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Palaeoenvironmental Record (palaeoenvironmental + record)
Selected AbstractsIsozyme variation and recent biogeographical history of the long-lived conifer Fitzroya cupressoidesJOURNAL OF BIOGEOGRAPHY, Issue 2 2000A. C. Premoli Abstract Aim Palaeoenvironmental records of Pleistocene glaciation and associated vegetation changes in Patagonia have led to the hypothesis that during the last glacial maximum (LGM) tree species survived locally in favourable habitats. If present populations originated from spread from only one refugium, such as an ice-free area of coastal Chile (Single Refugium hypothesis), we would expect that eastern populations would be genetically depauperate and highly similar to western populations. In contrast, if the ice cap was not complete and tree species persisted in forest patches on both slopes of the Andes (Multiple Refugia hypothesis), we would expect a greater degree of genetic divergence between populations either on opposite sides of the Cordillera (Cordillera Effect scenario) or towards its present-day southern distributional limit where the ice sheet reached its maximum coverage (Extent-of-the-Ice scenario). Location We tested this refugia hypothesis using patterns of isozyme variation in populations sampled over the entire modern range of the endemic conifer Fitzroya cupressoides (Mol.) Johnst. (Cupressaceae) in temperate South America. Methods Fresh foliage was collected from twenty-four populations and analysed by horizontal electrophoresis on starch gels. Results Twenty-one putative loci were reliably scored and 52% were polymorphic in at least one population. Populations from the eastern slope of the Andes were genetically more variable than those from the western slope; the former had a greater mean number of alleles per locus, a larger total number of alleles and rare alleles, and higher polymorphism. Genetic identities within western populations were greater than within eastern populations. Discriminant analyses using allelic frequencies of different grouping schedules of populations were non significant when testing for the Single Refugium hypothesis whereas significant results were obtained for the Multiple Refugia hypothesis. Main conclusions Our results indicate that present Fitzroya populations are the result of spreading from at least two, but possibly more, glacial refugia located in Coastal Chile and on the southern flanks of the Andes in Argentina. [source] Absence of post-Miocene Red Sea land bridges: biogeographic implicationsJOURNAL OF BIOGEOGRAPHY, Issue 6 2006Carlos A. Fernandes Abstract In a large number of studies concerned with species movements between Africa and Eurasia, including the migrations of hominids out of Africa, a frequently-cited dispersal route is across a hypothetical land bridge in the southern Red Sea, which is suggested to have emerged during glacial sea-level lowstands. This paper, however, unequivocally demonstrates that palaeoceanographic and palaeoecological data are incompatible with the existence of Red Sea land bridges since the Miocene. The case is made by presenting the first quantitative history of water depth above the Red Sea sill for the last 470,000 years, a time period that includes the four most recent glacial,interglacial cycles, and by discussing the predictable consequences of any land bridge formation on the Red Sea sedimentary and microfossil records. The absence of post-Miocene Red Sea land bridges has extensive implications for biogeographic models in the Afro-Arabian region. Genetic, morphometric and palaeontological patterns reported in the literature cannot be related to dispersals over a land bridge, or in the case of marine organisms, separation of the Red Sea from the Indian Ocean by a land bridge. If such patterns in terrestrial species are only congruent with a southern Red Sea dispersal route, then they need to be considered in terms of sweepstake rafting, anthropogenic introduction, or in the particular case of the Out-of-Africa migration by modern humans, seafaring. The constraints imposed by our palaeoenvironmental record on biogeographic reconstructions within and around the Red Sea will hopefully encourage both the review of previous works and the preference for multidisciplinary approaches in future studies. [source] A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central FinlandBOREAS, Issue 4 2003MIA TILJANDER High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980,1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580,1630 and AD 1650,1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago. [source] Revised age estimate of the Mjáuvøtn tephra A on the Faroe Islands based on Bayesian modelling of 14C dates from two lake sequences,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2010Jesper Olsen Abstract Tephra horizons are potentially perfect time markers for dating and cross-correlation among diverse Holocene palaeoenvironmental records such as ice cores and marine and terrestrial sequences, but we need to trust their age. Here we present a new age estimate of the Holocene Mjáuvøtn tephra A using accelerator mass spectrometry 14C dates from two lakes on the Faroe Islands. With Bayesian age modelling it is dated to 6668,6533,cal. a BP (68.2% confidence interval) , significantly older and better constrained than the previous age. Copyright © 2010 John Wiley & Sons, Ltd. [source] Detection of Lateglacial distal tephra layers in the NetherlandsBOREAS, Issue 2 2005SIWAN M. DAVIES Davies, S. M., Hoek, W. Z., Bohncke, S. J. P., Lowe, J. J., Pyne O'Donnell, S. & Turney, C. S. M. 2005 (May): Detection of Lateglacial distal tephra layers in the Netherlands. Boreas, Vol. 34, pp. 123,135. Oslo. ISSN 0300,9483. Three distal tephra layers or cryptotephras have been detected within a sedimentary sequence from the Netherlands that spans the last glacial-interglacial transition. Geochemical analyses identify one as the Vedde Ash, which represents the southernmost discovery of this mid-Younger Dryas tephra so far. This tephra was found as a distinct horizon in three different cores sampled within the basin. The remaining two tephras have not been geochemically ,fingerprinted', partly due to low concentrations and uneven distributions of shards within the sequences sampled. Nevertheless, there is the potential for tracing these tephra layers throughout the Netherlands and into other parts of continental Europe. Accordingly, the possibilities for precise correlation of Dutch palaeoenvironmental records with other continental, marine and ice-core records from the North Atlantic region are highlighted. [source] | ||||||||||