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Paleoceanographic Musings Oceanography

BY CHERYL LYN DYBAS , Volume 4, a quarterly journal of Th 19, Number photocopy machine, reposting, or other means reposting, is only photocopy machine, permitted

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 Copyright 2006 by Th Society. e Oceanography 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 Th of approval the with 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 Permission reserved. Society. All rights e Oceanography is gran tic, journey to the center of the Earth. SERENDIPITOUS START ‘thermometer’ that tells the temperatures all correspondence to: Society. Send [email protected] e Oceanography or Th 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 in teaching to and research. copy this for use Repu article 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 MD 20849-1931, USA. 1931, Rockville, Box PO Society, e Oceanography 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, 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. tive, resulting in blooms of diatoms and Rapid progress in paleoceanography “During the Cenozoic Era,” said Ken- an abundant supply of organic carbon happened in the past few decades, he be- nett, “Australia separated from Antarcti- to the seafl oor. Another sharp change lieves, as a result of engineering advances ca and ‘drifted’ northward, which opened happened about 14 million years ago, that enabled recovery of continuous the Tasmanian Gateway and allowed the when increasing sediment, wood frag- deep-sea sediment cores; development Antarctic Circumpolar Current to devel- ments, and organic matter were depos- of biostratigraphic correlations, which op. This current began to isolate Antarc- ited from adjacent land masses. Sedi- provided a temporal framework for in- tica from the infl uence of warm surface mentation took yet another turn about terpreting the cores; confi rmation of the currents from the north, and an ice sheet 600,000 years ago when large continental concept of plate tectonics, which gave a started to form.” ice sheets advanced to and retreated context for interpreting paleogeography; Eventually, conduits led to deepwater from New Jersey. and development of new geochemi- circulation between the southern In- In a later ODP leg, 174AX, an on- cal, mineralogical, and other techniques dian and Pacifi c Oceans and ultimately shore extension of an offshore expedi- that allowed for interpretations of the to “ocean conveyor belt” circulation. tion, Miller found that sea-level changes paleoenvironmental conditions under “Continuing Antarctic thermal isolation during the Late Cretaceous Period were which sediments were deposited. caused by this continental separation,” huge, more than 25 meters, and rapid, “Ocean drilling has resulted in spec- said Kennett, “contributed to the evolu- occurring on timescales of thousands to tacular paleoceanographic and geologic tion of global climate from relatively less than a million years. Ice formation revelations,” said Margaret Leinen, a pa- warm early Cenozoic ‘greenhouse’ to late in Antarctica likely caused these sea-level leoceanographer and NSF Assistant Di- Cenozoic ‘icehouse.’” changes—in a period previously thought rector for Geosciences. to be ice-free. Ice sheets confi ned to the Sediments Off New Jersey Tell Tale continent’s interior would explain the FIVE OUTSTANDING of Long-Ago Ice Sheet Formation fi nding, Miller believes. Although the CONTRIBUTIONS Sediments recovered off the New Jersey ice would not have reached the coast, it Gateways: Opening and Closing of coast on ODP Leg 150 tell a long-ago would have been enough to alter global Seaways Led to Ocean Circulation tale of sea-level rise and fall. Ken Miller, sea-level signifi cantly. and Climate Changes a geologist at Rutgers University in New Paleoceanographers discovered that rap- Jersey, was among scientists on ODP The Eocene: Rads Ruled id (decadal to centennial scale) climate Leg 150 who studied the sedimentary re- “Radiolaria ruled the Eocene,” said Ted shifts are a global phenomenon, and cord of sea-level changes extending back Moore, a paleoceanographer at the Uni- documented climate extremes, including 35 million years. Reading the sediment versity of Michigan, “if the stratigraphic ocean-wide anoxic events, said Leinen. layers, he gained clear insights into how record from that time is any indication.” “They confi rmed that a ‘hothouse world’ large, rapid global sea-level change results Moore has conducted paleoceanographic existed some 55 million years ago, when from the waxing and waning of Northern research on DSDP and ODP legs, includ- warm subtropical climates prevailed Hemisphere ice sheets. ing ODP Leg 199 in the central equatori- even at the polar regions.” The New Jersey continental margin al Pacifi c. There he and others found that Millions of years later, a passageway underwent a dramatic change during the path of plate motions carried a trace formed between Australia and Antarcti- Earth’s transition from hothouse to ice- of equatorial upwelling and productivity ca, found Kennett and colleagues, setting house. Miller and colleagues found cal- northward—in radiolarians preserved up a situation in which the hothouse cium carbonate chalks from a warmer in sediments. The sediments contain a era ended and a 40-million-year cooling climate lying beneath sands and muds carbonate and siliceous interval from the of the Earth began. Kennett and others deposited by glacial activity. About Holocene through the base of the Oligo- initially made the discovery on DSDP 22 million years ago, surface waters in cene. But through the Eocene and Paleo- Leg 29, then re-confi rmed it on the later this region became unusually produc- cene, the section is composed primarily

