Fine-resolution simulation of surface current and sea ice in the Arctic Mediterranean Seas

A fine-resolution model is developed for ocean circulation simulation in the National Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Chinese Academy of Sciences, and is applied to simulate surface current and sea ice variations in the Arctic Mediterranean Seas. A dynamic sea ice model in elastic-viscous-plastic rheology and a thermodynamic sea ice model are employed. A 200-year simulation is performed and a dimatological average of a 10-year period (141st-150th) is presented with focus on sea ice concentration and surface current variations in the Arctic Mediterranean Seas. The model is able to simulate well the East Greenland Current, Beaufort Gyre and the Transpolar Drift, but the simulated West Spitsbergen Current is small and weak. In the March climatology, the sea ice coverage can be simulated well except for a bit more ice in east of Spitsbergen Island. The result is also good for the September scenario except for less ice concentration east of Greenland and greater ice concentration near the ice margin. The extra ice east of Spitsbergen Island is caused by sea ice current convergence forced by atmospheric wind stress.     

Autochthonous block fields in southern Norway: Implications for the geometry,thickness, and isostatic loading of the Late Weichselian Scandinavian ice sheet

The consistent geographical and altitudinal distribution of autochthonous block fields (mantle of bedrock weathered in situ) and trimlines in southern Norway suggests a multi-domed and asymmetric Late Weichselian ice sheet. Low-gradient ice-sheet profiles in the southern Baltic region, in the North Sea, and along the outer fjord areas of southern Norway, are best explained by movement of ice on a bed of deforming sediment, although water lubricated sliding or a combination of the two, may not be excluded. The ice-thickness distribution of the Late Weichselian Scandinavian ice sheet is not in correspondence with the modern uplift pattern of Fennoscandia. Early Holocene crustal rebound was apparently determined by an exponential, glacio-isostatic rise. Later, however, crustal movements appear to have been dominated by large-scale tectonic uplift of the Fennoscandian Shield, centred on the Gulf of Bothnia, the region of maximum lithosphere thickness.     

Ex situ echo sounder target strengths of ice krill Euphausia crystallorophias

Ice krill is the keystone species in the neritic ecosystem in the Southern Ocean,where it replaces the more oceanic Antarctic krill. It is essential to understand the variation of target strength(TS in d B re 1 m 2) with the different body size to accurately estimate ice krill stocks. However,there is comparatively little knowledge of the acoustic backscatter of ice krill. The TS of individual,formalin-preserved,tethered ice krill was measured in a freshwater test tank at 38,120,and 200 k Hz with a calibrated split-beam echo sounder system. Mean TS was obtained from 21 individual ice krill with a broad range of body lengths(L :13–36 mm). The length( L,mm) to wet weight( W; mg) relationship for ice krill was W =0.001 218×103 × L 3.53( R 2= 0.96). The mean TS-to-length relationship were TS3 8 k Hz =-177.4+57log 10( L),( R 2 = 0.86); TS 120 k Hz =-129.9+31.56 log 10( L),( R 2 =0.87); and TS 200 k Hz =-117.6+24.66log1 0( L),( R 2 =0.84). Empirical estimates of the relationship between the TS and body length of ice krill were established at 38,120,and 200 k Hz and compared with predictions obtained from both the linear regression model of Greene et al.(1991) and the Stochastic Distorted Wave Born Approximation(SDWBA) model. This result might be applied to improve acoustic detection and density estimation of ice krill in the Southern Ocean. Further comparative studies are needed with in situ target strength including various body lengths of ice krill.     

