Stommel, Henry Melson
Stommel, Henry Melson
STOMMEL, HENRY MELSON
(b. Wilmington, Delaware, 27 September 1920; d. Boston, Massachusetts, 17 January 1992)
Until the second half of the twentieth century, most oceanographers believed that ocean currents were driven by winds and limited to the oceans’ upper, mixed layer. Deeper circulation, driven by density gradients induced by temperature or salinity differences, was intermittently advocated, notably by the German naturalist Alexander von Humboldt, the American hydrographer Matthew Fontaine Maury, and the British naturalist William B. Carpenter. In the 1870s, however, there was an acrimonious debate in Britain between Carpenter and James Croll over the role of wind vs. density in driving ocean currents density. When it was settled largely in Croll’s favor, most Anglophone oceanographers abandoned serious consideration of thermo-haline effects.
Deep density-driven currents gained credence in the late 1920s–1930s with the results of the German Meteor expedition of 1925, which demonstrated the existence of cold, dense, mid-layer waters apparently derived from polar regions, and with the development of a method to calculate the effects of density gradients caused by variations in temperature and salinity. But data from the abyssal ocean remained scarce, and absent evidence, most oceanographers presumed that the abyssal ocean was essentially still. For example, the leading textbook of the mid-twentieth century, The Oceans, Their Physics, Chemistry, and General Biology, held that below depths of 2,000 meters [6,600 feet], currents were likely to be “so weak that they are negligible” (Sverdrup et al., 1942, p. 392).
This presumption was refuted when Henry Stommel constructed the first widely accepted mathematical model of abyssal circulation. His model, which demonstrated that density- and wind-driven gradients could be understood as a coupled system that explained the observed surface circulation, predicted significant mid-layer and abyssal currents and demonstrated that the ocean had two potentially stable states.
Personal History and Early Career Brilliant, original, funny, and unpretentious, “Hank” Stommel was the son of a chemist, Walter Stommel, born in Germany, and Marian Melson Stommel. Hank built his scientific career on modest formal education. Growing up with his mother and his sister, Anne, in Brooklyn, New York, where his mother settled after divorcing his father, Stommel attended public schools populated by the children of Jewish and Scandinavian immigrants, where he saw “that application to school work was our only escape from uncertain employment” (Stommel Papers 1, Royal Society, London). He spent a year at the prestigious Townsend Harris High School, a competitive public school in the Bronx (the precursor of the Bronx High School of Science), before the family moved to Long Island. Stommel received a scholarship to Yale University, receiving his B.S. degree in astronomy in 1942, and then worked at the Yale Observatory while taking courses at the Divinity School, considering a career dedicated either literally or figuratively to the heavens.
In 1944 Stommel was offered a position at the Woods Hole Oceanographic Institution at Woods Hole, Massachusetts, where wartime funding was abundant for oceanographic research sponsored by the National Defense Research Committee (NDRC). Stommel joined as a research associate working with geophysicist Maurice Ewing, analyzing temperature-depth profiles taken during sound transmission exercises as part of the NDRC program in sub-surface warfare. Stommel remained at Woods Hole for the next sixteen years, his research largely sponsored by the newly established Office of Naval Research (ONR).
In 1948—at the age of twenty-eight and with no graduate training, save for his Divinity School experience—Stommel wrote the article that would establish his reputation. “On the Westward Intensification of Wind-driven Currents,” published in the Transactions of the American Geophysical Union in 1948, demonstrated that strengthening of currents along the western sides of ocean basins was a direct consequence of the variation of the Coriolis effect with latitude. This both explained the
strength and location of the Gulf Stream and predicted a deep countercurrent traveling towards the equator below it. This prediction was confirmed in 1957 by oceanographers John Swallow and Valentine Worthington and is often cited as a rare example of a successful prediction in the field of oceanography. Meanwhile, Stommel had extended his work into a full-fledged theory of ocean circulation. It began with a simple observational fact: the existence of the ocean thermocline.
The Ocean Thermocline The thermocline—the zone of rapid temperature transition between the ocean’s warm surface layer and frigid deeps—was studied in great detail during World War II for its importance to submarine warfare. As the temperature drops through the thermocline, the density of water increases and sound waves are refracted, creating acoustic shadow zones where submarines may hide. Moreover, while temperature falls with depth, salinity generally increases (because surface layers are diluted by rainfall), and these countervailing effects produce a velocity minimum zone—the “sound channel”—in which sound waves travel with little attenuation, a phenomenon exploited as the basis of cold war submarine surveillance systems. (See Figure 1.)
Stommel argued that any theory of ocean circulation had to account for the thermocline and the global presence of deep cold water. German oceanographers, including Alfred Merz, Albert Defant, and Georg Wüst, had argued that this cold water was transported from polar regions. But how? In a characteristic pattern, Stommel presented the answer qualitatively first, based on a physical insight, and then developed it quantitatively. The insight was that upward diffusion of deep water throughout the abyssal ocean could permit cold, dense waters to sink in the polar regions, while preventing warm surface waters from sinking. This suggested a picture of abyssal circulation dramatically different from the earlier models dating back to Humboldt: not a conveyor belt on which coherent water parcels sank at the poles, maintained their identity, and rose at the equator, but rather water that lost its identity as it diffused throughout the ocean.