180 Oceanography Vol. 19, No. 4, Dec. 2006 of radiolarian ooze and red clay, giving dioxide levels may have been 1,300 to preserved in DSDP and ODP sediment scientists a rare look at this important 2,300 parts per million (ppm). Today’s cores from 14 sites around the world. zone of upwelling through time. level is about 380 ppm, and rising. Fifty-fi ve million years ago, deep-ocean “Biostratigraphy, based on the pres- Bice’s research suggests that future circulation in the Southern Hemisphere ence of particular assemblages of fora- ocean warming from the build-up of abruptly stopped the conveyor belt- minifera, coccoliths, radiolaria. and dia- greenhouse gases may be much greater like process known as “overturning,” in toms, has been critical to understanding than predicted. which cold, salty water in the depths what sediments in cores have to tell us,” “switches” with warm water on the sur- said Moore. “When DSDP got under- Global Signals... face. But overturning became active in way, knowledge of the taxonomy and During January 2006, paleoceanogra- the north, even as it was shutting down stratigraphy of radiolarians blossomed. phy lost one of its greatest scientists in the south. This shift, the paleoceanog- Rads are very useful in paleoceanogra- and also announced one of its most far- raphers believe, drove unusually warm phy, especially in regions where calcium reaching discoveries. water to the deep sea, likely releasing carbonate in forams isn’t preserved well Paleoceanographer Nick Shackle- stores of methane from gas hydrates, or at all, such as in high-latitude oceans.” ton died on January 24, 2006 at age 69. which led to further warming. Dozens of species of radiolaria are pres- Shackleton discovered that oxygen The heat-up of 55 million years ago ent in Arctic and Antarctic seas, and in isotope variations recorded in foram happened in less than 5,000 years, a blip areas of the oceans where there is strong shells are dominated by changes in on geologic timescales. “Overturning is upwelling, such as the equatorial Pacifi c. Earth’s ice-volume. very sensitive to surface ocean tempera- On ODP Leg 199, Moore and col- “This insight,” wrote paleoclimatolo- tures,” said Norris. “This may be one of leagues used accumulation rates of bio- gist William Ruddiman of the University the best examples of global warming genic debris (such as fossilized rads) of Virginia in a tribute to Shackleton triggered by the massive release of green- to determine the position and strength published in the journal Science’s May 5, house gases. It gives us a perspective on of upwelling zones in the early Pa- 2006, issue, “meant that a common ice- what the long-term impact is likely to be leogene, a time of unexplained very volume signal is present in all carbon- of today’s human-caused warming.” warm temperatures. ate-bearing sediments, and that oxygen- isotopic signals can be used to correlate In Jules Verne’s A Journey to the Center of Oceans Warmer than a Hot Tub ice-age marine records on a nearly the Earth, Professor Hardwigg’s nephew Tropical Atlantic Ocean temperatures global basis.” catches a glimpse of what lies ahead on between 100 million and 84 million years When Nick Shackleton began his re- their journey into the unknown: “We ago reached 42°C—about 14°C higher search, wrote Ruddiman, “the investiga- followed an extraordinary spiral staircase than today. These temperatures are off tion of past climatic changes was an area down into a fi ssure in the earth. What the charts when compared to what was of ‘academic’ interest only. Four decades I see is incredible. My descent into the previously known, according to pale- later, his lifetime achievements defi ne interior of the earth is rapidly changing oceanographer Karen Bice of the Woods the emergence of our understanding of all preconceived notions, and day by day Hole Oceanographic Institution. To the operation of Earth’s natural climate preparing me for the marvelous.” determine these ancient ocean tempera- system. This understanding of the past is The very defi nition of the sediment tures, Bice and others analyzed sediment now central to efforts to predict the fu- record…and of paleoceanography. cores retrieved from the seafl oor off Suri- ture climate we have begun to create.” name in South America on ODP Leg 207. Indeed, those comments echo research ACKNOWLEDGEMENTS They used core samples to estimate both results published in the journal Nature The author thanks Jim Kennett, Bruce ocean temperatures and atmospheric on January 4, 2006, by Flavia Nunes and Malfait, Steve Bohlen, Ted Moore, Nick carbon dioxide levels: when the ocean Richard Norris, both of Scripps. Pisias, Howard Spero, and many others was hot-tub-hot, atmospheric carbon Nunes and Norris looked at forams who provided input.

Oceanography Vol. 19, No. 4, Dec. 2006 181