| 1. |
- Amman, B., et al.
(författare)
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Quantification of biotic responses to rapid climatic changes around the Younger Dryas – a synthesis.
- 2000
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182 .- 1872-616X. ; 159:3-4, s. 313-347
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Tidskriftsartikel (refereegranskat)abstract
- To assess the presence or absence of lags in biotic responses to rapid climatic changes, we: (1) assume that the delta(18)O in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the Younger Dryas without any lag at our two study sites of Gerzensee and Leysin, Switzerland; (2) derive a time scale by correlating the delta(18)O record from these two sites with the delta(18)O record of the GRIP ice core; (3) measure delta(18)O records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes; (4) analyse at Gerzensee and Leysin as well as at two additional sites (that lack carbonates and hence a delta(18)O record) pollen, plant macrofossils, chironomids, beetles and other insects, and Cladocera; (5) estimate our sampling resolution using the GRIP time scale for the isotope stratigraphies and the biostratigraphies; and (6) summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis. We conclude that, at the major climatic shifts at the beginning and end of the Younger Dryas, hardly any biotic lags occur (within the sampling resolution of 8-30 years) and that upland vegetation responded as fast as aquatic invertebrates. We suggest that the minor climatic changes associated with the Gerzensee and Preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site, but were more distinct at higher altitudes. Individualistic responses of plant and animal species to climatic change may reflect processes in individuals (e.g. productivity and phenology), in populations (e.g. population dynamics), in spatial distributions (e.g. migrations), and in ecosystems (e.g. trophic state). We suggest that biotic responses may be telescoped together into relatively short periods (50 to 150 years), perhaps disrupting functional interactions among species and thus destabilising ecosystems.
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| 2. |
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| 3. |
- Henriksson, Anders
(författare)
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Coccolithophore response to oceanographic changes in the Equatorial Atlantic during the last 200,000 years
- 2000
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182 .- 1872-616X. ; 156:1-2, s. 161-173
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Tidskriftsartikel (refereegranskat)abstract
- A deep-sea core from the eastern equatorial Atlantic (Meteor core 16772, 1 degrees 21'S, 11 degrees 58'W) revealed strong primary productivity variations (70-230 gC/m (super 2) /year) based on the relative abundance (%) of the deep living coccolithophore Florisphaera profunda with productivity maxima following temperature minima during the last 200,000 years. The response of the coccolithophore flora was investigated by relative and absolute abundance records of coccoliths. The wind strength and the resulting equatorial upwelling intensity are thought to comprise the most important control of coccolith abundance and species composition, which reflects the different abundance of coccolithophores living in the upper or lower photic zone. Relative abundances of the different species varies widely throughout the core. Although a wide range of species were present in the different samples, three different taxa dominated the assemblage. The lower photic zone species F. profunda was the most abundant, with a mean relative abundance of 49.4% throughout the core. The upper photic zone flora were divided into three groups. Emiliania huxleyi together with small Gephyrocapsa (<3mu m) was the second most abundant species group (mean 20.8%). Gephyrocapsa oceanica was the third most important species in the core and had a mean relative abundance of 16.8%. All other species together represented a mean of 13%. Highest absolute abundance of coccoliths (number/gram sediment) occurs in sediments deposited during periods of high SST, mainly in warm isotope stages 1 and 5. The accumulation rates of coccoliths (number/cm (super 2) /ky) show peaks in isotope stages 1 and 5, but also in some parts of cool isotope stages 4 and 6. High relative and absolute abundance of F. profunda were found in warm isotope stages, which suggests that a deep nutricline existed and that primary productivity was low. Absolute and relative abundance records of E. huxleyi and small Gephyrocapsa (<3mu m) mainly showed higher values in sediments from warm periods. The other upper photic zone coccolith species were generally more abundant during periods of low SST, particularly in isotope stages 2, 4, and 6, which were times of high primary productivity and a shallow nutricline. This suggest that E. huxleyi and small Gephyrocapsa probably were able to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone. In summary, the composition of the coccolith flora can be explained by the nutricline depth level with three different assemblages being recognized, a deep photic zone assemblage consisting of F. profunda, a middle-upper photic zone assemblage of E. huxleyi and small Gephyrocapsa and an upper photic zone assemblage consisting of all other species.
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| 4. |
- Lemdahl, Geoffrey
(författare)
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Lateglacial and Early Holocene insect assemblages from sites at different altitudes in the Swiss Alps - implications on climate and environment.
- 2000
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182 .- 1872-616X. ; 159:3-4, s. 293-312
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Tidskriftsartikel (refereegranskat)abstract
- Insect analyses from four sites at differentaltitudes in the SwissAlps are presented. The dominant insect group considered here is Coleoptera (beetles), though other insect orders are also recorded. The study includes the first detailed insect records dating to the Younger Dryas in Switzerland. The quantitative climatic reconstructions based on coleopteran assemblages were made using the MCR method. Mean temperatures of the warmest month similar to modern intensities are indicated at the end of Allerød interstadial (AL) and at the beginning of the Holocene (PB). The winters during the AL were rather colder, implying more continental conditions than at present. During the Younger Dryas stadial (YD), the mean temperatures of the warmest month were 5–8°C colder than those of the present day, and the mean temperatures of the coldest month were about 10–12°C colder than today. A rapid change in the faunal composition was found at the Gerzensee and Zeneggen sites during the transition YD/PB. The change is characterized by the disappearance of cold-adapted species between two contiguous samples (i.e. within 1.0 cm of sediment sampled). At Gerzensee, the cold-adapted species assemblage was immediately replaced by temperate species. The Coleoptera thus indicate extremely rapid and intense climatic oscillations at the Lateglacial–Holocene transition.
