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1.
本文通过分析南海南部１７９６４柱状样的孢粉记录,重建了该地区２６０００ａＢ．Ｐ．以来的植被和气候变化历史。南海南部末次盛冰期时高山雨林的范围可能是现在的２～３倍,表明气温明显下降;从末次盛冰期到冰消期,巽他陆架一直为热带低地雨林及红树林占据,表明在此期间湿度没有明显变化,但存在着千年级的准周期波动。这种波动一直持续到全新世中期。本地区在２０００ａＢ．Ｐ．以来芒萁孢子大量增加,一些高山雨林的成分重新出现,可能与人类活动所导致的低地植被的破坏有关。 相似文献
2.
Howard J. Falcon-Lang William A. DiMichele Scott Elrick & W. John Nelson 《Geology Today》2009,25(5):181-184
The development of coal forests during the Carboniferous is one of the best-known episodes in the history of life. Although often reconstructed as steamy tropical rainforests, these ancient ecosystems were a far cry from anything we might encounter in the Amazon today. Bizarre giant club-mosses, horsetails and tree ferns were the dominant plants, not flowering trees as in modern rainforests. At their height, coal forests stretched all the way from Kansas to Kazakhstan, spanning the entire breadth of tropical Pangaea. Most of what we know of their biodiversity and ecology has been quite literally mined out of the ground through two centuries of hard labour. Without coal mining, our knowledge would be greatly impoverished. Over the past few years, we've been exploring underground coal mines in the United States, where entire forested landscapes have been preserved intact over huge areas. Never before have geologists had the opportunity to walk out through mile upon mile of fossilized forest. In this feature article, we describe some of our recent explorations and attempt to shed new light on these old fossils. 相似文献
3.
4.
A new genus and species of tetrablemmid spider, Electroblemma bifida n. gen. et sp., is described, from two adult males found in Upper Cretaceous (Cenomanian) amber of Myanmar. The genus is distinguished by its enormous dorsal carapace projection and highly modified chelicerae. The new genus is referred to the tribe Tetrablemmini within the subfamily Tetrablemminae. The presence of a relatively derived tetrablemmid on the south-east Eurasian continent during the Late Cretaceous suggests that the family was already well diversified in tropical rainforests at this time. 相似文献
5.
The impact of climatic changes that occurred during the last glacial maximum and the Holocene on vegetation changes in the Amazon Basin and the Guiana Shield are still widely debated. The aim of our study was to investigate whether major changes in vegetation (i.e. transitions between rainforests and C4 savannas) occurred in northern French Guiana during the Holocene. We measured variations in the δ13C of soil organic matter at eight sites now occupied by forest or savannah. The forest sites were selected to cover two regions (forest refugia and peneplains) which are thought to have experienced different intensities of disturbance during the latest Pleistocene and the Holocene. We found that none of the forest sites underwent major disturbances during the Holocene, i.e. they were not replaced by C4 savannahs or C4 forest savannahs for long periods. Our results thus suggest that tropical rainforests in northern French Guiana were resilient to drier climatic conditions during the Holocene. Nevertheless, geographical and vertical variations in the 13C of SOM were compatible with minor changes in vegetation, variations in soil processes or in soil physical properties. 相似文献
6.
Chengyu Weng 《地球科学进展》2017,32(11):1163-1173
Sunda region, located in the tropical region of Southeast Asia, is one of the three main regions of the tropical rainforests with the highest biodiversity in the world, and also the most endangered ranges of species extinction. The high biodiversity in the region was due to several reasons: ①the lucky geographical location in the warm and moist tropics, ②joint zone between the two large tectonic plates Eurasia and India-Australia, ③with abundant of islands separated with different distances. ④In the cycles of glacial-interglacial during the geological history, the variations of the temperature and the fluctuations of the sea level created opportunities for the species interactions and gene mixture, therefore resulting in the formation of new species and contributing more species to the region. In particular, during Quaternary period, the continental shelves exposed repeatedly during the glacial times, and the many islands were often merged into one or a few continuous and large territories, making the gene flows within species easier. During the interglacials, the sea-level rose and the continental shelved were submerged, and the scattered and isolated territories might make the speciation and extinction occurred more frequently. Biological refugia might be important for many species’ survival. Today, with the rapid global warming and intensive human disturbance, the refugia may be more crucial for many species to survive. However, the extinction of many species may be inevitable. 相似文献
7.
