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Home , Antarctic Convergence, East Antarctic Ice Sheet, Ice sheet, Subantarctic, West Antarctic Ice Sheet

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 Sheets During Warm of the ? 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 surface . 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 , and composition of 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, -level his- hypothesis) or whether much of the tory, ’s heat budget, atmospheric disappeared ( composition and circulation, thermo- hypothesis) is ongoing. Paleoclimatic haline circulation, and the develop- data from high- 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 ocean- 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 than ~3 °C during the warmest Antarctic region to global warming. and the marine-based ice sheet on that is largely grounded below . The Pliocene intervals. A small rise in As a result, paleoclimatologists have history and stability of these ice sheets differ in that the West is less stable and Southern Ocean temperatures may developed later (late Miocene) than the , 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 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 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 climate due Drake Passage permitted circumpolar into a small (3.3 km3), to continental thermal isolation by flow, the Antarctic 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 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 important components of Earth’s cli- and formed under similar semi- arid desert conditions. The dry mate system, by strongly influencing 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 , 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). Ice Sheets continued from p. 1 as late Pliocene age—3.1 to 2.5 Ma; EVIDENCE FROM DEEP-SEA than today (Shackleton and Kennett, Webb and Harwood, 1991) in sedi- SEDIMENTS 1975; Hodell and Venz, 1992; Shackle- topography and by the westerly surface mentary deposits of the Sirius Group, ton et al., 1994). Different views exist, If such major warming and degla- wind stress, which is strongly depen- found at high altitudes (~2000–2500 however, as to the magnitude of tem- ciation occurred during the Pliocene, dent upon land-mass distribution m) in the . perature and ice reduction represented clear evidence should exist in marine (Gordon, 1988). These critical tectonic The Sirius Group consists of lodgment by the oxygen isotopic signal. At one sediments from the Southern Ocean factors were not appreciably different tills interbedded with glaciofluvial, extreme, Raymo (1992) suggested major and in glacioeustatic changes on conti- during the Pliocene than today (Lawver glaciolacustrine, and colluvial sedi- Antarctic deglaciation (50% reduction nental margins. Results from deep-sea et al., 1992). Faunal and sedimentologi- ments containing material in ice) during the early Pliocene, drilling in the Southern Ocean have led cal data indicate strong stability in the representing evidence for remarkable whereas Kennett (1977) argued for to major advances in the understand- position of the circumpolar current warmth, even as close as 500 km from relative stability of the ice sheets. ing of climate, oceanography, and the during the late Neogene; northward the (Webb and Harwood, Hodell and Venz (1992) provided biota of the Antarctic continent and and southward migrations of the Polar 1991; Hill and Truswell, 1993). The critical constraints on estimates of the surrounding ocean (Kennett and Bar- Front zone have been minor in relation are inferred to have lived in magnitude of Pliocene ice volume and ron, 1992). Marine sedimentary evi- to the vast breadth of the Southern marine basins within the Antarctic temperature change, using high-resolu- dence presented here supports relative Ocean (Lazarus and Caulet, 1993). craton and, together with associated tion oxygen isotopic records of benthic stability of the Antarctic cryosphere- The net effect of the relatively stable basinal sediments, were carried up the and planktonic foraminifera from climate-ocean system during the late position of the Antarctic circumpolar Transantarctic Mountains by develop- Ocean Drilling Program (ODP) Site Neogene. Geomorphological evidence current has been long-term thermal ing ice sheets after ~2.5 Ma, the age of 704 in the Subantarctic sector (47°S) from the continent also indicates that insulation of the Antarctic continent the youngest diatoms in Sirius sedi- of the southeast Atlantic (Fig. 3). Com- hyperarid, cold desert conditions have and resulting stability of the Antarctic mentary rock. pared with earlier results, this record persisted on Antarctica since about cryosphere. Other evidence cited in support has proven crucial for interpretations the middle Miocene (Fig. 2; Marchant of the deglaciation hypothesis includes of ice-sheet history because both plank- et al., 1993; Denton et al., 1993), with Deglaciation Hypothesis vertebrate and δ18O of bivalves tonic and benthic foraminifera were little temperature increase above mod- and the Sirius Group from the Vestfold Hills (Quilty, 1993), analyzed from a high-latitude location. ern values. highstands of sea level during the mid- Prior to 3.2 Ma in the Pliocene, benthic More recently, workers have dle Pliocene (Haq