Spatial and temporal variations in the thermodynamics since the Last Glacial Maximum at Jutulstraumen drainage basin,East Antarctica

A flow-line model is coupled to a 2D temperature model to simulate the thermodynamic changes of Jutulstraumen drainage basin due to grounding line retreat and increased surface temperature since the Last Glacial Maximum (LGM). The basin consists of a plateau drained by an outlet glacier, and the simulated ice volume reductions are 1% and 2% respectively of the current grounded volume. The mountain ranges H.U. Sverdrupfjella and Neumayerskarvet fringing the plateau were not overridden by ice at the LGM, while the Nashornet nunataks closer to the grounding line were. Today the glacier is almost in balance with the current climate, with the highest thinning rate?<?5.0×10^?3 ma^?1 at the plateau. The simulated present-day thermal regime of the outlet glacier shows a basal layer at the pressure melting point and negative temperature gradients with depth due to horizontal advection of cold ice from the plateau. Sensitivity studies show that strain heating and horizontal advection are important for the basal temperatures in the fast flowing outlet glacier and for about half of the wide basin at the polar plateau. Increased strain heating and horizontal advection since the LGM control the response time required to readjust to the new conditions, and it controls the present-day volume.     

磁暴期间南极South Pole站和McMurdo站电离层闪烁与GPS TEC时空变化相关性研究

目前,对电离层闪烁特性的研究大多集中在低纬度地区,而在极区,特别是在南极地区,由于测量数据稀少,所以研究十分有限。借助安装在南极South Pole站和Mc Murdo站的GPS闪烁监测仪,获取到实测的电离层闪烁数据,同时结合IGS网站提供的同址GPS观测数据,分析了2011年9月24—25日磁暴发生前,9月26日磁暴发生时以及9月27日磁暴发生后GPS L波段信号电离层相位闪烁和GPS TEC时空变化特征。分析显示,这次磁暴对电离层的一个重要的影响是在电离层扰动剧烈期间,相位闪烁活动及其强度在时间和空间分布上都显著增强。研究结果发现,在强电离层闪烁期间,实测的相位闪烁指数σ_Φ与由GPS观测数据推算的TEC变化率指数(ROTI)的变化非常相似,两者之间呈现出良好的相关性。从而证明,在如南极等缺乏独立电离层闪烁观测值的地区,GPS ROTI可以作为表征电离层闪烁的重要可选参数,进而可以借助全球分布的GPS观测数据来分析和研究电离层闪烁特性。     

Results of magnetotelluric and gravimetric measurements in western Nicaragua, Central America

Magnetotelluric and gravity data have been collected within a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. 2-D interpretation of the magnetotelluric (MT) data, collected at 13 stations, indicates four regions of high electrical conductivity in addition to the conductive coastal region. Two of these are associated with conducting sediments and pyroclastics in the upper part of the crust. Two other conductive structures have been defined at depth around 20 km and the one best defined is located below the depression. From the distribution of seismic events, volcanic activity in the depression and the similarity in geophysical characteristics with areas such as the Rio Grande Rift, this conductor is interpreted as a melt layer or a complex of magma chambers. Models of the upper lithosphere, constrained by the MT model, vertical electrical sounding (VES) data, seismic data and densities, have been tested using gravity data. A model that passes this test shows a gradual thickening of the crust eastwards from the Pacific coast. An anomaly centred over the depression is interpreted to have its origin in a thinning of the crust. In this model the melt layer is situated on top of the bulge of the lower lithosphere. A change in the composition of the crust, from the Pacific Coastal Plain to the Highland, is indicated from the change in character of the MT response and from the density distribution in the gravity model. This may support the hypothesis that the Pacific region is an accreted terrane. MT and gravity data indicate a depth to a resistive and high-density basement in the depression of ca. 2 km. On the basis of this, the vertical setting in the depression is estimated to be of the order of 2.5 km.     

Gravity measurements with a portable absolute gravimeter A10 in Syowa Station and Langhovde,East Antarctica

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10^?8 [m/s²]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection.     

Potassium alum and aluminum sulfate micro-inclusions in polar ice from Dome Fuji,East Antarctica

Water-soluble trace constituents affect the physicochemical properties of polar ice. Their structural distribution provides important insights into the formation history of ice and inclusions. We report the first finding of KAl(SO₄)₂·12H₂O (potassium alum) and Al₂(SO₄)₃·nH₂O (aluminum sulfate) micro-inclusions in the Dome Fuji ice core, East Antartica, using a micro-Raman technique. Eutectic temperatures of these water-soluble species determined using thermal analysis were −0.4 °C for potassium alum and −8.0 °C for aluminum sulfate. Although the formation process of the aluminum-bearing sulfates remains unclear, the occurrence of these salts largely depends on ice depth.     

