Walter Munk (1917-2019) a Founder of Modern Oceanography

COMMENT OBITUARY Walter Munk (1917-2019) A founder of modern oceanography.

alter Munk revolutionized our mixing. By about 1970, oceanographers understanding of the ocean and had begun to accumulate measurements of of Earth’s rotation. He synthe- temperature interpreted as ‘internal waves’. Wsized observations, theory and empirical Munk and postdoc Chris Garrett assumed rules to solve problems both fundamental that these, unlike wind-driven waves on the and practical — about waves, tides, mixing, surface, do not have periods of storm and circulation and more. His early work aided calm, nor predominant propagation direc-

Allied beach landings in the Second World tions. The Garrett–Munk (GM) spectrum CALIFORNIA UNIV. ANSEL ADAMS, War, and from 1968 he was part of JASON, of internal waves united a vast array of oth- the elite group of scientists that advises the erwise mystifying motions in one compara- US government on military matters. tively simple framework. There followed a Gregarious and intuitive, he anticipated flowering of theory and global observations. crucial, just-ripening questions — almost to Munk’s involvement with the military the end of his long life. Decades later, many spanned seven decades. He had an affinity of them remain the focus of huge efforts for solving practical problems by combining across almost all of physical oceanography his deep knowledge of the ocean with a con- and much of geophysics. It is doubtful that cern for people who had to work in it. He was anyone will again have such a generalist’s wider field of mathematical fluid dynamics. one of the earliest academics funded by the career. He loved going to sea, was adroit with And in 1951, he published a paper point- new US Office of Naval Research (ONR) fol- mathematics, had a deep understanding of ing out that his own theory would fail in the lowing the war. His last ONR contract, again statistical significance and had a feeling for Southern Ocean because of ocean-bottom for surface-wave work, was agreed about the ocean that, more than once, led him to the topography (W. H. Munk and E. Palmén 4 years ago, when he was 97. And he was an right answer despite mistakes along the way. Tellus 3, 53–55; 1951). Implications of these enthusiastic, early member of JASON, com- Born in Austria in 1917, Munk came from ideas are a current major focus of research. plementing the defence advice of luminaries a Viennese banking family. After working in a Meanwhile, Munk turned his attention of the nuclear-weapons and radar era with New York bank, his story as a scientist began to geophysics. He showed that a research insight into how the ocean behaved, thus when he followed a girlfriend to La Jolla, area thought of as the junkyard of astron- helping to work out real US Navy issues. California, in 1939. There, he discovered omy — variations in Earth’s polar motion and Beginning in the mid-1970s, his work physical oceanography — in particular, the rotation rate — was a fount of information on the propagation of sound underwater man who became his mentor and friend, across an extraordinary range of Earth sci- brought together many of his interests: waves, Harald Sverdrup, who was director of the ences. With collaborator Gordon MacDon- submarine detection, oceanic stratification, Scripps Institution of Oceanography, where ald, he wrote the classic textbook The Rotation time-series analysis and work at sea with Munk spent his career. of the Earth (1960). In the 1950s, he was a key new instruments. What is now called ocean In the early years, he was best known player in Project Mohole — an audacious acoustic tomography was perhaps an idea for his work with Sverdrup on predicting attempt to drill through Earth’s crust to obtain ahead of its time. It is likely that this tech- ocean-wave conditions. Shortly before Pearl a sample of the mantle at the boundary, the nique to measure temperatures and currents Harbor was bombed in December 1941, Mohorovičić discontinuity. Munk never hid over large regions will prove as revolutionary Sverdrup had Munk released from the US the fact that the project was a failure. He wrote as many of Munk’s other ideas. Army and ultimately sent as a civilian to the that he had not given it sufficient attention; A perpetual international traveller and Pentagon. Months before the coastal inva- historians would say that it was snared in oil- long-term visitor, Walter was an exemplar sion of North Africa in November 1942, the industry politics. Undaunted, he moved on. of the interplay of scientific and personal pair feared huge waves would spell disaster He returned to the large-scale ocean with charisma. He trained a long list of capable for the essential beach landings of Allied his 1966 “abyssal recipes” paper, explaining collaborators of all ages. And he loved to be troops. Combining theory and empiricism, the gross structure of temperature and salinity among people: it was a rare lunch or dinner at the Sverdrup–Munk method of wave predic- in the deep ocean as a balance of upwelling his house that did not have at least one guest. tion was first used successfully during the and mixing, an idea also embraced by chem- At home, his desk was in the entrance, amid North African invasion. Developed further, ists and biologists (W. H. Munk Deep Sea Res. everyone coming and going. It was fine, he it aided the Normandy and Pacific landings. Oceanogr. Abstr. 13, 707–730; 1966). By about liked to say, “as long as no one whispers”. ■ In 1950, Munk produced the first of a 2000, this picture was replaced by a mixing few extremely fertile papers on the large- regime involving sea-floor topography — Carl Wunsch is a visiting professor of scale (general) circulation of the oceans an outcome that led Munk to simply shrug. oceanography and climate at Harvard (W. H. Munk J. Meteorol. 7, 79–93; 1950). He His mantra was that the right questions were University, and professor emeritus at the reconciled the disparate ideas of Sverdrup and much more important than the right answers. Massachusetts Institute of Technology, of physical oceanographer Henry Stommel In the 1960s and 1970s, he and UK collab- Cambridge, USA. He met Walter Munk into a foundational theory of wind-driven orator David Cartwright revived the study of at MIT in 1964, becoming friends and ocean circulation. With the applied math- tides, a subject that had become mostly mor- collaborators on diverse subjects over the ematician George Carrier, he linked ocean ibund in the twentieth century and which next 55 years. currents such as the Gulf Stream to the much is now centre-stage in understanding ocean e-mail: [email protected]