Biogeography in the Sub-Arctic E-Book
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There is no escaping the fact that the island biogeography of the North Atlantic Region is singularly peculiar. Sitting in the north of the Atlantic Ocean, these islands have been subjected to largescale shifts in climate over the last few million years, unlike the other island groups further south which were likely more buffered from the vicissitudes of Quaternary climate changes. Uniquely for a group of islands there is only one documented extinction in the North Atlantic (the Great Auk), and those in the insects are local events relating to species that are distributed throughout the Palaearctic region. Over half the insect species in Iceland and Greenland are introduced. The faunas, excluding Greenland, are predominantly of Palaearctic origin and have close affinities with the faunas of Scandinavia and the British Isles and. These unique physical and biological characteristics have interested biologists and biogeographers for centuries.
The key debates concerning the biogeography of the North Atlantic islands still rumble on: Do the biota reflect cryptic refugia or otherwise, or tabula rasa and recolonization? How important were human communities in shaping the existing biota and biogeographical patterns? Throw into this mix current concerns over global warming, and we can now ask, how resilient is the biota to change, either natural or anthropogenic? This volume draws together a range of researchers with longstanding research interests in the region, from diverse academic backgrounds, to evaluate some of these questions.
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Table of Contents
Cover
Title Page
Copyright Page
List of Contributors
Introduction
References
Section I: Remote Origins
1 The Opening of the North Atlantic
Plate Tectonic Résumé
Magnetic Anomalies
Mantle Plumes
The Iceland Plume
Early Palaeocene Before the North Atlantic Opening
The Geographical Pattern of Break‐Up
Micro‐continent Formation
Magmatism Heralding the Birth of the New Ocean
Flood Basalt Eruptions
Seaward Dipping Reflectors
Ash Beds of Western and Central Europe
The Palaeocene–Eocene Thermal Maximum
Iceland
Evidence for Plume Pulsing
Continental Uplift after Ocean Formation
Summary
Acknowledgements
References
2 Cenozoic Vegetation and Phytogeography of the Sub‐arctic North Atlantic
Introduction
Paleogene Floras and Vegetation
Neogene Floras and Vegetation
Biogeographic Implications
Conclusion and Future Research
References
3 Interglacial Biotas from the North Atlantic Islands
Introduction
The Faroe Islands
Iceland
Greenland
Discussion and Conclusions
References
Section II: Origins of the Present Biota
4 Origin and Dispersal of the North Atlantic Vascular Plant Floras
North Atlantic Endemics – A History of Over‐Description and Rapid Hybrid Speciation
Colonisation History of North Atlantic Plants
Genetic and Floristic Relationships Among Five Atlantic Floras
Some Glacial Survivors After All?
Concluding Remarks
Acknowledgements
References
5 The Aquatic Fauna of the North Atlantic Islands with Emphasis on Iceland
Introduction
Aquatic Invertebrates
Endemism
Discussion
References
6 The Vascular Floras of High‐Latitude Islands with Special Reference to Iceland
Introduction
A Survey of High‐Latitude Islands
Patterns of Species Richness
Iceland and Its Vascular Flora
Summary
Acknowledgements
References
7 Quaternary Vertebrates from the North Atlantic Islands
Introduction
Fish
Birds
Pre‐Holocene Mammal Remains
Holocene Marine Mammals
Holocene Terrestrial Mammals
Discussion and Conclusions
Acknowledgements
References
8 North Atlantic Insect Faunas, Fossils and Pitfalls
Introduction
The Discussion About Refugia
The Modern Faunas
Human Impact and North Atlantic Faunas
Conclusions
References
Section III: Human Impact
9
Landnám
and the North Atlantic Flora
Introduction
The Faroe Islands
Iceland
Greenland
Discussion
Conclusions
Acknowledgements
References
10 Origin of the Northeast Atlantic Islands Bird Fauna
Introduction
Geological Overview and Climate Regimes
Origin of Bird Fauna
Colonization and Evolution
Immigration
Analysis of Colonization
Conservation Problems Concerning Birds
Economic Importance of Birds
References
11 Human Impact on North Atlantic Biota
Introduction
History of Settlement: Introduction, Exploitation and Modification of Vertebrate Biota
Ovigenic Landscapes or Adaptive Grazers?
Northern Fisheries
Conclusions
References
Section IV: Conservation in a Warming World
12 A Fleet of Silver
Introduction
Arctic Climate Change
Sea Ice and Locations of Iceland and Labrador
Impacts of Sea‐Ice Variations in Iceland and Labrador
Historical Sea‐Ice Data for Iceland and Labrador
Local and Indigenous Knowledge Systems
A Perspective from the Past: Iceland
A Perspective from the Present: Labrador/Nunatsiavut
Overview of Recent Sea‐Ice Variations
Conclusions
Acknowledgements
References
13 Biodiversity Conservation in the Faroe Islands Under Changing Climate and Land Use
Introduction
Changes in Flora since the Last Ice Age
The Vegetation and Flora
Impacts on the Flora
Status of the Flora and Fauna
References
14 Biodiversity Conservation in Iceland Under Changing Climate
Introduction
Conservation of Biodiversity in Iceland
Environmental Legislation in Iceland
Domestic Laws for Conservation of Species, Habitats and ‘Ecosystems’
International Laws, Agreements and Treaties About the Environment and Wild Organisms That Iceland Has Signed
Concluding Remarks
Acknowledgements
References
15 The Natural Environment and Its Biodiversity in Greenland During the Present Climate Change
Introduction
Recent Climate – The Last Hundred Years
The Biology of Greenland with Emphasis on Terrestrial Ecosystems
Distribution of Plant Communities in the North
Consequences of Climate Change at the Ecosystem Level
Concluding Remarks
References
Index
End User License Agreement
List of Tables
Chapter 5
Table 1 Distances (km) between North Atlantic islands.
Table 2 Number of species of aquatic insects on islands in the North Atlantic...
Table 3 Number of species of freshwater Crustacea on islands in the North Atl...