Envisat and SARAL/AltiKa Observations of the Antarctic Ice Sheet: A Comparison Between the Ku-band and Ka-band

The AltiKa altimeter onboard SARAL is a joint CNES/ISRO mission launched in February 2013 that has the same 35 days repeat orbit of the previous European altimeters, Envisat, and ERS-1/2. SARAL/AltiKa is thus a unique opportunity to extend the repeat observations of this orbit that have been surveyed since 1991. However, the altimeter operates in Ka-band, which is higher than the previous frequencies, and offers new paths of investigation. The penetration depth is theoretically reduced from around 10 m in Ku-band to less than 1 m in Ka-band, such that the volume echo originates from the near subsurface. Second, the sharper antenna aperture leads to a narrower leading edge that reduces the impact of the ratio between surface and volume echoes of the height retrieval. Indeed, the spatial and temporal observations of AltiKa at cross-over points and along-track indicate that the impact of backscatter changes on the height decreasesfrom 0.3 m/dB for the Ku-band to only 0.05 m/dB for the Ka-band. Therefore, the height measurement is stable over time. Moreover, the volume echo in the Ka-band results from the near subsurface layer and is mostly controlled by ice grain size, unlike the Ku-band.     

Concurrent Use of OSCAT and AltiKa to Characterize Antarctic Ice Surface Features

Radar altimetry provides an important geophysical parameter, backscatter coefficient (σ₀), which is useful in studying target surface characteristics. Ku-band (Oceansat-2 scatterometer- OSCAT) and Ka-band (SARAL-AltiKa altimeter) data are concurrently used to characterize polar surface features over the Antarctic region. Maximum-likelihood classification has been employed to classify combined data set (AltiKa and OSCAT) for discrimination among sea ice, open water, and ice sheet (interior and exterior). The sea ice region obtained using the current approach has been compared with sea ice boundary derived from passive microwave data.     

20世纪南极菲尔德斯半岛毛皮海豹食谱比例变化的同位素混合模型比较分析

稳定同位素比值分析已成功用于示踪动物的食物来源研究,近年来已发展了多个同位素混合模型用于计算混合物中多来源物质的组成比例。本文以过去百年来南极菲尔德斯半岛南极毛皮海豹(Arctocephalus gazella)毛发的C、N同位素数据为基础,运用同位素混合模型中的欧几里得距离法、线性模型和贝叶斯模型进行计算、分析和比较,得到毛皮海豹食谱中南极磷虾(Euphausia superb)、南极电灯鱼(Electrona antarctica)和尼氏裸灯鱼(Gymnoscopelus nicholsi)所占比例随时间的变化趋势。各模型计算得出的结果可分为两组,分别是欧几里得距离法公式(1)和(2)的结果,表现为近百年来毛皮海豹食谱中Euphausia superb比例与其毛发稳定N同位素比值呈同步上升的趋势;第二组为欧几里得距离法公式(3)、线性模型和贝叶斯模型的结果,Euphausia superb比例与毛皮海豹毛稳定N同位素比值呈反相关关系。综合对比研究区域气候、海冰环境变化背景和已有的南极磷虾种群密度调查资料分析,第二组模型结果与实际情况较为相符,可用于讨论食物比例的时间变化趋势。近百年来,菲尔德斯半岛毛皮海豹食谱中Euphausia superb的比例显著下降,很可能是由于区域气候快速变暖和海冰的消退造成的。本文的计算结果指示西南极半岛气候变暖已显著影响到区域海洋食物链变化。     