Analysis about the influence on the thermal regime in permafrost regions with different underlying surfaces

In the last several decades, the underlying surface conditions on the Qinghai-Tibet Plateau have changed dramatically, causing permafrost degradation due to climate change and human activities. This change severely influenced the cold regions environment and engineering infrastructure built above permafrost. Permafrost is a product of the interaction between the atmosphere and the ground. The formation and change of permafrost are determined by the energy exchange between earth and atmosphere system. Fieldwork was performed in order to learn how land surface change influenced the thermal regime in permafrost regions. In this article, the field data observed in the Fenghuo Mountain regions was used to analyze the thermal conditions under different underlying surfaces on the Qinghai-Tibet Plateau. Results show that underlying surface change may alter the primary energy balance and the thermal conditions of permafrost. The thermal flux in the permafrost regions is also changed, resulting in rising upper soil temperature and thickening active layer. Vegetation could prevent solar radiation from entering the ground, cooling the ground in the warm season. Also, vegetation has heat insulation and heat preservation functions related to the ground surface and may keep the permafrost stable. Plots covered with black plastic film have higher temperatures compared with plots covered by natural vegetation. The reason is that black plastic film has a low albedo, which could increase the absorbed solar radiation, and also decrease evapotranspiration. The ＂greenhouse effect＂ of transparent plastic film might effectively reduce the emission of long-wave radiation from the surface, decreasing heat loss from the earth＇s surface, and prominently increasing ground surface temperature.     

东南极格罗夫山地区冰碛石碎石带中高压麻粒岩和正片麻岩的锆石年代学研究及其构造意义

东南极的格罗夫山是普里兹造山带向南极内陆的延伸部分。对格罗夫山不同碎石带中收集的高压麻粒岩和正片麻岩进行锆石U-Pb年代学研究。四个高压麻粒岩的锆石多数为变质新生锆石,仅少数保留有继承核,其年龄为2633—2502 Ma。在变质锆石中获得~570 Ma和~555—545 Ma两个阶段变质年龄,锆石微量元素特征显示为重稀土亏损,结合前人研究结果,推测这两阶段年龄分别代表了变质作用过程中的进变质和高压峰期变质年龄。两个正片麻岩的锆石普遍发育核-边结构,由一个发育振荡环带的岩浆核和均匀无环带的变质边组成。正片麻岩的原岩年龄存在差异,在样品GR14-3-4的锆石核部获得了1060±40 Ma的上交点年龄,其原岩可能来自格罗夫山东南部的冰下高地,而在样品GR14-5-4的锆石核部获得的原岩年龄为917±4 Ma,与格罗夫山基岩中的基性麻粒岩和正片麻岩的原岩年龄一致。在锆石边部获得的变质年龄较为一致,为~530 Ma,与以前在高压麻粒岩中获得的退变质年龄相当。本次研究确认了高压麻粒岩在格罗夫山地区不同碎石带中分布的广泛性,表明其可能普遍存在于格罗夫山冰下高地之中。同时也进一步证明格罗夫山冰下高地并没有受到格林维尔期构造热事件的影响,而是只经历了泛非期的单相变质构造旋回。     

Study of seasonal snow cover influencing the ground thermal regime on western flank of Da Xing'anling Mountains, northeastern China

Although many studies relevant to snow cover and permafrost have focused on alpine, arctic, and subarctic areas, there is still a lack of understanding of the influences of seasonal snow cover on the thermal regime of the soils in permafrost regions in the mid-latitudes and boreal regions, such as that on the western flank of the Da Xing'anling(Hinggan) Mountains, northeastern China. This paper gives a detailed analysis on meteorological data series from 2001 to 2010 provided by the Gen'he Weather Station, which is located in a talik of discontinuous permafrost zone and with sparse meadow on the observation field. It is inferred that snow cover is important for the ground thermal regime in the middle Da Xing'anling Mountains. Snow cover of 10-cm in thickness and five to six months in duration(generally November to next March) can reduce the heat loss from the ground to the atmosphere by 28%, and by 71% if the snow depth increases to 36 cm. Moreover, the occurrence of snow cover resulted in mean annual ground surface temperatures 4.7–8.2 °C higher than the mean annual air temperatures recorded at the Gen'he Weather Station. The beginning date for stable snow cover establishment(SE date) and the initial snow depth(SDi) also had a great influences on the ground freezing process. Heavy snowfall before ground surface freeze-up could postpone and retard the freezing process in Gen'he. As a result, the duration of ground freezing was shortened by at least 20 days and the maximum depth of frost penetration was as much as 90 cm shallower.     

