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100 Million Years of Antarctic Climate Evolution: Evidence from Fossil Plants

Cooper, A. K., P. J. Barrett, H. Stagg, B. Storey, E. Stump, W. Wise, and the 10th ISAES editorial team, eds. (2008). Antarctica: A Keystone in a Changing World. Proceedings of the 10th International Symposium on Antarctic Earth Sciences. Washington, DC: The National Academies Press.

J. E. Francis,1 A. Ashworth,2 D. J. Cantrill,3 J. A. Crame,4 J. Howe,1 R. Stephens,1 A.-M. Tosolini,1 V. Thorn1

ABSTRACT

The evolution of Antarctic climate from a Cretaceous greenhouse into the Neogene icehouse is captured within a rich record of fossil leaves, wood, pollen, and flowers from the Antarctic Peninsula and the Transantarctic Mountains. About 85 million years ago, during the mid-Late Cretaceous, flowering plants thrived in subtropical climates in Antarctica. Analysis of their leaves and flowers, many of which were ancestors of plants that live in the tropics today, indicates that summer temperatures averaged 20°C during this global thermal maximum. After the Paleocene (~60 Ma) warmth-loving plants gradually lost their place in the vegetation and were replaced by floras dominated by araucarian conifers (monkey puzzles) and the southern beech Nothofagus, which tolerated freezing winters. Plants hung on tenaciously in high latitudes, even after ice sheets covered the land, and during periods of interglacial warmth in the Neogene small dwarf plants survived in tundra-like conditions within 500 km of the South Pole.

INTRODUCTION

The Antarctic Paradox is that, despite the continent being the most inhospitable continent on Earth with its freezing climate and 4-km-thick ice cap, some of the most common fossils preserved in its rock record are those of ancient plants. These fossils testify to a different world of globally warm and ice-free climates, where dense vegetation was able to survive very close to the poles. The fossil plants are an important source of information about terrestrial climates in high latitudes, the regions on Earth most sensitive to climate change.

Although plants of Permian and Triassic age provide a signal of terrestrial climates for the Transantarctic region for times beyond 100 million years (Taylor and Taylor, 1990), it is during the Cretaceous that the Antarctic continent reached the approximate position that it is in today over the South Pole (Lawver et al., 1992). Without the cover of ice Cretaceous vegetation flourished at high latitudes. Even when ice built up on the continent during the Cenozoic, fossil plants indicate that vegetation was still able to grow in relatively inhospitable conditions. The plant record thus provides us with a window into past climates of Antarctica, particularly during the critical transition from greenhouse to icehouse (Francis et al., forthcoming).

Reviews of the paleobotany that focus on floral evolution, rather than paleoclimate, can be found in the work of Askin (1992) and Cantrill and Poole (2002, 2005) and references therein. This paper is not intended to be an exhaustive review of all paleoclimate or paleobotanical studies but presents new information about Antarctic climate evolution deduced from some new and some selected published studies of fossil plants.

WARMTH IN THE CRETACEOUS GREENHOUSE

The most detailed record of Cretaceous terrestrial climates from plants comes from Alexander Island on the Antarctic

1

School of Earth and Environment, University of Leeds, UK.

2

Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517, USA.

3

National Herbarium of Victoria, Royal Botanic Gardens Melbourne, Private Bag 2000, South Yarra, Victoria 3141, Australia.

4

British Antarctic Survey, High Cross, Madingley Road, Cambridge, UK.



