Cretaceous polar conifer forests : composition, leaf life-span and climate significance
Fossil wood is abundant in sediments that were deposited at high latitudes during the Cretaceous. The wood provides evidence for forests growing in high latitudes in the past, at times when climate was warmer during greenhouse periods. However, computer climate models that try to simulate past clima...
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| Format: | Thesis |
| Language: | English |
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University of Leeds
2005
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| Online Access: | https://etheses.whiterose.ac.uk/26077/ https://etheses.whiterose.ac.uk/26077/1/422072.pdf |
| Summary: | Fossil wood is abundant in sediments that were deposited at high latitudes during the Cretaceous. The wood provides evidence for forests growing in high latitudes in the past, at times when climate was warmer during greenhouse periods. However, computer climate models that try to simulate past climates cannot reproduce the polar warmth necessary for the existence of forests but more commonly generate ice-covered polar regions. This may be due to the lack of a realistic vegetation component in the models. The aim of this project is to determine the leaf habit and leaf life-spans (LLSs) of conifers growing at high latitudes during the mid-Cretaceous. The results will be used to test the outputs of the University of Sheffield Conifer Model (USCM), a model that will produce a new reconstruction of high latitude vegetation for coupling with computer climate models to determine the effects of high latitude vegetation on climate systems in the past. Fossil conifer wood is studied from mid-Cretaceous sediments from the Canadian Arctic, Svalbard, Australia and Antarctica, all high latitude sites during the mid-Cretaceous. Identification of the woods indicates that Northern Hemisphere forests were composed of Piceoxylon, Laricioxylon, Cedroxylon, Taxodioxylon, Pinuxylon, Palaepiceoxylon, Taxoxylon, Juniperoxylon, Protocedroxylon, Araucariopitys, Xenoxylon and Cupressinoxylon. The Canadian Arctic was dominated by Pinuxylon and Svalbard by Taxodioxylon. In the Southern Hemisphere the conifers include Podocarpoxylon, Taxodioxylon, Araucariopitys, Cupressinoxylon, Agathoxylon, Protophyllocladoxylon, Sciadopityoxylon and Circoporoxylon. Antarctica was dominated by Taxodioxylon and in Australia the woods were dominated by Podocarpoxylon. Palaeoclimate analysis using nearest living relative and growth ring analyses indicate that the mid-Cretaceous climate in the Canadian Arctic was cool temperate and Svalbard was cool to warm temperate. In the Southern Hemisphere Australia appears to have been cool temperate whilst in Antarctica ... |
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