Spatial variations of Pb,As, and Cu in surface snow along the transect from the Zhongshan Station to Dome A,East Antarctica

The spatial distributions of lead, arsenic, and copper(Pb, As, and Cu, respectively) in surface snow along the transect from the Zhongshan Station to Dome A, East Antarctica, are presented. The mean concentrations of Pb, As, and Cu are1.04±1.56 pg/g, 0.39±0.08 pg/g, and 11.2±14.4 pg/g, respectively. It is estimated that anthropogenic contributions are dominant for Pb, As, and Cu. Spatially, Pb concentrations show an exponentially decreasing trend from the coast inland, while a moderate decreasing trend is observed for Cu concentrations in the coastal area(below 2,000 m above sea level(a.s.l.)).In the intermediate area(2,000–3,000 m a.s.l.), the concentrations and enrichment factors of all these elements show high variability due to the complicated characteristics of climate and environment. On the inland plateau(above 3,000 m a.s.l.),the high concentrations of As and Pb are induced by high deposition efficiency, the existence of polar stratospheric precipitation, and the different fraction deposition to East Antarctica. The extremely high concentrations with maximum values of9.59 pg/g and 69.9 pg/g for Pb and Cu, respectively, are suggested to result mainly from local human activities at the station. Our results suggest that source, transport pathway, and deposition pattern, rather than distance from the coast or altitude, lead to the spatial distributions of Pb, As, and Cu; and it is further confirmed by spatial variations of the three metals deposited over the whole continent of Antarctica.     

Lithology-derived structure classification from the joint interpretation of magnetotelluric and seismic models

Magnetotelluric and seismic methods provide complementary information about the resistivity and velocity structure of the subsurface on similar scales and resolutions. No global relation, however, exists between these parameters, and correlations are often valid for only a limited target area. Independently derived inverse models from these methods can be combined using a classification approach to map geologic structure. The method employed is based solely on the statistical correlation of physical properties in a joint parameter space and is independent of theoretical or empirical relations linking electrical and seismic parameters. Regions of high correlation (classes) between resistivity and velocity can in turn be mapped back and re-examined in depth section. The spatial distribution of these classes, and the boundaries between them, provide structural information not evident in the individual models. This method is applied to a 10 km long profile crossing the Dead Sea Transform in Jordan. Several prominent classes are identified with specific lithologies in accordance with local geology. An abrupt change in lithology across the fault, together with vertical uplift of the basement suggest the fault is sub-vertical within the upper crust.     

The effects of water flow and temperature on thermal regime around a culvert built on permafrost

Temperature and water flow through a culvert beneath the Alaska Highway near Beaver Creek,Yukon,were measured at hourly intervals between June and October 2013.These data were used to simulate the effect of the culvert on the thermal regime of the road embankment and subjacent permafrost.A 2-D thermal model of the embankment and permafrost was developed with TEMP/W and calibrated using field observations.Empirical relations were obtained between water temperatures at the entrance to the culvert,flow into the culvert,and water temperatures inside the structure.Water temperatures at the entrance and inside the culvert had a linear relation,while water temperatures inside the culvert and water flow were associated by a logarithmic relation.A multiple linear regression was used to summarize these relations.From this relationship,changes in the flow rate and water temperatures at the entrance of the culvert were simulated to obtain predicted water temperatures in the culvert.The temperatures in the culvert were used in the thermal model to determine their effects on the ground thermal regime near the culvert.Variation of ±10% in water flow rate had no impact on the thermal regime underneath the culvert.Variation of water temperature at the entrance of the culvert had a noticeable influence on the thermal regime.A final simulation was conducted without insulation beneath the culvert.The thaw depth was 30 cm with insulation,and 120 cm without insulation,illustrating the importance of insulation to the ground thermal regime.     

南极伊利莎白公主地250年来海、陆盐离子浓度特征

中国首次南极内陆冰盖考察获得的50m冰芯的雪冰化学资料研究表明:南极伊利莎白公主地海盐离子浓度季节变化特征明显,为冰芯定年提供了可靠的依据。伊利莎白公主地雪冰中Cl^-、Na⁺和Mg²⁺等海盐离子浓度与南极冰盖其它地方相当,而Ca²⁺含量异常的高,可能与局地较强的陆地源有关。近150年来,伊利莎白公主地海盐离子浓度具有明显升高的趋势,可能是整个南半球100多年来升温的结果。     

Temporal variations in the abundance and sinking flux of diatoms under fast ice in summer near Syowa Station, East Antarctica

To investigate the fate of ice algae released from sea ice, we investigated the abundance, species composition, and sinking flux of diatoms in the water column under fast ice near Syowa Station, Antarctica during the summer of 2005/2006. The diatom assemblage in the water column consisted of chain-forming planktonic species, in contrast to the under-ice assemblage dominated by pennate species reported from this site in the past; this dissimilarity suggests the presence of an unconsolidated platelet ice layer under the congelation ice, within which planktonic species can bloom. Among the dominant diatoms, Porosira pseudodenticulata and Pseudo-nitzschia cf. turgiduloides were dominant in the water column, and their water column stocks were higher than their mass sedimentation. These species apparently maintain their populations in the surface layer, as their production remains in the water column. In contrast, Fragilariopsis kerguelensis and Thalassiosira australis were scarce in the water column but rich in the flux, indicating active sinking and export of their production to the benthic ecosystem. This distinction in buoyancy control and sinking characteristics of the dominant diatoms on release from the fast ice influences the diatom species composition and carbon flow under the ice.