Palaeogene climates of Spitsbergen

The Palaeogene floras of Spitsbergen come from the Tertiary deposits of the Central Basin and from several isolated areas within the Tertiary foldbelt. The deposits of the Central Basin are divided into six formations (Major & Nagy 1972; Livshits 1974). The main plant-bearing beds occur at the bottom and at the top of this succession, in the Firkanten and Aspelintoppen Formations, respectively. They are separated by approximately one kilometre of marine formations. The Firkanten Formation is early Palaeocene in age, as indicated by flora, molluscs and by dinoflagellates of transitional early to late Palaeocene age in the overlying Basilika Formation (Manum & Throndsen 1986). The ages of the Aspelintoppen and the Renardodden flora are not well defined because of the lack of characteristic animal fossils. Geological data and comparison with other Arctic floras allow to suggest an early Eocene age for the Aspelintoppen Formation and a late Eocene age for the Renardodden flora (Manum & Throndsen 1986; Kvacek et al. 1994). The estimation of climatic parameters is based on investigation of large collections of fossil plants from the Komarov Botanical Institute (St. Petersburg) and from the Swedish Museum of Natural History (Stockholm). Palaeoclimatic interpretations of fossil floras are based on two approaches: 1) analysis of climatic range of nearest living forms of fossil plants, and 2) investigation of foliar physiognomy of woody angiosperms and analysis of modern climates, where vegetation with a similar foliar physiognomy is found. The floristic composition of the different Spitsbergen floras is rather similar (Budantsev 1983). The Tertiary Spitsbergen flora contains ferns, ginkgoes, conifers, and angiosperms. Ferns are poorly represented. The most characteristic genera are Coniopteris and Osmunda. Modern similar species Osmunda regalis L. usually occurs in warm-temperate swamp vegetation. Ginkgo is rather numerous in some localities. Modern species G. biloba L. is distributed in southern China, but can grow also in cooltemperate climate in parks. Conifers are mostly represented by modern genera but extinct species. They consist of both evergreen (Sequoia, Taiwania, Thuja, Mesocyparis, Fokieniopsis, Picea, Abies) and deciduous (Metasequoia, Taxodium, Glyptostrobus, Pseudolarix) taxa. Among them deciduous Taxodium, Glyptostrobus, and Metasequoia are very abundant and sometimes prevail over angiosperms. The genera of families Pinaceae and Cupressaceae are distributed in both warm-temperate and cool-temperate climate regions. An investigation of climatic tolerance of modern species of the family Taxodiaceae was made by Schweitzer (1980). Metasequoia and Taxodium are frost-tolerant plants, but unable to reproduce under a cool-temperate climate. The evergreen conifers Sequoia and Taiwania are more sensitive to frost, especially young branches and seedlings. These genera cannot exist in a cool-temperate climate. The modern Glyptostrobus and Taiwania are distributed in southern China and their occurrence in floras exclude the possibility of winter temperatures lower than 0°C. The mean annual temperatures in areas of modern distribution of Glyptostrobus and Taiwania reach 15–18°C. Angiosperms in the Spitsbergen Tertiary floras are represented mainly by deciduous broad-leaved species from the families Platanaceae, Hamamelidaceae, Betulaceae, Ulmaceae, Aceracea, Hippocastanaceae, Fagaceae, Cercidiphyllaceae, and others. Among them more than half are represented by modern genera (for example Platanus, Quercus, Carpinus, Acer, Corylus, Nyssa, Aesculus, Ulmus, Cercidiphyllum), which have living relatives in warm-temperate and moderately temperate deciduous forests of southeastern Asia and eastern part of North America. Leaves of angiosperms have thin texture and are on the average of moderate size. But several species can have extremely large leaf blades up to 20–30 cm. These characters indicate that precipitation and humidity were relatively high. The majority of angiosperms was deciduous and is characterized by leaves with dentate margin. Percentage of entire-margined species varies from 15 to 25% in different assemblages, but many of them have thin texture of leaf blade and probably were also deciduous. Only two species have pinnately veined leaves with entire margin and thick texture that suggest evergreen habit. Coryphoid palms from the Aspelintoppen flora also had evergreen leaves and indicate a rather warm climate. In the early Palaeogene Spitsbergen was situated above the Arctic Circle and possibly the polar nights were an additional seasonal factor that affected the morphology of plants. It seems, that this factor can increase the number of deciduous taxa in Spitsbergen floras. Thus, the Palaeogene climate at Spitsbergen can be evaluated on the whole as warm-temperate or moderately temperate with high precipitation. Because water in the Arctic Ocean was rather warm and had no permanent ice (Clark 1974), it is very possibly that winters were mild and frostless. It seems, that winter temperatures in polar regions were so high on account of heating of these areas by warm ocean upwellings (Nessov & Golovneva 1990; Nessov 1997). Morphological characters of woody angiosperm leaves correGFF volume 122 (2000), pp. 62–63. “Early Paleogene Warm Climates and Biosphere Dynamics”