of blew it off and thought this guy was off the wall a little, but as I got to know him, I now listen extremely carefully when he says things because almost always, he’s right.”

“Jack just pours out ideas,” Hart said. “All these ideas are free; he feels it’s his job.”

The wellspring of ideas has never run dry. In recent years, Whitehead has investigated how dense water at the ocean bottom can mix back up toward the surface to close the loop of global ocean circulation. And he has examined how far hot lava can rush through cold, tubular channels within volcanoes before it solidifies into rock.

Perhaps not surprisingly, outside the lab, Whitehead tended toward fluid and dynamic hobbies: music and marathons. He started training for marathons at age 45 and still runs them. And he plays the trombone in the Falmouth Town Band, which is conducted by his wife Lin, who is head of the music department in the Falmouth public school system.

During his career, he has amassed many awards, including induction into the American Academy of Arts and Sciences. In 2007, the American Meteorological Society gave Whitehead one of its highest honors: the Henry Stommel Research Award, named after the renowned WHOI physical oceanographer and Whitehead’s colleague for many years. Whitehead was cited “for his fundamental contributions to geophysical fluid dynamics and physical oceanography, for which his laboratory and observational studies of rotating hydraulic flows have been particularly illuminating.”

Though he officially retired and became a scientist emeritus in 2008, you can still find Whitehead most days in his office or lab. “There are many projects I'd like to do that I haven't done yet,” he said, his eyes gleaming. 

Jack Whitehead's research has been funded by the Office of Naval Research, the National Science Foundation, and the Paul M. Fye Chair for senior scientists at WHOI.

Originally published: February 20, 2009