Th or collective redistirbution of any portion article of any by of this or collective redistirbution ESSAY articleis has been published in Paleoceanographic Musings Oceanography BY CHERYL LYN DYBAS , Volume 19, Number journal of Th 4, a quarterly , Volume photocopy machine, reposting, or other means is permitted photocopy machine, only is reposting, means or other From the moment a strange Icelandic understand the document was to read that saline waters in the ocean should be parchment is discovered in an old book- it backwards.” richer in the heavier isotopes of oxygen seller’s shop, to an eventual descent into Similarly, to understand ocean and than fresh waters. the “dark hollow heart” of Earth itself, climate history, paleoceanographers “read “From a piece of uranium-bear- Jules Verne’s novel A Journey to the Cen- sediment backwards”: the story’s latest ing rock we can estimate the age of the e Oceanography Society. 2006 by Th Copyright ter of the Earth is a tale of pioneering ex- chapters are preserved at the beginnings earth; from a sliver of bone we can date ploration of new worlds. (tops) of sediment cores, and its opening a prehistoric camp site,” wrote Emiliani, In the novel, Professor Hardwigg and chapters are at the cores’ ends (bottoms). considered the father of modern pa- his precocious nephew uncover a secret In hundreds of thousands of meters of leoceanography, in a 1958 paper. “The passageway into Earth’s interior by trans- sediment recovered by drilling are keys to clocks that make such dating possible with the approval of Th lating Runic characters in an old manu- some of Earth’s most elusive mysteries. are radioactive isotopes of the elements. script. And so begins a hazardous, at Isotopes have provided us with another times frustrating, but ultimately fantas- PALEOCEANOGRAPHY’S tool for looking into a distant past—a gran is e Oceanography All rights Society. reserved. Permission tic, journey to the center of the Earth. SERENDIPITOUS START ‘thermometer’ that tells the temperatures or Th e Oceanography [email protected] Send Society. to: all correspondence Today, sediment cores retrieved by Answering many worldwide climatic, of ancient seas.” drilling into Earth’s oceanic crust— oceanic, and geologic questions began In paleoceanographic terms, Urey had through efforts like the former Deep with the study of micropaleontology. translated the Runic code in Jules Verne’s Sea Drilling Project (DSDP) and Ocean The fossil skeletons of some of Earth’s ancient Icelandic manuscript. Forams Drilling Program (ODP), and current tiniest oceanic life forms—protozoans were the characters. Integrated Ocean Drilling Program like foraminifera (“forams”) and ra- When forams and other planktonic (IODP)—are the equivalent of Verne’s diolarians (“rads”), the former made of life forms die, their skeletons rain down Icelandic parchment. calcium carbonate, the latter of opaline upon the ocean fl oor. Mixed with silt As Professor Hardwigg struggles to silica—contain chemical information and clay, they form oozes that carpet vast ted to copy this article Repu for use copy this and research. to ted in teaching decipher the meaning of the manu- that records environmental change. areas of the deep sea. The oozes accumu- script’s mysterious letters, his nephew As geologist Cesare Emiliani and late very slowly, averaging 1 to 3 centi- has a “Eureka!” moment: “I had got the chemist Harold Urey of the University meters every 1,000 years. Over millennia e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. clue,” he exults. “All you had to do to of Chicago (Emiliani later moved to the they pile up to great thicknesses. University of Miami) found in the early In the interval between 200 and Cheryl Lyn Dybas ([email protected]) is a 1950s, the ratio of the stable isotopes of 65 million years ago, especially from 100 staff member in the U.S. National Science oxygen in a fossilized microscopic shell to 65 million years ago, the abundance Foundation’s Offi ce of the Director and is refl ects the temperature of the water in and diversity of microscopic plankton a marine scientist and policy analyst by which the shell grew. in the oceans greatly increased. Dur- training. She also writes on a freelance basis “Paleoceanography originated in an ing the Cretaceous Period, sea level was blication, systemmatic reproduction, reproduction, systemmatic blication, about the seas for Th e Washington Post, almost casual remark,” remembered high, and shallow seas lapped onto con- BioScience, National Wildlife, and many Emiliani years later, recalling a lecture of tinents. The environment was favorable other publications. Urey’s in which he advanced the notion for an explosion in numbers of species of 178 Oceanography Vol. 19, No. 4, Dec. 2006 forams, radiolaria, and coccolithophores. year intervals,” said Emiliani. “If Mila- former Director, Ocean Drilling