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The difficulty in attempting to present a coherent picture of ocean sciences is that there is no such coherent picture—oceanography is whatever scientists interested in the ocean happen to do. Depending on the changing interests of the scientists practicing the art, ocean science can readily change focus and has done so many times over the last century. An early task was to make an inventory of what lives near the shore, and how. It was followed by exploration of coastal waters, and by systematic investigation of the global ocean—its physics, its chemistry, its biology, and its history and geologic framework . It is now the changing ocean that is at the center of attention. Motivations have varied as well. In the early years, questions concerning the rules and history of evolution were important , as well as the life histories of marine organisms, which documented in detail their exquisite adaptations to the environment and to each other. Also, it was the desire to understand , from first principles, why currents move the way they do, and how the physical environment controls the distribution of organisms. The needs of fisheries and of navies provided the main impetus for expansion within the first half of the twentieth century, and after World War II. These needs supported growing efforts in physical, chemical, and biological expeditions and laboratory studies for more than half a century. Lately, with the increase in human impacts, first along the coast and then on a global scale, motivation has shifted again. Much of exploration now is linked to assessing the scope of the impacts of polluting coastal water bodies, of overfishing, and of changes in the physics and biology of the ocean that may be attributable to global warming. When attempting such assessments, motivated by the desire to understand the response of the ocean to disturbance, and perhaps to guide remedial action where this is called for, a serious and pervasive problem soon emerges. It is that the natural condition, undisturbed by human influence, is no longer available for study and has not been available for several decades. Thus, it is not possible to clearly separate natural background from response to human disturbance, except in theory. As the nature of the ocean has changed, so has the science that deals with it. The great trends are well summarized in a review by 471 Epilogue THE GREAT TRENDS IN EXPLORATION AND THE CHALLENGES AHEAD Margaret Deacon, doyenne of the history of oceanography.1 She takes the period between 1880 and 1930 as the decades that laid the foundations for modern oceanography. It is a time of great expeditions, from the British Challenger Expedition at the beginning, to the British Discovery Expeditions and the German Meteor Expedition at its end. Perhaps the most famous of all the expeditions within this period was the Fram’s, venturing into the Arctic Sea, under the leadership of Fridtjof Nansen, explorer, allaround naturalist, and discoverer of important oceanographic processes, such as the drift-at-anangle mathematically explained by Ekman. The needs of commercial fisheries and whaling, and a general desire to understand the physical and biological workings of the ocean, were important driving forces in this phase of research. In her article, Deacon illustrates two discoveries from the founding period. One is the bottom topography of the Atlantic Ocean, as mapped by the Challenger scientists, which showed the existence of the Mid-Atlantic Rise, and different bottom -water temperatures on either side of the rise. The morphology of this mountain chain, elaborated in the early part of the twentieth century , posed a puzzle that would be solved, eventually , by the concept of seafloor spreading, in the 1960s. Deacon’s other illustration shows longitudinal oceanographic sections through the western and eastern basins, for salinity, which demonstrate the complicated stratification of the Atlantic Ocean. The sections are from Wüst’s synthesis of the Meteor survey. They are crucial for the understanding of the thermohaline circulation of the ocean. An Atlantic bias is evident in Deacon’s review, and quite understandably so: important contributions to this founding phase of research came from British, Scandinavian, and German scientists.2 The 1930s saw great expansion into sophisticated instrumentation, including seismic surveying and gravity measurements, besides routine temperature measurements (by bathythermograph ). Important insights came from experimental biological work on production in its dependency on light and nutrients, and on the vertical migration of zooplankton. In that decade, also, oceanographic work at North American institutions began to...

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