Home About us Contact
|
Home About us Contact | ||
|
|
||
Glacial Advance (glacial + advance)
Selected AbstractsComparative phylogeography of salmonid fishes (Salmonidae) reveals late to post-Pleistocene exchange between three now-disjunct river basins in SiberiaDIVERSITY AND DISTRIBUTIONS, Issue 4 2003E. Froufe Abstract. We use a comparative phylogeographical framework to evaluate the hypothesis of hydrological exchange during the Pleistocene among the now disjunct Lena, Amur, and Enisei basins in Siberia, and to provide evidence on the causal mechanism of their present day faunal dissimilarities. Approximately 600 bases of the mitochondrial control region were sequenced in five distinct lineages among three genera of salmonid fishes, Hucho, Brachymystax and Thymallus. All three basins were fixed for divergent (2,5.4%) lineages of Thymallus whereas a single shared haplotype was present in all three basins for Hucho taimen (Pallas, 1773) and one shared haplotype between the Lena and Amur basins out of a total of five for blunt-snouted and one out of five for sharp-snouted Brachymystax lenok (Pallas, 1773). For both blunt- and sharp-snouted lenok the haplotypes found within each basin did not form clades, so no relationship between genotypes and geographical occurrence was found. Our data support relatively recent hydrological mixing of the major river drainage systems in eastern and far-eastern Siberia, congruent with the hypothesis of large-scale palaeo-hydrological exchange stemming from glacial advance, retreat and melting during Pleistocene climate fluctuations. Furthermore, these results in conjunction with a comparison of overall faunal composition suggest that environmental differences rather than historical contingency may be responsible for the faunal dissimilarities of the Amur, Lena, and Enisei river basins. [source] Timing and style of Late Pleistocene glaciation in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2010Liubing Xu Abstract Glacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd. [source] The Upper Pleistocene to Holocene sediments on the Mediterranean island of Lampedusa (Italy)JOURNAL OF QUATERNARY SCIENCE, Issue 6 2004C. Giraudi Abstract The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic,environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central-southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd. [source] Surface exposure dating of the Great Aletsch Glacier Egesen moraine system, western Swiss Alps, using the cosmogenic nuclide 10BeJOURNAL OF QUATERNARY SCIENCE, Issue 5 2004Meredith A. Kelly Abstract Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The 10Be dates range from 10,460±1100 to 9040±1020,yr ago. Three 10Be dates between 9630±810 and 9040±1020,yr ago are based upon samples from the surfaces of granite boulders. Two 10Be dates, 10,460±1100 and 9910±970,yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young 10Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640±430,yr (including the weighted mean of two 10Be dates of the quartz vein), as a minimum age of deposition of the moraine. All 10Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog-bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The 10Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to 10Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with 10Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright © 2004 John Wiley & Sons, Ltd. [source] Calendar year age estimates of Allerød,Younger Dryas sea-level oscillations at Os, western NorwayJOURNAL OF QUATERNARY SCIENCE, Issue 5 2004Øystein S. Lohne Abstract A detailed shoreline displacement curve documents the Younger Dryas transgression in western Norway. The relative sea-level rise was more than 9,m in an area which subsequently experienced an emergence of almost 60,m. The sea-level curve is based on the stratigraphy of six isolation basins with bedrock thresholds. Effort has been made to establish an accurate chronology using a calendar year time-scale by 14C wiggle matching and the use of time synchronic markers (the Vedde Ash Bed and the post-glacial rise in Betula (birch) pollen). The sea-level curve demonstrates that the Younger Dryas transgression started close to the Allerød,Younger Dryas transition and that the high stand was reached only 200,yr before the Younger Dryas,Holocene boundary. The sea level remained at the high stand for about 300,yr and 100,yr into Holocene it started to fall rapidly. The peak of the Younger Dryas transgression occurred simultaneously with the maximum extent of the ice-sheet readvance in the area. Our results support earlier geophysical modelling concluding a causal relationship between the Younger Dryas glacier advance and Younger Dryas transgression in western Norway. We argue that the sea-level curve indicates that the Younger Dryas glacial advance started in the late Allerød or close to the Allerød,Younger Dryas transition. Copyright © 2004 John Wiley & Sons, Ltd. [source] Middle Weichselian glacial event in the central part of the Scandinavian Ice Sheet recorded in the Hitura pit, Ostrobothnia, FinlandBOREAS, Issue 1 2008VELI-PEKKA SALONEN The Hitura open pit exposes a sedimentary sequence up to 50 m thick representing Late Saalian to Holocene glacial and non-glacial sediments. The sequence was investigated using sedimentological methods, OSL-dating and pollen and diatom analyses to reconstruct the Middle Weichselian (MWG) glacial event in the central part of the Scandinavian Ice Sheet (SIS). The results indicate that the sediment succession represents two entire glacial advance and retreat cycles. The lowermost deposits are Late Saalian esker and delta sediments overlain by sediments that correlate with the early Eemian lacustrine phase. Remnants