Pro- At the end of the Cretaceous, many nkovitch’s theory [of cycles] is correct, grams, at the National Science Founda- of Earth’s life forms suddenly became about 10,000 years from now there will tion. “Sediment retrieved in short piston extinct, including many microscopic ma- be another advance of the glaciers, bury- cores [obtained from conventional re- rine species. Comparatively few survived. ing Chicago, Berlin, and Moscow under search vessels] became used primarily in The long snowfall of material to the thousands of feet of ice.” paleoclimatology, while material from ocean fl oor was “suddenly” less biogenic. Emiliani based his deductions on DSDP’s and ODP’s much longer cores Clays temporarily became more wide- sediments retrieved with an early piston fostered the development of paleocean- spread, forming a centimeters-thick layer corer developed in the 1940s. With the ography as we know it today.” and marking a boundary in time. advent in the late 1960s of DSDP’s more Added Pisias, “With the development Ocean sediment cores would thus advanced coring technology, and the re- of the hydraulic piston corer in DSDP shed light on questions left unanswered fi nement of isotopic analyses, paleocean- and the advanced piston corer in ODP by evidence on land, Emiliani believed. ography entered a new era. Some would [which provided high-quality core ma- say that’s when the fi eld really began. terials] parts of the two communities of DESCENT INTO THE UNKNOWN “The fi rst attempt to take a global look scientists were reunited.” Emiliani was right: seafl oor sediment at paleoclimate in the oceans occurred in Hence, the terms paleoclimatology cores allowed scientists to make dis- the CLIMAP [Climate/Long Range Inves- and paleoceanography are often used coveries from confi rmation of the cata- tigation Mappings and Predictions] proj- interchangeably. Paleoceanography is strophic impact of a meteorite 65 million ect in the 1970s,” said paleoceanographer defi ned, however, as the study of all fea- years ago, to the opening and closing of Nick Pisias of Oregon State University. tures of the past oceans—temperature, gateways between continents and their “CLIMAP showed the value of the ocean salinity, ocean circulation, biogeochem- effect on global climate. sediment record in understanding the istry, carbon cycling, and others. Early fi ndings were about the causes history of ocean circulation and its infl u- Paleoceanographer James Kennett of of Earth’s ice ages. “Current research,” ence on Earth’s climate.” the University of California at Santa Bar- wrote Emiliani in 1950s scientifi c papers, Results from CLIMAP led to a turn- bara has identifi ed three paradigm shifts “supports the theory worked out in the ing point in paleoceanography. Geolo- in the history of the fi eld: the fi rst, from 1920s by Serbian physicist Milutin Mila- gists James Hays of Columbia University, the mid-1960s to mid-1970s, concentrat- nkovitch: fl uctuations in the Earth’s orbit John Imbrie of Brown University, and ed on plate tectonics through evidence and in its axis of rotation periodically Nick Shackleton of Cambridge Univer- retrieved by rotary coring; a second from change the pattern of reception of heat sity published a paper based on CLIMAP the late 1970s to early 1990s, in which from the sun, so that there are long peri- data in the December 10, 1976, issue of undisturbed sediment could be recov- ods when the summers are cool and the Science. They advanced the idea that ma- ered through newer coring methods, led winters mild, alternating with periods of jor long-term changes in past climate are to a focus on understanding the basic hot summers and cold winters.” associated with variations in the geome- tenets of paleoceanography; then fi nally In cool Northern Hemisphere sum- try of Earth’s orbit; these changes, stated an evolution from 1990 to the present of mers, during which most winter snow Hays, Imbrie, and Shackleton, are linked an integrated global view of the planet, stays frozen, ice covers a much larger to orbital variations with periods of as the study of Earth system history. part of Earth. Milankovitch calculated 20,000 years and longer. Their paper— “We’ve gone from studying the litho- that the coolest summers would arrive “Variations in Earth’s Orbit: Pacemaker sphere to the hydrosphere, from the at intervals some 40,000 years apart. of the Ice Ages”—led to major accep- atmosphere to the cryosphere to the bio- “The analysis of the microfossils in cores tance of the Milankovitch hypothesis. sphere,” said Kennett. “Now we’re trying indicates that the low points in ocean “After CLIMAP, the fi eld essentially to understand the whole picture in the temperatures indeed occurred at 40,000- split into two parts,” said Bruce Malfait, ‘anthrosphere,’ which includes our effects Oceanography Vol. 19, No. 4, Dec. 2006 179 on the globe.” ODP Leg 189.