et al., 1988; Dowsett δ18O values were always less than or proposed a competing hypothesis Pliocene Climatic History: and Cronin, 1990), and warming of equal to Holocene values (i.e., 3‰) (“deglaciation”) suggesting that pre- Oxygen Isotopic Evidence Antarctic surface waters inferred from and fluctuated by only ~0.5‰. The ice sheets were smaller and Pliocene planktonic microfossil assem- One of the most useful tools for full range of the planktonic oxygen iso- of lower profile than today and were blages (Abelman et al., 1990; Ishman estimating past changes in temperature topic variations (0.75‰) were slightly formed in much warmer conditions and Rieck, 1992). and global ice volume is the measure- greater than the benthic fluctuations, (Webb and Harwood, 1991; Barrett The deglaciation hypothesis ment of stable isotopes of oxygen in reflecting larger surface-water tempera- et al., 1992). This model also invokes implies that the Antarctic ice sheets foraminiferal tests. Since the δ18O of ture changes. However, minimum large changes in the volume of the are unstable and susceptible to decay calcite is dependent on both the tem- foraminiferal δ18O values were never Antarctic cryosphere; reductions to during times of warm climatic condi- perature and oxygen isotopic composi- more than 0.5‰ to 0.6‰ lower than about two-thirds of the present size tions such as those reached during tion of seawater (controlled largely by Holocene values (i.e., 2.3‰). The δ18O of the East Antarctic ice sheet during the Pliocene. By analogy, Barrett (1991) ice volume), separating the temperature signal from Site 704 can be interpreted Pliocene intervals, complete loss of the suggested that the ice sheets may be- and ice volume signals has proven diffi- to represent either a maximum 2.5 °C West Antarctic ice sheet, and consider- come unstable at elevated CO levels cult for paleoclimatic reconstructions. warming of Subantarctic surface waters able warming (>5 °C) of Antarctic sur- 2 and temperatures predicted to be Increased temperature and reduced or a maximum 60% reduction in conti- face waters. Support for major deglacia- extant, due to global warming, by global ice volume have long been in- nental ice volume (Hodell and Venz, tion and warming of Antarctica is the year 2100. ferred for the early Pliocene from oxy- largely inferred from the presence of gen isotopic values that were lower Ice Sheets continued on p. 11 reworked oceanic diatoms (as young

Future continued from p. 9 affiliatory diversity—with insights and loy. Both have extensive experience in metropolitan New York news area. He information on such topics as what media interface training. Yannacone is has first-hand knowledge about highly information will be made available to is newsworthy; how to make news, an environmental lawyer whose past controversial news issues and the inter- participants through the World Wide become news, present news, and dis- experience includes successful litiga- face of federal, state, and local political Web on the Internet, or through direct tribute news; how to select the most tion related to banning the use of DDT, jurisdictions with their concomitant requests to IEE. effective medium for a story; news as saving the Florissant (Colorado) Fossil bureaucratic turf wars. Among geo- At the GSA Annual Meeting in public information and education; Beds, and filing the initial class action science topics he covers on a regular Seattle, IEE sponsored its first workshop ethical obligations and responsibilities; complaint that later became known as basis are ground-water remediation and on public information and education and establishing credibility with the the Agent Orange litigation. Molloy is the effects of pollution on sole-source techniques. The objectives were to pro- media. an award-winning journalist and edi- aquifers, the impact of storms and lit- vide a group of geoscientists—repre- The workshop in Seattle was led by -in-chief of a chain of weekly news- toral drift on barrier beaches, and the senting geographic, disciplinary, and Victor J. Yannacone, Jr., and Kevin Mol- papers on within the effects of salinity changes in estuarine environments.

EXPERTISE (check all that apply) PROFESSIONAL ADDITONAL CATEGORY POTENTIAL GEPOP ROLES Future Involvement APPLICATION INTERESTS (check all that apply) (check all that apply) Archaeological geology The success of the Seattle ______Education ___ Ongoing Activities Computers/mathematical geology endeavor, as indicated by postwork- Education, primary Media liaison Economic geology shop comments of the participants, Engineering geology Education, secondary Leadership liaison has led to the planning of four addi- Environmental geology Education, higher Info clearinghouse Education, public Speakers’ bureau tional media workshops this spring in Geochemistry, aqueous/organic ______Geochemistry, other Natural Science Network coordination conjunction with the GSA Section ___ Geoscience education/information Ecosystem management Events meetings in Hartford, Connecticut, /tectonophysics Energy resources Organization Knoxville, Tennessee, Lincoln, Ne- Hydrogeology Engineering Publicity braska, and Bozeman, Montana. Victor Hazard mitigation Speaking Yannacone and Kevin Molloy will Marine geology Land use management Teaching again lead the workshops, which will Mineral resources Materials