Discovering the Chesapeake: Profiles in Science
Journey to the James River
An Oceanographer Discovers an Estuary
Don Pritchard (with pipe) measures current speeds at different depths along the James River. The crew lowers a $15 tool called a "biplane," and Pritchard records the angle of the line, numbers that will help reveal the two-layer flow of the estuary. Credit: photograph courtesy of the Pritchard family
This is the third article in a series about the pioneers of Chesapeake Bay science.
ON A JUNE MORNING IN 1950, along a deep-water creek near Annapolis, a scientist named Don Pritchard climbs aboard an 85-foot research vessel, lights his pipe and gives his crew the order to cast off for the southern reaches of Chesapeake Bay. His ship is the Joan Bar II, a converted motor yacht. His crew includes a ship's captain and several other scientists. Their mission: help figure out what forces were behind some mysterious booms and slumps in the harvests of oysters and blue crabs and finfish in the largest estuary in the country.
Only 27 years old, Pritchard is already used to leading men on science missions. When he was 22, he waded ashore on Omaha Beach on D-Day-plus-two to lead a squad of soldiers to the bluffs above the beaches of the Normandy invasion. His mission on the cliffs: figure out a daily forecast for sea swell and surf conditions so all those American and British ships floating out there in the English Channel could keep offloading tanks and trucks and soldiers. In the photos from that war, he was wiry, black-haired, and bespectacled, already a pipe smoker, a good leader, said one of his team, an outgoing guy who got things done.
Heading out onto Chesapeake Bay, Pritchard is now one year into his first professional job: setting up a new marine lab at Johns Hopkins University, a lab jointly funded by the U.S. Navy and by both Maryland and Virginia, two states that share the estuary but seldom agree on how to manage it. This new Chesapeake Bay Institute is focusing, for the first time, on the entire estuary, and Pritchard, still a year shy of his Ph.D., is the first professional oceanographer to investigate an ecosystem where the harvests of oysters and blue crabs and finfish produce more seafood per acre than any other estuary on the planet.
As an oceanographer, Pritchard is here to focus on the physics — not the biology — behind that up-and-down bounty. His goal is to discover and describe the different water masses that are sloshing around the Chesapeake system and measure their force and flow. How are those water masses affecting all the life forms that float or swim in the Bay or grow along its bottom?
Nearly half a century later six famous Bay scientists would gather at a 1998 meeting where they would be asked a different question: who made the decisive discovery in the history of Chesapeake Bay science?
Five of the six picked Don Pritchard. The sixth scientist at the meeting was Pritchard. He politely nominated someone else.
They picked Pritchard because his work had created a paradigm shift, a turning point for Bay science. According to Gene Cronin, former director of the Chesapeake Biological Laboratory, Pritchard's discovery changed the way biologists thought about the Bay more than any other single piece of research.
And the key evidence for that discovery came from his journeys down along the James River during the dawn of his career.
As the Joan Bar II nears the southern end of the Bay the young Pritchard turns the yacht west, sailing past Hampton, Virginia, before veering northwest to head up the historic James River, home of the Bay's richest beds for seed oysters. Ten miles upriver of Newport News, the boat approaches the sprawling anchorage for the Navy reserve fleet, a "ghost fleet" that holds more than 800 war ships, troop ships, and transport ships left over from World War II, all empty now and lashed together in long gray lines, waiting for the next war.
In the shadow of the Ghost Fleet, the crew drops anchor — not a simple job on this kind of research cruise. Instead of one anchor, Pritchard wants four anchors put out, a technique that will nail the ship stiffly in place in one barely moving position in this ever-moving, tidal river. Once they get the boat well tethered to Pritchard's satisfaction, the crew begin hauling out a collection of tools, some of them adapted from deep-water oceanography, some of them newly designed by scientists and engineers that Pritchard has recruited for his new lab.
They know they're in for a busy day. Work life on these cruises is usually hectic for the first 48 hours: they have long watches to stand and 12 stations to hit along the river. When the cook announces lunch, Pritchard, still in Army mode, is heard to snap, "We didn't come out here to eat." He's on the hunt for his data.
Already a pipe smoker in his early twenties, Pritchard got his introduction to oceanography during World War II when he worked out forecasts for sea swells and surf conditions for the Normandy invasion (above). At left, Pritchard with a tank damaged during offloading. Credits: photographs courtesy of the Pritchard family
One of the odd tools the crew pulls out on deck is a $15 homemade current drag. Pritchard calls it a biplane but it looks more like a primitive paddle wheel with four plywood panels (see photo on p. 12). He uses it to measure currents by hoisting the whole contraption over the side of the boat. As his crew lowers his paddle wheel sideways into the river, they pause every five feet so they can note which way the current is pulling the drag. Pritchard can then measure the angle of the drag line and calculate the speed of the current at different depths. Near the surface, the current is usually pulling downriver. Near the bottom, it's usually pulling upriver.
