Aspects of Ocean History

MA03CH01-Prefatory-Berger ARI 17 November 2010 6:37 Geologist at Sea: Aspects of Ocean History Wolfgang H. Berger Scripps Institution of Oceanography, University of California, La Jolla, California 92093-0244; email: [email protected] Annu. Rev. Mar. Sci. 2011. 3:1–34 Keywords First published online as a Review in Advance on ocean history, deep-sea sediments, Quaternary, Cenozoic, whale evolution, October 26, 2010 by Dr John Klinck on 07/15/11. For personal use only. climate history The Annual Review of Marine Science is online at marine.annualreviews.org Abstract This article’s doi: Ocean history is largely read from deep-sea sediments, using microscopic 10.1146/annurev-marine-120709-142831 Annu. Rev. Marine. Sci. 2011.3:1-34. Downloaded from www.annualreviews.org fossils, notably foraminifers. Ice age fluctuations in the ocean’s sediments Copyright c 2011 by Annual Reviews. provided for a new geologic understanding of climate change. The discovery All rights reserved of rapid decay of ice masses at the end of glacial periods was especially 1941-1405/11/0115-0001$20.00 important, yielding rates of sea level rise reaching values of 1 to 2 m per century for millennia. Thanks to deep-ocean drilling, the overall planetary cooling trend in the Cenozoic was recognized as occurring in three large steps. The first step is at the Eocene–Oligocene boundary and is marked by a great change in sedimentation patterns; the second is in the middle Miocene, associated with a major pulse in the buildup of Antarctic ice masses and the intensification of upwelling regimes; and the third is within the late Pliocene and led into the northern ice ages. Evolution in the sea is linked to these various steps. 1 MA03CH01-Prefatory-Berger ARI 17 November 2010 6:37 INTRODUCTION In recent decades, geologists have learned to see geologic history in entirely new ways. Whatever was taught in freshman geology in the 1950s is now considered wrong in large parts. Those of us who were students in the 1960s realized that a revolution was under way, as we watched distinguished professors struggle with new ideas. Of the new ideas that became the new dogma as a result of drilling, we must mention orbitally driven climate cycles, the great cooling steps in the Cenozoic, the oxygen-stressed seas in the Cretaceous, and especially, plate tectonics and its ramifications. My own work, which informs the main areas of focus for this essay, has been largely concerned with two of these items, that is, certain aspects of the reconstruction of the ice ages (time scale measured in terms of 10,000-year steps) and of Cenozoic cooling steps (million-year time scale), with much attention to associated changes in the operation of the marine carbon cycle. The intended audience for this essay is not my colleagues in paleoceanography—many of them know more than I do about the topics discussed. But I do hope that my colleagues in related fields might find things of interest in this review, and perhaps it might serve as a useful introduction to some of the problems arising in paleoceanography, for graduate students and for college teachers concerned with the subject. Much background on the various thoughts here discussed may be found in my recent book Ocean, from which I have drawn some of the material here presented (Berger 2009). ON THE RISE OF HISTORICAL STUDIES IN OCEAN SCIENCE Marine geology and marine biology have common origins. The iconic founding hero of this con- nection was Charles Darwin (1809–1882), who started his career as a geologist on the H.M.S. Beagle. Having Darwin on board made its circumnavigation (1831–1836) famous. To many sci- entists, Darwin’s book On the Origin of Species, which is commonly linked to observations on the Galapagos Islands during said voyage, is the most important biologic work ever written and cer- tainly the most important scientific treatise published in the nineteenth century. Some, on the other hand, have found much to criticize, armed with new knowledge gained in the twentieth century. by Dr John Klinck on 07/15/11. For personal use only. Whatever the merits of such discussions, the fact is clear that Darwin was a geologist first, and that he saw geology and biology and environmental change as complementary aspects of the same thing, that is, natural history. He followed Charles Lyell (1797–1875) in emphasizing the dominant role of observable processes active over incredibly long time spans. Annu. Rev. Marine. Sci. 2011.3:1-34. Downloaded from www.annualreviews.org In spite of Darwin’s iconic stature, his various insights must not be treated as dogma. For example, regarding the origin of atolls, it was the realization that sea level fluctuated over a considerable depth owing to the buildup and decay of major ice sheets that provided a new focus—away from Darwin’s sinking-volcano concept. With sea level many times dropping well below the present sea surface, erosion of exposed