南极的日地物理观测研究

南极是进行日地物理观测研究的重要场所。本文介绍在南极进行的日地物理观测研究的过去和现状，评述这一领域国际研究的动向和展望未来的发展     

松嫩沙地晚更新世以来的孢粉记录及古植被古气候

松嫩沙地的形成演化经历了一个漫长的地质历史过程, 孢粉记录反映出这个地区从晚更新世以来植被曾被发生过多次更替, 经历了半荒漠(半荒漠草原)→疏林草原→干草原的演替, 气候经过多次冷暖-干湿波动, 沙漠化也经历了多次扩张和收缩。与中国北方其它沙漠化土地一样, 气候变干是松嫩沙地形成和扩张的决定因素, 而人类的各种活动对这一地区的土地沙漠化起着诱发和促进作用     

南极布兰斯菲尔德盆地重力异常研究

１９９１年，“海洋四号”科学考察船在南极布兰斯菲尔德海峡采集了大量的地球物理资料。本文在利用地震调查资料的基础上，根据现有的重力测量数据，研究引起重力异常的各种地质因素，对实测剖面重力异常进行正演拟合，建立了布兰斯菲尔德盆地的密度模型，并推导出该地区莫霍面深度－布格异常关系表达式，绘制出盆地的莫霍面深度图。     

西南极利文斯顿岛百耳斯半岛火山岩的同位素年龄

以Ｋ－Ａｒ稀释法和４０Ａｒ／３９Ａｒ阶段加热法对利文斯顿岛百尔斯半岛的熔岩和次火山岩测定了同位素年龄。新的年龄数据表明,该区火山活动在晚侏罗纪末即已开始,一直持续到晚白垩世,存在着三期火山活动的产物。侏罗纪末～早白垩世初的火山活动除有熔岩（１４６Ｍａ,１３７Ｍａ）喷出外,还发育有辉长岩侵入体（１３５Ｍａ）和辉绿岩岩墙（１２９Ｍａ）等次火山岩。安山岩（１１４Ｍａ）和石英斑岩（９４Ｍａ）则是早白垩世火山活动的结果。半岛东部具沉积夹层的玄武岩（７１Ｍａ）是区域上晚白垩世～早第三纪火山活动的代表。     

南极沿海伯尔顿盐湖双刺镰状水蚤种群生态及其与盐湖环境的关系

对南极沿海伯尔顿盐湖浮游桡足类双刺镰状水蚤(Drepanopus bispinosus)种群生态进行了全年连续观察和研究,结果表明,该水蚤为一年一代,其个体发育周期,雄性约为10～12个月,雌性约为12～18个月。种群密度随季节不同而差异较大,其成体高密度期约在6～9月份,幼体高密度期大约在11～12月份,主要为无节幼体,桡足幼体Ⅰ期的高密度期出现在1月份。该水蚤繁殖期大约从6月至翌年1月,期间出现两次生殖高峰,7～8月为前一高峰期,所出现的无节幼体受环境因子主要是湖中食物和含氧量不足的影响而不能继续发育至桡足幼体Ⅰ期以上的阶段,后一高峰大约在10～12月,所出期的无节幼体能继续发育至桡足幼体各期直至成体。伯尔顿湖双刺镰状水蚤种群生态特征及其出现两次生殖高峰的现象,可能与该湖环境的季节变化有关。     

南极乔治王岛早第三纪古气候

根据植物化石证据,在早第三纪早、中期,南极乔治王岛地区曾出现过温暖、潮湿的气候,作者认为,当时南半球各板块的相对位置以及由此而引起的洋流的变化,很可能是造成这种温暖气候的主要原因。     

西南极菲尔德斯半岛岩浆作用非平衡过程的自组织现象

对西南极菲尔德斯半岛早第三纪火山岩岩石学、地球化学特征及岩浆作用过程的具体分析表明，其岩浆演化过程是岩浆系统与周围环境（介质）进行能量和物质交换的热能耗散过程，具有动态平衡和阶段性的特点。岩浆结晶的多级复合结构和高位岩浆房中的分带构造，是岩浆作用非平衡过程的自组织现象。这种自组织现象也称作耗散结构     

西南极洲纳尔逊冰帽的表面运动

本文通过对纳尔逊冰帽冰面速度和应变率的分析,得出冰帽边缘的最大夏季表面速度为2058m/a,最大年平均表面速度为15.5m/a,探求了冰面运动速度的空间分布和季节性变化,冰帽顶部的表面应变率为+0.0079/a和+0.0034/a。还讨论了冰面应变率从冰帽顶点到边缘的变化特点及其与冰面裂隙的关系。并将这些特征同我国大陆型冰帽进行了对比,从冰川动力学的角度阐明了纳尔逊冰帽的某些特征。     

