Munk's career in oceanography and geophysics touched on disparate and innovative topics. A pattern of Munk's work was that he would initiate a completely new topic; ask challenging, fundamental questions about the subject and its larger meaning; and then, having created an entirely new sub-field of science, move on to another new topic. As
Carl Wunsch, one of Munk's frequent collaborators, commented: This included two types of
friction: horizontal friction between water masses moving at different velocities or between water and the edges of the oceanic basin, and friction from a vertical velocity gradient in the top layer of the ocean (the
Ekman layer).
Project Mohole In 1957, Munk and
Harry Hess suggested the idea behind
Project Mohole: to drill into the
Mohorovičić discontinuity and obtain a sample of the Earth's
mantle. While such a project was not feasible on land, drilling in the open ocean would be more feasible, because the mantle is much closer to the
sea floor. Initially led by the informal group of scientists known as the
American Miscellaneous Society (AMSOC), a group that included Hess,
Maurice Ewing, and
Roger Revelle, However, the project was mismanaged and grew in expense after the construction company
Brown and Root won the contract to continue the effort. Toward the end of 1966, Congress discontinued the project. While Project Mohole was not successful, the idea and its innovative initial phase directly led to the successful NSF
Deep Sea Drilling Program for obtaining sediment cores.
Ocean swell to measure waves traveling across ocean basins. Starting in the late 1950s, Munk returned to the study of
ocean waves. Thanks to his acquaintance with
John Tukey, he pioneered the use of
power spectra in describing wave behavior. This work culminated with an expedition that he led in 1963 called "Waves Across the Pacific" to observe waves generated by storms in the Southern Indian Ocean. Such waves traveled northward for thousands of miles across the Pacific Ocean. To trace the path and decay of the waves, he established measurement stations on islands and at sea (on
R/P FLIP) along a great circle from
New Zealand, to the
Palmyra Atoll, and finally to
Alaska. Munk and his family spent nearly the whole of 1963 on
American Samoa for this experiment. Walter and Judith Munk collaborated in making a film to document the experiment. The results show little decay of wave energy with distance traveled. This work, together with the wartime work on wave forecasting, led to the science of
surf forecasting, one of Munk's best-known accomplishments.
Ocean tides Between 1965 and 1975, Munk turned to investigations of
ocean tides, partly motivated by their effects on the Earth's rotation. Modern methods of
time series and
spectral analysis were brought to bear on
tidal analysis, leading to work with
David Cartwright developing the "response method" of tidal analysis. With
Frank Snodgrass, Munk developed deep-ocean pressure sensors that could be used to provide tidal data far from any land. One highlight of this work was the discovery of the semidiurnal
amphidrome midway between California and Hawaii.
Internal waves: The Garrett–Munk spectrum At the time of Munk's dissertation for his master's degree in 1939,
internal waves were considered an uncommon phenomenon. According to Munk, according to the year of publication of the revised model. Although Munk expected the model to be rapidly obsolete, it proved to be a universal model that is still in use. Its universality is interpreted as a sign of profound processes governing internal wave dynamics, turbulence and fine-scale mixing. With Peter Worcester and Robert Spindel, eventually motivated the 1991 "Heard Island Feasibility Test" (HIFT), to determine if man-made acoustic signals could be transmitted over
antipodal distances to measure the ocean's
climate. The experiment came to be called "the sound heard around the world." During six days in January 1991, acoustic signals were transmitted by sound sources lowered from the
M/V Cory Chouest near
Heard Island in the southern Indian Ocean. These signals traveled half-way around the globe to be received on the east and west coasts of the United States, as well as at many other stations around the world. The follow-up to this experiment was the 1996–2006
Acoustic Thermometry of Ocean Climate (ATOC) project in the North Pacific Ocean. Both HIFT and ATOC engendered considerable public controversy concerning the possible effects of man-made sounds on marine mammals. which continues to be an area of active interest. Acoustic thermometry has also been used to determine changes to global-scale ocean temperatures using data from acoustic pulses traveling from Australia to Bermuda. Tomography has come to be a valuable method of ocean observation, exploiting the characteristics of long-range acoustic propagation to obtain synoptic measurements of average ocean temperature or current. Applications have included the measurement of deep water formation in the Greenland Sea in 1989, measurement of ocean tides, and the estimation of
ocean mesoscale dynamics by combining tomography,
satellite altimetry, and
in situ data with ocean dynamical models. Munk advocated for acoustical measurements of the ocean for much of his career, such as his 1986
Bakerian Lecture Acoustic Monitoring of Ocean Gyres,
Tides and mixing In the 1990s, Munk returned to the work on the role of tides in producing mixing in the ocean. In a 1966 paper "Abyssal Recipes", Munk was one of the first to assess quantitatively the rate of mixing in the abyssal ocean in maintaining
oceanic stratification. At that time, the tidal energy available for mixing was thought to occur by processes near ocean boundaries. According to
Sandström's theorem (1908), without the occurrence deep mixing, driven by, e.g.,
internal tides or tidally-driven turbulence in shallow regions, most of the ocean would become cold and stagnant, capped by a thin, warm surface layer. The question of tidal energy available for mixing was reawakened in the 1990s with the discovery, by acoustic tomography and satellite altimetry, of large-scale internal tides radiating energy away from the
Hawaiian Ridge into the interior of the North Pacific Ocean. Munk recognized that the tidal energy from the scattering and radiation of large-scale internal waves from mid-ocean ridges was significant, hence it could drive abyssal mixing.
Munk's enigma In his later work, Munk focused on the relation between changes in ocean temperature, sea level, and the transfer of mass between continental ice and the ocean. This work described what came to be known as "Munk's enigma", a large discrepancy between observed rate of sea level rise and its expected effects on the earth's rotation. == Awards ==