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Cooper, A. K., P. J. Barrett, H. Stagg, B. Storey, E. Stump, W. Wise, and the 10th ISAES editorial team, eds. (2008). Antarctica: A Keystone in a Changing World. Proceedings of the 10th International Symposium on Antarctic Earth Sciences. Washington, DC: The National Academies Press. 100 Million Years of Antarctic Climate Evolution: Evidence from Fossil Plants J. E. Francis,1 A. Ashworth,2 D. J. Cantrill,3 J. A. Crame,4 J. Howe,1 R. Stephens,1 A.-M. Tosolini,1 V. Thorn1 ABSTRACT climate and 4-km-thick ice cap, some of the most common fossils preserved in its rock record are those of ancient The evolution of Antarctic climate from a Cretaceous plants. These fossils testify to a different world of globally greenhouse into the Neogene icehouse is captured within a warm and ice-free climates, where dense vegetation was able rich record of fossil leaves, wood, pollen, and flowers from to survive very close to the poles. The fossil plants are an the Antarctic Peninsula and the Transantarctic Mountains. important source of information about terrestrial climates in About 85 million years ago, during the mid-Late Cretaceous, high latitudes, the regions on Earth most sensitive to climate flowering plants thrived in subtropical climates in Antarctica. change. Analysis of their leaves and flowers, many of which were Although plants of Permian and Triassic age provide a ancestors of plants that live in the tropics today, indicates signal of terrestrial climates for the Transantarctic region for that summer temperatures averaged 20°C during this global times beyond 100 million years (Taylor and Taylor, 1990), it thermal maximum. After the Paleocene (~60 Ma) warmth- is during the Cretaceous that the Antarctic continent reached loving plants gradually lost their place in the vegetation and the approximate position that it is in today over the South were replaced by floras dominated by araucarian conifers Pole (Lawver et al., 1992). Without the cover of ice Creta- (monkey puzzles) and the southern beech Nothofagus, which ceous vegetation flourished at high latitudes. Even when ice tolerated freezing winters. Plants hung on tenaciously in high built up on the continent during the Cenozoic, fossil plants latitudes, even after ice sheets covered the land, and during indicate that vegetation was still able to grow in relatively periods of interglacial warmth in the Neogene small dwarf inhospitable conditions. The plant record thus provides us plants survived in tundra-like conditions within 500 km of with a window into past climates of Antarctica, particularly the South Pole. during the critical transition from greenhouse to icehouse (Francis et al., forthcoming). INTRODUCTION Reviews of the paleobotany that focus on floral evolu- tion, rather than paleoclimate, can be found in the work of The Antarctic Paradox is that, despite the continent being Askin (1992) and Cantrill and Poole (2002, 2005) and refer- the most inhospitable continent on Earth with its freezing ences therein. This paper is not intended to be an exhaustive review of all paleoclimate or paleobotanical studies but presents new information about Antarctic climate evolution deduced from some new and some selected published studies 1 School of Earth and Environment, University of Leeds, UK. of fossil plants. 2 Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517, USA. WARMTH IN THE CRETACEOUS GREENHOUSE 3 National Herbarium of Victoria, Royal Botanic Gardens Melbourne, Private Bag 2000, South Yarra, Victoria 3141, Australia. The most detailed record of Cretaceous terrestrial climates 4 British Antarctic Survey, High Cross, Madingley Road, Cambridge, UK. from plants comes from Alexander Island on the Antarctic 19

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20 ANTARCTICA: A KEYSTONE IN A CHANGING WORLD FIGURE 1 Map of Antarctica showing locations mentioned in the text. Peninsula (Figure 1). Here the mid-Cretaceous (Albian) Fos- reconstruction portrays spacing of the large trees, such as sil Bluff Group sediments include a series of marine, subma- ginkgos, podocarps, and araucarian conifers, as accurately rine fan, fluviatile, and deltaic sediments formed as the infill as possible from field data. The undergrowth consists of of a subsiding fore-arc basin. Floodplains and midchannel ferns, cycadophytes, liverworts, mosses, and small shrubby bars of braided and meandering river systems (Triton Point angiosperms. The extinct plant Taeniopteris formed thickets Formation, Nichols and Cantrill, 2002) were extensively in the disturbed clearings in the forest (Cantrill and Howe, forested by large trees with a rich undergrowth. 2001). The picture also shows the volcanoes on the adjacent Many of the plants are preserved in their original posi- arc that were the source of volcaniclastic sediment, much of tions, having been encased by sheet flood and crevasse splay which was deposited as catastrophic deposits that engulfed deposits during catastrophic flooding events. In addition, standing trees (in the distance in this picture). finely laminated flood deposits draped small plants, preserv- Paleoclimatic interpretation using fossil plants on Alex- ing them in place. ander Island is based mainly on comparison with the ecologi- The in situ preservation of the plants has allowed cal tolerances of similar living Southern Hemisphere taxa detailed reconstructions of the forest environments by (Falcon-Lang et al., 2001). This indicates that the climate Howe (2003). Three vegetation assemblages were identified was generally warm and humid to allow the growth of large through statistical analysis of field data: (1) a conifer and conifers, with mosses and ferns in the undergrowth. Accord- fern assemblage with mature conifers of mainly araucarian ing to Nichols and Cantrill (2002), river flow is considered type and an understory of Sphenopteris ferns; (2) a mixed to have been perennial, based on sedimentary evidence, but conifer, fern, and cycad assemblage with araucarian conifers with periodic floods indicative of high rainfall. and ginkgo trees; and (3) a disturbance flora of liverworts, Evidence from fossil soils, however, provides a some- Taeniopteris shrubs, ferns, and angiosperms. Reconstruc- what different climate story. The paleosols, in which trees tions of these assemblages and their depositional setting are are rooted, have structures such as blocky peds, clay cutans, presented in Figure 2. and mottling that are typical of modern soils that form under An artist’s reconstruction is presented in Figure 3. This seasonally dry climates (Howe and Francis, 2005). Although