西南极菲尔德斯半岛长城站地区深部电性结构

本文分析了1992年12月长城站附近三个测点的大地电磁测深资料(1s到4096s的低频信号数据),得出菲尔德斯半岛风谷断裂电性主轴为北东110°,半岛地壳厚度为22.3km,壳内含四个主要电性层,厚度分别为:1.3km,6.7km,1.2km和13.3km,其中上地壳为9.2km,下地壳为13.1km。     

我国历史时期的湖泊围垦与湖泊退缩

根据历史资料记载,我国历史时期的湖泊围垦可分为三个时期,即魏晋——南北朝、南宋和明末清初。近乎90％的古湖泊消失于这些时期。大多数学者认为,人口增长导致湖泊围垦、退缩。本文进一步的研究表明,湖泊田垦时期与气候干旱期、黄河和长江的低水位期相吻合:与此同时,湖泊也处于低水位期。     

东南极拉斯曼丘陵中晚全新世湖泊生物量的变化记录

对东南极拉斯曼丘陵莫愁湖ZH沉积柱进行了生态地质学的研究,通过AMS-14C定年构建年龄框架,采用550℃烧失量、粒度和元素地球化学指标等,恢复了中晚全新世该地区较高分辨率的湖泊生物量记录。结果显示,距今6600-6100年、5400-4800年、4650-3750年和3500年-2850年为莫愁湖生物量高值期,气候相对温暖适宜,湖泊生产力旺盛;距今6100-5400年、4800-4650年和3750-3500年为湖泊生物量低值期,气候相对寒冷,湖泊生产力相对较弱。而且在整体较暖的气候环境下,出现了其它无冰区沉积物中鲜有记录的距今4800-4650年、4400年前后和3750-3500年的气候快速变冷事件。根据莫愁湖湖泊生物量恢复的东南极拉斯曼地区高分辨的气候变化特征,与太阳活动强度和东南极大陆冰芯记录相吻合,为东南极中晚全新世多样的气候格局研究提供了新的依据。     

西南极利文斯顿岛含砾泥岩层的发现及其地质意义

西南极南设得兰群岛利文斯顿岛赫德半岛中分布的一套主要由复理石相岩石组成的低级变质沉积岩（迈尔斯陡崖组）被认为是中－ 新生代火山岩的基底（晚古生代－ 早中生代？）。以前含砾泥岩在迈尔斯陡崖组局部地点曾有零星报道,但详细的地质填图确认此地有四层含砾泥岩分布。研究表明,这些含砾泥岩可能是水下碎屑流沉积,其生成环境可能是海底扇中扇的水道。对比在南极半岛所发现有大量的含砾泥岩,则进一步表明利文斯顿岛早期地质特征可与南极半岛相比,两者在中－ 新生代岩浆弧形成之前处于相同的构造环境。     

南极菲尔德斯半岛陆地、淡水、潮间带、浅海各生态系统的结构及其相互关系的研究

根据我国在南极菲尔德斯半岛地区１０年的各项研究成果和南极其它相关地区的研究结果,综合分析了菲尔德斯半岛地区陆地、淡水、潮间带及浅海４个生态系统的结构和相互关系。研究结果表明,营养物质的流动使得这４个生态系统相互联系形成一个整体。在这种物质流动的过程中,动物的作用尤其关键,如海鸟（企鹅、黑背鸥等）以及海豹的繁殖、取食等活动对营养盐的搬运有利地促进和疏通了营养物质在系统间的流动。此外,物理作用（如雨水的冲刷、潮汐作用和径流的带动等）也有重要影响。     

MELTWATER FEATURES THAT SUGGEST MIOCENE ICE-SHEET OVERRIDING OF THE TRANSANTARCTIC MOUNTAINS IN VICTORIA LAND, ANTARCTICA