Figure 2, published in 1959, contains all the conceptual elements of Stommel’s insight but lacked mathematical development.
“The above presentation is in the nature of a tour-deforce,” Stommel wrote. “One cannot pretend that it describes the abyssal circulation accurately in detail” (Stommel, 1959, p. 82). For that, Stommel turned to Arnold Arons.
Arons was a physicist who had been drawn into oceanography by Cold War–related issues, including the dispersal of nuclear fallout in the oceans and the base surge produced by large explosions in shallow water harbors. In 1954 he was invited to a meeting organized by the U.S. Atomic Energy Commission (AEC) at Woods Hole on ocean disposal of civilian nuclear waste. One issue raised at the meeting was the potential effects of radiogenic heat from waste packages on the thermohaline circulation. Arons recalled:
The AEC people pointed with concern to the mounting volume of wastes being stored [at power plants] but no oceanographer was sanguine about [oceanic] disposal. … On the other hand, no one was prepared to make categorical predictions. … It was about this time that Stommel and I had begun thinking about abyssal circulation and … the work that led to what is now usually called the Stommel-Arons model. (Arons, personal communication, 16 October 2000)
The model was laid out in a five-part paper published over the course of twelve years. Most critical were the first two, published in Deep-Sea Research in 1960 by Stommel and Arons. They concluded that it was wrong to think of the ocean as having two different forms of circulation: one wind-driven and the other density-driven. It was better, they said, to envisage a single system in which the surface effects were in part dependent on vertical transport and vice versa. Wind could be viewed as a source or a sink, no more or less than sinking or upwelling of water masses. Moreover the requirements of geostrophy and the conservation of mass led to western boundary currents irrespective of the location of sources and sinks, a conclusion that had important consequences for the stability of earth’s climate. Stommel and Arons wrote: “The exact location of the sources is … more or less a climatological accident. One could disappear and another appear somewhere else … with changing climatic conditions, but these would be accompanied by no major modifications of the interior region of the abyssal circulation, and with no major change of the amplitude of the overall abyssal circulation.” This perspective was odds with the conventional wisdom, which held that the magnitude of the abyssal circulation would be controlled by the amount of winter cooling in polar regions and “that a warming of polar regions of only a few degrees would largely stop the abyssal flow.” Instead, they concluded, “warming of polar regions of one or two degrees would not affect deep transports except possibly to shift the location of the sources, and to reshuffle the western boundary currents” (“On the Abyssal Circulation of the World Ocean II,” 1960, p. 225).
There was, however, another factor to consider. Because heat transfer tends to be faster and more efficient than the processes that change salinity—mainly evaporation, but also mixing, diffusion, and sea ice formation— in the natural world temperature effects tend to dominate. But one could imagine a situation in which salinity differences predominate, and to determine how likely that would be, one could calculate the relative effects of temperature and salinity on density.
In “Thermohaline Convection with Two Stable Regimes of Flow” (1961), Stommel imagined two adjacent idealized basins with different temperature and salinity conditions and solved the equations for heat and salinity transfer between them. In the case where two vessels were connected by a capillary tube at the bottom (through which more dense water could move) and an overflow connector at the top (through which less dense water could move), there were two stable solutions to the equations: one in which temperature effects dominated and one in which salinity effects dominated. This implied that two stable regimes might exist in nature. Stommel wrote:
The fact that even in a very simple convective system … two distinct stable regimes can occur … suggests that a similar situation may exist somewhere in nature. One wonders whether other, quite different states of flow are permissible in the ocean or some estuaries and if such a system might jump into one of these with a sufficient perturbation. If so, the system is inherently fraught with possibilities for speculation about climatic change. (1961, p. 228)
In the context of anthropogenic global warming, these possibilities are a topic of heightened concern in the early twenty-first century, and their recognition is part of Stommel’s lasting legacy.
Rise of “Big Oceanography.” Stommel’s life spanned a period in which American oceanography was transformed in size and scope by the influx of financial and logistical support from the U.S. Navy, and his feelings about this transformation were ambivalent. Although his fame rested on work funded by the navy, Stommel repeatedly expressed misgivings over the application of science to warfare. Reflecting back on his early career, Stommel later recalled: “I was troubled by the morality of killing in war, and it seemed to me that antisubmarine warfare was the least immoral of any military application of science that I could do. At any rate, it did not involve civilian targets” (Stommel Papers 1, Royal Society, London). In 1960 he helped to lead a rebellion of faculty at Woods Hole—the “palace revolt”—over the question of military funding and direction of research, feeling that the director, Paul Fye, was pushing the institution too far in the direction of “mission-driven” research and leaving insufficient opportunities for individual initiative and creativity. When Fye dismissed this as nostalgic “pastoralism,” Stommel responded with a memo in which he suggested that if the director did not want his scientists to be shepherds, evidently he wanted them to be sheep. The revolt culminated in a faculty vote of no confidence, but when the trustees backed Fye, many of the faculty involved left. Stommel was among them, working for the next sixteen years as a university professor—briefly at Harvard, then at MIT—and returning to Woods Hole on the retirement of Paul Fye in 1977.