of the Eemian soil post-dating the lacustrine phase were also observed. The area was ice-free during the entire Early Weichselian (EWG). The first glacial advance recorded in the sediments is related to the MWG. It started 79 kyr ago, deformed underlying sediments and deposited an immature till, including large detached sediment pods containing remains of organic material, soils and fluvial sediments representing allochthonous material from EWG ice-free stadials and interstadials. The glacial deposits are conformably overlain by glaciolacustrine and littoral accumulations, indicating MWG deglaciation between 62 and 55 kyr ago. Based on the fabric measurements from the till unit overlying the MWG sediments, ice advance during the Late Weichselian (LWG) was initially from the west and later from a north-northwesterly direction. The Hitura strata provide the first dating of the MWG deglaciation (55 to 62 kyr ago) from central parts of the SIS. It can be considered as a key site for studying the growth and decay of SIS during the poorly known early parts of the glaciation. [source] A high-resolution diatom record of late-Quaternary sea-surface temperatures and oceanographic conditions from the eastern Norwegian SeaBOREAS, Issue 4 2002CHRISTOPHER J. A. BIRKS Core MD95-2011 was taken from the eastern Vøring Plateau, near the Norwegian coast. The section between 250 and 750 cm covers the time period from 13 000 to 2700 cal. yr BP (the Lateglacial and much of the Holocene). Samples at 5 cm intervals were analysed for fossil diatoms. A data-set of 139 modern sea-surface diatom samples was related to contemporary sea-surface temperatures (SSTs) using two different numerical methods. The resulting transfer functions were used to reconstruct past sea-surface temperatures from the fossil diatom assemblages. After the cold Younger Dryas with summer SSTs about 6°C, temperatures warmed rapidly to about 13°C. One of the fluctuations in the earliest Holocene can be related to the Pre-Boreal Oscillation, but SSTs were generally unstable until about 9700 cal. yr BP. Evidence from diatom concentration and magnetic susceptibility suggests a change and stabilization of water currents associated with the final melting of the Scandinavian Ice Sheet at c. 8100 cal. yr BP. A period of maximum warmth between 9700 and 6700 cal. yr BP had SSTs 3,5°C warmer than at present. Temperatures cooled gradually until c. 3000 cal. yr BP, and then rose slightly around 2750 cal. yr BP. The varimax factors derived from the Imbrie & Kipp method for sea-surface-temperature reconstructions can be interpreted as water-masses. They show a dominance of Arctic Waters and Sea Ice during the Younger Dryas. The North Atlantic current increased rapidly in strength during the early Holocene, resulting in warmer conditions than previously. Since about 7250 cal. yr BP, Norwegian Atlantic Water gradually replaced the North Atlantic Water, and this, in combination with decreasing summer insolation, led to a gradual cooling of the sea surface. Terrestrial systems in Norway and Iceland responded to this cooling and the increased supply of moisture by renewed glaciation. Periods of glacial advance can be correlated with cool oscillations in the SST reconstructions. By comparison with records of SSTs from other sites in the Norwegian Sea, spatial and temporal changes in patterns of ocean water-masses are reconstructed, to reveal a complex system of feedbacks and influences on the climate of the North Atlantic and Norway. [source] A Bayesian hierarchical extreme value model for lichenometryENVIRONMETRICS, Issue 6 2006Daniel Cooley Abstract Currently, there is a tremendous scientific research effort in the area of climate change. In this paper, our motivation is to improve the understanding of historical climatic events such as the Little Ice Age (LIA), a period of relatively cold weather around 1450,1850 AD. Although the LIA is well documented in Europe, its extent and timing are not known in areas of the globe where climatological records were not kept during this period. To study the climate, which predates historical records, proxy climate records must be used. A proxy record for the timing of climatic cooling events are the ages of the moraines left behind by glacial advances. Unfortunately, to determine the ages of these moraines in alpine environments there is little material available but lichens. Hence, lichenometry was developed to determine the ages of glacial landforms by using lichen measurements. To our knowledge, this article provides the first attempt at deriving a comprehensive statistical model for lichenometry. Our model foundation is based on extreme value theory because only the largest lichens are measured in lichenometry studies. This application is novel to extreme value theory because the quantities of interest (the ages of climatic events) are not the measured quantities (lichen diameters), i.e., it is a inverse problem. We model the lichen measurements with the generalized extreme value (GEV) distribution, upon which a Bayesian hierarchical model is built. The hierarchical model enables estimation of the hidden covariate ages of the moraines. The model also allows for pooling of data from different locations and evaluation of spatial differences in lichen growth. Parameter inference is obtained using a straightforward Markov Chain Monte Carlo method. Our procedure is applied to data gathered from the Cordillera Real region in Bolivia. Copyright © 2006 John Wiley & Sons, Ltd. [source] Timing and style of Late Pleistocene glaciation in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau,JOURNAL OF QUATERNARY SCIENCE, Issue 6 2010Liubing Xu Abstract Glacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd. [source] First