| 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. |
- Abbott, P. M., et al.
(författare)
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Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region : The cryptotephra record
- 2014
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 409, s. 153-168
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies of marine sequences from the Faroe Islands region have identified a series of coarse-grained tephra horizons deposited during Marine Isotope Stage (MIS) 5. Here we reassess the MIS 5 tephrostratigraphy of the Faroe Islands region and focus on the cryptotephra deposits preserved within the fine-grained fraction of marine core LINK 16. We also extend the record to encompass the late MIS 6 and early MIS 4 periods. A density separation technique, commonly used for tephra investigations in lacustrine settings but rarely applied to marine sediments, is utilised to explore the fine-grained material and EPMA and LA-ICP-MS are employed to determine the major and trace element composition of individual tephra shards. In total, 3 basaltic and 3 rhyolitic Icelandic cryptotephra deposits with homogeneous geochemical compositions are identified - all of which have the potential to act as isochronous tie-lines. Geochemical results highlight that the Grimsvotn volcanic system of Iceland is the predominant source of the basaltic horizons and the Oraefajokull or Torfajokull systems are the likely sources of the rhyolitic deposits. Three of the horizons have been previously recognised in Faroe Islands region marine sequences, with two of these deposits traceable into a Norwegian Sea sequence. An early MIS 4 rhyolitic horizon is the most widespread deposit as it can be traced into the Norwegian Sea and to the south into a record from the Rockall Trough. Basaltic and rhyolitic horizons deposited during late MIS 6 have not been recognised in other sequences and represent new additions to the regional tephrostratigraphy.
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| 6. |
- Agic, Heda, et al.
(författare)
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Life through an Ediacaran glaciation : Shale- and diamictite-hosted organic-walled microfossil assemblages from the late Neoproterozoic of the Tanafjorden area, northern Norway
- 2024
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 635
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Tidskriftsartikel (refereegranskat)abstract
- New organic-walled microfossil (OWM) assemblages are reported from upper Neoproterozoic glacial and interglacial siliciclastic deposits in Finnmark, northern Norway. A nearly continuous sedimentary succession of the Vestertana Group contains two glaciogenic units, the Smalfjorden and Mortensnes formations, interpreted as end-Cryogenian Marinoan and Ediacaran glaciations, respectively. We investigated the OWM record in the Nyborg, Mortensnes, and St ' ahpogieddi formations to assess the impact of a glacial interval on the diversity of microscopic eukaryotes. A modified acid-extraction technique was applied to recover OWM from the diamictite matrix. The upper Nyborg Formation contains morphologically complex Doushantuo-Pertatataka acritarchs (DPA), restricting the age of the Nyborg Formation to early-mid Ediacaran. DPA occur below the dolostones that record a negative carbon isotope excursion correlated with the Shuram anomaly and below a glacial diamictite. A decline in species richness and compositional change is observed in the Mortensnes glacial assemblage. DPA are replaced by bacterial filaments and cell aggregates. The overlying Indreelva Member, St ' ahpogieddi Formation contains Ediacara-type biota and palaeopascichnids, but only a depauperate OWM assemblage of leiosphaerids and flask-shaped microfossils characteristic of the late Ediacaran.The succession of assemblages in the Vestertana Group demonstrates a turnover from large eukaryotic OWM to a microbial community in the glacial interval, to a low diversity post-glacial assemblage during the rise of macroscopic life. We compared the Vestertana record to global DPA occurrences. Although one DPA assemblage zone postdates the Shuram excursion, no DPA occur above Ediacaran glacial diamictites in successions where those deposits are present. Considering this, and the community changes in the Vestertana succession, we suggest that DPA were affected by the onset of an Ediacaran glaciation. Lastly, we combined the biostratigraphic markers in the Vestertana Group to constrain the age of the Mortensnes diamictite.
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| 7. |
- Albanesi, Guillermo L., et al.
