2 Cenozoic Vegetation and Phytogeography of the Sub‐arctic North Atlantic

       Friðgeir Grímsson1, Thomas Denk2 and Reinhard Zetter3

       1 Department of Botany and Biodiversity Research, University of Vienna, Vienna, Austria

       2 Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden

       3 Department of Palaeontology, University of Vienna, Vienna, Austria

      This chapter provides a review of Cenozoic plant assemblages from the sub‐arctic North Atlantic region and their biogeographic implications. Previous work is reviewed and new data are presented that considerably change our understanding of the role of the northern North Atlantic for plant dispersal and evolution of plant lineages during the Paleogene and Neogene. Paleogene plant fossils in this region are known from West and East Greenland, the Faroe Islands and Scotland. In contrast to the widely held view that most Paleogene plant taxa of Greenland belong to extinct lineages, we provide evidence for the presence of several extant genera in these floras (e.g. Fagus, Quercus). Thus, Engler’s hypothesis about the ‘Arcto‐Tertiary element’ remains a fundamental hypothesis about the origin of northern temperate tree genera. In general, a remarkable diversity of extinct and modern lineages of Fagaceae is documented for Palaeocene and Eocene floras. Neogene fossils are found in Iceland and provide records of climate evolution in the sub‐arctic North Atlantic and of the duration of a functioning land bridge for plant migration between North America and Europe. Counter to the traditional view suggesting a functioning land bridge only during the Paleogene, there is now convincing evidence that this link was available for plants until the latest Miocene. This has important implications for understanding low genetic differentiation documented in extant plant groups having a disjunct distribution in northern temperate regions of Europe, North America and East Asia. Relatively warm conditions persisted in the sub‐arctic North Atlantic until the end of the Zanclean (early Pliocene) based on plant fossil evidence from Iceland. The shift to modern tundra conditions occurred during the Piacenzian (late Pliocene) and is documented in the Pliocene and Pleistocene fossil plant assemblages of Iceland.

Introduction

Palaeobotanical investigations in the sub‐arctic regions of the North Atlantic date back to the middle nineteenth century (Heer 1859 et seq., Iceland, Greenland, Svalbard; Gardner 1887, Island of Mull; Hartz 1903, Faroe Islands). The first mention of fossil plants in this region dates back to 1772 (Ólafsson 1772). Heer believed all the Arctic floras to be of Miocene age (e.g. Heer 1868), based on comparison with the (truly) Miocene flora of Öhningen. This age estimate was questioned by Gardner (1884), who suggested an Eocene age for the floras of Mull, Spitsbergen and Greenland based on the presence of Macclintockia in these floras. Gardner's assessment was later corroborated by evidence from molluscs (Ravn 1922). With the general acceptance of plate tectonics in the early 1960s and subsequent first radiometric dating of basalts bordering the North Atlantic basin (e.g. Moorbath and Bell 1965), the modern picture of the evolution of the North Atlantic region emerged. The Cenozoic floras of the northern North Atlantic region belong to the Brito‐Arctic Igneous (floral) Province (BIP; Figure 1) according to Boulter and Manum (1989). The BIP floras are the result of the initial break‐up of the northern North Atlantic during the early Cenozoic and the widening of the North Atlantic during the Neogene (cf. Denk et al. 2011). Whereas the floras at the western (Greenland) and eastern (Scotland, Faroe Islands) margins of the North Atlantic are of Paleogene age, the intra‐basaltic plant‐bearing sedimentary rocks of Iceland are of Neogene age (Figure 2). As such, all these palaeofloral assemblages provide a unique and almost continuous archive of Cenozoic vegetation development in the sub‐arctic North Atlantic region.