preparation Mineralogy include “hands-on” activity in which Remediation ___ Ideas Paleoceanography/ participants practice the techniques. Paleontology/paleobotany Restoration, ground-water Network recruitment Enrollments for the individual work- Petroleum geology Restoration, Issue identification Petrology, igneous/metamorphic Waste management Topic identification shops will necessarily be limited, but Water resources Sponsor identification all interested geoscientists are encour- geology ______Geomorphology/ Social Science aged to submit an application even if Remote sensing/GIS Community relations Other (please specify) they are not available for the currently Sedimentary geology Decision making ______scheduled workshops. The application Soil science Dispute resolution ______form is printed on p. 9 of this issue of Stratigraphy Economics, environmental GSA Today. Ethics, environmental IEE is interested in your ideas Structural geology/tectonics If you are interested in participat- Ethics, professional on topics, audiences, and Volcanology ing in the IEE public outreach program Other (please specify) Journalism, environmental activities for the outreach on geology and the environment, or ______Law, environmental program, and on your in- ______Planning, land use sights regarding obstacles to simply wish to be kept informed about Policy development environmental decision mak- IEE activities, please complete the Send to: Geological Society of America Regulatory development ing. Referrals of people or GEPOP Network Enrollment Form on Institute for Environmental Education Sustainable development other relevant programs are P.O. Box 9140 p. 9 and 10 and mail or fax it to the also welcome. Use a separate ■ Boulder, CO 80301 Other (please specify) address on the form. sheet if necessary. Thank you. Fax: 303-447-1133 ______

10 GSA TODAY, January 1995 Figure 3. Oxygen iso- by 5 m, and melting of the related to major continental deglacia- topic record of benthic ice sheet would raise sea level by 7.4 m. tion, nor were they necessarily related (Cibicidoides) and plank- We assume that the Greenland ice to major changes in ice-sheet volume. tonic (Globigerina bul- loides) foraminifers from sheet would not have survived in the ODP Site 704 (Hodell case of major melting of Antarctic ice. Ice-Sheet History: and Venz, 1992). The With the exception of that of Haq et al. Ice-rafted Detritus vertical lines represent (1988), most estimates of sea-level rise The presence of ice-rafted detritus the present Holocene would not permit total deglaciation (IRD) in sediments far to the north of values at Site 704 for of Antarctica during the Pliocene. A the Antarctic continent in northern Cibicidoides (3.0‰) reduction in Antarctic ice volume to Antarctic and Subantarctic waters is a and G. bulloides (2.3‰). two-thirds of present volume, as sug- clear indication of major continental Note that during the gested by Webb and Harwood (1991), Pliocene prior to ~3.0 ice sheets. IRD is transported - would require a sea-level rise of ~54 m Ma, δ18O values were ward when are common and (47 m for East Antarctica; 7 m for generally less than Holo- sea-surface temperatures cold enough Greenland). cene values, indicating to prevent rapid melting. IRD is absent Stratigraphic studies at Enewetak less ice volume and/or or rare far to the north of the continent higher temperatures in Atoll indicate early Pliocene sea-level during times of reduced continental the Subantarctic than highstands up to 29–36 m above that glaciation and a warmer Southern today. The minimum of the present (Wardlaw and Quinn, Ocean. A reduction in Antarctic ice δ18O values, however, 1991). Similarly, Krantz (1991) esti- volume by two-thirds and an increase are only 0.6‰ less than mated early Pliocene sea-level high- in Southern Ocean sea-surface tempera- those of the Holocene, stands up to 25–35 m for the U.S. Mid- and the amplitude of the ture by more than 5 °C would have led dle . For the same signal is dampened, indi- to a major decrease in the flux of IRD region, Dowsett and Cronin (1990) cating relative climatic and a southward contraction in its estimated a sea-level highstand of 35 stability. The deglaciation distribution. ± 18 m between 3.5 and 3.0 Ma. The hypothesis (see right column) predicts warming of 5 °C and ~60% reduction in Antarctic ice The stratigraphic distribution of volume, which would result in minimum δ18O values ~1.85‰ less than those of the Holocene; oxygen isotopic records do not neces- IRD was presented quantitatively by such low values are not observed in the record. sarily preclude a maximum sea-level Warnke et al. (1992) for late Neogene rise of 35 m (= 0.35‰ assuming a late Subantarctic sequences of the South Pleistocene δ18O ice volume calibra- Atlantic (50°S). IRD in this area was tion), but the amount of warming transported in icebergs from the Wed- Ice Sheets continued from p. 10 would be too small (1.4 °C at most or Pliocene Sea-Level History dell Sea area. In the southwest Atlantic equivalent to 0.35‰) to have caused (ODP Sites 699 and 701), IRD first 1992). The most reasonable interpreta- Evidence for marine transgressions major Antarctic deglaciation in the first appeared at ~6 Ma and has been pre- tion is that the lower δ18O values re- has been widely reported for the Plio- place. Average sea-surface warming