Chapter 6
Table 1 A comparison of the selected northern and southern hemisphere islands...
Table 2 Floristic affinities of the vascular flora of Iceland. Note that the ...
Table 3 A comparison of the species richness of arctic genera that are well r...
Chapter 7
Table 1 Selected radiocarbon ages of vertebrate remains from Greenland.
Chapter 8
Table 1 List of Coleoptera found on late‐glacial sites on the Scandinavian co...
Table 2 Anthropochorous and synanthropic species (highlighted in grey) from t...
List of Illustrations
Chapter 1
Figure 1 The bathymetry of the North Atlantic, based on satellite sea‐surfac...
Figure 2 The pattern of magnetic stripes in the North Atlantic, 2005. Geolog...
Figure 3 (a) Conglomerate from a 2–3 m thick stratum separating Cretaceous s...
Figure 4 Fault pattern in the North Atlantic region on a map restored to con...
Figure 5 Map showing the orogenic belts on either side of the North Atlantic...
Figure 6 A coastal section on Cape Searle Island, Baffin Island, Canada, sho...
Figure 7 Map showing the break‐up pattern showing the eastward displacement ...
Figure 8 Distribution of the early Paleogene lavas, subaerial and submarine....
Figure 9 (a) Flat‐lying basalts of the Geikie Plateau Formation, Gåseland, E...
Figure 10 Kap Hammer on the East Greenland coast (67°40′N), within the zone ...
Figure 11 Sub‐aerial (picritic) lavas on the Svartenhuk peninsula, West Gree...
Figure 12 Dark ash layers contrasting with white diatomite sediments on the ...
Figure 13 Lava fountaining along a fissure (Krafla volcano) northern Iceland...
Chapter 2
Figure 1 The northern North Atlantic part of the Brito‐Arctic Igneous (flora...
Figure 2 Relative age of Cenozoic (pre‐Holocene) volcanics and sedimentary r...
Figure 3 Palaeocene fossil leaves from West Greenland (Agatdalen, Atanikerlu...
Figure 4 Palaeocene leaves and Eocene pollen from West Greenland (Agatdalen,...
Figure 5 Palaeocene fossil leaves from Atanikerluk, West Greenland. (A)
Fago
...
Figure 6 Eocene fossil pollen from Hareø, West Greenland. (A, B)
Fagus
sp. (...
Figure 7 Eocene fossil leaves from Hareø, West Greenland. (A)
Fagus
sp., S11...
Chapter 3
Figure 1 Map of the North Atlantic region showing the location of place name...
Figure 2 Stratigraphical overview of the Quaternary (the last 2.6 Ma) showin...
Figure 3 (a) Mt. Stöð with an outcrop of the Búlandshöfði Formation showing ...
Figure 4 Examples of leaf imprints of vascular plants from interglacial depo...
Figure 5 (a) A log of
Larix
sitting in sandy deposits of the Kap København F...
Figure 6 Drawings of plant remains from the Kap København Formation in North...
Figure 7 Scanning electron microscope photographs of beetle and ant remains ...
Figure 8 Maps of the northern parts of the Earth, showing present geographic...
Figure 9 Scanning electron microscope photographs of fruits from extinct pla...
Figure 10 Scanning electron microscope photographs of plant remains from las...
Figure 11 Scanning electron microscope photographs of beetle remains from la...
Figure 12 Maps of the northern part of the Earth, showing the present‐day ra...
Figure 13 Maps of the northern parts of the Earth, showing the present‐day g...
Figure 14 Scanning electron microscope photographs of remains of insect rema...
Figure 15 Maps of the Earth’s northern parts with arrows that show immigrati...
Chapter 4
Figure 1 Reconstruction of the Late Weichselian (25 000–10 000 years ago) ma...
Figure 2 Colonisation of the Svalbard archipelago with source regions inferr...
Figure 3 (a) Main (thick arrows) and additional (thin arrows) long‐distance ...
Figure 4 Genetic patterns detected in two west‐arctic species, providing qui...
Chapter 5
Figure 1 Numbers of Cladocera species on the North Atlantic islands and the ...
Figure 2 Numbers of Trichoptera species on the North Atlantic islands and th...
Figure 3 Number of species of Ephemeroptera, Plecoptera, Trichoptera, and Di...
Chapter 6
Figure 1 Location of the selected islands in the northern (left) and souther...
Figure 2 (a) The log–log species area relationship for the 17 high‐latitude ...
Figure 3 (a) Native vascular species richness (upper black columns) and ende...
Figure 4 The relationship between the degree of Pleistocene glaciation (exte...
Figure 5 Four hypothetical scenarios for the history of the Icelandic vascul...
Chapter 7
Figure 1 Map of the North Atlantic region showing the location of selected p...
Figure 2 Two examples of vertebrate remains from Greenland. (a) A pelvic spi...
Figure 3 Two examples of remains of marine mammals from Greenland. (a) A ver...
Figure 4 Maps of Greenland showing Holocene and modern natural geographical ...
Figure 5 Two examples of musk‐ox (
Ovibos moschatus
) skull fragments. (a) A s...
Figure 6 Temporal ranges of selected vertebrates from Greenland.Reprinte...
Chapter 8
Figure 1 Different distribution patterns between long and short winged forms...
Figure 2 Map of distribution of the ground beetle
Notiophilus biguttatus
in ...
Figure 3 Map of distribution of the littoral rove beetle
Micralymma brevilin
...
Figure 4 Affinities of Coleoptera of North Atlantic Islands which strongly i...
Figure 5 Affinities of Diptera in the North Atlantic islands. Atmospheric sy...
Figure 6 Map of the North Atlantic during the beginning of the Holocene show...
Figure 7 Map of the North Atlantic with early Norse colonization routes and ...
Chapter 9
Figure 1 Map of the North Atlantic showing the pattern and approximate timin...
Figure 2 Sites and places within the Faroe Islands that are named in the tex...
