Describing the path of the Gulf Stream and other major ocean currents was an early challenge to physical oceanographers who based their interpretations on very sparse data collected from oceanographic ships. For example, using data from a multiship survey, Fuglister and Worthington (1951) proposed the Multiple Current Hypothesis, which suggested that an instantaneous chart of the Gulf Stream would show a number of disconnected filaments of current that change in time (Figure 8.1). Furthermore, they concluded that three Gulf Stream configurations were possible: a single filament (Figure 8.1a), a branching current with two filaments (Figure 8.1b), or a number of irregular disconnected filaments (Figure 8.1c). In subsequent years, ship data could not distinguish between these three and other interpretations. However, in the mid-1970s the synoptic view provided by satellite thermal infrared imagery showed that the Gulf Stream was a single filament, albeit following a tortuous and time-changing path (Figure 8.2).

Over many years synoptic views of the Gulf Stream were obtained via satellite radiometers. These results showed considerable interannual variability in the path of the stream based on the position of the “North Wall”—the boundary at which strong temperature gradients (fronts) between warm Gulf Stream waters and colder waters of the Northwest Atlantic demarcate the northernmost extent of the stream (Lee and Cornillon 1995). These interannual motions were subsequently shown to be important to fisheries (Olson 2001) and to the productivity of the Slope Sea (Schollaert et al. 2004).

FIGURE 8.1 Fuglister’s multiple current hypothesis. SOURCE: Stommel (1965). Reprinted with permission from the University of California Press, copyright 1965.

FIGURE 8.2 SST image showing the Gulf Stream in the Atlantic Ocean. SOURCE: Provided by Otis Brown and Bob Evans.