of sent continuously, although in varying flect both increased temperature and cene (Haq et al., 1988; Dowsett and 2 °C at high southern and sea amounts, up to the present time decreased ice volume. This is because Cronin, 1990). These sea-level high- level 25 m higher than today are con- (Fig. 4). The IRD record in Antarctic it is unlikely that major deglaciation stands were almost certainly glacio- ceivable for brief periods during the of the East Antarctic and possibly the eustatic in origin, but the absolute Pliocene. However, the amount of West Antarctic ice sheets could have magnitude of the sea-level rise is warming and deglaciation would have Ice Sheets continued on p. 12 occurred in the absence of significant debated. Haq et al. (1988) estimated been less than these maximum esti- Antarctic warming (Huybrechts, 1992). the rise to be up to 60 m, a figure con- mates in most of the Pliocene. A 0.6‰ decrease in oceanic δ18O sidered too high by other workers (e.g., Sea-level changes during Pliocene- might potentially reflect a 60% reduc- Greenlee and Moore, 1988). Melting Pleistocene time led to multiple ice- tion in Antarctic ice volume, but only of all Antarctic ice would raise sea level sheet grounding episodes over the in the absence of any increase in tem- by about 70 m, melting of just the West Antarctic continental shelf (Alonso perature, which we believe is unten- Antarctic ice sheet would raise sea level et al., 1992), but these events were not able. The “deglaciation” hypothesis predicts an increase in high-latitude surface-water temperatures of 5 °C and a two-thirds reduction in Antarctic ice volume (Webb and Harwood, 1991). This amount of warming and deglacia- tion would result in a decrease of ~1.85‰ in δ18O values, compared to the observed decrease of only ~0.6‰. The melting of only one-third of the Antarctic cryosphere would cause a decrease of ~0.3‰ in ocean δ18O values, but the remaining ~0.3‰ decrease would represent a maximum surface-water temperature increase of only ~1.5 °C. The upshot is that the observed oxygen isotopic changes in the early Pliocene of the Subantarctic are insufficient to accommodate both substantial Southern Ocean warming and major deglaciation. The relatively small amplitude of the δ18O signal during the Pliocene (~±0.25‰) indicates that the Antarctic , as reflected in ocean water temperatures and ice volume, operated within relatively narrow lim- its during the early Pliocene (Hodell and Venz, 1992). The Pliocene varia- tion in δ18O (0.5‰–0.6‰) represents only about one-third of the 1.6‰ to 1.8‰ signal observed during the late Pleistocene. The dampened of the Pliocene δ18O signal also is sup- ported by high-resolution records of Pliocene benthic δ18O variations from an eastern equatorial Pacific drilled site (Shackleton et al., 1994). The mini- mum benthic δ18O values during the early Pliocene at this site were also only ~0.6‰ to 0.7‰ less than today’s value. This permits major decreases in ice volume only in the absence of warming of deep Pacific waters (Shackleton et al., 1994).

GSA TODAY, January 1995 11 Ice Sheets continued from p. 11 warmer waters had displaced cold Antarctic waters far to the south during waters of the Kerguelen Plateau (ODP the Pliocene, the Antarctic biota would Site 751; 58°S; Breza, 1992) and Maud have lost much of its . Rise (65°S; Kennett and Barker, 1990) Instead, biotic exchange between shows an upward increase in IRD abun- Antarctica and lower latitudes has been dance during the early Pliocene. The very limited. For instance, Antarctic Pliocene was marked by persistent waters have been marked by strong delivery of IRD in many parts of the endemic radiolarian since the Southern Ocean, with no suggestion middle Miocene (Lazarus and Caulet, of significant reduction in the north- 1993). The modern Antarctic inverte- ward distribution of sediment brate and vertebrate fauna contain transport (Warnke et al., 1992). This abundant taxa exhibiting considerable almost certainly would have occurred specialization to the environmental in response to large-scale deglaciation extremes, suggestive of long-term of Antarctica. The records indicate con- environmental stability. Such stability tinued existence of major continental is also suggested by within-site inverte- ice sheets on Antarctica during the brate diversity as high as anywhere in Pliocene. the world (Clarke and Crame, 1989). Figure 4. Apparent mass accumulation rate (AMAR) of coarse-grained ice-rafted detritus (IRD) Pliocene warming must have been of Pliocene History of at ODP Site 699 (lat 51°32.5'S, long 30°40.6'W) and 701 (51°9.1'S, 23°12.7'W) from the Sub- insufficient magnitude to reverse devel- the Polar Front (Opal- antarctic sector of the southwest (from Warnke et al., 1992). The persistent oping endemism of the Antarctic biota, Carbonate Transition) occurrence of IRD in the Subantarctic throughout the Pliocene argues against major deglaciation including plankton (Barron and Bal- of the Antarctic continent. dauf, 1989; Abelmann et al., 1990; The Polar Front zone is marked by Lazarus and Caulet, 1993). a transition from biosiliceous produc- tivity and ooze to the south to Terrestrial Vegetation: dominantly biocalcareous productivity Southern Ocean, and calcareous micro- debated. Estimates for average Antarctic Marine Sediment Evidence and foram-nannofossil