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50 Years of Ocean Discovery: National Science Foundation 1950—2000
G. Deuser of the Woods Hole Oceanographic Institution, funded by NSF, adopted the Honjo sediment trap design and undertook a pioneering effort to make time-series sediment trap measurements in the Sargasso Sea. Deuser and coworkers documented that there was a seasonal flux of particles to the deep Sargasso Sea (e.g., Deuser and Ross, 1980; Deuser et al., 1981). These oceanic time series measurements built on the Station S measurements off Bermuda, conducted by Hank Stommel for years, and continued by several individuals for years thereafter, and were staged from the Bermuda Biological Station for Research. This effort stimulated other measurements to assess time-variant fluxes of particles to the deep ocean and was a key to initiation of the present time-series measurements in the Joint Global Ocean Flux Study (JGOFS) program.
Dissolved Trace Metals, Biological Processes, and Paleoceanography
While the large particles were being captured and analyzed, significant efforts were underway to measure dissolved trace metals in seawater using new, improved "clean" techniques largely provoked by the work of Patterson and coworkers on measuring lead in seawater (Martin, 1991). As Pilson (1998, p. 209) describes the situation, "The first real breakthrough in attempts to learn the true concentrations of these metals in seawater came in 1975 with the publication by Boyle and Edmond of a paper showing that their data from measurements of copper in surface waters south of New Zealand made sense when plotted against another oceanographic variable, in this case nitrate" (Boyle and Edmond, 1975). Boyle continued this line of research with other examples such as relationships between cadmium and phosphate. Bruland and coworkers and others added several more examples of dissolved trace-metal depth profiles (e.g., see review by Donat and Bruland, 1995). Boyle took the connection of selected trace metal and nutrient cycles and depth profiles a step further in the significant finding that cadmium could be used as a paleoceanographic tracer (Boyle, 1988).
Progress in analytical chemistry has been crucial to many of the advances in our knowledge of trace-metal biogeochemistry, and other biogeochemical processes in the oceans, as it was in the early days of chemical oceanography-marine geochemistry (Johnson et al., 1992). Figure 4, taken from the Johnson et al. (1992) paper, provides an impressive compilation of the 15 orders of magnitude range of concentrations of seawater components now measured in studies of the oceans.
Figure 4 Plot of concentrations of seawater components spanning 15 orders of magnitude in concentration. Source Figure 1 in Johnson et al. (1992). Reproduced with permission from Analytical Chemistry, volume 68, pp. 1065-1075. Copyright 1992 by the American Chemical Society.
The Iron Hypothesis and a Return to One "Root" of Modern Chemical Oceanography
Nearly simultaneous with the sediment trap research of Honjo and Deuser and their colleagues, the VERTEX Program, led by John H. Martin of Moss Landing Marine Laboratory, and Ken Bruland and Mary Silver of the University of California-Santa Cruz, undertook efforts to study the fluxes of particles in the upper ocean and midwater regions and to couple these with both chemical and biological processes (Martin et al., 1983). From these and other studies (e.g., Martin and Fitzwater, 1988), Martin and his coworkers obtained results that led them to an important and stimulating hypothesis that iron was limiting productivity in many areas of the open ocean (Martin, 1991). This hypothesis involves atmospheric transport of dust and associated iron to the iron-limited areas of the oceans where the iron, as an essential limiting factor, stimulates biological primary production. There is even a link to carbon dioxide and climate; Martin suggested that during glacial times, atmospherically transported dust would increase in the southern ocean areas and cause higher productivity, thereby drawing down carbon dioxide levels in the atmosphere. Earlier in this volume, Dick Barber discusses this from the perspective of biological productivity.
This example from the work of Martin and coworkers returns us to one of the early and continuing themes in chemical oceanography noted in the beginning paragraphs of this