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21 FRANCIS ET AL. FIGURE 2 Reconstruction of paleoenvironment and community structure of (a) an open woodland community that grew on areas of the floodplain distal to a meandering river channel but subjected to frequent, low-energy floods; (b) a patch forest community of mature conifers and ferns, growing on floodplain areas affected by catastrophic floods; and (c) disturbance vegetation growing in back-swamp areas of a braided river floodplain, subjected to frequent low-energy flood events and ponding (Howe, 2003). evidence of intermittent flooding is apparent from the fluvial paleoclimate. The leaves represent the remains of vegetation sandstones and mudstones that volumetrically dominate the that grew at approximately 65°S on the emergent volcanic rock sequence, the paleosols indicate that this high-latitude arc that is now represented by the Antarctic Peninsula. They mid-Cretaceous environment was predominantly seasonally were subsequently transported and buried in marine sedi- dry. Whereas the flood sediments are likely to have been ments in the adjacent back-arc basin, and are now preserved deposited relatively rapidly (days or weeks), the paleosols as impressions and compressions in volcaniclastic siltstones likely represent hundreds to thousands of years for soil and carbonate concretions (Hayes et al., 2006). development and forest growth, suggesting a predominantly The angiosperm leaf morphotypes have been tentatively dry climate for this high-latitude site. compared with those of living families such as Sterculia- Climate models for the mid-Cretaceous predicted ceae, Lauraceae, Winteraceae, Cunoniaceae, and Myrtaceae warm, humid climates for this region. Valdes et al. (1996) (Hayes et al., 2006) (Figure 4). Most of these families today predicted high summer temperatures of 20-24°C and low can be found in warm temperate or subtropical zones of the winter temperatures just above freezing. There is no evidence Southern Hemisphere. Sterculiaceae is a tropical and sub- of freezing in the paleosols. However, it is likely that the tropical family found in Australia, South Asia, Africa, and more significant climate parameter that influenced the soils northern South and Central America. The Laurales today live was rainfall and soil moisture. The models of Valdes et al. in tropical or warm temperate regions with a moist equable (1996) of seasonal mean surface soil moisture distribution climate. Both the Cunoniaceae and Elaeocarpaceae are (the balance between precipitation and evaporation) predict tropical and subtropical trees and shrubs found in equato- a seasonal moisture regime with dry conditions in summer rial tropical regions, and the Winteraceae are concentrated but wet in winter, supporting the seasonal signature seen in in wet tropical montane to cool temperate rainforests of the the paleosols. southwest Pacific and South America. Younger Cretaceous strata preserved within the James A more quantitative analysis of the leaves based on Ross Island back-arc basin, and which crop out on James physiognomic aspects of the leaves, using leaf margin analy- Ross, Seymour, and adjacent islands, contain a series of sis and simple and multiple linear regression models, pro- fossil floras that are providing new information about biodi- vided data on paleotemperatures and precipitation. Estimates versity and climate. During the Late Cretaceous angiosperms of mean annual temperatures (MATs) range from 15.2 (±2) (flowering plants) became an important component of the to 18.6 (±1.9)°C for the Coniacian, and 17.1 (±2)°C to 21.2 vegetation. The Coniacian Hidden Lake Formation (Gustav (±1.9)°C for the late Coniacian-early Santonian. Averaging Group) and the Santonian-early Campanian Santa Marta all data from all methods gives a MAT for the Coniacian of Formation (Marambio Group) in particular contain fos- 16.9°C and 19.1°C for the late Coniacian-early Santonian sil angiosperm leaves that have yielded information about (Hayes et al., 2006). Estimates of annual precipitation range

