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The vegetational history of the penultimate glacial period, Marine Isotope Stage (MIS) 6 (c. 185–135 ka), has remained relatively unexplored. Here we present a new record from the Ioannina basin, north‐west Greece, which constitutes the highest‐resolution terrestrial pollen record for this interval produced to date. It shows that the vegetation history of MIS 6 in this region can be divided into two parts: an early period (185–155 ka) with pronounced oscillations in tree population extent, and a later period (155–135 ka) with much smaller tree populations and subdued oscillations. This pattern is analogous to the MIS 3/MIS 2 division during the last glacial in the same sequence, although the early part of MIS 6 had larger Pinus populations and fewer temperate trees relative to the equivalent interval in MIS 3. This implies cooler and wetter conditions, which is somewhat counterintuitive given the high summer insolation during MIS 6e, but is in line with other palaeoclimatic evidence from the Mediterranean. Comparison with North Atlantic records suggests that despite the absence of pronounced iceberg discharges during MIS 6, North Atlantic millennial‐scale variability had a significant downstream impact on tree populations in north‐west Greece. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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V. Margari P.L. Gibbard C.L. Bryant P.C. Tzedakis 《Quaternary Science Reviews》2009,28(13-14):1317-1339
This paper presents high-resolution results of palynological and sedimentological analyses undertaken on two sediment cores from the Megali Limni (ML) basin, an area characterised by serpentine soils, in the southeastern part of Lesvos Island, Greece. Six tephra horizons and multiple radiocarbon dates provide independent controls towards the development of a chronological framework. The composite pollen record spans the period from 22 to 62 thousand years ago (ka) BP and shows a number of oscillations between steppe, forest-steppe and forest, in concert with North Atlantic millennial-scale variability. Vegetation during the late Marine Isotope Stage (MIS) 4 was grassland/steppe, indicating cold and arid conditions, while sediment composition suggests increased erosion rates. Arboreal populations (dominated by Pinus and to a lesser extent deciduous Quercus) expanded during MIS 3 interstadials, suggesting increases in precipitation and temperature. Within the course of the longer interstadials, changes in vegetation composition point to a trend towards increased aridity and sometimes decreasing winter temperatures. During intervening stadials, vegetation was composed mainly of Artemisia, Chenopodiaceae and Gramineae, indicating reversals to arid and cold conditions, with most extreme conditions recorded during stadials corresponding to Heinrich Events. During the course of MIS 3, the basin was progressively infilled with sediments. Only a small portion of MIS 2 is represented in the sequence, showing a short-lived expansion of arboreal populations. Comparisons with other pollen sequences from southern Europe underscore the important role of Pinus throughout the last glacial period, a reflection of the serpentine soils of the Megali Limni area, where Pinus brutia dominates today. 相似文献
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BELATTMANIA Zahir CHAOUTI Abdellatif REANI Abdeltif MACHADO Margari ENGELEN Aschwin H SERR&#;O Ester A SABOUR Brahim 《海洋学报(英文版)》2018,37(10):190-194
The littoral paranthurid isopod crustacean Paranthura nigropunctata (Lucas, 1846) is recorded for the first time from the littoral of El Jadida located on the Atlantic northwest coast of Morocco. Specimens were obtained from the invasive brown seaweed Sargassum muticum and the natives Bifurcaria bifurcata and Cystoseira tamariscifolia in January 2015. This new record further confirms a significant southward distribution of P. nigropunctata and contributes to the knowledge of the biogeography of this isopod. Heretofore, the species was only known from the western and eastern Mediterranean and some Atlantic coasts. The present finding is the first of the species from Moroccan Atlantic shores, and suggests that the species may also be present in other coastal localities from Morocco and Africa. Some data on morphology, ecology and spatial distribution of the species are provided. 相似文献
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This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March(JFM),April-June(AMJ),July-September(JAS)and October-December(OND)from 1968-1998.For each season,the preferential tracks of these disturbances in the 3-10-day band periods were computed and spatialized,as well as their associated wavelength,velocity and main period,which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean.During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N.From AMJ to JAS these tracks migrate northward;in JAS,they merge into one over the northern tropical Atlantic along 17.5°N.The associated wavelength fields exhibit a meridional gradient,with large wavelengths(greater than 4000 km) around the equator,between 5°N and 5°S,and smaller wavelengths outside of this latitude band(between 2500-3500 km).The phase speed is also found to exhibit poleward decreasing values from 12-6 m s-1. Over the north Atlantic track,6-9-day disturbances were found to occur from January to May and approximately from October to December.From June to September,the 3-5-day waves dominate the synoptic activity.Over the south Atlantic track,between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur. 相似文献
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A non-hydrostatic, fully compressible, regional-scale numerical model of the atmosphere that includes parameterization of cloud microphysics is run in a two-dimensional mode. It uses two different observed vertical profiles of temperature, relative humidity and wind to simulate the local circulation evolution and impact on convection and nocturnal fog occurrence in São Paulo, Brazil. Theatmospheric behaviour generated by the model is similar to the observations of the two summer days with and without sea breeze progression over the plateau. The convective development occurs in the afternoon of the two experiments but with different features and intensities. In the experiment with sea-breeze progression, there is fog formation over the plateau during the following night, in accordance with the observations. A strong northwesterly flow acting in the lower troposphere, with intensity varying between 7 and 10 m s-1,appears as an inhibiting agent of the sea-breeze progression over the plateau and of convective development in the afternoon and of the nocturnal fog occurrence. In this case, observed gusts during the night are well simulated and appear to be related to the topography. 相似文献
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