Early Pleistocene vegetation in upland southeastern Australia included diverse rainforests and sclerophyll forests, which alternated on precessional timescales. The nature and timing of transitions between these biomes, and the role of fire in maintaining or driving transitions between them, are uncertain. Here we present a high‐resolution pollen record from Stony Creek Basin, a small Early Pleistocene palaeolake in southeastern Australia. The pollen record documents a pattern of vegetation change, over ca. 10 ka at ca. 1590–1600 ka, between sclerophyll forests, dominated by Eucalyptus, Callitris (Cupressaceae) or Casuarinaceae, and rainforests dominated by either angiosperms or conifers of the family Podocarpaceae. Transitions between these biomes typically occurred within ca. 1–2 ka. The associated charcoal record suggests that greatest biomass combustion occurred when local vegetation was dominated by Eucalyptus, and the least biomass combustion occurred when local vegetation was dominated by Podocarpaceae. However, local fires burnt in both sclerophyll and angiosperm‐dominated rainforest vegetation, at least once every several centuries. Fire was very rare (less than about one fire per millennium) only when the local vegetation was rainforest dominated by Podocarpaceae. This suggests that fire was an irregular presence in both sclerophyll‐ and angiosperm‐dominated rainforest biomes during the late Neogene, though was largely absent in Podocarpaceae‐dominated rainforests. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Patricio I. Moreno 《第四纪科学杂志》2004,19(1):35-47
A pollen record from Lago Condorito (41°45'S, 73°07'W) shows prominent vegetation and climate changes at millennial time‐scales, superimposed on multimillennial trends in temperature and westerly activity in northwest Patagonia during the past 15 000 yr. The record shows that evergreen temperate rainforests have dominated the landscape over this interval, with floristic changes ranging from cold‐resistant North Patagonian forests with podocarp conifers to Valdivian forests with thermophilous, summer‐drought resistant species. The long‐term trend shows that cool‐temperate and humid conditions prevailed between 15 000 and 11 000 cal. yr BP, followed by an extreme warm and dry phase between 11 000 and 7600 cal. yr BP, and subsequent cooling events and increase in precipitation that peaked at ca. 5000 cal. yr BP, when Southern Hemisphere alpine glaciers achieved their first Neoglacial maximum. Modern conditions were established at ca. 1800 cal. yr BP, following a warm and dry phase between ca. 2900 and 1800 cal. yr BP. These results suggest that millennial‐scale climate variability during deglacial and post‐glacial times also affected the mid‐latitude region of the South Pacific, supporting the idea that changes in the tropical Pacific might be a key factor in the initiation and/or propagation of millennial‐scale climate variability at regional, hemispheric and global scales. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
HAIDEE CADD MICHAEL‐SHAWN FLETCHER MICHELA MARIANI HENDRIK HEIJNIS PATRICIA S. GADD 《第四纪科学杂志》2019,34(7):491-498
Tasmania's montane temperate rainforests contain some of Australia's most ancient and endemic flora. Recent landscape‐scale fires have impacted a significant portion of these rainforest ecosystems. The complex and rugged topography of Tasmania results in a highly variable influence of fire across the landscape, rendering predictions of ecosystem response to fire difficult. We assess the role of topographic variation in buffering the influence of fire in these endemic rainforest communities. We developed a new 14 000‐year (14‐ka) palaeoecological dataset from Lake Perry, southern Tasmania, and compared it to neighbouring Lake Osborne (<250 m distant) to examine how topographic variations influence fire and vegetation dynamics through time. Repeated fire events during the Holocene cause a decline in montane rainforest taxa at both sites; however, in the absence of fire, rainforest taxa are able to recover. Montane temperate rainforest taxa persisted at Lake Perry until European settlement, whilst these taxa were driven locally extinct and replaced by Eucalyptus species at Lake Osborne after 2.5 ka. Contiguous topographic fire refugia within the Lake Perry catchment probably provided areas of favourable microclimates that discouraged fire spread and supported the recovery of these montane temperate rainforests. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
10.
We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes. 相似文献
11.
云南南部与东南部热带地区在地理上接近,具有类似的热带季风气候和热带雨林植被,它们的植物区系均以热带成分占优势,在现代植物区系分区上都属于热带亚洲或印度—马来西亚植物区系。研究发现在云南东南部植物区系中具有丰富的东亚植物区系的代表成分,如木兰科、山茱萸科、菝葜科、茶科、安息香科、山矾科、忍冬科、冬青科、卫矛科等,意味着它... 相似文献
12.