Figure 3 Gróthusvatn viewed from the north. A storm beach separates the lake...
Figure 4 Selected taxa pollen diagram for Gróthusvatn, Sandoy. Depths are me...
Figure 5 Sites and places within Iceland that are named in the text. Key to ...
Figure 6 Percentage pollen diagram for Reykholtsdalur, west Iceland, showing...
Figure 7 Sediment profile from Mosfell in Mosfellsdalur, southwest Iceland, ...
Figure 8 Sites and places within the Eastern Settlement of Greenland that ar...
Figure 9 Mixed birch‐willow scrub and woodland covering sheltered valley slo...
Figure 10 Sites and places within the Western Settlement of Greenland that a...
Figure 11 Percentage pollen diagram for Tasiusaq, Eastern Settlement of Gree...
Figure 12 Lyme grass (
Elymus arenarius
L. spp.
mollis
) growing on the ruins ...
Chapter 10
Figure 1 The extent of the Ice Age glaciation about 20 000 years ago.
Figure 2 Number of bird species recorded in Iceland (black) and the Faroe Is...
Chapter 11
Figure 1 Cod sizes from Quoygrew and Stackelbrae (Viking Age and medieval si...
Figure 2 Quoygrew and Stackelbrae saithe sizes, sieved dataset.
Chapter 12
Figure 1 North Atlantic Ocean Currents. The red arrows (light shading) refle...
Figure 2 Comparison of Labrador/Newfoundland (blue/dark shading) and Iceland...
Chapter 13
Figure 1 From the top of Sandfelli (790 m a.s.l.) in the northern part of Ey...
Figure 2 The distribution of the red‐listed species in the five IUCN categor...
Figure 3 The distribution of the red‐listed species in the lowland, the low‐...
Figure 5 Oysterplant,
Mertensia maritima
, is one of the threatened plant spe...
Chapter 14
Figure 1 Map of protected areas in Iceland using data from the Environment A...
Figure 2 The preservation area in Surtsey.
Chapter 15
Figure 1 Map of Greenland with ice cap borderline shown and name of localiti...
Figure 2 Retreating ice sheet permitting the first pioneer lichens (
Stereoca
...
Figure 3 Photo from July in the high arctic near Thule. The more favourable ...
Figure 4 July landscape in the Thule area. The border of the Greenland ice c...
Guide
Cover Page
Title Page
Copyright Page
List of Contributors
Introduction
Table of Contents
Begin Reading
Index
Wiley End User License Agreement
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Biogeography in the Sub‐Arctic
The Past and Future of North Atlantic Biota
Edited by
Eva Panagiotakopulu
University of EdinburghUK
Jon P. Sadler
University of BirminghamUK
This edition first published 2021#169; 2021 John Wiley & Sons Ltd
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Eva Panagiotakopulu and Jon P. Sadler to be identified as the authors of the editorial material in this work has been asserted in accordance with law.
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Limit of Liability/Disclaimer of WarrantyWhile the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging-in-Publication Data is applied for
ISBN 9781118561478
Cover Design: WileyCover Image: © Eva Panagiotakopulu
List of Contributors
Inger G. AlsosThe Arctic University Museum of NorwayTromsøNorway
Ole BennikeGeological Survey of Denmark and GreenlandCopenhagenDenmark
Jens BöcherZoological MuseumCopenhagenDenmark
Christian BrochmannThe Natural History MuseumUniversity of OsloOsloNorway
Thomas DenkDepartment of PalaeobiologySwedish Museum of Natural HistoryStockholmSweden
Gaston R. DemaréeRoyal Meteorological Institute of BelgiumBrusselsBelgium
Kevin J. EdwardsDepartment of Geography and Environment andDepartment of ArchaeologySchool of Geosciences, University of AberdeenAberdeenUKScott Polar Research Institute and McDonald Institute for Archaeological ResearchUniversity of CambridgeCambridgeUK
Egill ErlendssonDepartment of Geography and TourismFaculty of Life and Environmental SciencesUniversity of IcelandReykjavíkIceland
Anna Maria FosaaFaroese Museum of Natural HistoryTórshavnFaroe Islands
Gísli Már GíslasonInstitute of Life and Environmental SciencesUniversity of IcelandReykjavíkIceland
Friðgeir GrímssonDepartment of Botany and Biodiversity ResearchUniversity of ViennaViennaAustria
Jennifer HarlandArchaeology InstituteUniversity of the Highlands and IslandsOrkney CollegeKirkwallUK
Erlingur HaukssonFornistekkur 14ReykjavíkIceland
Henning Heide‐JørgensenDepartment of BiologyUniversity of CopenhagenCopenhagenDenmark
Brian T. HillInstitute for Ocean TechnologyNational Research CouncilCanada
Ib JohnsenDepartment of BiologyUniversity of CopenhagenCopenhagenDenmark
Ingrid MainlandArchaeology InstituteUniversity of the Highlands and IslandsOrkney CollegeKirkwallUK
Astrid E. J. OgilvieStefansson Arctic InstituteAkureyri IcelandInstitute of Arctic and Alpine Research(INSTAAR)University of ColoradoBoulder COUSA
Bergur OlsenFaroe Marine Research Institutre Faroe Islands
Eva PanagiotakopuluSchool of GeoSciencesUniversity of EdinburghEdinburghUK
Aevar PetersenBrautarland 2ReykjavíkIceland
Jon P. SadlerSchool of GeographyEarth and Environmental SciencesThe University of BirminghamBirmingham UK
J. Edward SchofieldDepartment of Geography and EnvironmentSchool of GeosciencesUniversity of AberdeenAberdeenUK
Thóra Ellen ThórhallsdóttirInstitute of Life and Environmental SciencesUniversity of IcelandReykjavíkIceland
Brian G. J. UptonSchool of GeoSciencesUniversity of EdinburghEdinburghUK
Bernd WagnerInstitute of Geology and MineralogyUniversity of CologneCologneGermany
Reinhard ZetterDepartment of PalaeontologyUniversity of ViennaViennaAustria
Introduction
Jon P. Sadler1 and Eva Panagiotakopulu2
1 School of Geography, Earth and Environmental Sciences, The University of Birmingham, Birmingham, UK
2 School of GeoSciences, University of Edinburgh, Edinburgh, UK
There is no escaping the fact that the island biogeography of the North Atlantic Region is singularly peculiar. While it has aspects of the characteristics of many island groups in terms of disharmonic and impoverished species pools (Coope 1986), it lacks true endemics (Buckland 1988; Downes 1988, but cf. Böcher 1988), although it is home to a wide number of putative subspecies and races (e.g. Lindroth 1968; Löve and Löve 1963). Sitting in the north of the Atlantic Ocean these islands have been subjected to large‐scale shifts in climate over the last few million years, unlike the other island groups further south which were likely buffered from the vicissitudes of Quaternary climate changes (Sadler 2001). Unlike island groups elsewhere, there is only one documented extinction on these island groups (the Great Auk) and those in the insects are local events relating to species that are distributed throughout the Palaearctic region. Over half the insect species in Iceland and Greenland are non‐indigenous and many of these were first introduced to the islands by the Norse colonists (Buckland 1988; Panagiotakopulu 2014; Sadler 1990). The faunas, excluding Greenland (Böcher 1988, are predominantly Palaearctic (Buckland 1988; Downes 1988; Lindroth 1931), and have close affinities with the faunas of the British Isles and Scandinavia. These unique physical and biological characteristics have interested biologists and biogeographers for centuries (Hooker 1862).
