• francisco.machin@ulpgc.es

On this day in history...

...in 1920, Lawrence Valentine Worthington was born on March 6 in Chelsea, London, England. Known throughout his career simply as Val, he attended Westminster School and graduated in 1938, the same year he crossed the Atlantic to enrol at Princeton University. He never went back to live in England. In 1941, before completing his degree, he joined the staff of the Woods Hole Oceanographic Institution as a bathythermograph technician. A two-year interruption for service in the U.S. Navy during the Second World War aside, WHOI would be his professional home for the next four decades. He rose from technician to hydrographic analyst, then to physical oceanographer, then to senior scientist, and finally to chairman of the Physical Oceanography Department from 1974 to 1981. He retired in 1982 and was named Scientist Emeritus that year. In retirement he moved to the Bahamas, where he died on February 10, 1995, at the age of 74.

Val Worthington aboard a research vessel

Worthington's early work at WHOI placed him at the centre of efforts to describe the structure and variability of the Gulf Stream, a problem that absorbed much of the institution's attention in the postwar years. He produced detailed cross-sections of the current, examined its downstream volume increase, and contributed to the first direct measurements of deep currents in the western North Atlantic, carried out jointly with John Swallow using neutrally buoyant floats in 1957. That collaboration was one of the first observational confirmations that deep flow in the ocean was not the slow, uniform drift that earlier theories had assumed, but could be organised and directional in ways that challenged existing pictures of the thermohaline circulation.

The work for which Worthington is best remembered came in 1959, when he published a short but consequential paper in Deep-Sea Research describing what he called 18° Water. Analysing hydrographic data stretching back to the HMS Challenger expedition of the 1870s, Worthington identified a thick, vertically homogeneous layer in the interior of the northern Sargasso Sea with a remarkably constant temperature of approximately 18°C, constant salinity, and constant density. This body of water, he argued, was not a transient feature but a persistent and geographically coherent water mass, formed each winter when cold winds blowing off the North American continent stripped heat from the surface of the Sargasso Sea and drove convection deep enough to homogenise a substantial layer of the water column. The result was a mass of water that effectively preserved the thermal signature of a cold winter long after the surface had warmed again. Worthington's paper introduced the concept of mode water to physical oceanography: a water mass defined not by an extreme of temperature or salinity but by its vertical homogeneity, by the fact that it occupies a sharp mode in the volumetric distribution of ocean water. The concept proved enormously fertile. It was extended to the Pacific by Masuzawa in 1969 and subsequently identified in ocean basins worldwide; it is now understood as a key mechanism linking the atmosphere and the ocean interior, with implications for heat storage, carbon uptake, and the variability of the large-scale circulation.

In 1976 Worthington published his monograph On the North Atlantic Circulation, a synthesis of decades of hydrographic observations that laid out his interpretation of how water masses form, spread, and interact across the basin. The book was controversial: Worthington held unconventional views on the relative importance of different components of the overturning circulation, and several of his conclusions were contested by colleagues. A tribute volume published by the Journal of Marine Research in 1982 at his retirement, subtitled "Cold Wind — Two Gyres" (a translation of the Japanese nickname his colleagues had given him), made explicit reference to two of his more disputed interpretations. That the volume gathered papers from 41 oceanographers was itself a measure of the degree to which his ideas had shaped the field, even where they provoked disagreement. In 1980 he contributed a detailed volumetric census of the water masses of the world ocean, a fine-scale analysis that extended and refined earlier work by Montgomery and by Wright and Worthington, and that provided one of the most comprehensive quantitative descriptions of the global thermohaline structure assembled up to that point.

Worthington's contributions to physical oceanography cover several interconnected areas:

  • Discovery of 18° Water and the concept of mode water: His 1959 paper introduced the first identified mode water, established the mechanism of its winter formation by deep convection in the Sargasso Sea, and created a conceptual framework that transformed how oceanographers think about the connection between atmospheric forcing and the ocean interior.
  • Deep current measurements in the western North Atlantic: His collaborative work with Swallow in 1957, using neutrally buoyant floats, provided some of the earliest direct evidence of organised deep flow in the Atlantic and helped establish that the thermohaline circulation had structure well beyond what could be inferred from hydrographic sections alone.
  • North Atlantic circulation synthesis: The 1976 monograph brought together a large body of observational evidence into a coherent, if debated, picture of basin-scale circulation and water mass exchange, and remained a standard reference for researchers working on North Atlantic dynamics.
  • Volumetric census of ocean water masses: His fine-scale analysis of the temperature-salinity structure of the world ocean provided a detailed quantitative baseline for the global thermohaline inventory, building on and substantially improving earlier census work.
  • Gulf Stream structure and variability: His early work on Gulf Stream cross-sections and ring formation contributed to the detailed observational picture of the current that underpinned later dynamical studies of western boundary currents and mesoscale variability.

Val Worthington was not a scientist who sought the limelight. His colleagues remembered him as much for his storytelling and his skill as a fisherman as for his science. But the water he named in 1959 outlasted any controversy: 18° Water is now a standard entry in the vocabulary of physical oceanography, studied by successive generations of researchers trying to understand how the North Atlantic breathes. His final contract report, submitted to the Office of Naval Research on retirement, closed with a footnote that said everything: "The ocean is in good hands. I feel I can retire to the Bahamas with a clear conscience."

Sources

Reference date
6 Mar

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