In recent years, tropical cyclones on the Pacific Northwest have decreased. We cannot infer that tropical cyclones impact China have reduced, because the Pacific Northwest is not homogeneous, and the variation characteristics of tropical cyclones in different sea areas are not clear. This paper uses gray relational density clustering algorithm to cluster tropical cyclone data sets between 1949 and 2008, according to the generated position of tropical cyclones, generated density and the possibility of landing. The Pacific Northwest is divided into different sea areas. Then, we analyze the risk of tropical cyclones generated in these sea areas. The results show that the probability of tropical cyclones landing generated in some sea areas is very high, reached 74 %, but the probability of tropical cyclones landing generated in other sea areas is only 2 %. Tropical cyclones generated in some sea areas are more likely to develop into typhoons, strong typhoons and so on, but the intensity of tropical cyclones generated in other sea areas is lower, there is little risk for China. Finally, according to the climate change stage trends, we divide the period 1949–2008 into three stages and analyze the tropical cyclone risk of each sea areas. 相似文献
13.
热带平流层准两年振荡对热带对流层顶和深对流活动的影响 总被引：1，自引：0，他引：1
利用NCEP/NCAR再分析资料通过合成分析的方法研究了热带平流层准两年振荡(QBO)影响热带对流层顶及深对流活动的基本特征及可能的物理机制。研究发现,QBO对对流层顶和大气射出长波辐射(OLR)的影响存在明显的季节和空间上的差异。QBO对对流层顶和OLR的影响在冬、秋季最大,春、夏季相对较弱。与QBO造成的对流层顶高度和温度异常所不同是,QBO造成的OLR异常并没有呈现出一样的沿热带的带状分布特征,OLR异常沿赤道区域有正有负。另外,QBO对OLR的影响主要在热带对流活跃区域,尤其是在印度尼西亚和西太平洋区域,QBO东风位相下的对流活动要强于QBO西风位相下的对流活动。QBO造成的OLR异常和对流层顶异常在水平分布上有显著的差异,表明QBO对对流层顶的影响主要是与QBO风切变的异常有关,QBO影响热带深对流活动进而影响对流层顶温度的作用是次要的。进一步研究QBO影响对流活动可能的机制发现,QBO造成的浮力频率异常和对流层有效位能(CAPE)异常与OLR异常在水平分布上有较一致的变化,说明QBO不仅通过调节对流层顶高度和温度影响热带的深对流活动,还可以通过调节对流层的静力稳定度、CAPE来影响热带地区深对流活动。 相似文献
14.
Since tropical rainfall is important in the global energy and hydrologic cycle, the tropical rainfall changes under global warming have attracted extensive attention around the world in recent decades. The advances in the observational studies and model projection for the tropical rainfall changes under global warming were reviewed here. The frontiers in the mechanism of regional tropical rainfall changes and the approaches of rainfall change research are summarized. The large intermodel spread in the multi-model projections, the sources of uncertainty and the methods to reduce the uncertainty were also introduced. Finally, the challenges about the tropical rainfall changes were discussed. 相似文献
15.
Stephen Vermette 《Natural Hazards》2007,42(1):91-103
The tropical storm database used in this study was obtained from the National Oceanic and Atmospheric Administration’s (NOAA)
Coastal Service Center, using the Historical Hurricane Tracks tool. Queries were used to determine the number of storms of
tropical origin that have impacted the State and each of its counties. A total of 76 storms of tropical origin passed over
New York State between 1851 and 2005. Of these storms, 14 were classified as hurricanes. The remaining hurricanes passed over
New York State as weaker or modified systems—27 tropical storms, 7 tropical depressions, and 28 extratropical storms (ET).
Long Island experiences a disproportionate number of hurricanes and tropical storms. The average frequency of hurricanes and
storms of tropical origin (all types) is one in every 11 years and one in every 2 years, respectively. September is the month
of greatest frequency for storms of tropical origin, although the storms of greatest intensity tend to arrive later in the
hurricane season and follow different poleward tracks. While El Nino Southern Oscillation (ENSO) cycles appear to show some
influence, the frequency and intensity of storms of tropical origin appear to follow a multidecadal cycle. Storm activity
was greatest in both the late 19th and 20th centuries. During periods of increased storm frequency and intensity storms reached
New York State at progressively later dates. While the number and timing of storms of tropical origin is likely to increase,
this increase appears to be attributed to a multidecadal cycle, as opposed to a trend in global warming. 相似文献
16.
本文回顾了近年来有关热带内外地区相互作用的研究进展。它主要包括三个方面：（１）热带外扰动对热地区的影响；（２）热带地区大气了研究；（３）热带对热带外地区的影响。本文内容涉及了有关观测资料分析、理论研究以及数值试验三个方面的研究成果。 相似文献
17.
