Origin of freshwater fauna of the North-Atlantic islands: present distribution in relation to climate and possible migration routes

摘要

This paper considers the origin of freshwater fauna of the northern North-Atlantic islands, notably, Iceland, the Faroes, Svalbard, Shetland and the Orkney, as well as Greenland. The history and possible migration routes are discussed, and a faunal relationship with Scandinavia and Great Britain is evaluated in conjunction with climatic fluctuations and major tectonic events since the Tertiary. The Tertiary climate was warm with relatively small latitudinal gradients. During the Palaeocene (66-57 My ago) and into the Eocene, most of Earth enjoyed an equable and moist climate, and a tropical to subtropical flora and fauna flourished in Europe, reaching as far north as Svalbard and Ellesmere Island (Downes 1988). Towards the end of the Eocene (34 My ago), a cooling trend became evident, first at high latitudes. The climate warmed again during Miocene but then progressive cooling set in, culminating in the onset of the Ice Age some 2.6 My ago. During the last glacial maximum (18 Ky ago), ice covered almost all of Greenland, the present evidence indicating that only isolated nunataks and possibly fragments along coastal shelves remained ice-free (Brochmann et al. 2003). The late Weichselian ice sheet similarly covered virtually all of Svalbard, Iceland, Scandinavia, Scotland and the Scottish isles, extending as far as southern Ireland and southern England (Brochmann et al. 2003, CLIMAP 1976).