The first professional oceanographer to work the Chesapeake arrived here over 50 years ago, shortly after World War II, and within a decade made the decisive discovery that changed the history of science on the Bay.

First trained as a meteorological cadet, Don Pritchard had been one of a select group of Army soldiers sent to the Scripps Oceanographic Institution to learn new techniques for forecasting sea conditions for amphibious landings. Shortly after D-Day, he landed on Omaha Beach to head the sea swell forecasting team for the Normandy invasion.

For six months he and his partner, Robert Reid, worked up daily forecasts for weather, wave conditions and tides, enabling the Allies to keep offloading troops, tanks and artillery across the beaches. Unloading on the beaches worked, enabling the Allies to head inland in force while the Germans kept thousands of troops tied up waiting to defend the port cities of Northern France. Don Pritchard found himself at the hinge of history. He was 22 years old.

After the war he returned to Scripps, recruited by Harald Sverdrup, the famous Norwegian oceanographer who was creating the first full-scale graduate program in oceanography in America. Sverdrup's students, some called them "apostles," would find a hot job market when they finished, and they would form the core of the first great generation of American oceanographers. Even before he completed his Ph.D., Don Pritchard was hired by Johns Hopkins University to head up a newly created Chesapeake Bay Institute. He was now 27 years old.

His hiring was the result of an unusual agreement among two marine labs and the United States Navy. When Reginald Truitt, head of Maryland's Chesapeake Biological Lab, wanted to recruit a scientist to study the Bay's hydrology, he went to the Office of Naval Research, and he brought with him Nelson Marshall, the head of the Virginia Institute of Fisheries. They found the Navy eager to maintain America's new edge in ocean science and willing to put up funds for a new Chesapeake Bay Institute.

Pritchard compiled a long-term record that suggested anoxia and hypoxia were occasional but recurring events, especially during late spring and summer.

The funds came with two conditions: The two state-run labs would have to help fund the new facility, but the new Institute would operate independently of them. Truitt and Marshall agreed to ante up $30,000 each, a sizeable sum from each lab's budget, and the Navy matched them with another $30,000. That was a lot of money in 1949. With $90,000 Pritchard would have enough to set up a lab, buy some boats, hire scientists and technicians, and launch the most ambitious research yet attempted on the Bay.

Truitt and Marshall, in turn, had their own conditions. The new Institute would focus mainly on the physics of the Bay, with some chemistry and geology thrown in. It would not compete with the Maryland and Virginia labs in biology and fisheries science. After all, both directors ran their labs largely with funds directed at research on the Bay's highly profitable and heavily harvested commercial fisheries for oysters, blue crabs and striped bass. As Pritchard later explained the deal, "The original conception was: you needed someone working on the whole Bay, not just on the two halves, someone who would look at how the Bay functions, not necessarily the living resources in it."

By putting that much money on the table, Truitt and Marshall were rolling the dice, making an early big-time bet on oceanography. And on a young war veteran who was now expected to produce major discoveries, plus a payoff for all those biologists studying oysters and blue crabs.

Bill Boicourt begins his day on the R.V. Henlopen with a bet of his own, a small bet about oxygen levels in the Bay.

By the time he scrambles out of his bunk for his 4:00 a.m. watch, the Henlopen has re-entered the Bay, taken a right turn and headed north, towing the ScanFish through the dredged-out deeps of the York Spit channel, then through the natural deeps of the Virginian Sea Trench.

Entering the science lab, he sits down in front of three computer screens, sips on his coffee and checks on the data streaming up from the ScanFish. "We ought to make a bet, a best guess about what the oxygen depletion is just below the Bay Bridge," he says to Xinsheng Zhang, the scientist who is going off watch. "Let's see who's right."

The Bay Bridge, near Annapolis, is still more than 100 miles north, and nearly 20 hours away, but Boicourt, awake and wired with coffee, is pushing for predictions. "I want your best guess, Xinsheng." Down here along the Virginia Sea Trench, waters at depth are fairly well oxygenated with dissolved oxygen running around 5 milligrams per liter. That's a touch low for this time of year, Boicourt notes, but still healthy for fish life. Waters falling below 4 milligrams, on the other hand, are labeled hypoxic (for low oxygen). Below 2 milligrams, they are labeled anoxic (for no oxygen) and unable to support life, except for anaerobic bacteria.

Don Pritchard observed levels of anoxia back in 1949, the first year he took samples on the Bay. Over the next 20 years he compiled a long-term record that suggested anoxia and hypoxia were occasional but recurring events, especially during late spring and summer. When spring rains and runoff bring high inputs of sewage, fertilizer and animal waste, all these nutrients overfertilize the Bay's waters, producing blooms of algae and phytoplankton. When those plankton die, they sink to the sediments where they cause another kind of bloom: a population explosion among bottom-dwelling bacteria. As they feed on and decompose dead plankton, these bacteria suck oxygen out of the water.

Pritchard's oceanographers also worked out the physics that helped create these events. They identified a boundary called the pycnocline that can block the normal mixing of bottom waters with oxygen-rich surface waters. When a strong pycnocline develops, the result is extreme stratification with little or no mixing. Anoxic waters remain capped in a "dead zone" along the bottom. Fish kills and crab kills usually follow.

Boicourt and Zhang aren't the only contemporary scientists watching dissolved oxygen. Anoxic episodes are now public events, stirring up debates among scientists and launching news releases from environmentalists. State agencies in Maryland and Virginia track oxygen closely, considering it one of the key indicators of general ecosystem health. The Environmental Protection Agency's (EPA) Chesapeake Bay Program has set a Bay-wide average of 5 milligrams per liter as the goal for the restoration effort.

A numerical modeler working on plankton populations, Zhang finally settles on a guess of 4.0 for oxygen at the Bay Bridge before heading off for his bunk. Boicourt's bet is more precise and less optimistic: He picks 3.43. He's predicting the waters at the Bay Bridge - even this early in April - will already be hypoxic.

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