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Varve

About: Varve is a research topic. Over the lifetime, 1177 publications have been published within this topic receiving 40589 citations.


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Journal ArticleDOI
TL;DR: In this article, the results of a somewhat exploratory investigation of the chemical composition of cores taken from the sediments of a number of lakes of the English Lake District were reported.
Abstract: This paper reports the results of a somewhat exploratory investigation of the chemical composition of cores taken from the sediments of a number of lakes of the English Lake District. All the lakes studied are of glacial, and therefore presumably of synchronous, origin. The depth of post-glacial sediment varies from lake to lake but is normally between 4 and 6 m. This material, with which the paper is mainly concerned, was laid down during the biologically active phase following the end of glaciation approximately 10 000 years ago. Below the organic muds of the post-glacial period, the sediment consists of glacial clays, usually varved, which pass downward into silty clays and sands the total depth of which is at present unknown. The variation in composition of the sediments with depth and therefore with time presents a pattern of change which is observed to recur in most of the lake sediments studied. This pattern of change is most strikingly seen in the variation of carbon content with depth, but related sequences of change may be observed in the distribution of major inorganic components, for example sodium, potassium and magnesium. The observed changes in composition of the sediment can most easily be explained if the sediment is regarded as a sequence of soils derived from the drainage areas of the lakes. The composition of the residues eventually reaching the lake bed can then be accounted for in terms of the rate of erosion of the drainage basin rather than in terms of changing rates of organic productivity either on the drainage basin or in the lake waters. The composition of the sediments does not appear to be greatly influenced by events within the lakes themselves except in the case of elements which may migrate more readily under the reducing conditions which may arise in soils and in lake muds. Examples of these are iron and manganese, and the distribution of these elements in the sediment may be used to deduce the redox conditions in the soils of the drainage basin in past times, or in the muds and hypolimnetic waters of the lakes themselves. Biological activity within the lake waters may also influence significantly the distribution in the sediments of distinctly biophile elements, of which phosphorus and sulphur are examples. Even in the case of phosphorus, however, it seems likely that co-precipitation reactions may have more influence on deposition efficiency than does incorporation into biological tissues. The cause of the apparently synchronous changes in erosion intensity recorded in the sediments of the various lakes remains in doubt. Some evidence derived from the halogen and boron content of the sediments is presented which may suggest at least a synchronism between major climatic changes and the variations in erosional activity. Since halogens and perhaps boron are largely derived from oceanic air-streams, the rate of deposition of these elements may be expected to be related to the 'oceanicity' of the climate at the time of deposition of the sediment. A direct relationship is observed between the deduced intensity of erosional activity and the halogen and boron content of the sediment. The meaning of this relationship is rendered somewhat ambiguous however by consideration of possible changes in soil ionic balance attributable to progressive loss by leaching of soil-derived anions with the passage of time. Although the gross composition of the sediment is largely dependent on conditions in the drainage system rather than in the lake waters, some deductions may be made which indicate the availability of nutrients dissolved in the waters of the lakes in past times. If material is rapidly removed from the drainage basin by erosion, nutrient elements are lost to the sediment locked in the lattice of unleached mineral particles. If however the rate of erosive removal of soil from the land surface is reduced, the mineral particles are held in the soil column in a position which allows more efficient leaching of soluble components, which then become available to the living populations of the lake.

516 citations

Journal ArticleDOI
TL;DR: In this article, stable-isotopic, geochemical, pollen and charcoal analyses were performed to find evidence of past regional climatic changes and human impact in the semi-arid region of eastern Anatolia, Turkey.
Abstract: Annually laminated sediments from Lake Van, spanning about 13000 varve years, were sampled for stable-isotopic, geochemical, pollen and charcoal analyses in order to find evidence of past regional climatic changes and human impact in the semi-arid region of eastern Anatolia, Turkey. The Lateglacial period was cold and dry, with steppe vegetation and saline lake water. During the Younger Dryas the lake level dropped dramatically, and the vegetation turned to a semi-desert. Geochemical and isotopic records indicate a strong increase in moisture at the onset of the Holocene, and Artemisia-chenopod steppes were partly replaced by grass steppe and pistachio scrub. A delay of about 3000 years in the expansion of deciduous oak woodlands and high steppe-fire frequencies suggest dry spring and summer weather during the early Holocene. At 8200 yr BP, a shift in the regional climate regime facilitated the transport of more moisture into the interior areas of the Taurus mountains and caused a change in the seasonal distribution of precipitation. The steppe-forests dominated by Quercus advanced and reached their maximum extention at about 6200 yr BP. All the proxy data indicate optimum climatic conditions, low water salinity and high lake level between 6200 and 4000 yr BP. After 4000 yr BP, aridity increased again and the modern climatic situation was established. Human impact in the catchment of Lake Van started at 3800 yr BP and was intensified during the last 600 years.

503 citations

Journal ArticleDOI
20 Feb 1998-Science
TL;DR: The results confirm the (recently revised) floating German pine chronology and are consistent with data from European and marine varved sediments, and combined uranium-thorium and carbon-14 dating of corals up to the Last Glacial Maximum.
Abstract: More than 250 carbon-14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from Lake Suigetsu (Japan) provide a first atmospheric calibration for almost the total range of the radiocarbon method (45,000 years before the present). The results confirm the (recently revised) floating German pine chronology and are consistent with data from European and marine varved sediments, and combined uranium-thorium and carbon-14 dating of corals up to the Last Glacial Maximum. The data during the Glacial show large fluctuations in the atmospheric carbon-14 content, related to changes in global environment and in cosmogenic isotope production.

416 citations

Journal ArticleDOI
TL;DR: In this paper, a study of the lower Van Normal reservoir after the 1971 San Fernando, California earthquake revealed three zones of deformational structures in the 1m-thick sequence of sediments exposed over about 2 km2 of the reservoir bottom.

413 citations

Journal ArticleDOI
TL;DR: In this article, a multidisciplinary approach is proposed to establish a varve chronology, which can be applied to precisely date events like volcanic ash layers, earthquakes or human impact, as well as short and long-term climate (temperature, precipitation, wind, hydroclimatic conditions or flooding) and environmental changes (eutrophication, pollution).

336 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202336
202264
202127
202027
201930
201828