排序方式: 共有47条查询结果,搜索用时 406 毫秒
31.
Zh. A. Antipushina N. K. Kiseleva B. F. Khassanov A. V. Pakhnevich O. A. Krylovich B. I. Sirenko A. B. Savinetsky 《Russian Journal of Ecology》2009,40(2):128-136
Studies on invertebrate remains from the cultural layer of an ancient Aleut settlement on Adak Island have shown that the faunistic composition of invertebrates in the study area had not changed significantly during the Late Holocene. The traditional mode of natural resource use by the ancient Aleuts had no impact on the abundance of valuable species and biodiversity in general. Changes in the temperature regime were found to have taken place in the history of deposit formation. The period from the 8th to the mid-11th century was relatively cold. Climate warming took place between the mid-11th and the mid-12th centuries and between the mid-16th and the 19th centuries, with an intervening cooling period (from the mid-12th to the mid-16th century). This cooling was most distinct between the 15th and the mid-16th centuries. 相似文献
32.
西南地区全新世气候变化概述 总被引:2,自引:1,他引:2
本文较为系统地分析了西南地区石笋、泥炭和湖泊沉积物等自然记录恢复古气候的其本原理,概述了西南地区全新世(近万年来)气候变化研究的主要进展。鉴于西南地区古气候研究的现状,未来应着重加强三个方面的研究:1)加强石笋、泥炭和湖泊沉积物等代用指标记录气候变化的机理研究,建立更为有效的古气候定量/半定量重建方法;2)加强高分辨率、多指标的综合对比研究,揭示重大气候变化事件(如8.2 ka事件4、.2 ka事件和小冰期等)的性质及其对西南地区生态环境的影响;3)加强不同区域气候变化的对比研究,为揭示气候变化驱动力和合理预测西南未来可能出现的气候变化提供科学基础。 相似文献
33.
A geological perspective on the degradation and conservation of western Atlantic coral reefs 下载免费PDF全文
Continuing coral‐reef degradation in the western Atlantic is resulting in loss of ecological and geologic functions of reefs. With the goal of assisting resource managers and stewards of reefs in setting and measuring progress toward realistic goals for coral‐reef conservation and restoration, we examined reef degradation in this region from a geological perspective. The importance of ecosystem services provided by coral reefs—as breakwaters that dissipate wave energy and protect shorelines and as providers of habitat for innumerable species—cannot be overstated. However, the few coral species responsible for reef building in the western Atlantic during the last approximately 1.5 million years are not thriving in the 21st century. These species are highly sensitive to abrupt temperature extremes, prone to disease infection, and have low sexual reproductive potential. Their vulnerability and the low functional redundancy of branching corals have led to the low resilience of western Atlantic reef ecosystems. The decrease in live coral cover over the last 50 years highlights the need for study of relict (senescent) reefs, which, from the perspective of coastline protection and habitat structure, may be just as important to conserve as the living coral veneer. Research is needed to characterize the geological processes of bioerosion, reef cementation, and sediment transport as they relate to modern‐day changes in reef elevation. For example, although parrotfish remove nuisance macroalgae, possibly promoting coral recruitment, they will not save Atlantic reefs from geological degradation. In fact, these fish are quickly nibbling away significant quantities of Holocene reef framework. The question of how different biota covering dead reefs affect framework resistance to biological and physical erosion needs to be addressed. Monitoring and managing reefs with respect to physical resilience, in addition to ecological resilience, could optimize the expenditure of resources in conserving Atlantic reefs and the services they provide. 相似文献
34.
本文通过调研长江、黄河流域全新世古洪水研究相关文献,开展了两大流域全新世古
洪水发生频次空间对比研究。现有资料表明,两大流域全新世古洪水在6000 a BP 以前发生较
少;6000—4000 a BP 古洪水频次上升,在4000 a BP、3000 a BP 前后均出现一个洪水多灾期;
3000 a BP—1000 a BP 两大流域古洪水记录频次呈递减趋势;1000 a BP 以来,两大流域整体上
表现为递增的趋势,而值得注意的是1000 a BP 后,两大流域古洪水记录频次呈现出反相位变化
的趋势。与太阳活动记录对比,发现两个流域洪水发生均与太阳活动相关,但是两个流域洪水
发生对太阳活动的响应相反,长江流域在太阳活动较弱的时期,洪水多发,而黄河流域在太阳
活动较强的时期,洪水多发。 相似文献
35.