cosmogenic 10Be constraints on LGM glaciation on New Zealand's North Island: Park Valley, Tararua Range,JOURNAL OF QUATERNARY SCIENCE, Issue 8 2008Martin S. Brook Abstract We report the first direct ages for late Quaternary glaciation on the North Island of New Zealand. Mt Ruapehu, the volcanic massif in the North Island's centre, is currently glaciated and probably sustained glaciers throughout the late Quaternary, yet no numeric ages have been reported for glacial advances anywhere on the North Island. Here, we describe cosmogenic 10Be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the Tararua Range, part of the axial ranges of the North Island. Results indicate that a limited valley glaciation occurred, culminating in recession at the end of the last glacial coldest period (LGCP, ca. 18,ka). This provides an initial age for deglaciation on the North Island during the last glacial,interglacial transition (LGIT). It appears that glaciation occurred in response to an equilibrium-line altitude (ELA) lowering of ,1400,m below the present-day mean summer freezing level. Ages for glaciation in the Tararua Range correspond closely to exposure ages for the last glacial maximum (LGM) from the lateral moraines of Cascade Valley in the South Island, and in Cobb Valley, in northern South Island. The corollary is that glaciation in the Tararua Range coincided with the phase of maximum cooling during MIS 2, prior to the Antarctic Cold Reversal (ACR), during the LGCP. Copyright © 2008 John Wiley & Sons, Ltd. [source] Late Quaternary deglacial history of the Mérida Andes, Venezuela,JOURNAL OF QUATERNARY SCIENCE, Issue 7-8 2005Nathan D. Stansell Abstract Radiocarbon-dated sediment cores from seven lakes and two bogs spanning the Cordillera de Mérida in the Venezuelan Andes were used to identify and date the regional history of late Pleistocene and Holocene glacial activity. Coring sites were selected at different elevations across a pronounced rain shadow from southeast (wet) to northwest (dry). Sediment lithostratigraphy and magnetic susceptibility, in conjunction with AMS radiocarbon dates on macrofossils and charcoal, were used to constrain deglaciation. The local expression of the Last Glacial Maximum occurred between 22,750 and 19,960,cal.,yr,BP. On the wetter southeastern side of the Cordillera de Mérida, glaciers had significantly retreated by 15,700,cal.,yr,BP, followed by several minor glacial advances and retreats between 14,850 and 13,830,cal.,yr,BP. At least one major glacial readvance occurred between 13,830 and 10,000,cal.,yr,BP in the wetter southeastern sector of the region. The drier northwest side of the Cordillera de Mérida records initial glacial retreat by 14,240,cal.,yr,BP. Multiple sites on both sides of the Mérida Andes record a further phase of extensive deglaciation approximately 10,000,cal.,yr,BP. However, the north-northwest facing Mucubají catchment remained partially glaciated until ca. 6000,cal.,yr,BP. Deglacial ages from the Venezuelan Andes are consistently younger than those reported from the Southern Hemisphere Andes, suggesting an inter-hemispheric deglacial lag in the northern tropics of the order of two thousand years. Copyright © 2005 John Wiley & Sons, Ltd. [source] Comparative phylogeography of the two pink salmon broodlines: an analysis based on a mitochondrial DNA genealogyMOLECULAR ECOLOGY, Issue 6 2002D. Churikov Abstract Over most of their natural northern Pacific Ocean range, pink salmon (Oncorhynchus gorbuscha) spawn in a habitat that was repeatedly and profoundly affected by Pleistocene glacial advances. A strictly two-year life cycle of pink salmon has resulted in two reproductively isolated broodlines, which spawn in alternating years and evolved as temporal replicates of the same species. To study the influence of historical events on phylogeographical and population genetic structure of the two broodlines, we first reconstructed a fine-scale mtDNA haplotype genealogy from a sample of 80 individuals and then determined the geographical distribution of the major genealogical assemblages for 718 individuals sampled from nine Alaskan and eastern Asian even- and nine odd-year pink salmon populations. Analysis of restriction site states in seven polymerase chain reaction (PCR)-amplified mtDNA regions (comprising 97% of the mitochondrial genome) using 13 endonucleases resolved 38 haplotypes, which clustered into five genealogical lineages that differed from 0.065 to 0.225% in net sequence divergence. The lineage sorting between broodlines was incomplete, which suggests a recent common ancestry. Within each lineage, haplotypes exhibited star-like genealogies indicating recent population growth. The depth of the haplotype genealogy is shallow (,0.5% of nucleotide sequence divergence) and probably reflects repeated decreases in population size due to Pleistocene glacial advances. Nested clade analysis (NCA) of geographical distances showed that the geographical distribution observed for mitochondrial DNA (mtDNA) haplotypes resulted from alternating influences of historical range expansions and episodes of restricted dispersal. Analyses of molecular variance showed weak geographical structuring of mtDNA variation, except for the strong subdivision between Asian and Alaskan populations within the even-year broodline. The genetic similarities observed among and within geographical regions probably originated from postglacial recolonizations from common sources rather than extensive gene flow. The phylogeographical and population genetic structures differ substantally between broodlines. This can be explained by stochastic lineage sorting in glacial refugia and perhaps different recolonization routes in even- and odd-year broodlines. [source] | ||||||||||