In their seminal book North Atlantic Biota and Their History, Löve and Löve (1963) concluded that plants survived the heavily glaciated Atlantic areas, in ‘glacial refuges’ or ‘nunataks’, dismissing the earlier ‘now merely historical’ tabula rasa idea – the hypothesis that the current Atlantic floras were established following postglacial immigration from source areas situated outside the ice sheets. The virtually complete consensus among plant biogeographers (with notable exceptions among some palaeoecologists) at that time was based on two main arguments, the occurrence of (a) disjunct and (b) endemic taxa in the North Atlantic region. Firstly, the presence of disjuncts was believed to necessitate in situ glacial survival because long‐distance dispersal in general and trans‐oceanic dispersal in particular was considered to be extremely rare, if not impossible, because many amphi‐Atlantic disjuncts lacked adaptations for long‐distance dispersal. Secondly, the occurrence of endemics was believed to necessitate in situ glacial survival because the postglacial period was considered to be far too short to allow for evolution of endemic taxa, an argument that has been supported in later studies (e.g. Dahl 1987). The pervading view was to postulate in situ glacial survival not only during the last glaciation but throughout the entire Pleistocene, to explain the occurrence of disjuncts and endemics in the North Atlantic region. Other research on insects, principally by Lindroth (1957), also argued for early immigration via landbridges and glacial refugia to explain the biogeographical affinities of the biota. More recent work also supports the refugial hypothesis (Maggs et al. 2008).
Löve and Löve (1963) perceptively pointed to the fact that conclusive tests of these varying colonization hypotheses must await a more extensive fossil record. Indeed, recent investigations of a rich plant fossil record seem to support the view that a North Atlantic Land Bridge facilitated plant migration between North America and Europe until the late Miocene (e.g. Brochmann et al. 2003). The Quaternary fossil record is now very extensive and has been used by many to support tabula rasa and post‐glacial colonization via ice rafting at the terminal phase of the last glaciation (Buckland et al. 1988; Coope 1986). Moreover, the fossil beetle fauna demonstrates that even at the beginning of the previous interglacial period a similar situation might have occurred, capable of transporting European taxa over the North Atlantic to Greenland (Bennike and Böcher 1994; Böcher 2012).
Unlike several island archipelagos (e.g. Pacific and Indian oceans) and continental shelf islands (e.g. Magascar), Pre‐European settlement in the North Atlantic was restricted to Greenland where Inuit settlers colonized the islands in the mid‐Holocene (Andreasen 1996; Jensen 2006). Although some scholars have consistently argued for pre‐Viking settlement of the Faroe and Iceland (e.g. Church et al. 2013; Hermanns‐Audardóttir 1991), the first major European settlement of the North Atlantic region was undertaken by Norse or Viking colonists who reached Faroe by CE 850, Iceland by CE 870, Greenland by CE 986 and ultimately America (Newfoundland) by CE 1000 (Fitzhugh and Ward 2000). In Greenland, however, European settlements were abandoned by the sixteenth century (Arneborg 2003), although the island was recolonized by Norwegians some 200 years later. The role that these human colonists played in shaping biogeographical patterns shows pulses of European introductions linked to Norse arrival (e.g. Panagiotakopulu 2014). The impact of the settlers on the island ecosystems also had an indirect influence in shaping habitats and therefore assemblage dynamics. Palynological work has tracked the Landnám ‘footprints’ of the Norse settlers in the region (Edwards et al. 2008, 2011) and Dugmore et al. (2012) have recently presented a comprehensive review of the environmental impact of Norse farming practices on ecosystem management, soils and pasture management. Wholescale environmental modification of this magnitude has left its mark on the biota in terms of assemblage changes and local extinctions (Buckland and Panagiotakopulu 2010; McGovern et al. 2007).
Some 40 years have elapsed since Löve and Löve's (1963) volume was published and the key debates concerning the biogeography of the North Atlantic islands still rumble on. Was it cryptic refugia (Stuart and Lister 2001) or otherwise (Willis and Whittaker 2000), or tabula rasa and recolonization (Buckland and Dugmore 2010)? How important were human communities in shaping the existing biota and biogeographical patterns? Throw into this mix current concerns over global warming, we can now add how resilient is the biota to change, either natural or anthropogenic? This volume draws together a range of researchers with longstanding research interests in the region, from diverse academic backgrounds, to evaluate these questions.