The tides, of course, move up and down the river twice a day, so Pritchard has to subtract out the force of these flood tides and ebb tides. That calculation gives him the net movement at different depths of the river. Near the surface, the net movement is downriver. Near the bottom, it is upriver.
All his samples for temperature and salinity tell him something else: the water masses near the surface are very different from those near the bottom. The surface waters moving down the river are low-salinity freshwater. The bottom waters moving up the river are high salinity.
On trips like this, the work grows less hectic after the first two days, and the Joan Bar II sometimes makes one more stop, a swimming station, not a data station. Most of the crew members strip off their clothes and leap naked into the river.
Estuaries have a structure, Pritchard will soon write, a structure composed of two distinct layers. Along the surface is river water sliding seaward. Along the bottom is ocean water pushing up the estuary. In the Chesapeake Bay, the salty ocean layer is shifted towards the east side of the estuary, pushed there by the rotation of the earth. In any estuary, salinities are highest at the mouth and decline steadily towards the head of the estuary.
What Pritchard described accurately for the first time was the basic two-layer flow, the secret structure that dominates water movement throughout the tidal Chesapeake and its tributary estuaries. That is the simple core of his discovery. It is "the fundamental insight" says a contemporary oceanographer.
It's an insight based on measurements and mathematics. From all his data points, so painstakingly acquired, Pritchard worked out the basic equations of motion that describe the circulation of the James River and then scaled his equations to explain the circulation for the entire Chesapeake Bay. His model of estuarine physics applied well beyond the Bay: it helped define what an estuary is, and when he published his paper on "Estuarine Hydrography," it revolutionized ideas about estuaries around the world.
"Don Pritchard created a whole new world for us when he revealed that estuaries have a typical circulation pattern," said Gene Cronin. "It had been going on for thousands of years, but he brought it to our attention. He had the tools, he invented some of them, to observe that process. To discover it."
Why was Pritchard the first to see the pattern? He brought the right tools to the job, but he brought something more: he brought the right ideas, the concepts that would let him look at the Chesapeake Bay in a way no one had ever tried before.
But where did he get those ideas? Don Pritchard went to college to be a chemical engineer, not an oceanographer.
When the Japanese bombed Pearl Harbor in 1941, he was a sophomore at the California Institute of Technology working through his required courses and playing quarterback on the JV football team. Cal Tech, of course, was noted not for football but for its science, engineering, and math courses, a fact that would change his life, but not in ways he expected. He expected to become starting quarterback on the varsity, graduate, get a job as a chemical engineer, and marry Thelma Alming, his high school girlfriend. That was the plan.
Harald Sverdrup, a renowned Norwegian scientist and Arctic explorer, taught Pritchard and other American oceanographers to become meteorologists of the ocean by focusing on the movement of masses of water and the underwater "fronts" they cause. During WWII, Sverdup worked with Walter Munk to develop the surf forecasting technique that saved American lives during amphibious assaults. As director of the Scripps Institution of Oceanography, he founded the country's first professional graduate program in oceanography. Credit: Scripps Institution of Oceanography
The outbreak of war brought a new plan: Pritchard decided to serve his country with his chemistry. When he volunteered to be an aerial photographic cadet, however, he learned that the Army had its own plans for Cal Tech students. It was setting up schools at UCLA and the University of Chicago, hoping to turn scientists into meteorologists who could forecast weather for air missions and amphibious landings. "They were looking for anybody with math and physics," said Pritchard. The Army accepted their volunteer and sent him to UCLA.
In his new school, Pritchard prepared for the Second World War by studying under Jacob Bjerknes, the Norwegian scientist who used the First World War to create some of the key concepts of modern meteorology. In the rainy port city of Bergen, Bjerknes worked at a research center during WWI where he collaborated with his father Wilhelm Bjerknes, the physicist who first began applying the principles and equations of fluid dynamics to understanding weather. To create their wartime forecasts, the father and son began collecting massive amounts of data from all over Norway. They set up a network of 75 weather stations that reported observations three times a day, and Jacob Bjerknes and his co-workers then drew up daily synoptic maps, creating large-scale pictures of regional weather conditions. The result was a breakthrough insight — and a new theory.
Weather events, he observed, seem to be driven by collisions of cold air masses with warm air masses. Jacob Bjerknes called these collision zones "fronts," comparing these battlefields in the sky to the front line clashes of World War I. He then developed a theory explaining how cold and warm fronts can interact to form cyclonic storm systems that rotate around low pressure centers. When he was 20 years old, Bjerknes spelled out his revolutionary ideas in an eight-page paper, and the Bergen School became the the launching pad for modern meteorology.