ooze to the remained rare to absent in Plio- surface-water temperatures range from north. Deep water wells up south of the cene sediments (Lazarus and Caulet, >~10 °C, from silicoflagellates (Ciesiel- Except for occasional reworked zone and creates weakly stratified, 1993). Experimental studies indicate ski and Weaver, 1974), to ~5 to 10 °C, palynomorphs, pollen and spores are chemically homogeneous waters of that sediment-forming calcareous based on radiolarians and diatoms absent in late Neogene Southern Ocean the Antarctic circumpolar current. nannoplankton do not form coccoliths (Abelmann et al., 1990), to <3 °C, sequences (Burckle and Pokras, 1991). The results in high diatom (calcareous platelets) at temperatures based on an absence of calcareous If major deglaciation had occurred dur- productivity and formation of the below 3 °C (Burckle and Pokras, 1991). nannofossils (Burckle and Pokras, ing the Pliocene, it is likely that vegeta- biosiliceous ooze belt. The history Furthermore, coccoliths are almost 1991). These estimates compare with tion would have been present, at least of the Antarctic biosiliceous belt is completely absent in sediments south average modern sea-surface tempera- in coastal areas, supplying pollen and well known from deep-sea drilled sites. of the Polar Front today. Absence of tures of ~1 °C in winter and <3.5 °C in spores to nearby marine sediments. Siliceous biogenic sediments appeared calcareous nannofossils in Antarctic . In close agreement with Bur- This would be expected especially if in the Antarctic during the late Oligo- Pliocene sedimentary deposits suggests ckle and Pokras (1991), our interpreta- the fossil vegetation associated with cene–early Miocene, reflecting a pro- that surface-water temperatures were tions of oxygen isotopic data suggest high-altitude Sirius deposits is of gressive increase in upwelling, as a then also lower than 3 °C. The sedi- that Pliocene Antarctic sea-surface Pliocene age as interpreted by Webb result of the development of circum- mentologic data provide no compelling temperatures were higher than those and Harwood (1991). No evidence of polar flow when the Drake Passage evidence to support major southward of today but lower than 3 °C. If δ18O terrestrial vegetation has been found opened (Kennett and Barker, 1990). migration of the biosiliceous belt dur- values in Site 704 are interpreted in numerous sites drilled close to the On Maud Rise, for example, sedimenta- ing the Pliocene, implying that a broad solely as a temperature signal, then continent. The youngest pollen assem- tion was almost exclusively biosiliceous zone of cold Antarctic waters contin- Subantarctic waters were no more than blages reported from Antarctica that from the middle late Miocene to the ued to isolate the continent. 2.5 °C warmer than today. unequivocally reflect coeval continen- Quaternary. This and other evidence The Southern Ocean biota is tal vegetation are in age indicates that the biosiliceous belt, and Planktonic Microfossils and among the most distinctive on Earth. (Truswell, 1986; Mildenhall, 1989). presumably the Antarctic circumpolar Antarctic Surface–Water It contains a very high level of en- The absence of Neogene pollen has current, has remained well established Temperatures demism in many taxonomic groups, generally been interpreted to reflect far north of the Antarctic continent reflecting relative isolation of the fauna the demise of continental vegetation Early Pliocene siliceous planktonic since at least the late Miocene. since the formation of the Polar Front during the middle Cenozoic in microfossil assemblages in Antarctic A major warming and southward zone (Clarke and Crame, 1989). A large response to the development of the waters have long been considered retreat of the Polar Front zone during fraction of the Antarctic siliceous micro- Antarctic cryosphere (Truswell, 1986). indicative of temperatures warmer the Pliocene would have caused a fossil planktonic assemblage from the than the present day (Ciesielski and southward retreat of the siliceous-cal- early Pliocene consists of endemic Weaver, 1974; Abelmann et al., 1990). careous boundary. Instead, biosiliceous (Barron and Baldauf, 1989; However, the amount of warming is Ice Sheets continued on p. 13 sediments continued to dominate the Abelmann et al., 1990). If significantly

Penrose Conference Scheduled margin of Laurentia has been proposed ited support is planned for qualified as a source for the exotic terrane. graduate students. The Argentine Precordillera: Confirmation of an eastern or Formal invitations will be mailed southeastern Laurentian source for in May 1995. Co-conveners of the con- A Laurentian Terrane? this terrane and the timing of its ference are: Ian W. D. Dalziel, Institute transfer to Gondwana will radically for Geophysics, University of Texas alter conventional understanding of at Austin, 8701 N. Mopac Blvd., Austin, October 14–20, 1995 global early Paleozoic paleogeography, TX 78759-8397, (512) 471-0431, fax paleoenvironmental development, 512-471-8844, E-mail: [email protected]. and tectonics prior to the assembly utexas.edu; Allison R. (Pete) Palmer, A Geological Society of America field, and discuss in San Juan, the evi- of Pangaea. Institute for Cambrian Studies, 445 N. Penrose Conference, “The Argentine dence for the hypothesis