This book is organized into sections each examining a particular theme. Section I focuses on the remote origins of the islands, diving deep into the early history of the region. Upton (Chapter 1) examines the opening of the North Atlantic from a geological perspective, charting its origin from super‐continent in the lower Palaeozoic, approximately 420–430 million years (Ma) ago, to the development of the North Atlantic Ocean as a late product of the disintegration of Laurasia, a part of Pangaea, which split to form North America, Greenland, Europe and Asia. The Cenozoic vegetation and phytogeography of the sub‐arctic areas are discussed by Grímsson et al. (Chapter 2). They examine the ‘Arcto‐Tertiary element’ hypothesis and present data that demonstrate that several north temperate tree taxa thrived in the sub‐arctic during the Paleogene, while also noting evidence for the presence of several ‘Arcto‐Tertiary elements’ in Greenland. They then go on to evaluate the possible role for the ‘The North Atlantic Land Bridge’, reviewing recent investigations of the rich plant fossil record, and demonstrate that the NALB facilitated plant migration between North America and Europe until the late Miocene. Moving forward in time, Bennike and Böcher (Chapter 3) examine the biotal record from the last interglacial period. They review the refugia‐tabula rasa debate in light of this record and point to areas where knowledge is lacking, such as the role of microclimate and insolation in supporting the former. They illustrate that during the interglacials there was a rich biota in suitable biotopes on the North Atlantic.
Section II of the volume examines the contentious issue of biotal origins. Brochmann and Alsos (Chapter 4) present new genetic evidence based on a total of 9018 plants from 1140 populations to re‐evaluate their earlier conclusions (Brochmann et al. 2003) on the origins and dispersal of the North Atlantic vascular plant floras. The data point towards postglacial immigration of a highly dispersive flora, although they note convincing molecular evidence suggesting in situ glacial persistence of some elements of the ‘west‐arctic’ species group. Gíslason (Chapter 5) examines the aquatic fauna of the North Atlantic islands with a particular emphasis on Iceland. He notes that the islands have few aquatic species, almost no aquatic endemics, but their faunas are closely related. He goes on to discuss how the proportion of continental (Norway and Britain) species present on the islands is much higher among crustaceans than other groups. Despite low levels of endemism found amongst crustaceans in subterranean groundwater systems, the patterns indicate a Holocene (post glacial) origin for the biota.
Thórhallsdóttir (Chapter 6) evaluates and analyses data on the vascular floras of high‐latitude islands, again with special reference to Iceland, corralling independent lines of evidence that all favour the view that the Icelandic flora is young, i.e. of Holocene descent. In Quaternary vertebrates from the North Atlantic islands, Bennike and Wagner (Chapter 7) review the meagre fossil record of mammals from the main islands of Greenland, Iceland and Faroe, pointing out the incomplete record and the need for other independent lines of evidence such as genetic analyses. Panagiotakopulu (Chapter 8) reviews the North Atlantic insect fauna data revealing the effect of climate change and their early immigration to the islands but emphasizing the importance of the arrival of Europeans in the North Atlantic region in terms of introduction of species to the region but also the biological impact that they have had on the fauna.
Section III picks up on this key theme of human impact on the islands. Edwards et al. (Chapter 9) use the archaeological and palaeoecological records to examine the impact of Landnám and the North Atlantic flora. The review highlights the fact that the impacts of landnám on vegetation were broadly similar across that region, but that there are subtle differences in the Norse ‘footprint’ when examined at finer spatial scales which varied according to the interplay of the climatic, pedogenic, topographic and anthropogenic factors at each location.
Petersen and Olsen (Chapter 10) review the status of the bird fauna of Iceland and Faroe and discuss its colonization and Mainland and Harland (Chapter 11) explore the profound impact of farming on North Atlantic vertebrate biota, reviewing evidence for the introduction of domesticated faunas and rapid and widespread changes to the island landscapes and environments as a result of pastoralism and the exploitation of marine resources. The former (Chapter 10) characterizes the patterns in bird dispersal and extinctions and extirpations and its conservation significance of the avian fauna, while the latter (Chapter 11) presents comprehensive evidence showing that farming and fishing were vital to subsistence and trade as well as being core to island and community identity in the past, roles they continue to play out to the current day.
The prospects for the future environmental systems of the region is addressed in Section IV. Ogilvie et al. (Chapter 12) use a rich historical dataset to provide an elegant perspective on the significance and importance of sea ice patterns and flows to both historical and contemporary communities. Fosaa (Chapter 13) returns to a biodiversity theme and reviews the influence of both climate change and direct human impact on the flora of Faroe, including the threats posed by introduced species pointing to elements in Faroese flora that are of some conservation concern. The policy and legislative frameworks for biodiversity and conservation in Iceland under a changing climate is evaluated in considerable detail by Hauksson (Chapter 13). Johnsen and Heide‐Jørgensen (Chapter 14) examine the natural environment and its biodiversity in Greenland during the present climate change, presenting observations of the biological response related to an increasing greenhouse effect and stratospheric ozone depletion with an emphasis on terrestrial plant ecology.
It is appropriate that we conclude this introduction with a tribute to one of the region's leading scientists for whom this volume was conceived. Professor Paul C. Buckland blended his early (doctoral) training from the related fields of archaeology and geology, work on tephrochronology of East Africa lakes, a detailed evaluation of the value of insect fossils in the interpretations of archaeological deposits across the world, into a unique, innovative and complementary skillset for examining the biological conundrum that was (and to some extent still is) the biogeography of the North Atlantic. Like many researchers and colleagues (several authors of chapters in this volume), both editors of this book have been small cogs in this body of research and benefitted greatly from Paul Buckland's supervision and tutorage as doctoral researchers. Having developed a love for the environments, plants, animals and people of the North Atlantic region in a research career spanning some four decades, this book and contributions within it are a fitting tribute to his unique contribution to our understanding of the biogeography of the region.
