Early Tertiary Vegetation of Arctic Canada and Its Relevance to Paleoclimatic Interpretation

Abstract

Early Tertiary fossil plants representing polar Arcto-Tertiary vegetation are found on Ellesmere and Axel Heiberg islands, northernmost of the Canadian Arctic Archipelago. Growing at a paleolatitude of 75–80 °N, these forests experienced prolonged periods of continuous daylight in the summer and continuous darkness in winter. The primarily deciduous vegetation, including members of the Taxodiaceae, Cupressaceae, Pinaceae, Ginkgoaceae, Platanaceae, Juglandaceae, Betulaceae, Menispermaceae, Cercidiphyllaceae, Ulmaceae, Fagaceae, and Magnoliaceae, clearly indicates that summer growing conditions were mild and moist, a conclusion supported by breadth and uniformity of annual growth increments of wood and by estimates of structure and productivity of forests. More significantly, probable frost-sensitive members of, for example, the Taxodiaceae, as well as fossil crocodilians and other frost-sensitive animals indicate that severe frost never occurred, even during the long, dark winter. Cold month mean temperatures of 0–4 °C, warm month mean of >25 °C, and mean annual temperature of 12–15 °C are estimated. These estimates are higher than those derived from physiognomic analogy, probably because dark polar winters in the high paleolatitudes and cold winter temperatures in the modern mid-latitudes similarly effect vegetation and enforce deciduousness. The transition from ‘greenhouse’ to icehouse’ began during the mid-Tertiary. The onset of climatic decline may be apparent in the appearance of diverse evergreen Pinaceae in the Eocene Axel Heiberg Island assemblages and other contemporaneous floras of the Eocene mid- to high latitudes. Neogene floras of northern Canada indicate that mixed evergreen coniferous/deciduous broad-leaved vegetation typical of modern boreal ecosystems persisted throughout the Arctic Archipelago until the onset of Pleistocene glaciation.