腐殖化度作为气候代用指标首次用于我国泥炭的古气候研究 ,较好的记录了红原地区全新世的气候变化。对红原泥炭14 C测年和腐殖化度分析 ,获得了距今 12 0 0 0年较高分辨率红原地区气候变化记录 :11.815~ 10 .9kaB .P .,气候干冷 ;10 .9~ 5 .6kaB .P .,气候湿暖 ;5 .6~ 3.9kaB .P .,气候干冷 ;3.9~ 1.7kaB .P .,气候干冷、湿暖波动 ;1.7~ 0kaB .P .,气候干冷。总体而言 ,大约 5 .6kaB .P .是红原地区由早中全新世的湿暖气候向晚全新世干冷气候变化的转折点。同时 ,红原泥炭记录的降温事件在北半球具有普遍性 ,反映了青藏高原对全球气候变化的响应。 相似文献
36.
How Climate and Vegetation Influence the fire Regime of the Alaskan Boreal Biome: The Holocene Perspective 总被引:2,自引:0,他引:2
Feng Sheng Hu Linda B. Brubaker Daniel G. Gavin Philip E. Higuera Jason A. Lynch T. Scott Rupp Willy Tinner 《Mitigation and Adaptation Strategies for Global Change》2006,11(4):829-846
We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal
ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with
the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred
at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should
not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable
P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests
dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where
fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of
P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime
and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial
array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation
remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will
require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge
of how sedimentary charcoal records fire events.
In this paper, charcoal refers to macroscopic (≥180 μm) as opposed to microscopic (< 180 μm) particles unless indicated otherwise.
Radiocarbon ages were converted to calibrated years before AD 1950 using the atmospheric calibration data set (Stuiver et
al. 1998). 相似文献
37.
通过对塔克拉玛干沙漠北部,塔里木河泛滥平原典型剖面的沉积物粒度特征、化学元素的变化和沉积相特征的研究,并结合~(14)C测年,揭示了本区域全新世以来的环境变化规律,本区全新世以来的多风、高温、干燥的气候形成是以全球气候波动为背景,叠加内陆干旱封闭盆地影响而成的。但在干燥气候条件下曾有过几次空气湿度较大的偏湿期。本区沉积相主要以河流冲积作用形成的粘土层和风力作用下形成的风砂层为主,剖面中的亚粘土与现代河流相特征一致,剖面中风砂土与现代流沙性质趋同。全新世以来本区共发生3次明显的河流泛滥期,可以同全新世以来的间冰期对应。 相似文献
38.
A comprehensive study of paleobotanical materials collected in the northern part of the Eastern Sayan was performed, including botanical analysis of peat, palynological and carpological analysis, and radiocarbon dating. The results provided a basis for reconstructing in detail the spatiotemporal distribution of ecocenotic complexes and corresponding paleoclimate types and calculating quantitative gradients of heat and moisture supply in the Late Holocene, beginning from 3500 ka. 相似文献
39.
Aarno T. Kotilainen Laura Arppe Slawomir Dobosz Eystein Jansen Karoline Kabel Juha Karhu Mia M. Kotilainen Antoon Kuijpers Bryan C. Lougheed H. E. Markus Meier Matthias Moros Thomas Neumann Christian Porsche Niels Poulsen Peter Rasmussen Sofia Ribeiro Bjørg Risebrobakken Daria Ryabchuk Semjon Schimanke Ian Snowball Mikhail Spiridonov Joonas J. Virtasalo Kaarina Weckström Andrzej Witkowski Vladimir Zhamoida 《Ambio》2014,43(1):60-68
Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change. 相似文献
40.
华北平原东部全新世古年地表径流量的估算 总被引:1,自引:0,他引:1
利用以现代数据建立的年平均降水量、年平均温度与年平均地表径流深间的关系式和全新世古年降水量、古年温度的推测值估算了华北平原东部的全新世古年地表径流深,并将估算结果与已有的古水文数据作了对比。 相似文献