reef surface during glacial periods became an important topic (Daly 1934, Purdy & Winterer 2006, Winterer 2009). Likewise, the question about potential rates of upward growth of reefs became urgent, considering that sea level rose at rates of more than 1 m per century for millennia whenever the great ice sheets wasted. John Murray (1841–1914) was another illustrious pioneer with regard to the combination of different fields of knowledge in the pursuit of ocean history. He was among the first to realize that the calcareous sediments on the seafloor are largely produced in surface waters, by shelled plankton. He was present when the Challenger Expedition established that there is no abyssal azoic environment, as was earlier surmised by Edward Forbes (1815–1854), the marine biologist who 2Berger MA03CH01-Prefatory-Berger ARI 17 November 2010 6:37 established that bottom-living organisms prefer their own depth zones. Yet another task brought negative results: Murray and colleagues did not find the “living fossils” that some of the expedition organizers may have hoped for, figuring that the deep sea would be unchanging, hence likely to harbor ancient life forms. Instead, the life forms found in the dredges of the Challenger looked thoroughly modern. We are no longer surprised: The deep ocean has changed markedly in several great steps of cooling of the planet, for the last 40 million years or so. Thus, like everything else on the planet, the organisms of the deep sea are geologically young, adapted to an ever-changing environment. The purely geologic legacy of Murray’s is equally remarkable: The sediments he studied became the means for the detailed reconstruction of ocean history, for the entire Cenozoic and the preceding Cretaceous. ( Jurassic sediments have largely disappeared into the trenches, unless they rest on continental crust.) The nature of these sediments, first clarified by Murray, define the scope of what the ocean can remember. Much has been learned since the time of these pioneers, from an intensive study of long cores, and from drilling into ocean sediments. Analysis of cores from the Swedish Albatross expedition led the way (e.g., Arrhenius 1952, Phleger et al. 1953, Emiliani 1955, Parker 1958, Olausson 1965). In later years, much more material became available from coring expeditions at several oceanographic institutions, especially at Lamont Geological Observatory. The enormous Lamont collection formed the basis for important studies on the nature of glacial periods (e.g., CLIMAP Project Members 1976, Hays et al. 1976, and later work). From 1968, material from deep-ocean drilling became available. Some of the results are sum- marized in textbooks of the 1980s and 1990s (Kennett 1982, Seibold & Berger 1996), and in various specialty symposia (e.g., Warme et al. 1981, Kennett & Warnke 1992, Summerhayes et al. 1992, Cullen & Clark 1994, Wefer et al. 1996, and references therein). Valuable summaries and highlights are in various workshop reports concerned with the planning of drilling operations (e.g., Mountain & Katz 1991, Baker & McNutt 1996, Kappel & Farrell 1997, Becker et al. 2002). In addition to a voluminous specialty literature and a long series of reports of the expeditions (e.g., Initial Reports of the Deep Sea Drilling Project; Proceedings of the Ocean Drilling Program), there are a few publications aimed at education and outreach (e.g., Hsu¨ 1992). Of special interest to ocean historians are treatises on biostratigraphy and paleoceanography (e.g., Bolli et al. 1985, Gersonde & Hodell 2002, McGowran 2005). Also, much relevant infor- by Dr John Klinck on 07/15/11. For personal use only. mation may be found in the encyclopedias edited by Steele et al. (2001) and by Gornitz (2009), with numerous entries reflecting recent insights into the workings of the sea and its history. The report by Arrhenius (1952) on cores retrieved during the Swedish Deep Sea Expedition established a new paradigm for the study of ocean history: The environment of growth of shelled Annu. Rev. Marine. Sci. 2011.3:1-34. Downloaded from www.annualreviews.org plankton organisms can be reconstructed, and thus its changes can be used to probe the biological response of the ocean to climatic change, in a heuristic approach that simulates experiment— otherwise impossible on time scales beyond the human life span. This paradigm has since been much applied, both with respect to the great cycles of climate change in the Quaternary (e.g., Hays et al. 1976, Imbrie et al. 1984, Berger & Herguera 1992) and with regard to the great cooling steps of the Cenozoic (e.g., Savin et al. 1975, Shackleton & Kennett 1975, Miller et al. 1987, Berger & Wefer 1996, and references therein). For the geologic history beyond the Quaternary, cores raised in steel tubes from regular re- search vessels have long lost their status as a preferred source of sediment for study.

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