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Section IRemote Origins
1The Opening of the North Atlantic
Brian G. J. Upton
School of GeoSciences, University of Edinburgh, UK
The northern landmasses, namely North America, Greenland and Europe/Asia were part of one global super‐continent in the lower Palaeozoic, approximately 420–430 million years (Ma) ago. This super‐continent (Pangaea) resulted from continental collisions. Driven by convective flow deep in the interior of the Earth it is the nature of continents to break apart, re‐join and to come apart again. Such a separation and amalgamation constitutes ‘the Wilson Cycle’, which takes several hundred million years to run its full course. No sooner had Pangaea come into existence than it became subject to tectonic stresses that tended to disrupt it. The North Atlantic Ocean is a late product of the disintegration of Laurasia, a part of Pangaea, which split to form North America, Greenland, Europe and Asia. Continental separation had begun in the south Atlantic region at ca 130 Ma and spread north by 60–50 Ma.
Plate Tectonic Résumé
Before considering the birth and growth of the North Atlantic, a brief résumé concerning plate tectonics is in order. Volumetrically the greater bulk of the planet is composed of the mantle. The latter, itself covered by thin veneers of crust, hydrosphere and atmosphere, extends down to a depth of 2885 km, i.e. to the outer boundary of the core from which it receives heat. The mantle is composed of various magnesium‐rich silicates and oxides and is deduced to behave as a ductile material that is in constant slow convective motion, flowing whilst remaining (almost entirely) in the solid state. The flowage is due to variations in its composition and temperature (principally the latter) that confer different densities to some parts. Consequently, the relative buoyancy of those parts with lower density causes them to rise while, simultaneously, other denser parts sink to take their place.
Whereas most of the mantle is thought to behave in a ductile manner, a relatively thin outer layer differs in being mechanically rigid and is known as the lithosphere. The lower and larger part of this comprises the lithospheric mantle whilst the upper layer (the crust) consists of less magnesian and more siliceous and aluminium‐rich rocks. The lithosphere is sub‐divided into some 30 major tectonic plates and a host of micro‐plates. These tectonic plates, floating on the convecting underlying mantle, move relative to each other in one of three ways. They may (a) slide past each other without colliding, (b) collide and under‐ or over‐ride another plate or (c) just move apart. Typically, the continental lithosphere has a thickness of >100 km but under the oceans the lithosphere is much thinner, ranging from zero (at the mid‐ocean ridges) to ~100 km. Older, colder and thicker parts of the oceanic lithosphere sink back into the deeper mantle at subduction zones where they undergo re‐cycling. This loss of oceanic lithosphere is counterbalanced by continuous growth of new lithosphere along the ‘mid‐ocean ridges’ or ‘constructive plate boundaries’, where the plates move apart. This juvenile lithosphere is formed from material arising from the underlying ductile mantle. In the context of oceanic lithosphere, ‘old’ means having ages of up to ~200 Ma whereas the rocks of the continental lithosphere have ages of anything up to 4000 Ma.
Continental lithosphere differs from its oceanic counterpart not only in being older and thicker but in composition, complexity and overall lower density. The last of these causes it to ‘float’ higher so that most rises above sea‐level and the remainder is covered only by shallow seas and constitutes the continental shelves. By contrast, because of its higher density, the oceanic lithosphere lies at lower levels than its continental counterpart and its surface is almost invariably submarine, with the ocean floors generally lying at depths of ~4 km. The oceanic lithosphere, with its constructive plate boundaries (mid‐ocean ridges) and corresponding destructive plate boundaries (along subduction zones, generally demarcated by deep ocean trenches), covers some 5/7th of the Earth's surface. The continental shelves slope steeply down from depths of ~2 km to the deep ocean floors. Consequently, the submarine 2 km contour approximates the change‐over from one type of lithosphere to the other. On the western side of the North Atlantic the continental shelf is very narrow, contrasting with the European side where it is much broader.
The first mid‐ocean ‘ridge’ to be recognized was the ‘mid‐Atlantic Ridge’ along the Atlantic axis (Heezen et al. 1959: Figure 1, see Plate section). This was subsequently shown to be merely a part of a great circum‐global ridge system, some ~80 000 km long, rising to heights of 3 km or more from the deep (‘abyssal’) oceanic plains. Typically, these ridges bear a rift‐valley along their crests that can be up to 10–20 km wide and with a relief of ~1 km (Bown and White 1994).
The ocean floor moves away symmetrically on either side of the mid‐ocean ridges as new lithosphere is generated along them. The process of ocean‐floor spreading causes a reduction of pressure along the axes which in turn promotes partial melting, to the extent of some 10–15%, of the asthenospheric mantle that underlies the lithosphere. The melt product is basaltic magma that, being less dense than the residual solid mantle, ascends towards the surface. Losing heat as it does so, most crystallizes to form intrusive rocks within the oceanic crust and the remainder erupts as lava on the ocean floor. Although the volume of lava erupted from the mid‐ocean ridges is estimated to be between 2 and 3 km3/year, a much greater volume is estimated to crystallize to form the underlying intrusions.
The spreading process confers bilateral symmetry to the mid‐ocean ridges as juvenile material is welded on either side to the pre‐existing lithosphere. The mantle rocks that are not consumed in the melting remain behind, contributing to the lower part of the oceanic lithosphere. Sea‐floor spreading occurs at rates that can exceed 100 mm/year, whilst that in the North Atlantic is roughly 25 mm/year (Bown and White 1994).
When extensional stresses acting on a ridge sector become too great, rupturing (rifting) occurs along its crest and the new‐formed magma rises up a vertical fissure to form an intrusive ‘dyke’. The dykes cool to form tabular, near‐vertical intrusions, typically not more than a few metres wide. Their repeated generation produces a ‘sheeted complex’ in which the youngest are those newly formed along the spreading axis and the oldest are those furthest away. Dykes can compose virtually the entirety of the sheeted complexes lying beneath the lavas extruded on the ocean floor.
