Vol. 5, No. 1 January 1995 INSIDE • 1995 GeoVentures, p. 4 • Environmental Education, p. 9 GSA TODAY • Southeastern Section Meeting, p. 15 A Publication of the Geological Society of America • North-Central–South-Central Section Meeting, p. 18 Stability or Instability of Antarctic Ice Sheets During Warm Climates of the Pliocene? James P. Kennett Marine Science Institute and Department of Geological Sciences, University of California Santa Barbara, CA 93106 David A. Hodell Department of Geology, University of Florida, Gainesville, FL 32611 ABSTRACT to the south from warmer, less nutrient- rich Subantarctic surface water. Up- During the Pliocene between welling of deep water in the circum- ~5 and 3 Ma, polar ice sheets were Antarctic links the mean chemical restricted to Antarctica, and climate composition of ocean deep water with was at times significantly warmer the atmosphere through gas exchange than now. Debate on whether the (Toggweiler and Sarmiento, 1985). Antarctic ice sheets and climate sys- The evolution of the Antarctic cryo- tem withstood this warmth with sphere-ocean system has profoundly relatively little change (stability influenced global climate, sea-level his- hypothesis) or whether much of the tory, Earth’s heat budget, atmospheric ice sheet disappeared (deglaciation composition and circulation, thermo- hypothesis) is ongoing. Paleoclimatic haline circulation, and the develop- data from high-latitude deep-sea sed- ment of Antarctic biota. iments strongly support the stability Given current concern about possi- hypothesis. Oxygen isotopic data ble global greenhouse warming, under- indicate that average sea-surface standing the history of the Antarctic temperatures in the Southern Ocean ocean-cryosphere system is important could not have increased by more for assessing future response of the Figure 1. Elevation of Antarctic ice sheets showing the continental ice sheet on East Antarctica than ~3 °C during the warmest Antarctic region to global warming. and the marine-based ice sheet on West Antarctica that is largely grounded below sea level. The Pliocene intervals. A small rise in As a result, paleoclimatologists have history and stability of these ice sheets differ in that the West Antarctic ice sheet is less stable and Southern Ocean temperatures may developed later (late Miocene) than the East Antarctic ice sheet, which is believed to have devel- turned their attention to times when have caused limited melting of the oped to its approximate present form by the middle Miocene (~14 Ma). (From The Antarctic Ice climate was warmer than today. The ice sheets and associated marine by U. Radok, copyright ©1985 by Scientific American, Inc. All rights reserved.) early Pliocene was one such interval. transgression, but maximum sea During that time (4.8 to 3.2 Ma), cli- level rise was likely less than 25 m mate was warmer than at any other above the present level. Recently dis- time within the past 7 m.y. (Kennett covered evidence from the Antarctic the cold circum-Antarctic current thermally decoupled from lower lati- and Vella, 1975; Elmstrom and Ken- dry valleys indicate relative stability (“stability hypothesis”—Shackleton tudes. By 20 Ma, during the early nett, 1986). Did this early Pliocene of the Antarctic climate-cryosphere and Kennett, 1975; Kennett, 1977; Miocene or shortly thereafter, a vigor- warmth lead to major deglaciation of system since middle Miocene time Clapperton and Sugden, 1990; Kennett ous circumpolar current had undoubt- the Antarctic ice sheets and significant (~14 Ma). and Hodell, 1993). This implies that edly been established (Kennett, 1977; warming of the Southern Ocean? the Antarctic cryosphere-ocean system Lawver et al., 1992). Today the Drake INTRODUCTION Stability Hypothesis is robust and that the ice sheet is diffi- Passage imposes a unique dynamic cult to remove because of powerful constraint on poleward transport of The Antarctic cryosphere is the Until recently, most workers thermal inertia of the Antarctic circum- warm water because persistent westerly largest accumulation of ice on Earth believed that the East Antarctic ice polar current and strong negative feed- winds in the circumpolar belt deflect and comprises some 30 × 106 km3 (Fig. sheet had grown to its approximate backs tending to maintain stability. warm surface waters northward. Also 1). If all Antarctic ice melted, sea level present form by the middle Miocene Once tectonic changes such as the the position of the Antarctic circum- would rise by ~70 m. The Antarctic ice (~14 Ma) and then remained relatively opening of the Tasmanian Seaway and polar current is fixed partly by seafloor sheets are divided at the Transantarctic stable under polar desert climate due Drake Passage permitted circumpolar Mountains