ABSTRACT. We illustrate here spectacular meltwater features associated with outburst floods beneath an ice sheet that overrode the Transantarctic Mountains in southern Victoria Land. Because of long-term hyperarid polar climate, these features are part of an ancient landscape preserved for about 14 million years. Some channels are associated with areal scouring of basement rocks extending from sea level to as much as 1200–2100 m elevation in coastal regions. Scablands with scallops, potholes and plunge pools are cut in Beacon Super group sandstones and Ferrar Dolerite and cover wide areas of high western plateaus near the mountain crest. Subglacial channel systems commonly originate near divides and converge downhill toward the northeast. We argue that the landforms were created beneath a major Antarctic Ice Sheet that submerged the whole area, with the possible exception of the high peaks of the Royal Society Range, as it flowed northeastward toward the outer Antarctic continental shelf. Areal scouring, associated with warm-based regimes, is restricted to the lower slopes close to the coast. In the higher terra in, meltwater channels and scabland alongside preserved patches of regolith are best explained by the breaching of cold-based ice on the mountain rim by subglacial melt water outbursts. Melt from warm-based ice, along with subglacial lakes trapped upstream of the mountain rim, are possible sources of the meltwater necessary to form the channel systems and scablands.     

ASSESSING THE SUITABILITY OF THE EPIC CROP MODEL FOR USE IN THE STUDY OF IMPACTS OF CLIMATE VARIABILITY AND CLIMATE CHANGE IN WEST AFRICA

The EPIC (Erosion Productivity Impact Calculator) crop model, developed by scientists of the United States Department of Agriculture (USDA), has been successfully applied to the study of erosion, water pollution, crop growth and production in the US but is yet to be introduced for serious research purposes in other countries or regions. This paper reports on the applicability of the EPIC 8120 crop model for the assessment of the potential impacts of climate variability and climate change on crop productivity in sub‐Saharan West Africa, using Nigeria as the case study. Among the crops whose productivity has been successfully simulated with this model are five of West Africa's staple food crops: maize, millet, sorghum (guinea corn), rice and cassava. Thus, using the model, the sensitivities of maize, sorghum and millet to seasonal rainfall were demonstrated with coefficients of correlation significant at over 98 per cent confidence limits. The validation tests were based on a comparison of the observed and the model‐generated yields of rice and maize. The main problems of validation relate to the multiplicity of crop varieties with contrasting performances under similar field conditions. There are also the difficulties in representing micro‐environments in the model. Thus, some gaps appear between the observed and the simulated yields, arising from data or model deficiencies, or both. Based on the results of the sensitivity and validation tests, the EPIC crop model could be satisfactorily employed in assessing the impacts of and adaptations to climate variability and climate change. Its use for the estimation of production and the assessment of vulnerabilities need to be pursued with further field surveys and field experimentation.     

EARLY PLIOCENE ALPINE GLACIATION IN ANTARCTICA: TERRESTRIAL VERSUS TIDEWATER GLACIERS IN WRIGHT VALLEY

ABSTRACT. Alpine glacier deposits in the McMurdo Dry Valleys of Antarctica have been interpreted to indicate that early Pliocene climate in that region was not warmer than it is today. Correlation of these alpine‐glacier till sheets to marine deposits that contain evidence consistent with warmer‐than‐present climate has been used to constrain the age of both deposits, preclude the warm interpretation of the marine evidence, and constrain mountain uplift as determined from the marine deposit. We tested the interpretation that, in the early Pliocene, the alpine glaciers in Wright Valley terminated in a fjord and, thereby, constrain the age, temperature, and depth of the fjord. We did this by mapping the surficial geology in this region using the newly available microtopography based on the light detection and ranging (LIDAR) technique. Stratigraphic issues like these need to be resolved in order to quantify early Pliocene climate in Antarctica and contribute to understanding warm global‐climate dynamics. We found that the Pliocene Alpine‐IIIA (A‐IIIA), A‐IIIB and A‐IV drift sheets were more likely deposited from terrestrial alpine‐glacier lobes than glaciers terminating either at tidewater or with a floating appendage. The principal evidence is the occurrence of moraine fragments well below the minimum elevation of the early Pliocene fjord surface, and moraine arrangement in arcs indicative of arcuate glacier fronts without flairing near the proposed shoreline. Our A‐IIIA till is more widespread in the proglacial areas of the five alpine glaciers examined than previously proposed. We propose that the existing distribution of A‐IIIB till reflects glaciers even less extensive than today rather than truncation at a hypothetical fjord surface. Additionally, the A‐IV moraine remnants outline glaciers that were significantly larger than those associated with A‐III moraines. If we are correct, the age of the A‐III till, 3.4 ± 0.1 Ma at maximum, does not constrain the age of the Prospect fjord episode which can be closer to 5.5 ± 0.4 Ma as previously inferred. Moreover, if the alpine tills are not as old as the Prospect fjord episode, the polar paleoclimatic interpretation from those tills does not preclude the high temperature (0–3°C) and reduced salinity previously inferred for the Prospect fjord. However, if alpine glacier extent was not limited by Prospect fjord surface elevation, then paleoclimate during the A‐IIIA, A‐IIIB, and A‐IV glacial episodes can be quantitatively reconstructed. The Prospect fjord might have been deep, not shallow, and, hence, mountain uplift might be greater than currently thought which would explain minimal alpine‐glacier erosion into the valley sides.     