that the early The conference will bring together Cedarbrook Rd., Boulder, CO 80304- Precordillera: A Laurentian Terrane?” Paleozoic age rocks in the provinces of an international group of geologists 0417, (303) 443-1375, fax 303 443-1375, and associated field trips will be held San Juan and Mendoza are parts of an best equipped to evaluate the hypothe- E-mail: [email protected]; October 14 to 20, 1995, in San Juan, exotic terrane displaced from eastern ses discussed above. This group will Luis H. Dalla Salda and Carlos A. , in the foothills of the or southeastern Laurentia during the include North American geologists Cingolani, Centro de Investigaciones Argentine Precordillera. It will be fol- Ordovician. These rocks represent familiar with the Cambrian and Geológicas, University of La Plata, calle lowed immediately by a related 1–2- Cambrian and Early Ordovician age Ordovician faunas and depositional 1 Nro. 644, 1900 La Plata, Argentina, day conference in Jujuy, Argentina, carbonate bank and adjacent slope- systems and the early Paleozoic tecton- fax 54-21-25-8696. and a 5-day trans-Andean field trip facies sediments similar in stratigraphy ics of the Appalachian and Ouachita Application Deadline: April 1, across northern Argentina and and faunas to coeval rocks of eastern orogens, and Argentine and European 1995. To apply for the conference, sponsored by IGCP Project 376 (Lau- or southeastern Laurentia. Recently, geologists familiar with the stratigra- please provide the following informa- rentia-Gondwana Connections Before Grenville ages for the basement of phy and faunas of the exotic terrane tion: (1) name and position; (2) organi- Pangaea). (For information about the this terrane have been determined, and the tectonics of the early Paleozoic zation and mailing address; (3) phone Jujuy conference, contact Victor Ramos, and Ordovician (Iapetus) K-bentonites orogen adjacent to its inboard margin. number, fax number, and E-mail Dept. de Geología, Universidad de have been found, further supporting Participation in the conference will address if available; (4) your field of Buenos Aires, Ciudad Universitaria, the connection to eastern or southeast- be limited to about 70 persons. The interest; and (5) a brief statement as 1428 Buenos Aires, Argentina; E-mail: ern Laurentia. Paleomagnetic data are conference fee, which is not yet deter- to what your interest and experience [email protected].) consistent with a possible collision of mined, will include registration, food have been with regard to the confer- The main objective of the Penrose eastern Laurentia with western Gond- and lodging, and field trip costs. Lim- ence topic. Send applications to Ian Conference will be to review in the wana in the Ordovician. The Ouachita W. D. Dalziel at address above. ■

12 GSA TODAY, January 1995 Ice Sheets continued from p. 12 feedback loops that drive the system University of Florida are funded by deglaciation three million years ago: Nature, v. 359, p. 816–818. toward greater stability. Thus, once a the National Science Foundation and CONCLUSIONS large ice sheet is formed, it will not dis- have benefited from long association Barron, J. A., and Baldauf, J. G., 1989, Tertiary appear unless climate becomes much with the Deep Sea Drilling Project cooling steps and paleoproductivity as reflected Marine sediments contain a com- by diatoms and biosiliceous sediments, in Berger, warmer than during its formation. and the Ocean Drilling Program. We pelling range of evidence indicating W. H., et al., eds., Productivity of the ocean: Pre- We believe that with the formation appreciate useful critical reviews by sent and past (Dahlem Workshop Life Research that ocean and terrestrial climates of of both ice sheets by the end of the Margaret L. Delaney and Eugene W. Report, 44): Chichester, UK, John Wiley & Sons, Antarctica and the Southern Ocean p. 341–354. Miocene, the modern Antarctic cryo- Domack, and helpful discussions remained cold and relatively stable sphere-ocean system became well with many colleagues. Breza, J. R., 1992, High resolution study of ice- during early Pliocene global warmth rafted debris, ODP Leg 120, Site 751 southern established (Kennett, 1977). The deep- and that Antarctica did not experience Kerguelen Plateau, in Proceedings of the Ocean sea sediment record from the Southern REFERENCES CITED Drilling Program, Scientific Results, Volume 120: major deglaciation. We suggest that Ocean supports relative stability of the College Station, Texas, Ocean Drilling Program, isotopic and other data from deep-sea Abelmann, A., Gersonde, R., and Speiss, V., 1990, Antarctic cryosphere-ocean system p. 207–221. sediments are inconsistent with a two- Pliocene-Pleistocene paleoceanography of the since the late Miocene. This interpreta- —Siliceous microfossil evidence, in Burckle, L. H., and Pokras, E. M., 1991, Implica- thirds ice volume decrease (= > 47 m tion is in conflict with the deglaciation Bleil, U., and Thiede, J., eds., Geological history tions of a Pliocene stand of Nothofagus (southern sea-level rise) and 5 °C high-latitude of the polar : versus Antarctic: beech) within 500 kilometres of the South Pole: hypothesis. We suggest that an assigned surface-water warming advocated by Amsterdam, Kluwer, p. 729–759. Antarctic Science, v. 3, p. 389–403. late Pliocene age for the Sirius Group the