into a small (3.3 km3), to continental thermal isolation by flow, the Antarctic continent became Ice Sheets continued on p. 10 marine-based sheet in the west and a larger (26 km3), continent-based sheet to the east (Fig. 1). The West Antarctic ice sheet is grounded below sea level Figure 2. Oblique aerial view and may thus be vulnerable to small looking south across the west- ern Olympus Range toward the changes in surface temperatures of the western Asgard Range in the Southern Ocean and in sea level (Mer- dry valleys sector of the Trans- cer, 1978). In contrast, the more stable antarctic Mountains, Antarctica. East Antarctic ice sheet is largely Note detached mesas and grounded on bedrock above sea level. buttes, remnants of the upper The Antarctic ice sheets and adja- planation surface. Denton et al. cent Southern Ocean act together to (1993) suggested that these form the Antarctic ocean-cryosphere upland landscapes resemble system, representing one of the most those on the Colorado Plateau important components of Earth’s cli- and formed under similar semi- arid desert conditions. The dry mate system, by strongly influencing valley landscapes date to the global atmospheric and ocean circu- middle-to-late Miocene and lation (Cattle, 1991). The Southern exhibit remarkable slope sta- Ocean is an integral part of the Antarc- bility, indicating a hyperarid, tic environmental system because the cold desert environment since cold, circumpolar current maintains that time. This geomorphologi- thermal isolation of the continent. cal evidence argues against The ocean is bounded to the north major deglaciation and warm by the Antarctic convergence, or Antarctic climates during the Polar Front zone that separates cold, Pliocene. Photo from Denton et al. (1993, p. 171; used with nutrient-rich Antarctic surface waters permission). IN THIS ISSUE GSA Stability or Instability of Antarctic Ice Sheets Officers During Warm Climates of the Pliocene? ................... 1 and Officers and Councilors—1995 ...... 2 Councilors In Memoriam ....................... 2 for 1995 Forum.............................. 3 David A. Stephenson Eldridge M. Moores William R. Dickinson David E. Dunn 1995 GeoVentures .................. 4 President Vice-President Past President Treasurer Seattle wrap-up ..................... 6 South Pass Resources, Inc. University of California Tucson, Arizona University of Texas—Dallas Scottsdale, Arizona Davis, California Richardson, Texas Students’ Corner .................... 6 1994 Presidential Address (abstract) .. 7 Councilors (1993–1995) Councilors (1994–1996) Councilors (1995–1997) New GSA Bulletin Editors ............. 8 Gail M. Ashley Keros Cartwright Maryellen Cameron IEE and GEPOP ..................... 9 Rutgers University Illinois State Geological Survey National Science Foundation Piscataway, New Jersey Champaign, Illinois Arlington, Virginia Penrose Conference Scheduled ...... 12 Mark Cloos John A. Cherry James A. Helwig Letter from Washington ............. 13 University of Texas at Austin University of Waterloo Mobil Oil Corporation Austin, Texas Waterloo, Ontario, Canada Dallas, Texas GSAF Update ....................... 14 Sharon Mosher George H. Davis Thomas L. Holzer Southeastern Section Meeting ....... 15 University of Texas at Austin University of Arizona U.S. Geological Survey Austin, Texas Tucson, Arizona Menlo Park, California North-Central–South-Central Meeting 18 Anthony J. Naldrett Leigh H. Royden Orrin H. Pilkey, Jr. Alternates Receive Research Grants . 22 University of Toronto Massachusetts Institute of Technology Duke University Toronto, Ontario, Canada Cambridge, Massachusetts Durham, North Carolina Classifieds .......................... 22 Call for applications and nominations for GSA TODAY January Vol. 5, No. 1 1995 GSA BOOKS SCIENCE EDITOR GSA solicits applications and nominations of persons qualified to serve as GSA Books Science Editor. The term of the current Editor will GSA TODAY (ISSN 1052-5173) is published end December 31, 1995, and the new Editor will begin a three-year term at that time. monthly by The Geological Society of America, Inc., with offices at 3300 Penrose Place, Boulder, Colorado. Mailing This is not a salaried position, but GSA pays expenses for secretarial assistance, mail, telephone, and copying and for travel to meetings of address: P.O. Box 9140, Boulder, CO 80301-9140, U.S.A. the GSA Publications Committee. The GSA headquarters staff handles copyediting and production of books from accepted manuscripts. Second-class postage paid at Boulder, Colorado, and at additional mailing offices. Postmaster: Send address Interested persons should submit a vita, a list of publications, and a letter describing relevant qualifications, experience, and objectives. changes to