(författare)
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Darriwilian (Middle Ordovician) delta C-13(carb) chemostratigraphy in the Precordillera of Argentina: Documentation of the middle Darriwilian Isotope Carbon Excursion (MDICE) and its use for intercontinental correlation
- 2013
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 1872-616X .- 0031-0182. ; 389, s. 48-63
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Tidskriftsartikel (refereegranskat)abstract
- Although documented from Estonia, Latvia, Sweden, eastern North America, and China, the Middle Ordovician (Darriwilian) positive delta C-13 excursion known as the MDICE has previously not been recognized with certainty in South America. The most promising region in South America for detailed Middle Ordovician carbon isotope research is the Precordillera of western Argentina, where there are many excellent exposures of biostratigraphically well-dated carbonate successions spaning the Tremadocian through Sandbian stratigraphic interval. For this project, we collected numerous isotope and conodont samples from the middle Darriwilian Las Chacritas and Aguaditas formations at their type localities, which yielded important biostratigraphic data as well as informative delta C-13(carb) values. In the E. pseudoplanus Zone in the upper half of the Las Chacritas Formation, there is a relatively modest but distinct delta C-13(carb) excursion. Because its stratigraphic position and magnitude closely agree with the MDICE in other parts of the world, we recognize it as the first firm record of this excursion in South America. The fact that the delta C-13(carb) curve from the Las Aguaditas Formation shows no such excursion is due to the existence of a stratigraphic gap between the Lower and Middle Members of this formation that cuts out the excursion interval. The Precordilleran MDICE is used for detailed long-range correlations with successions in Baltoscandia, Newfoundland, and China illustrating the usefulness of also this delta C-13(carb) excursion as a global stratigraphic tool. A recent proposal of a greatly extended chronostratigraphic range of the Table Head Group on Newfoundland is rejected based on well-established biostratigraphic evidence. (C) 2013 Elsevier B.V. All rights reserved.
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| 8. |
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| 9. |
- Andrén, Elinor, et al.
(författare)
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Medieval versus recent environmental conditions in the Baltic Proper, what was different a thousand years ago?
- 2020
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier. - 0031-0182 .- 1872-616X. ; 555
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Tidskriftsartikel (refereegranskat)abstract
- A sediment record from the western Gotland Basin, northwestern Baltic Proper, covering the last 1200 years, was investigated for past changes in climate and the environment using diatoms as a proxy. The aim is to compare the environmental conditions reconstructed during Medieval times with settings occurring the last century under influence of environmental stressors like eutrophication and climate change. The study core records more marine conditions in the western Gotland Basin surface waters during the Medieval Climate Anomaly (MCA; 950–1250C.E.), with a salinity of at least 8 psu compared to the present 6.5 psu. The higher salinity together with a strong summer-autumn stratification caused by warmer climate resulted in extensive long-lasting diatom blooms of Pseudosolenia calcar-avis, effectively enhancing the vertical export of organic carbon to the sediment and contributing to benthic hypoxia. Accordingly, our data support that a warm and dry climate induced the extensive hypoxic areas in the open Baltic Sea during the MCA. During the Little ice Age (LIA; 1400–1700C.E.), the study core records oxic bottom water conditions, decreasing salinity and less primary production. This was succeeded during the 20th century, about 1940, by environmental changes caused by human-induced eutrophication. Impact of climate change is visible in the diatom composition data starting about 1975C.E. and becoming more pronounced 2000C.E., visible as an increase of taxa that thrived in stratified waters during autumn blooms typically due to climate warming.
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| 10. |
- Bajdek, Piotr, et al.
(författare)
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Putative dicynodont coprolites from the Upper Triassic of Poland
- 2014
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 411, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- A significant number (more than 100) of brownto dark and silty, carbonate or pyrite-mineralized, in part organic carbon-rich, spherical or oval-shaped structures have been collected fromthe Upper Triassic (uppermost NorianlowerRhaetian) sediments of the Lipie Śląskie clay-pit at Lisowice near Lubliniec town, Poland. Their geological context, morphology, content, geochemistry and association with skeletal remains suggest they are fecal masses of a sizable herbivorous tetrapod. The only large herbivore known from the site is a giant 5 meter-long dicynodont (Synapsida: Anomodontia), represented by numerous bones and also by large, oval-shaped footprints. The putative dicynodont coprolites were collected from mudstone and siltstone with numerous organic remains that were deposited in anoxic conditions. In addition, REEs and other trace element concentrations suggest that the burial environment and diagenesis of these coprolites were under anoxic conditions. SEM and thin section images of the coprolite matrix show numerous nests with pyrite (probably bacterial in origin) and large amount of mineral particles. The putative dicynodont coprolites contain also amorphous, dark organic matter, poorly preserved palynomorphs, small fragments of plant cuticle. Detailed characteristic of these coprolites reveals possible implications for the ecology and physiology of the source animal species. The δ 13C values of the gymnospermcuticle and dark organic matter measured in three coprolites are −23.4‰, −21.2‰and −20.3‰, all average. The evidence from these coprolites suggests that dicynodonts processed plant soft elements into very small pieces, but wood fragments were found also in a mass accumulation in two coprolites.
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