During World War II, Jacob Bjerknes would try to explain his ideas to Army soldiers at UCLA — but not always successfully. "Cadets would march in after lunch," said Robert Reid, a classmate with Pritchard, "and Bjerknes would turn off the lights and start showing slides." In his soft, soothing voice inflected with a Norwegian accent, Bjerknes would try to interest his audience in cold fronts, warm fronts, cyclonic storm patterns, and the math used to describe them. "When Bjerknes turned the lights on again," said Reid, "about half the students were asleep."
Pritchard, however, stayed awake long enough to finish near the top of his class. Out of 100 soldiers in his group, the Army picked Pritchard and Reid and about ten others and sent them south to the Scripps Institution of Oceanography in La Jolla, California. There they studied a secret new technique for forecasting sea swell and surf conditions during amphibious assaults. The would-be chemical engineer was on his way to becoming an oceanographer. His instructor would be yet another Norwegian scientist: Harald Sverdrup, the co-creator of the secret forecasting technique, the director of Scripps, and the most famous oceanographer of his era.
When Pritchard excelled again, this time in Sverdrup's classes, he was assigned to the forecasting team that would advise Dwight Eisenhower on when to launch the largest military landing in history — the Normandy invasion. Two days after D-Day, Pritchard landed on Omaha Beach and climbed up Pointe du Hoc, the bloody clifftop taken two days earlier by Army Rangers. There he got to play quarterback for the varsity, taking charge of Detachment YK of the 21st Weather Squadron, a team of two officers and up to six enlisted men.
Don Pritchard was working at the hinge of history. For six months he and his squad operated out of tents, creating forecasts for waves, sea swells, and surf conditions as Allied ships offloaded troops, tanks, and artillery across the beaches. Forecasting waves, according to Reid, was still more an art than a science. Standing atop German bunkers, Pritchard and Reid would peer through binoculars, count waves, and try to estimate wave heights. Their forecasts helped the Allies turn the beaches of France into the doorway to Europe, enabling troops to head inland in force while the Germans kept thousands of soldiers tied up waiting to defend the port cities of France and the Netherlands.
After the war, Pritchard found himself present at another hinge point: the creation of modern American oceanography. Recruited back to Scripps by Harald Sverdrup, he joined the country's first graduate program in oceanography, a program encouraged and supported by a U.S. Navy now eager to expand America's edge in ocean sciences. At Scripps, Pritchard studied with a number of former "weather warriors" also recruited by Sverdrup. As graduates from his new program, they would soon be called Sverdrup's "apostles" as they began creating and staffing new departments of oceanography at universities around the country.
Sverdrup, who had studied meteorology with both Wilhelm and Jacob Bjerknes, had good reason to think weather warriors would make excellent oceanographers. "What Sverdrup did was to take the model of meteorology that he learned from Bjerknes and apply it to the oceans," says Naomi Oreskes, a science historian at the University of California, San Diego. "Sverdrup thinks about the oceans in terms of the movement of masses of water in the same way that Bjerknes trained him to think about the movement of masses of air."
Bjerknes trained Sverdrup, and both trained Pritchard. By the time he arrived at Johns Hopkins, Pritchard was well primed to go hunting for whatever hidden water masses could be at work in the Chesapeake Bay.
There is a weather under the ocean and the estuary, and it's the job of oceanographers to figure it out. That was the way Pritchard went about looking at the Bay when he arrived at Johns Hopkins and that's the way he trained the new oceanographers who worked with him there. "We are sort of the meteorologists of the ocean," says Bill Boicourt, a Pritchard protege who is now a research professor at the Horn Point Laboratory of the University of Maryland Center for Environmental Science.
An oceanographer reads a weather made up of water masses, sliding above or below or bumping against each other, often mixing in various ways, the result of winds and tides, salinities and temperatures, and topography. And this weather features fronts of all kinds including upwelling fronts, lateral fronts, and plume fronts at the mouths of major rivers.
Figuring out the physics of all these forces would keep Pritchard busy for decades and leave plenty to do for oceanographers who followed him, most of whom went to work expanding and revising and critiquing Pritchard's basic model.
Oceanographers would eventually identify estuarine features like turbidity maximum zones, eddies, internal waves, lee waves, hydraulic control points, vertical mixing, stratification, and anoxic zones — features that can move fish, fish larvae, and fish food, creating biological hot spots in some areas and deserts in others.
