As the Henlopen motors north through the night, Boicourt stands his watch sitting on a stool and eyeballing three separate computer screens that track the ScanFish's progress up the Bay. Out in the black water behind the stern, the flying wing alternately climbs towards the surface, then noses over into a steep dive. Water is forced through tubes that can instantly measure temperature, salinity, oxygen and fluorescence, an indicator for algae and their oxygen-creating chlorophyll. The student is getting to play with instruments his mentor never had.

Boicourt first heard of Don Pritchard when he was a senior at Amherst weighing his options. The physics major got a call from the oceanographer asking him if he was coming to Johns Hopkins University for graduate school. "I had no idea who he was," says Boicourt, but he knew Hopkins had great lacrosse teams and he knew he didn't want to be a laboratory physicist. "I had this image of a physicist in a white lab coat and glasses and a pocket protector," he says. "And I didn't want to be in a lab." No place for a lacrosse player, better the back deck of a research vessel out on the Continental Shelf at midnight. Oceanography sounded like something that would keep him out of the office. With Pritchard on the phone, he chose a career. "Okay," said Boicourt. "I'll come."

Trained in Pritchard's model of estuarine dynamics, he soon began exploiting new field techniques and collecting data that challenged some of its key concepts. Lucky enough to start graduate work during an era of steady funding from the Navy, Boicourt worked with a scientific and technical team that was designing and testing new devices for measuring ocean flow, including current meters that could be moored in place to collect long-term data. While still a graduate student, Boicourt headed up the first Hopkins expedition to try anchoring current meters out on the Continental Shelf. That experiment deployed meters 20 miles out from the mouth of the Bay. Later missions - after a lot of trial and error and advice - would put buoys 100 miles out.

It was Boicourt's long-term data from these off-shore and in-bay current meters that threatened to disrupt Pritchard's classic model of estuarine circulation. Instead of a slow-moving, two-layer flow, Boicourt reported tremendous variability in water flows - the result of wind power on water movement. In the country's largest estuary, there's plenty of space for the wind to crank up, building waves and shoving water up or down the Bay. Wind motions and tidal surges can nearly bury any signal of an underlying pattern. "Here I come with long-term current measurements," says Boicourt, "And sure enough I can't see the steady two-layer flow very easily because of all this wild wind motion."

The wind effect was clear to anyone who saw Hurricane Isabel push Bay waters far up the streets of Annapolis and Baltimore last year. It was clear to Pritchard also. From his surf forecasting work on the beaches of the Normandy Invasion, he knew that wind could move water quickly, but the mentor never had the tools or the long-term measurements that his students later had.

Out of Boicourt's pioneering work, both offshore and in the Bay, came a whole line of research on the way wind can alter the estuarine circulation pattern. It's a classic example of how science often progresses: from mentor to student, from simple to complex. A paradigm is established, then challenged. New data from new tools gradually expand and complicate and occasionally replace the old model.

At the Chesapeake Bay Institute one group of oceanographers was constantly challenging Pritchard, sometimes to his annoyance, pointing to their new data on winds and currents and the forcing functions of distant water. "It is just natural of young people to say: 'Oh, this is wrong, I want to throw over the paradigm,'" says Boicourt.

For the "Young Turks," as Boicourt calls them, it was a case, perhaps, of paradigm envy. Pritchard had been first in the field - he had "the open slate," as Boicourt puts it - and no amount of new data could overturn or erase his basic discovery. "Has there been as fundamental a change in our understanding of estuaries since Pritchard's two-layer flow?" asks Boicourt before answering his own question: "No. That is a fundamental process. And we still have trouble working out all the physics about it."

The end result was paradigm enrichment. A second generation of oceanographers began building models to account for wind forces and other sources of variability in Pritchard's basic two-layer flow. "It is not totally fair to describe what we do as a mop-up operation," says Boicourt. "But in some sense it has been - scientifically."

Pritchard, late in his life, often admitted that his discoveries came from being first in the Bay, but he also said he would like to start over with the tools that were available now. The mentor, it seems, was capable of instrument envy.

And with good reason: devices like the ScanFish and the Chesapeake Bay Observing System would lead to discoveries barely dreamt of in his paradigm.

One of those discoveries lies just north of the Rappahannock River where a great hump of sand sprawls across the bottom of Virginia's Bay, blocking deep-water passage northwards.

The Chesapeake is known as a shallow estuary (average depth 18 feet), but there are valleys and ridges and plateaus running along its bottom. The bathymetry of the Bay plays a big role, not only in ship navigation, but in circulation patterns that affect food chains, fish migrations and levels of dissolved oxygen.

The Deep Trench (90 to 160 feet) stretches from the Bay Bridge south through the mainstem. It follows the paleochannel for the Susquehanna River that ran through here during the last Ice Age. The Trench ends in an abrupt rise at the Rappahannock Shoals (38 to 44 feet), creating a Hydraulic Control Point where south-flowing surface water has to squeeze past salty, north-flowing bottom water.

Below the Shoals, the bottom drops again, but not as deeply, into the Virginian Sea, a wide swath of water that includes a trench nearly 70 feet deep and a hole nearly 150 feet deep.

MAP SOURCE: EPA REGION III.

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