南极半岛东北海域表层沉积有机质来源及其沉积环境

采用气相色谱-质谱技术对南极半岛东北海域海底表层沉积物的总有机碳、有机质碳同位素(δ13 Corg)和生物标志化合物等进行了测试分析。研究区表层沉积物总有机碳TOC平均值高于现代深海沉积物中的平均含量。δ13 Corg的变化说明该海域有机碳来源呈海洋水生生物来源和陆源混合的特征。正构烷烃的峰型分布、主峰碳、饱和烃轻重比C-21/C+22和(C21+C22)/(C28+C29)、甾烷组合和藿烷组合证实研究区西部表层沉积物有机质来源以陆源高等植物为主,其陆源可能来自于附近的南极半岛和南舍得兰群岛;研究区东部表层沉积物有机质来源偏以海源为主,且以低等浮游生物、藻类及细菌生物等海源输入为主。碳优势指数(Carbon preference index,CPI)、奇偶优势指数(Odd-even Predominance,OEP)和甾烷C29ααα20S/(20S+20R)比值显示研究区D1-7站位和D5-9沉积物有机质演化程度较高,D5-2和D2-4站位的有机质演化程度低,其他站位介于中间状态。饱和烃中姥鲛烷、植烷及其比值(Pr/Ph)等组合显示研究区西部以氧化-弱还原的沉积环境为主,其可能是受高温低盐别林斯高晋海水流和附近火山喷发的影响所致;研究区东部以还原—强还原沉积环境为主,可能是受低温高盐的威德尔底层水(WSBW)和威德尔海深层水(WSDW)影响所致。     

基于小波变换和HIS变换的海冰SAR与光学遥感影像融合方法研究

Sea ice as a disaster has recently attracted a great deal of attention in China. Its monitoring has become a routine task for the maritime sector. Remote sensing, which depends mainly on SAR and optical sensors, has become the primary means for sea-ice research. Optical images contain abundant sea-ice multi-spectral information, whereas SAR images contain rich sea-ice texture information. If the characteristic advantages of SAR and optical images could be combined for sea-ice study, the ability of sea-ice monitoring would be improved. In this study, in accordance with the characteristics of sea-ice SAR and optical images, the transformation and fusion methods for these images were chosen. Also, a fusion method of optical and SAR images was proposed in order to improve sea-ice identification. Texture information can play an important role in sea-ice classification. Haar wavelet transformation was found to be suitable for the sea-ice SAR images, and the texture information of the sea-ice SAR image from Advanced Synthetic Aperture Radar(ASAR) loaded on ENVISAT was documented. The results of our studies showed that, the optical images in the hue-intensity-saturation(HIS) space could reflect the spectral characteristics of the sea-ice types more efficiently than in the red-green-blue(RGB) space, and the optical image from the China-Brazil Earth Resources Satellite(CBERS-02B) was transferred from the RGB space to the HIS space. The principal component analysis(PCA) method could potentially contain the maximum information of the sea-ice images by fusing the HIS and texture images. The fusion image was obtained by a PCA method, which included the advantages of both the sea-ice SAR image and the optical image. To validate the fusion method, three methods were used to evaluate the fused image, i.e., objective, subjective, and comprehensive evaluations. It was concluded that the fusion method proposed could improve the ability of image interpretation and sea-ice identification.     

北极中央区海冰密集度与云量相关性分析

本文使用海冰密集度以及低云、中云、高云的日平均数据,借助滑动相关分析方法,研究了北极中央区海冰密集度与云量之间的相关性,分析了海冰与云的相互作用机制。研究表明,在春季海冰融化季节(4、5月)、秋季海冰冻结季节(10、11月),低云与海冰密集度之间表现为较好的负相关,表明在这段时间内冰区海面蒸发强烈,对低云的形成有重要贡献。在10月和11月,中云与海冰密集度也有很好的负相关,表明秋季低云可以通过抬升形成中云。高云与海冰密集度之间并没有明显的相关性,可能原因:一方面海冰的空间分布对高云无影响,另一方面,高云主要影响到达的短波辐射,从而影响海冰的融化和冻结速度,与海冰厚度有直接显著的关系,而与海冰密集度的关系不明显。此外,在海冰密集度与低云存在较好负相关的情况下会出现某些年份相关性不好的情况,我们的研究发现这是北极中央区与周边海区发生了海冰交换或云交换的结果。     

An assessment of arctic sea ice concentration retrieval based on “HY-2” scanning radiometer data using field observations during CHINARE-2012 and other satellite instruments

A retrieval algorithm of arctic sea ice concentration (SIC) based on the brightness temperature data of “HY-2” scanning microwave radiometer has been constructed. The tie points of the brightness tempe...