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22 ANTARCTICA: A KEYSTONE IN A CHANGING WORLD FIGURE 3 Reconstruction of the forest environment on Alexander Island during the Cretaceous, based on the work of Howe (2003) and British Antarctic Survey geologists (see text and references). SOURCE: Image is a painting by Robert Nicholls of Paleocreations.com, and is housed at the British Antarctic Survey. from 594 to 2142 (±580) mm for the Coniacian and 673 to many sites (e.g., Clark and Jenkyns, 1999; Huber et al., 1991 (±580) mm, for the late Coniacian-early Santonian, 2002), and possibly attributed to rising atmospheric CO2 with very high rainfalls of 2630 (±482) and 2450 (±482) mm levels due to a tectonically driven oceanographic event in for the growing seasons, respectively, comparable with those the opening of the equatorial Atlantic gateway (Poulsen et of equatorial tropical rainforests today. However, these data al., 2003). must be considered with caution as some important aspects The high levels of Cretaceous climate warmth are also of leaf morphology related to rainfall are not preserved in recorded in an unusual assemblage of late Santonian fossil the fossil assemblage. plants from Table Nunatak on the east side of the Antarc- These fossil plants are thus indicative of tropical and tic Peninsula. A small isolated outcrop has yielded layers subtropical climates at high paleolatitudes during the mid- of charcoal, produced by wildfires, within a sequence of Late Cretaceous, without extended periods of winter tem- sandstones, siltstones, and mudstones, deposited in shallow peratures below freezing and with adequate moisture for marine conditions at the mouth of an estuary or in a delta growth. In other Antarctic paleoclimate studies evidence for distributary channel. The charcoal layer contains the remains strong warmth at this time was found by Dingle and Lavelle of burnt plants, including megaspores; fern rachids; conifer (1998) in their analyses of clay minerals and from analysis of leaves, wood, shoots, seeds and pollen cones; angiosperms fossil woods (Poole et al., 2005). This warm peak may have leaves, fruits and seeds (Eklund et al., 2004). also been the trigger for the expansion of the angiosperms in The most unusual of these fossils are tiny fossil flowers, the Antarctic, represented by a marked increased abundance the oldest recorded from Antarctica. Eklund (2003) identified of angiosperm pollen in Turonian sediments (Keating et al., several types of angiosperm flowers, some of which are most 1992). On a global scale this corresponds to the Cretaceous likely related to the living families Siparunaceae, Wintera- thermal maximum, from about 100-80 Ma, reported from