Figure 1 The bathymetry of the North Atlantic, based on satellite sea‐surface altimetry, model DNSC08. The symmetrical disposition of the mid‐Atlantic ridge relative to the bounding continents is well exhibited.
Source: Based on Anderson, O.B. & Knudsen, P. 2009.
Because of this mechanism the spreading (and thus growth of the oceanic plate) does not take place continuously but in a jerky, spasmodic manner. For example, generation of a new fissure 1 m wide every 50 years would correspond to an averaged spreading rate of 20 mm/year. Hence, whilst the spreading ocean floors can be crudely considered as analogous to moving walkways, it is intermittent with intervals of tens to hundreds of years intervening between the intrusion of one dyke and the next. The relatively hot rocks composing the axial region have a lower density so that they rise to form the mid‐ocean ridges. With age and cooling they subside to the depths of the abyssal plains.
The mid‐ocean ridges are offset by faults of a type known as transform faults. The motions along these fractures (which can have offsets ranging up to hundreds of kilometres) are dominantly horizontal. In the North Atlantic there are several of these major fractures that subdivide the mid‐ocean ridge between Greenland and Norway. The most prominent are the Senja fracture zone to the south of Spitzbergen and the Jan Mayen fracture zone at ~52°N.
Magnetic Anomalies
As a result of processes in the Earth's core, the magnetic field spontaneously reverses at irregular intervals averaging at 500,000 years. The direction of magnetization is recorded within the oxide minerals that crystallize from the magmas, much as in a compass needle. As they cool, these minerals retain a memory of the field at the time of their formation. As sea‐floor spreading proceeds, alternating strips of ‘normally magnetized’ (i.e. with the magnetic field as it is currently) and those with ‘reversed magnetization’ are left on the ocean floor (Figure 2, see Plate section). It was the discovery of these ocean floor magnetic anomalies by Vine and Matthews (1963) that provided confirmation of Hess's (1962) ocean‐floor spreading hypothesis. Vine and Matthews demonstrated that continuous growth of the ocean floor, in conjunction with the periodic reversals, produces distinct magnetic stripes, developed as mirror‐images on either side of the spreading ridge.
These magnetic signatures record the past positions of the ridge axis and, since specific ages can now be assigned to the reversals, the age of the ocean floor from new‐formed crust to oldest (first‐formed) crust can be determined.
Mantle Plumes
Masses of mantle rock rise convectively when their composition and/or temperature confers buoyancy. Temperature, however, is regarded as the dominant factor and great volumes of abnormally hot rock are thought to detach periodically from deeper parts of the mantle to rise as so‐called mantle plumes. Although the concept of mantle plumes dates back to the early 1970s, it remains controversial with opponents of the idea referring simply to foci of high temperature phenomena as ‘hot‐spots’ and denying that such plumes arise from the deep mantle (e.g. Anderson 2005).
The idea that mantle plumes have a mushroom‐like shape, with a massive plume head and an extremely hot tail, is based on fluid‐dynamical studies. The most voluminous magmatic events during the Earth's history have been related in space and time to an impact at the base of the lithosphere by such a plume head. Such a ‘hot‐spot’ model was outlined for the North Atlantic by White (1988), postulating a central plume causing raised asthenospheric temperatures across a wide region. A review of conflicting hypotheses with respect to the North Atlantic by Meyer et al. (2007) concluded that it would be difficult to present a model explaining both the records of igneous activity and associated uplift (discussed below) without appealing to an up‐rise of hot mantle beneath the lithosphere. Because the various arguments cannot be rehearsed in this chapter the author adopts a partisan attitude, regarding the plume model as the more robust and better supported by evidence.
The Iceland Plume
The sudden and massive onset of magmatic activity in what may be broadly termed the north Atlantic region during the early Cenozoic (i.e. in the Palaeocene and Eocene epochs, between 66 and 34 Ma) has been attributed to a dramatic increase in the temperature of the underlying mantle starting at around 62 Ma. The most plausible explanation for this is that it was due to the arrival at shallow levels of an abnormally hot mantle body, namely a mantle plume. However, some sea‐mounts in the Rockall Trough, dated at 70+/−1 Ma, may indicate some precursor plume activity commencing in the Cretaceous (O'Connor et al. 2000).
Figure 2 The pattern of magnetic stripes in the North Atlantic, 2005. Geological Map of the World. Scale: 1 : 50 000 000.
Source: Published by CGMW & UNESCO.
The opening of the North Atlantic (and the subsidiary opening of Baffin Bay west of Greenland) is believed to have involved complex interaction between this plume (the proto‐Iceland plume evolving to the Iceland plume) and ‘normal’ sea‐floor spreading processes (White 1997; White and McKenzie 1989; Fitton and Larsen 2001; Smallwood and White 2002). The abundant generation of magma gave rise to a great igneous province prior to and accompanying the sundering of Laurussia and the creation of the embryonic North Atlantic Ocean. This province embraced a large region including eastern Greenland, a large part of the Norwegian shelf (the Vøring Plateau), the Faeroes and the Hebridean and Northern Irish parts of the British Isles. The cause of this magmatic activity is held to be partial melting generated by the proto‐Iceland plume as is the, approximately contemporaneous, activity that occurred across part of western Greenland and eastern Baffin Island. The magmatism commenced abruptly and was also relatively short‐lived, being mostly confined within 2–3 million years (White 1988). Not only were prodigious quantities of basaltic magma produced but also unusually magnesian (‘picritic’) magmas signifying exceptionally high temperatures were erupted, mainly in the opening stages of the activity. The time interval between the start of continental lithosphere stretching and creation of embryonic ocean was short, perhaps only 4–6 Ma (Smallwood and White 2002). This suggests that injection of great volumes of magma into the continental lithosphere weakened it, facilitating rapid thinning leading to its eventual failure.
