Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 26

A prolonged period of global warming commencing at 55 Ma (Palaeocene–Eocene thermal maximum) is attributed to the effects of the proto‐Iceland plume. This was ‘a period of climatic turmoil’ that lasted for over 100,000 years during which ocean temperatures increased by 3–10 °C (Nisbet et al. 2009). On land, this period saw the extinction of a large number of mammalian groups that had been dominant in the Palaeocene and the appearance of three modern mammalian orders. These evolutionary changes have been linked to diversification and dispersal in response to rapid environmental changes at this time (Hallam 2004). In the oceans the principal casualties were the benthic foraminifera, the most abundant deep‐water organisms. At ~55 Ma about half of all benthic Foraminifera species were wiped out (a greater loss than had occurred at the Cretaceous–Palaeocene boundary (best known for the extinction of the dinosaurs). This calamity for the foraminiferans has been ascribed to ocean warming and acidification as a result of rising CO₂ content (Hallam 2004; Lovell 2010).

Methane hydrates (clathrates) are solids resembling ice, composed of water + gas and stable at high pressures and low temperatures that occur beneath the sea floor. Destabilization of these compounds yields free methane, which is a more efficacious ‘greenhouse gas’ for absorption of solar heat than CO₂ (Svenson et al. 2004). There are numerous hypotheses regarding the actual process by which the ‘greenhouse’ gases were emitted. It has been suggested that arrival of the mantle plume resulted in short‐term sea‐floor uplift that caused both a sea‐temperature rise, pressure reduction and consequent dissociation of the hydrates (MacLennan and Jones 2006). Yet another hypothesis is that a great emission of methane came from an enclosed marine basin in which enormous amounts of methane briefly existed. One such basin, specifically suggested, between Norway and Greenland (called ‘the Kilda Basin) and the triggering of gas was related to a rise of the Iceland Plume (Nisbet et al. 2009).