And Pritchard, mindful that he was hired to clarify the ups and downs in fish harvests, began lecturing biologists about how physics affects fish. Oyster larvae spawned in the lower reaches of the James River, he wrote, are able to reach the upstream seed beds by hitching a ride along the saltier, low-level ocean waters that were surging upstream. Early stage croaker spawned in the ocean can move up the Bay by hitching a ride on the same train. If they stay 20 feet down, he said, they can move 130 miles up the Bay in only 20 days. Blue crab larvae, on the other hand, could be heading in the opposite direction. Spawned near the mouth of the Bay, they could be washing out to sea on surface waters.
It became quickly clear to biologists that the life cycle of nearly every major fish species in the Chesapeake was shaped in some way by the physics of all this underwater weather. "In terms of understanding how the Bay works," said Gordon "Reds" Wolman of Johns Hopkins, "Don Pritchard's physical model was absolutely essential."
"It is possible to establish a picture of the circulation pattern," wrote Don Pritchard in 1951. And this is his picture: Freshwater flows into the estuary from rivers and moves seaward. It slides atop a lower layer of heavier, salty ocean water pushing in from the mouth of the estuary. The dotted line marks the boundary between the two layers, the point of no net motion. The curving lines show the transfer of salty water into the river water above, the mixing that creates a brackish water estuary. Graphic source: Chesapeake Bay Institute
Pritchard's science would last but his new lab would not. The Chesapeake Bay Institute (CBI) that he led was, in essence, the creation of the U.S. Navy, and that connection, though hugely profitable at first, would eventually help sink the lab.
The lab began with a 1947 proposal by the Office of Naval Research (ONR): the Navy would help fund a new research center to study the hydrography of the entire Chesapeake Bay — but Maryland and Virginia had to chip in matching monies. That deal gave Don Pritchard the kind of core funding seldom seen today. He could set up a lab, rent some boats, hire scientists and technicians, and launch the most ambitious research forays yet attempted on the Bay. And he could put his new lab in the middle of a fast-growing funding stream. American oceanography was entering a golden age fueled for nearly two decades by the U.S. Navy and by the new National Science Foundation.
The result was an outburst of exploration both in the Bay and in nearby coastal waters. "Ship time was unlimited," says Bill Boicourt. And so were research funds. "I spent about $150,000 by myself as a student," he says, "not even realizing where the money came from." While still a graduate student he could ask for and get the money and boat time and authority to lead six-week cruises out along the waters of the continental shelf.
There was a method behind this mad rush to explore, says Jerry Schubel, a student of Pritchard who is now director of the Aquarium of the Pacific. "Don's approach to science was that you picked problems that were interesting and important and that you asked good questions," says Schubel. "If you had an idea and needed a few days of ship time to test it out, you had it."
The rationale for the Navy was national defense: it wanted a physical and chemical profile of the Chesapeake. The result, however, was an in-depth analysis of a shallow-water estuary, the kind of basic research that Maryland and Virginia had never been able to fund. Under Pritchard the lab also did plenty of applied research. State agencies wanted to know where to place dredge spoils from shipping channels. The Atomic Energy Commission wanted to know where to place nuclear power plants.
The funding stream was strong enough to erect on the Johns Hopkins campus a new building jointly paid for by the Office of Naval Research, the National Science Foundation, and the Atomic Energy Commission, a building designed to house the Department of Oceanography and the Chesapeake Bay Institute.
Don Pritchard adapted the tools of oceanography to the study of estuaries. He also invented new tools for data gathering. Credit: photograph courtesy of the Pritchard family
The day in 1964 when the new McAuley Hall opened may have been the high tide point for Pritchard's lab. In one of the ironies of history, military connections that were a bonus during the post-World War II era soon became a liability during the Vietnam War era. "Receiving support from any part of the defense department was controversial, especially with students," says Schubel. "If you did semi-classified research, as we did with the Navy and the Atomic Energy Commission, you were looked at with great scrutiny."
There were other apparent liabilities. "The fact that CBI did applied research was looked down upon by some of the more academic departments," says Schubel. Pritchard's Department of Oceanography would be absorbed into a larger department. His Chesapeake Bay Institute would be moved out of the building and eventually relocated off campus. The Navy affiliation would end.
Academic wars, according to witnesses, can leave some bitterness. And this one did. At the height of the conflict, Don Pritchard withdrew as director to recover from cancer. Jerry Schubel, associate director under Pritchard, left in 1974 to lead a new marine research center at what is now Stony Brook University, on Long Island. "At the end," said Schubel, "it was not very much fun being at Johns Hopkins."
When Pritchard recovered from cancer, he also left for Stony Brook to be its associate director and play a major role in building another major marine research center, this one focused on Long Island Sound.
In 1992, Johns Hopkins University closed its research center focused on Chesapeake Bay. The people were gone, but a research record remained. "The Chesapeake Bay Institute had a greater impact on our understanding of estuaries than any organization anywhere," says Schubel. "And the person largely responsible for that was Don Pritchard."