The classification and influencing factors of modern marine productivity were reviewed at the beginning. We discussed the pros and cons of different paleoproductivity proxies. Based on these discussions, we collected paleoproductivity reconstructions in tropical marine from previous studies and focus on the glacial-interglacial features, periodicity and forcing mechanisms of tropical marine productivity. We found that the productivity in most tropical sites decreased from MIS 2 to MIS 1. The productivity was not always higher in glacial: The glacial-interglacial pattern of productivity turned at MIS 22 in western Pacific. There were remarkable differences between tropical productivity and high latitude productivity. The precession and obliquity bands were more significant in tropical productivity and ~30 ka cycles caused by the superimposing of different orbital cycles were common in tropical. The coccolith based productivity seemed to have a quasiperiod of 400 ka and more researches are needed to discover the relationship between productivity and global 13C in this band. 相似文献
18.
Bangladesh is highly susceptible to tropical cyclones. Unfortunately, there is a dearth of climatological studies on the tropical
cyclones of Bangladesh. The Global Tropical Cyclone Climatic Atlas (GTCCA) lists historical storm track information for all
the seven tropical cyclone ocean basins including the North Indian Ocean. Using GIS, tropical cyclones that made landfall
in Bangladesh during 1877–2003 are identified and examined from the climatological perspective. For the convenience of study,
the coast of Bangladesh is divided into five segments and comparisons are made among the coastal segments in terms of cyclone
landfall and vulnerability. There is a large variability in the year-to-year occurrence of landfalling tropical cyclones in
Bangladesh. Most of the tropical cyclones (70%) hit in the months of May–June and October–November generally show the well-known
pattern of pre- and post-monsoon cyclone seasons in that region. 相似文献
19.
利用美国NCAR CAM3大气环流模式,分析了末次盛冰期（LGM）两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外（赤道东太平洋和热带大西洋）热带SST异常的敏感性。结果表明： 1）SST异常首先引起大气环流的改变。 赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场（如SST）影响很大; 2）大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。 140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少; 而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。 相似文献
20.
Dominik Brill Katharina Seeger Anna Pint Felix Reize Kay Thwe Hlaing Martin Seeliger Stephan Opitz Khin Mi Mi Win Win Thuzar Nyunt Nilar Aye Aung Aung Kyaw Kyaw Frauke Kraas Helmut Brückner 《Sedimentology》2020,67(3):1431-1459
The catastrophic storm surge of tropical cyclone Nargis in May 2008 demonstrated Myanmar's exposure to coastal flooding. The investigation of sediments left by tropical cyclone Nargis and its predecessors is an important contribution to prepare for the impact of future tropical cyclones and tsunamis in the region, because they may extend the database for long-term hazard assessment beyond the relatively short instrumental and historical record. This study, for the first time, presents deposits of modern and historical tropical cyclones and tsunamis from the coast of Myanmar. The aim is to establish regional sedimentary characteristics that may help to identify and discriminate cyclones and tsunamis in the geological record, and to document post-depositional changes due to tropical weathering in the first years after deposition. These findings if used to interpret older deposits will extend the existing instrumental record of flooding events in Myanmar. Evaluating deposits that can be related to specific events, such as the 2006 tropical cyclone Mala and the 2004 Indian Ocean tsunami, indicates similar sedimentary characteristics for both types of sediments. Landward thinning and fining trends, littoral sediment sources and sharp lower contacts allow for the differentiation from underlying deposits, while discrimination between tropical cyclone and tsunami origin is challenging based on the applied methods. The modern analogues also demonstrate a rather low preservation potential of the sand sheets due to carbonate dissolution, formation of organic top soils, and coastal erosion. However, in coastal depressions sand sheets of sufficient thickness (>10 cm) may be preserved where the shoreline is prograding or stable. In the most seaward swale of a beach-ridge plain at the Rakhine coast, two sand sheets have been identified in addition to the deposits of 2006 tropical cyclone Mala. Based on a combination of optically stimulated luminescence, radiocarbon and 137Cs dating, the younger sand layer is related to 1982 tropical cyclone Gwa, while the older sand layer is most probably the result of an event that took place prior to 1950. Comparison with historical records indicates that the archive is only sensitive to tropical cyclones of category 4 (or higher) with landfall directly in or a few tens of kilometres north of the study area. While the presented tropical cyclone records are restricted to the last 100 years, optically stimulated luminescence ages of the beach ridges indicate that the swales landward of the one investigated in this study might provide tropical cyclone information for at least the past 700 years. 相似文献