Evidence of continental uplift preceding the magmatism is plausibly attributed to the arrival (‘impact’) of the buoyant and abnormally hot mantle plume. Uplift and magmatism preceded the continental rupturing that marked the genesis of a new ocean floor. At its earliest arrival the plume axis is inferred to have lain beneath west‐central Greenland but, as Greenland drifted westwards across the axis of the plume, the latter came to underlie a more central site under Greenland by 55 Ma (Lawver and Müller 1994; Saunders et al. 1997).
After first encountering the continental lithosphere the plume, with a temperature some 150 °C hotter than the normal mantle, spread out rapidly beneath the lithosphere in a crudely circular disposition ~2500 km diameter (White and McKenzie 1995; Smallwood and White 2002). It caused transient crustal uplift, large‐scale volcanism and complementary intrusive activity in conjunction with stretching and thinning of the continental lithosphere. Eventually the continental lithosphere parted, sea‐floor spreading commenced and the North Atlantic Ocean was born.
The Kangerdlugssuaq area of East Greenland is believed to have lain above the plume head at some stage (Brooks 2011). Striking evidence relating to the East Greenland uplift is provided by a horizon of conglomerate a few metres thick (Figure 3a and b, see Plate section). This distinctive conglomerate was noted by Maync (1942) and Koch and Haller (1971) and was referred to as ‘the breakup unconformity’ (Larsen and Saunders 1998). It crops out at intervals along the east Greenland coast from Wollaston Forland (76°N) and the Hold with Hope peninsula (73–74°N: Upton et al. 1980) to the Kangerdlugssuaq region (67°N; Soper et al. 1976) and abruptly overlies fine‐grained marine Cretaceous sediments. It indicates change to a high‐energy sedimentary environment and reflects significant tectonic uplift of the source region, inferentially at no great distance to the west (Upton et al. 1980). Although this unconformity is merely one of a number of Palaeogene unconformities spread in time and place over the North Atlantic region, now regarded as reflecting variations in flux of the Iceland plume, its position immediately beneath the volcanic sequence suggests that its description as ‘the’ break‐up unconformity may not be inept.
Figure 3 (a) Conglomerate from a 2–3 m thick stratum separating Cretaceous shales from the base of the overlying plateau lavas on Wollaston Forland, East Greenland (75° N). Cobbles are of quartzite and muscovite granite. (b) Aerial photograph of the same (white) stratum on Kap Broer Ruys, East Greenland (73°30′N). Well‐stratified dark grey Cretaceous shales beneath and brown/black lavas above.
Source: B.G.J. Upton.
Early in the Eocene mantle temperatures in the head of the plume may have fallen rapidly (Smallwood and White 2002) and the plume is inferred to have assumed a narrower sub‐cylindrical form with a ‘central core’ about a 100 km across. Magmatism due to this ‘plume tail’ marked out the shallow submarine welt of the Greenland–Iceland–Faeroes ridge as the Greenland/American tectonic plate migrated westwards. This ridge is characterized by an abnormal thickness (30–40 km) of oceanic crust and rises to shallow depths. The plume tail itself (the Iceland plume) is now considered to underlie eastern Iceland.
Early Palaeocene Before the North Atlantic Opening
Before the arrival of the postulated mantle plume, the landscapes of Greenland, Norway and Britain largely consisted of relatively high ground composed of early Palaeozoic and Precambrian metamorphic rocks transected by low‐lying faulted basins. The latter, developed during Mesozoic extensional tectonics, were subject to occasional marine inundation. The faulting had structurally preconditioned a tract of the Laurasian continent to a state ripe for exploitation by later rifting and magmatism in the Palaeocene. The embryonic ocean first appeared at approximately 56 Ma around the Palaeocene–Eocene boundary (currently defined at 55.8 ± 0.2 Ma). For the previous 10 Ma we may visualize rifted landscapes roughly comparable to those of Kenya and Ethiopia at present and which appears to have been well vegetated with an equable climate (Walker 1979).
Figure 4 presents a reconstruction of the geography of Greenland, Norway and the British Isles before the ocean opening and shows the pattern of faulting (Jolley and Bell 2002). These ‘normal faults’, generally dipping away from what were to become the Greenland and European hinterlands, presented barriers so that the Mesozoic marine transgressions rarely extended much to the west of the Greenland coastline nor much to the east of the western European coasts. Some of these fault escarpments were rejuvenated to play a role in the Palaeocene–Eocene when they prevented the floods of basaltic lavas from spreading west and east onto what were to become the continental hinterlands.
Figure 5 (see Plate section) shows that the eventual localization of the new ocean approximately followed the axis of the early Palaeozoic Caledonide Orogeny.
Episodes of raised Mesozoic sea‐levels saw the transgression of shallow seas across these low‐lying rifted basins. Whilst there is an abundant environmental and ecological record within the accompanying marine sediments, we can only surmise that during the millions of years between the transgressions there were widespread forested landscapes and little hindrance to intermixing of flora and fauna between North America/Greenland and Eurasia. In the early Palaeocene, before volcanism commenced, shallow non‐marine lakes or swamps formed in these rifts and sedimentary deposits accumulated. Fossil plants in the latter (occasionally forming thin coals) testify to the proximity of vegetated shores. Accordingly, when the first magmas reached surface levels they frequently encountered water or wet sediments and high‐pressure steam generation led to explosive (phreatomagmatic) eruptions. The resultant disrupted particles of basalt magma from these eruptions cooled rapidly to glassy material, the accumulations of which are called hyaloclastites. These are typically accompanied by characteristic sub‐aqueous lava forms, referred to as pillow‐lavas on account of their rounded, tube‐like pillowy forms. As the rates of magma outflow increased and the crust inflated, the waters were expelled and there was evolution from sub‐aqueous to sub‐aerial eruptions. Figure 6 (see Plate section), a coastal section in Baffin Island (East Canada), shows a rift‐related sequence of sediments followed by sub‐aqueous and sub‐aerial volcanic rocks that is broadly similar to the successions generated along the East Greenland coast.
Figure 4 Fault pattern in the North Atlantic region on a map restored to continental dispositions prior to ocean opening.
Source: Jolley and Bell (2002).
Figure 5
