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71.
应用 1 951- 2 0 0 2年NINO特征指数 (NINO1 +2 ,NINO3 ,NINO4 ,NINO3 .4)和 1 973-1 998年南极海冰北界范围以及 1 950- 2 0 0 1年SODA海洋温度资料。首先分析探讨了在ElNi no期间 ,堆积于赤道东太平洋的异常暖水在南半球的传播途径 ,进而研究了ENSO以及东南太平洋异常海温场与南极海冰之间的关系。结果表明 ,在ElNino期间 ,堆积于赤道东太平洋的异常暖水 ,是沿秘鲁和智利沿岸向极传播。其传播过程持续大约 1年的时间 ,但未发现沿南赤道流的西传现象。ENSO循环过程与南极海冰变化存在一定联系 ,特别是Amundsen Belling shausen海和南极半岛海冰的变化与ENSO暖事件 (ElNino)较为密切。当ElNino事件发生后 ,时滞 2年左右的时间 ,Amundsen Bellingshausen海和南极半岛的海冰将出现明显的减少现象 ,特别是南极半岛的海冰减少最为明显。ElNino事件对南极海冰的影响过程是 ,堆积于赤道东太平洋的大量异常暖水 ,沿南美 (秘鲁和智利 )沿岸近海向极地传播 ,异常暖水的这种向极传播过程将引起近极的海温场出现异常升高 ,最终导致Amundsen Bellingshausen海和南极半岛地区的海冰减少。自 2 0世纪 80年代以来 ,Amundsen Bellingshausen海和南极半岛的海冰出现明显减少的趋势 ,与这一时期的ElNino事件的频繁发生 相似文献
72.
73.
大多数火山喷发以强酸 (主要是硫酸 )的形式在极地冰芯中留下痕迹 ,通过冰芯连续电导率 (ECM)或各个雪冰样品SO42 - 浓度测定能够恢复历史上的火山作用。极地冰芯中已知年代的火山喷发还可用于冰芯定年。极地冰芯记录的火山信号大小依赖于火山喷发的规模和类型 ,火山喷发的地理位置和酸性气体组成 ,大气气溶胶传输 ,以及沉降地点的年积累率和沉积后生过程等。单个火山喷发通常会导致数月至数年的半球乃至全球范围的气候相对变冷 (这种现象在极区变得更明显 ) ,但过去大规模的爆炸性火山喷发对气候的影响及其与气候变化之间的联系仍有待于进一步研究 相似文献
74.
覆盖在北极海洋上的广阔海冰为其内部生存的微生物群落提供了一个独特的生境。研究表明 ,大量海冰细菌能够分泌产生胞外酶 ,其中产蛋白或脂质水解酶细菌的比例远高于产多糖水解酶的细菌。温度、盐度是直接影响海冰细菌生存与活力的 2个主要环境因子。 76%的产酪蛋白酶海冰细菌为低温菌 ,菌株只能在 <35°C条件下生长 ;而 98%的酪蛋白酶最适作用温度≥ 35°C ,其中 62 %的酶最适作用温度≥ 45°C。几乎所有的产酪蛋白酶海冰细菌都耐盐或嗜盐 相似文献
75.
76.
Floodplains are ecotones that form a transition between aquatic and terrestrial environments. These important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface. Hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system. This paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large Australian floodplain to a river channel, and the effects of land and water developments on these exchanges. The paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach—a recognition of the importance of the three disciplines hydrology, geomorphology and ecology. Large-scale water-resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the Lower Balonne floodplain, Australia. The magnitude, frequency and duration of flooding events have all been reduced. The construction of levees and water storages has also reduced the reactive floodplain surface area. The presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation. Annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less. Some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water-resources and floodplain developments. 相似文献
77.
The Colville basin drains the North Slope of Alaska and is one of several large Arctic river systems located within permafrost. The timing and style of fluvial processes in the earth's permafrost regions differ from those occurring in midlatitude settings. Moreover, in comparison to temperate-zone systems, rivers located entirely within permafrost perform most of their work during relatively short periods of time. This paper examines river ice hydrology and the resulting geomorphic processes that occur within the Colville delta, Alaska. Fluvial processes and landform development within the Colville delta occur after the flood-pulse is initiated by the breakup of river ice. During this 4-month period, the geomorphic processes are largely influenced by the movement of ice. The flood-pulse and accompanying river ice influences erosional and depositional processes and results in unique styles of sediment transport, deposition, and riverbank erosion. 相似文献
78.
Habitat, occurrence and conservation of Saharo-Arabian-Turanian element Forsskaolea tenacissima L. in the Iberian Peninsula 总被引:1,自引:0,他引:1
Javier Cabello Domingo Alcaraz Francisco Gmez-Mercado Juan F. Mota Javier Navarro Julio Peas Esther Gimnez 《Journal of Arid Environments》2003,53(4):491-500
The aim of this study is to assess the Iberian populations of Forsskaolea tenacissima L. according to its biogeographical interest, habitat, geographical range and conservation status. Results point out that they are restricted to gravel wadis of Tabernas Desert (SE Spain), are scarcely included in protected areas and represent historically isolated populations with relict behaviour. We also describe a new association, Senecioni-Forsskaoleetum tenacissimae. Conservation status of species is cause for concern and two conservation actions must be carried out. Firstly, protected areas should house Forsskaolea populations and secondly, phytosociological characterization of a community allows inventorying its habitat and directing conservation efforts to community level. 相似文献
79.
80.
Impact of precipitation seasonality changes on isotopic signals in polar ice cores: a multi-model analysis 总被引:1,自引:0,他引:1
For Central Greenland, water isotope analysis indicates a temperature difference of about 10°C since the Last Glacial Maximum (LGM). However, borehole thermometry and gas diffusion thermometry indicate that LGM surface temperatures were about 20°C colder than today. Two general circulation model studies have shown that changes in the seasonal precipitation timing in Central Greenland might have caused a warm bias in the LGM water isotope proxy temperatures, and that this bias could explain the difference in the estimated paleotemperatures. Here we present an analysis of a number of atmospheric general circulation model simulations mostly done within the framework of the Paleoclimate Modeling Intercomparison Project. The models suggest that the seasonal cycle of precipitation and surface mass balance over Central Greenland at the LGM might have been very different from today. This supports the idea that the accuracy of the water isotope thermometry at the LGM in Greenland might be compromised as a result of a modified surface mass balance seasonality. However, the models disagree on the amplitude and sign of the bias. For Central East Antarctica, a strong seasonality effect on the LGM isotopic signal is not simulated by any of the analyzed models. For the mid-Holocene (6 kyr BP) the models suggest relatively weak isotope paleothermometry biases linked to changes in the surface mass balance seasonality over both ice sheets. 相似文献