Stommel was also ambivalent about the growth of “big oceanography”—viewing it, like the military largesse that enabled much of it—as a threat to individual curiosity and creativity. Yet he became involved in several highly political, even bureaucratic, big-science projects of the 1970s, including the Global Atmospheric Research Program (GARP), the GARP Atlantic Tropical Experiment (GATE), the Mid-Ocean Dynamics Experiment (MODE), and the World Ocean Circulation Experiment (WOCE). While referred to as “experiments,” these were for the most part large-scale data gathering efforts, which Stommel accepted as necessary to advance oceanography even as he worried that they were risky to the autonomy and creativity of the individuals involved with them. His own scientific hero was John Swallow, the gentle and modest inventor of the neutrally buoyant float, whom Stommel admired to the end of his life for being a “full sized observer in the old-fashioned one-man way” (Stommel Papers 4: Correspondence 1990).
Honors and Awards Stommel married Elizabeth Brown on December 6, 1950. They had three children, two boys and a girl. He had a dynamic personality that graduate students and colleagues found highly appealing. His success as a scientist was based on his wide-ranging curiosity, prodigious powers of intuition and visualization, and a wry sense of humor. Stommel’s many honors and awards included the (U.S.) National Medal of Science, the Craaford Prize of the Royal Swedish Academy, the Huntsman Award of the Bedford Institution of Oceanography, his election to the (U.S.) National Academy of Sciences in 1959, and his foreign membership in the Royal Society of London, the Soviet Academy of Sciences, and the Académie des Sciences de Paris.
WORKS BY STOMMEL
“On the Westward Intensification of Wind-driven Currents.” Transactions of the American Geophysical Union29 (1948): 202–206.
“The Abyssal Circulation of the Ocean.” Nature180, no. 4589 (1957): 733–734.
“A Survey of Ocean Current Theory.” Deep-Sea Research 4 (1957): 149–184.
“The Abyssal Circulation.” Deep-Sea Research 5 (1958): 80–82.
With Arnold Arons and A. J. Faller. “Some Examples of Stationary Planetary Flow Patterns in Bounded Basins.”Tellus 10 no. 2 (1958): 179–187.
With Allan R. Robinson. “The Oceanic Thermocline and the Associated Thermohaline Circulation.” Tellus 3 (1959): 295–308.
With Arnold B. Arons. “On the Abyssal Circulation of the World Ocean I. Stationary Planetary Flow Patterns on a Sphere.” Deep-Sea Research 6 (1960): 140–154.
With Arnold B. Arons. “On the Abyssal Circulation of the World Ocean II. An Idealized Model of the Circulation Pattern and Amplitude in Oceanic Basins.” Deep-Sea Research6 (1960): 217–233.
“Thermohaline Convection with Two Stable Regimes of Flow.” Tellus13 (1961): 131–149.
“The Large-Scale Oceanic Circulation.” In Advances in Earth Science, edited by Patrick M. Hurley. Cambridge, MA: MIT Press, 1966.
With Arnold B. Arons. “On the Abyssal Circulation of the World Ocean: III. An Advection–lateral Mixing Model of the Distribution of a Tracer Property in an Ocean Basin.” Deep-Sea Research 14 (1967): 441–457.
With Arnold B. Arons. “On the Abyssal Circulation of the World Ocean: V. The Influence of Bottom Slope on the Broadening of Inertial Boundary Currents.” Deep-Sea Research 19 (1972): 707–718.
Collected Works of Henry M. Stommel. Edited by Nelson G. Hogg and Rui Xin Huang. 3 vols. Boston: American Meteorological Society, 1995.
Arons, Arnold. “The Scientific Work of Henry Stommel.” In Evolution of Physical Oceanography: Scientific Surveys in Honor of Henry Stommel, edited by Bruce A. Warren and Carl Wunsch. Cambridge, MA: The MIT Press, 1981.
Sverdrup, Harald; Martin W. Johnson; and Richard H. Fleming. The Oceans, Their Physics, Chemistry, and General Biology. Fleming, NY: Prentice-Hall, 1942.
Swallow, John C., and L. Valentine Worthington. “Measurements of Deep Currents in the Western North Atlantic.” Nature179, no. 4571 (1957): 183–1184.
Veronis, George. “A Theoretical Model of Henry Stommel.” In Evolution of Physical Oceanography, edited by Bruce A. Warren and Carl Wunsch. Cambridge, MA: The MIT Press, 1981.
Warren, Bruce A. “Arnold B. Arons (1916–2001).” EOS: Transactions of the American Geophysical Union 82, no. 30 (2001): 328.
———, and Carl Wunsch, eds. Evolution of Physical Oceanography: Scientific Surveys in Honor of Henry Stommel. Cambridge, MA: The MIT Press, 1981.
Wunsch, Carl. “Henry Melson Stommel: September 27, 1920–January 17, 1992.” National Academy of Sciences Biographical Memoir 72 (1997): 331–350.