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23 FRANCIS ET AL. FIGURE 4 A selection of fossil leaves from the Hidden Lake Formation: (a) D.8754.1a, Morphotype 2 (Sterculiaceae); (b) D.8754.8.54a, Morphotype 11 (Laurales); (c) D.8754.8.57a, Morphotype 11 (Laurales); (d) D.8621.27a, Morphotype 10 (unknown affinity). Botanical names in parentheses refer to most similar modern family (Hayes et al., 2006). Scale bar 5 mm for all leaves. Numbers refer to the British Antarctic Survey numbering system. ceae, and Myrtaceae, as well as several unidentified types. bonate concretions within the shallow marine Campamento The Siparunaceae family is now confined to the tropics, and allomember of Marenssi et al. (1998) (equivalent to Telm the Winteraceae (e.g., mountain pepper tree) and Myrtaceae 3 of Sadler [1988]). This unit has been dated as 51.5-49.5 (e.g., eucalypts) are warm-cool temperate types from the Ma through links with global eustatic lowstands (Marenssi, Southern Hemisphere. Interestingly, the Siparuna-like fos- 2006) and by Sr dating by Stephens, which yielded a latest sil flowers have a flat-roofed structure with a central pore, early Eocene (late Ypresian) age. which in the living plants acts as a landing platform for gall The flora is unusual in that it is dominated by leaves, midges that lay their eggs inside the flower head. Since the cone scales, and leafy branches of araucarian conifers, very developing gall midge larvae usually destroy the flowers as similar in all respects to living Araucaria araucana (monkey they grow (Eklund, 2003), the preservation of such flowers puzzle) from Chile. Study of three-dimensional arrange- as fossils would normally be extremely unlikely. The fortu- ment of leaves using the technique of neutron tomography itous occurrence of wildfires during the Cretaceous has thus illustrates that leaf and branch arrangement is characteristic helped preserve such flowers as rare fossils. of living Araucaria araucana (Figure 5). A limited array of angiosperm leaves are preserved in the nodules and include morphotypes that are similar to leaves of living Lauraceae, FROM GREENHOUSE TO ICEHOUSE Myricaceae, Myrtaceae, and Proteaceae. It is notable that After the peak warmth of the mid-Late Cretaceous, climate many of the fossil leaves appear to have particularly thick appears to have cooled globally during the latest part of the carbonaceous compressions and, indeed, the living equiva- Cretaceous, as seen also in the Antarctic fossil wood record lents are evergreen Southern Hemisphere trees that have (Francis and Poole, 2002; Poole et al., 2005). However, warm thick waxy cuticles. This may signal taphonomic sorting of climates returned to the high latitudes during the Paleocene some kind rather than a climate signal, as the more fragile and early Eocene, as is reflected in fossil plants. leaves, including Nothofagus, are unusually absent from this The Paleogene sedimentary sequence on Seymour Island flora. Climate interpretation of this flora, based on the nearest (Figure 1) contains plant-rich horizons that hold signals to living types, especially the araucarian conifers, suggests that ancient climates. An unusual new flora from La Meseta the latest Eocene climate was cool and moist. Oxygen isotope Formation has been studied by Stephens (2008). The flora analyses of marine molluscs in the same concretions yielded is dominated by permineralized branches of conifers and cool marine paleotemperatures of 8.3-12.5°C, comparable compressions of angiosperm leaves, and found within car- to other estimates for Telm 3 from marine oxygen isotopes

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24 ANTARCTICA: A KEYSTONE IN A CHANGING WORLD FIGURE 5 Image of three-dimensional leafy branch of fossil araucarian conifer from La Meseta Formation, Seymour Island (sample DJ.1103.189). (a) The branch as it appears in hand specimen. (b) Reconstruction from tomographic image showing the leafy branch in three dimensions. Neutron tomography to create the figure was undertaken at the Institut Laue Langevin facility, Grenoble, France. of 8-13.2°C (Pirrie et al., 1998) and 10.5-19.6°C (Dutton et families of subtropical and cool-temperate nature and rep- al., 2002). resents cool-warm temperate mixed conifer-broad-leaved New paleoclimate data have also been derived from new evergreen and deciduous forest, dominated by large trees of collections of fossil angiosperm leaves from the Nordenskjold Nothofagus (southern beech) and araucarian and podocarp flora in the Cross Valley Formation of Late Paleocene age conifers, with other angiosperms as mid-canopy trees and (Elliot and Trautman, 1982) and from the Middle Eocene understorey shrubs. In comparison the Middle Eocene flora Cucullaea 1 flora (Telm 5 of Sadler [1988], Cucullaea 1 shows a 47 percent decrease in diversity with only 19 leaf allomember of Marenssi et al. [1998], dated as 47-44 Ma by morphotypes. The flora is dominated by Nothofagus, most Dutton et al. [2002]). In the Late Paleocene flora 36 angio- similar to modern cool-temperate types, and has much rarer sperm leaf morphotypes were identified, along with two subtropical and warm-temperate types, such as Proteaceae. pteridophytes (ferns), and podocarp and araucarian conifers. The decline in diversity indicates a substantial cooling of The angiosperm leaf component is dominated by types with climate over this interval. possibly modern affinities to the Nothofagacae, Lauraceae, Paleoclimate data were derived using CLAMP (Climate and Proteaceae, along with other types, such as Myrtaceae, Leaf Analysis Multivariate Program) (Wolfe and Spicer, Elaeocarpaceae, Winteraceae, Moraceae, Cunoniaceae, and 1999) and several leaf margin analysis techniques based on Monimiaceae, some of which have no identifiable modern physiognomic properties of the leaves. CLAMP results are affinities as yet. The fossil assemblage contains a mix of given below. A MAT of 13.5 ± 0.7°C was determined for the