deglaciation hypothesis (Webb Alonso, B., Anderson, J. B., Diaz, J. I., and Bartek, Cattle, H., 1991, Global climate models and requires reevaluation, since this is the and Harwood, 1991). Antarctic surface- L., R., 1992, Pliocene-Pleistocene seismic stratigra- Antarctic climatic change, in Harris, C., and foundation of the deglaciation hypoth- phy of the : Evidence for multiple ice Stonehouse, B., eds., Antarctica and global water temperatures are unlikely to have esis. Studies are also required to estab- sheet grounding episodes: Contributions to climatic change: Boca Raton, Florida, Lewis increased by more than ~3 °C. Signifi- Antarctic Research, v. 3, Antarctic Research Publishers, p. 21–34. lish alternative mechanisms for the cant warming in the Arctic during the Series 57, p. 93–103. emplacement of late Neogene diatoms Ciesielski, P. F., and Weaver, F. M., 1974, Early Pliocene is not matched by equivalent in Sirius Group outcrops. Barrett, P. J., 1991, Antarctica and global climate Pliocene temperature changes in the Antarctic warming in the Antarctic. The relative change: A geological perspective, in Harris, C., and : Geology, v. 2, p. 511–515. robustness of the late Neogene Antarc- Stonehouse, B., eds., Antarctica and global climate ACKNOWLEDGMENTS change: Boca Raton, Florida, Lewis Publishers, Clapperton, C. M., and Sugden, D. E., 1990, Late tic climate system is supported by mod- p. 35–50. Cenozoic glacial history of the Ross Embayment, eling experiments by Robin (1988), Our studies on Antarctic paleoenvi- Antarctica: Quaternary Science Reviews, v. 9, Barrett, P. J., Adams, C. J., McIntosh, W. C., p. 252–272. who suggested that the Antarctic ronmental evolution at the University Swisher, C. C., and Wilson, G. S., 1992, Geo- cryosphere expands in steps due to of California, Santa Barbara, and the chronologic evidence supporting Antarctic Ice Sheets continued on p. 22

the progress of legislation that led to of state population, the number of Letter from Washington passage of the Clean Air Act and con- staff working in Senator Daschle’s veys the excitement of science policy- office is relatively small. That fact Jill Schneiderman making on Capitol Hill. guarantees that I will have substantial We lunched and spoke with opportunities to work on a range of Senator Jay Rockefeller (D—W. Va, issues in a variety of venues. I am work- I’m happy to have the opportunity mission Commerce, Science and Transportation ing closely with a legislative assistant to communicate with my colleagues to edu- committee) and Representative George responsible for environmental issues about my activities and experiences cate in Brown (D—Calif., Science, Space and who is trained as a forest ecologist. up on Capitol Hill as GSA’s 1994–1995 science and science appreciation those Technology committee, chair); over- Our complementary expertise will serve Congressional Science Fellow. For those who will and will not be scientists.” loaded on resources available to us the Senator well as we work on policy readers unfamiliar with the program, This sentiment prompted me to apply from the Congressional Research Ser- issues grounded in a respectful appreci- the American Association for the for the GSA fellowship, for I believe vice; visited and tried to absorb the ation of the earth as a system of inter- Advancement of Science has, since that an interdisciplinary science cur- mission of the Office of Technology acting reservoirs: geosphere, hydro- 1973, administered the Congressional riculum integrating policy issues with Assessment, General Accounting Office, sphere, biosphere, and atmosphere. Science and Engineering Fellowship investigations in natural sciences is and White House Office of Science and Though only two weeks into my Program. During the first 20 years of critical for dynamic undergraduate sci- Technology Policy; and toured the Old assignment (as I write this), I’ve already the program, more than 500 scientists ence education. In my role as Congres- Executive Office Building, a magnifi- done substantive work (reading, writ- and engineers sponsored by 40 profes- sional Science Fellow, I see myself as a cent Victorian building with mansard ing, reporting) on an ecosystem man- sional organizations worked as Fellows liaison between government and the roofing constructed between 1871 agement bill for U.S. Forest Service on the staffs of approximately 200 per- geoscience community working toward and 1888 to house the State, War, land, a proposal to form a National sonal and committee offices in the comprehension of policy and science and Navy departments. Institute for the Environment, and leg- House and Senate, and within the Con- issues in reciprocal arenas. I am eager After entertaining practical sugges- islation related to interstate transporta- gressional Budget Office, the Congres- to share this year’s “insider’s” view of tions from former science Fellows on tion of municipal solid waste. We also sional Caucus for Women’s Issues, the the policy-making process with our col- how to search for and locate a poten- anticipate working on mining law Congressional Research Service, and leagues and to articulate their potential tially stimulating office to work in for reform, Superfund, wetlands issues as the Office of Technology Assessment. role in it. our fellowship year, we occupied an part of a farm bill, pesticide legislation, The purpose of the program is (1) to The first eight weeks of the fellow- office in the Hart Senate Office Building and the Clean Water Act when the teach policy making to scientists by ship included a three-week orientation, and began the job interview process. 