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| 5. |
- Dahlqvist, Peter, et al.
(författare)
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Late Ordovician palaeoceanographic changes as reflected in the Hirnantian-early Llandovery succession of Jamtland, Sweden
- 2004
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 210:2-4, s. 149-164
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Tidskriftsartikel (refereegranskat)abstract
- A study of the Upper Ordovician-Lower Silurian strata in Jamtland, central Sweden, shows that large-scale changes in shelf deposition took place close to the systems boundary. These changes include unconformity development and the replacement of a siliciclastic shelf with a carbonate-dominated shelf, suggesting the interaction of allocyclic controls such as changing eustatic sea-level and climate. The 6-m-thick Ede Formation is a key lithosome for interpretation of this transition. Its sediments were deposited in the Caledonian foreland basin, situated east of the closing Iapetus Ocean on the western margin of the Baltic craton. A major part of the late. Caradoc to late Ashgill (into the Hirnantian) was characterised by continuous and uniform deposition over wide areas (Kogsta Formation), whereas erosional surfaces and complex lateral facies relationships characterise the Ordovician-Silurian boundary strata (Ede Formation and lateral equivalents). The Ede Formation represents the end of terrigenous deposition, which in the middle Aeronian was followed by regional expansion of carbonate deposition (Berge Formation). A syn-sedimentary erosional surface, with at least I in of relief locally, forms the lower boundary of the Ede Formation. This surface is overlain by two types of conglomerate. Lower parts of the Ede Formation consist of medium to thick-bedded quartzites. A second erosional surface with only minor (few centimetres) relief occurs on top of these quartzites. The upper parts of the Ede Formation consist of a thin, basal favositid biostrome overlain by thin bedded, calcareous sandstones, limestones and intensely bioturbated shales. Analysis of stratigraphic boundaries and the facies succession suggests that the lower Ede Formation represents a major downward shift in coastal onlap and by-pass sedimentation that created the lower erosional surface. The erosional surface in the middle of the Ede Formation is inferred to have formed during the subsequent maximum lowstand or as a ravinement surface, and is interpreted as an unconformity. The succession is subdivided into four facies associations, each corresponding to a specific systems tract: (a) a Shale-Siltstone Association (uppermost Kogsta Formation), deposited during a highstand situation in mid-outer shelf areas; (b) a Quartzite Association (the lower Ede Formation), deposited during forced regression in a shoreface environment; (c) a Mixed Carbonate-Siliciclastic Association (the upper Ede Formation), deposited during transgression in a wave-dominated, proximal shelf environment when elastic supply was reduced; and (d) a Micritic Limestone Association (lowermost Berge Formation), deposited during a second highstand situation in a low-energy, offshore environment. Conodont data, together with a previously reported Hirnantia fauna, constrain the position of the Ordovician-Silurian boundary to the lower 1.65 m of the Ede Formation, or less likely, to the uppermost metre of the underlying Kogsta Formation, i.e., within a 2.65-m-thick uncertainty interval. The base of the Berge Formation is about 4 m above the top of the uncertainty interval, and is dated as being mid-Aeronian in age, suggesting condensation and/or a hiatus close to, or at, the Ordovician-Silurian boundary. These data tie the unconformity and the regional facies change from a siliciclastic to a carbonate-dominated shelf to Late Ordovician-Early Silurian eustatic and climatic changes. (C) 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Hildebrand-Habel, Tania, et al.
(författare)
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Calcareous dinoflagellate associations and Maastrichtian-Tertiary climatic change in a high-latitude core (ODP Hole 689B, Maud Rise, Weddell Sea)
- 2003
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - 0031-0182. ; 197, s. 293-321
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of calcareous dinoflagellates has been analysed for the Maastrichtian to Miocene interval of ODP Hole 689B (Maud Rise, Weddell Sea). The investigation thus represents a primary evaluation of the long-term evolution in high latitude calcareous dinoflagellate assemblages during the transition from a relatively warm Late Cretaceous to a cold Neogene climate. Major assemblage changes during this interval occurred in characteristic steps: (1) an increase in relative abundance of tangentially structured species – particularly Operculodinella operculata – at the K/T boundary; (2) a diversity decrease and several first and last appearances across the middle–late Eocene boundary, possibly attributed to increased climate cooling; (3) a diversity decrease associated with the dominance of Calciodinellum levantinum in the late early Oligocene; (4) the reappearance and dominance of Pirumella edgarii in the early Miocene, probably reflecting a warming trend; (5) monogeneric assemblages dominated by Caracomia spp. denoting strong middle Miocene cooling. The results not only extend the biogeographic ranges of many taxa into the Antarctic region, but also indicate that the evolution of high latitude calcareous dinoflagellate assemblages parallels the changing environmental conditions in the course of the Cenozoic climate transition. Therefore, calcareous dinoflagellates contribute to our understanding of the biotic effects associated with palaeoenvironmental changes and might possess the potential for reconstructing past conditions. The flora in the core includes one new taxon: Caracomia arctica forma spinosa Hildebrand-Habel and Streng, forma nov. Additionally, two new combinations are proposed: Fuettererella deflandrei (Kamptner, 1956) Hildebrand-Habel and Streng, comb. nov. and Fuettererella flora (Fütterer, 1990) Hildebrand-Habel and Streng, comb. nov.
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