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25 FRANCIS ET AL. Late Paleocene. A strongly seasonal climate was implied, George Island. Ivany et al. (2006) have also reported the gla- with a warm month mean of 25.7 ± 2.7°C and a cold month cial deposits of possible latest Eocene or earliest Oligocene mean of 2.2 ± 2.7°C, with 2110 mm annual rainfall. By the age from Seymour Island. Middle Eocene the climate had cooled considerably; the MAT was 10.8 ± 1.1°C with a warm month mean of 24 ± PLANTS IN THE FREEZER 2.7°C, and a cold month mean of –1.17 ± 2.7°C, with 1534 mm annual rainfall. This suggests that the climate was still Despite the onset of glaciation and the growth of ice sheets markedly seasonal but that winter temperatures were often on Antarctica during the latest Eocene or earliest Oligocene, below freezing. vegetation was not instantly wiped out but clung on tena- The Late Paleocene floras thus represent warm Antarc- ciously in hostile environments. Even though many warmth- tic climates probably without ice, even in winter. However, loving plant taxa disappeared during the mid-Eocene, floras Seymour Island floras suggest that by the Middle Eocene dominated by Nothofagus remained for many millions (47-44 Ma) climates had cooled considerably and ice may of years. Single leaves of Nothofagus of Oligocene and have been present on the Antarctic continent, at least dur- Miocene age have been found in CRP-3 and CIROS-1 drill ing winter months. Several Eocene macrofloras dominated cores, respectively (Hill, 1989; Cantrill, 2001), but one of the by Nothofagus from King George Island, South Shetland most remarkable Antarctic floras is preserved within glacial Islands, suggest mean annual temperatures of about 10-11°C diamictites of the Meyer Desert Formation, Sirius Group, at (seasonality unknown) (e.g., Birkenmajer and Zastawniak, Oliver Bluffs (85°S) in the Transantarctic Mountains. 1989; Hunt and Poole, 2003), and the highest latitude Eocene In a meter-thick layer of sandstone, siltstone, and mud- floras, from Minna Bluff in the McMurdo Sound region, stone sandwiched between tillites, small twigs of fossil Noth- are suggestive of cool temperate climates (Francis, 2000). ofagus wood are preserved entwined around cobbles (Figure Other geological evidence also points to significant cool- 6). The twigs are the branches and rootlets of small dwarf ing by the latter part of the Eocene; fluctuating volumes of shrubs preserved within their positions of growth. Fossil leaf ice on Antarctica from about 42 Ma have been implied by mats of Nothofagus leaves (Nothofagus beardmorensis) (Hill Tripati et al. (2005) from isotope measurements of marine et al., 1996) are also preserved in the same horizon. Several sediments and, from the Antarctic region, Birkenmajer et other fossil plants have also been recovered, including moss al. (2005) proposed a glacial period from 45-41 Ma, based cushions, liverworts, and fruits, stems, and seeds of several on valley-type tillites of Eocene-Oligocene age from King a b e d c FIGURE 6 Sirius Group sediments and fossil plants, Oliver Bluffs, Transantarctic Mountains. (a) General view of Oliver Bluffs. (b) View of bluff composed of glacial diamictites. Arrow points to meter-thick horizon of glacial sandstone, equivalent to plant-bearing horizon. (c) Nothofagus leaves from upper part of plant-bearing horizon. (d) Small branch of fossil wood in growth position within paleosol horizon. (e) Small branch in situ in paleosol horizon, with delicate bark still attached. Scale bars represent 1 cm.