104th Congress convenes this month providing them an immediate role in two weeks of placement interviews, We’d been advised to take our time and (January 1995). legislative processes; (2) to train scien- one week at the annual GSA meeting, use the opportunity to educate our- Campaign rhetoric was mean- tists to participate effectively in policy and two weeks learning my way selves through interviews about the spirited, wealthy candidates spent making; and (3) to bring science exper- around my new office. It has been tre- structure, processes, and goals of Senate personal fortunes to get elected, and tise to members of Congress. mendously eye-opening and thought- and House personal offices and com- voters were cynical or lazy. Though free Societies including the American provoking. The orientation was an mittees. We began this process on television time and postage for bona Geophysical Union, American Veteri- exhaustive introduction to the work- September 22, two weeks before the end fide candidates and an election day nary Medical Association, Triangle ings of the U.S. government, executive, of the 103rd Congress. The interviews holiday would alleviate pressures on Coalition for Science and Technology legislative, and judiciary branches. Top- in congressional offices at that frantic candidates and voters, such simple Education, Federation of American level policymakers explored with us moment afforded us a glimpse of the measures were not taken. Still, approxi- Societies of Food Animal Sciences, topics including: domestic and interna- pace and agenda of politics in a waning mately 59 new democracies have American Chemical Society, American tional perspectives on post–Cold War Congress that we’d not have seen had started since 1989, and most of them Society of Mechanical Engineers, Soil science and technology policy; science we been Fellows beginning in an odd have chosen our system of government Science Society of America, National and technology as instruments of for- year (1993 or 1995). I interviewed with or a mixed system that includes sub- Society of Professional Engineers, eign policy; historical perspectives on 15 personal offices (House and Senate) stantial aspects of democracy. I look American Psychological Association, White House science advising; mega- and four committees. forward to using this forum as a means American Physical Society, American science projects and international After weighing several options to engage our colleagues in considera- Institute of Physics, and Institute of cooperation; science and technology (there are always more offices looking tions of the role of geoscientists in Electrical and Electronics Engineers policy and U.S. economic competitive- for Fellows than there are Fellows to policy-making in what Sir Winston have sponsored 29 Fellows on Capitol ness; science, technology, and global go around), I chose to work for Senator Churchill called “the worst form of Hill this year. We are a diverse lot: environmental issues; intellectual prop- Tom Daschle (D—S. Dak.). He is a sec- government, except all those other recent Ph.D.s, research scientists, erty rights; international security; exec- ond-term Senator, not up for reelec- forms that have been tried from time educators, engineers, racetrack veteri- utive branch and congressional budget tion, is co-chair of the Democratic Pol- to time.” ■ narians, psychologists, and scientists processes; legislative process; congres- icy Committee, and serves on the Jill S. Schneiderman, 1994–1995 GSA embarking on careers in science policy. sional committees and floor proce- following committees: Finance, Veter- Congressional Science Fellow, is serving on the “Science in the National Interest,” dures; lobbying the Congress; and ans’ Affairs, Indian Affairs, Select staff of Senator Thomas Daschle (S. Dak.). Schneiderman may be contacted at (202) 224- President Clinton’s August 1994 report communicating science policy news. Ethics, and Agriculture, Nutrition and 2321. The one-year fellowship is supported by that outlines goals for fundamental What we tried to understand could Forestry. He also chairs the Subcommit- GSA and by the U.S. Geological Survey, Depart- science and education, quoted Vassar have been at least a semester-long tee on Agricultural Research, Conserva- ment of the Interior, under Assistance Award No. College alumna Vera Rubin of the course in science policy. One education tion, Forestry and General Legislation, 1434-94-G-2509. The views and conclusions which has jurisdiction over U.S. For- contained in this document are those of the Carnegie Institution of Washington: resource I recommend from this orien- author and should not be interpreted as necessar- “… scientists both in and outside of tation is the film “An Act of Congress”; est Service lands. Since the number of ily representing the official policies, either academia must take seriously their narrated by E. G. Marshall, it chronicles staff in a Senator’s office is a function expressed or implied, of the U.S. govenment.

GSA TODAY, January 1995 13