西南极利文斯顿岛火山岩地质

本文综合近年研究中新获得的资料和证据，对利文斯顿岛火山岩的地质特征和火山作用特点作了综合性的介绍。百耳斯建造是该岛最老的火山岩地层，由晚侏罗世至早白垩世生成的玄武岩、玄武安山岩质熔岩和火山碎屑岩、集块岩以及泥岩、页岩等组成，分布在岛西部的百耳斯半岛。中白垩世的鲍勒斯山组主要出露在岛的中部，是由安山岩质熔岩和火山碎屑岩夹层组成的一套蚀变火山岩系。汉那角剖面的火山碎屑岩和熔岩及史莱夫角的橄榄玄武岩均具有中白垩世的年龄。晚白垩世火山活动的产物以粗玄岩为代表，集中出露在西多斯角一带。伴随着火山活动，始新世英云闪长岩侵入白垩系火山岩地层。更新世至现代则有依诺特角组橄榄玄武岩在岛的东北部产出。上述火山活动随时间演进而自北西向南东不断迁移的特点，与整个南设得兰群岛火山作用的发展趋势相符。岩石化学和地球化学资料表明，百耳斯半岛熔岩、史莱夫角的橄榄玄武岩和西多斯角的粗玄岩等白垩纪火山岩基本属于钙碱性岩系并且具有低钾低镁的特点。早第三纪的英云闪长岩继承了橄榄玄武岩和粗玄岩的成分特点，同是南设得兰群岛岩浆弧中生代－新生代火山作用的产物，在钙碱性岩系岩浆演化的晚期生成。而鲍勒斯山组的熔岩和汉那角的熔岩表现出岩相学和岩石化学性质上的     

南极阿德雷岛企鹅粪土沉积物分子地球化学特征

本文分析了南极阿德雷岛Y2湖企鹅粪土沉积层的有机地球化学组成与分布。结果表明企鹅粪土沉积层中正构烷烃以C23为主峰,主要来源于冻土湖沼苔藓植物,样品中高含量的烯烃说明其有机质保存良好。醇类以高浓度的植醇和胆甾烷醇为主,胆甾烷醇和胆甾醇浓度曲线一致,并与企鹅粪土层中的无机元素标型组合的曲线相似,可以作为灵敏的企鹅数量指示剂。酸类组分中以C18饱和脂肪酸为主,在南极低温的环境下,C18∶2酸浓度很低,在很多层次中未检测到,可能是因为Y2沉积物中C18酸以及C18∶2酸主要受企鹅粪影响,而非植被影响。同时在酸性组分中也发现高浓度的胆甾酸。Y2湖中的甾类标志物,甾烯、甾醇、胆甾酸均以C27结构为主,组成单一,低浓度的甾烯和高浓度的甾醇,胆甾酸说明甾类化合物主要受企鹅粪便影响,甾醇和胆甾酸保存良好。综合Y2湖的生物标志物的性质,该沉积物有机质保存良好,主要来源于企鹅粪。     

南极威尔克斯地SGR钻孔处雪冰转化过程中的密度变化特征

本文着重描述了SGR钻孔处冰盖上的积雪在密实化过程中的特征变化,并对该过程进行了分段的和全面的回归分析.结果表明,冰盖密度随深度增大,但增长幅度随深度减小.作者提出密度变化减小度的概念.计算得出的所研究冰芯钻取点的密度变化减小度为-0.15kg/m~3·m~2,粒雪成冰前的密实速率平均值为4.08kg/m~3·a.本文得到的冰盖密度变化“临界点”与以往报道的有所不同.分析这一现象时,作者强调当积雪还在活动层时冰盖温度的影响,并以此解释密度剖面的异常变化以及离差的回升.特别指出,积雪的密度变化具有气候学意义,它在一定程度上能够反映出积雪形成及变化过程中气候变化的某些信息.本文由密度变化确定的钻孔点雪冰转化深度为50米.