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26 ANTARCTICA: A KEYSTONE IN A CHANGING WORLD Cantrill, D. J. 2001. Early Oligocene Nothofagus from CRP-3, Antarctica: vascular plants, as well as remains of beetles, a gastropod, Implications for the vegetation history. Terra Antarctica 8:401-406. bivalves, a fish, and a fly (Ashworth and Cantrill, 2004). Cantrill, D. J., and J. Howe. 2001. Palaeoecology and taxonomy of Pentoxyl- All the evidence for paleoclimate from these remarkable ales from the Albian of Antarctica. Cretaceous Research 22:779-793. fossils (Ashworth and Cantrill, 2004), from growth rings Cantrill, D. J., and I. Poole. 2002. Cretaceous to Tertiary patterns of diver- in the twigs (Francis and Hill, 1996), and from paleosols sity changes in the Antarctic Peninsula. In Palaeobiogeography and Biodiversity Change: A Comparison of the Ordovician and Mesozoic- (Retallack et al., 2001) points toward a tundra environment Cenozoic Radiations, eds. A. W. Owen and J. A. Crame, Geological with a mean annual temperature of about –12°C, with short Society of London Special Publication 194:141-152. summers up to +5°C but with long cold winters below freez- Cantrill, D. J., and I. Poole. 2005. Taxonomic turnover and abundance ing. Dated as Pliocene in age but disputed (see Ashworth and in Cretaceous to Tertiary wood floras of Antarctica: Implications for Cantrill, 2004), this periglacial or interglacial environment changes in forest ecology. Palaeogeography, Palaeoclimatology, Pal- aeoecology 215:205-219. existed at a time when glaciers retreated briefly from the Clark, L. J., and H. C. Jenkyns. 1999. New oxygen isotope evidence for Oliver Buffs region, allowing dwarf shrubs to colonize the long-term Cretaceous climatic change in the Southern Hemisphere. exposed tundra surface only about 500 km from the South Geology 27:699-702. Pole. Dingle, R., and M. Lavelle. 1998. Late Cretaceous-Cenozoic climatic As Antarctica’s climate cooled further into the Pleisto- variations of the northern Antarctic Peninsula: New geochemical evi- dence and review. Palaeogeography, Palaeoclimatology, Palaeoecology cene deep-freeze, vascular plants were lost from the conti- 141:215-232. nent. However, its rich fossil plant record retains its legacy Dutton, A., K. Lohmann, and W. J. Zinsmeister. 2002. Stable isotope and of past warmth. minor element proxies for Eocene climate of Seymour Island, Antarc- tica. Paleoceanography 17(5), doi:10.1029/2000PA000593. Eklund, H. 2003. First Cretaceous flowers from Antarctica. Review of Pal- ACKNOWLEDGMENTS aeobotany and Palynology 127:187-217. Eklund, H., D. J. Cantrill, and J. E. Francis. 2004. Late Cretaceous plant New information presented here was obtained during post- mesofossils from Table Nunatak, Antarctica. Cretaceous Research graduate research projects of Howe (Alexander Island) and 25:211-228. Stephens (Seymour Island), funded by Natural Environment Elliot, D. H., and T. A. Trautman. 1982. Lower Tertiary strata on Seymour Research Council and the British Antarctic Survey (BAS). Island, Antarctic Peninsula. In Antarctic Geoscience, ed. C. Craddock, pp. 287-297. Madison: University of Wisconsin Press. Stephens wishes to thank Martin Dawson (Leeds) and Falcon-Lang, H. J., D. J. Cantrill, and G. J. Nichols. 2001. Biodiversity Andreas Hillenbach and Hendrik Ballhausen (Institut Laue and terrestrial ecology of a mid-Cretaceous, high-latitude floodplain, Langevin, Grenoble) for help with neutron tomography. New Alexander Island, Antarctica. Journal of the Geological Society of data on fossil plants from Seymour Island were collected as London 158:709-724. part of a NERC-Antarctic Funding Initiative project AFI1/01 Francis, J. E. 2000. Fossil wood from Eocene high latitude forests, McMurdo Sound, Antarctic. In Paleobiology and Palaeoenvironments of to Francis, Cantrill, and Tosolini. BAS is thanked for field Eocene Rocks, McMurdo Sound, East Antarctica, eds. J. D. Stilwell and support in all these projects. Work in the Transantarctic R. M. Feldmann, Antarctic Research Series 76:253-260, Washington, Mountains was funded by NSF/OPP grants 9615252 and D.C.: American Geophysical Union. 0230696 to Ashworth. The Trans-Antarctic Association and Francis, J. E., and R. S. Hill. 1996. Fossil plants from the Pliocene Sirius Geological Society of London are thanked for additional group, Transantarctic Mountains: Evidence for climate from growth rings and fossil leaves. Palaios 11:389-396. support. This work has been aided by discussions with Francis, J. E., and I. Poole. 2002. Cretaceous and early Tertiary climates of Hunt, Falcon-Lang, Hayes, Poole, Eklund (Leeds/BAS), Antarctica: Evidence from fossil wood. Palaeogeography, Palaeoclima- and Roof. tology, Palaeoecology 182:47-64. Francis, J. E., S. 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