Change Analysis of Three Major Antarctic Ice Shelves Based on Multi-source Remote Sensing Data

In recent years, melting and calving happen in the Antarctic ice shelves. In this paper, seven periods of coastlines were applied to provide an analysis of the ice front changes of Ross, Filchner-Ronne and Amery ice shelves with the inclusion of 1997 and 2000 Radarsat products, 2003/2004 and 2008/2009 MODIS products and 2006, 2012, 2015 coastline which were extracted from MODIS images. Change area, SCE (Shoreline Change Envelope) and NSM (Net Shoreline Movement) were applied to analyze the variation of the ice shelf front. The results shows that, the ice front of Amery ice shelf has advanced since 1997 and the total outward extension distance of the ice front was about 20 to 25 km while the advance area reached 3.03×10³ km². Ross ice shelf and Filchner-Ronne ice shelf continued to advance after ice calving events under the driver action of glacier. However, the advance area was less than the retreat area and the net change area is respectively -9.39×10³ km² and -5.86×10³ km². The retreat distance of the collapse area were up to 53 km and 39 km in the two biggest ice shelves.     

小冰期时中国南方地区降水模式的差异研究

小冰期是过去一千年中全球气候变化的重要事件之一。关于小冰期时中国季风区和西风影响区气候变化的对比研究众多,但是缺乏中国南方地区降水模式时空差异的研究,难以了解中国南方地区降水变化规律。为了系统地了解小冰期时中国南方地区降水的复杂性,本文将中国南方地区划分为东南—华南沿海地区、中部地区以及西南地区三个区域,总共选取了19条高分辨率的古气候记录进行对比研究,主要有以下几点认识:(1)相对于中世纪暖期而言,小冰期期间中国南方东南—华南沿海地区的气候偏湿,这可能与雨带在中国南方的滞留时间延长和沿海地区受台风的影响增强有关。(2)中国中部地区秦岭南麓和神农架高山林区在小冰期时期主要呈"冷湿"的模式,差异在于秦岭南麓区域主要在小冰期中后期偏湿,这与中部其他区域偏"冷干"的模式不同。这种区域差异可能是由于地形地势和大气环流的复杂性导致。(3)中国西南地区受印度夏季风和东亚夏季风的共同影响,且该区域地形复杂,其气候变化在小冰期时期存在更加明显的空间差异,没有呈现出比较一致的降水模式。与小冰期期间的降水变化不同的是,近30年东南—华南沿海地区除了台湾和雷州半岛,其他区域降水明显减少,可能受气温和人类活动等因素的影响。通过结合高分辨率的古气候记录,我们系统分析了中国南方小冰期的干湿模式在时空上的差异及其可能的影响因子,这对于认识小冰期时中国南方不同区域降水的复杂性及未来旱涝灾害的防控具有一定意义。     

Unveiling buried aeolian landscapes: reconstructing a late Holocene dune environment using 3D ground-penetrating radar

Across the UK, sandy beaches and dunes protect coastal infrastructure from waves and extreme water levels during large-scale storms, while providing important habitats and recreational opportunities. Understanding their long-term evolution is vital in managing their condition in a changing climate. Recently, ground-penetrating radar (GPR) methods have grown in popularity in geomorphological applications, yielding centimetre-scale resolution images of near-surface stratigraphy and structure, thus allowing landscape evolution to be reconstructed. Additionally, abrupt changes in palaeo-environments can be visualized in three dimensions. Although often complemented by core data, GPR allows interpretations to be extended into areas with minimal ground-truth control. Nonetheless, GPR data interpretation can be non-intuitive and ambiguous, and radargrams may not initially resemble the expected subsurface geometry. Interpretation can be made yet more onerous when handling the large 3D data volumes that are facilitated with modern GPR technology. Here we describe the development of novel semi-automated GPR feature-extraction tools, based on ‘edge detection’ and ‘thresholding’ methods, which detect regions of increased GPR reflectivity which can be applied to aid in the reconstruction of a range Quaternary landscapes. Since reflectivity can be related to lithological and/or pore fluid changes, the 3D architecture of the palaeo-landscape can be reconstructed from the features extracted from a geophysical dataset. We present 500 MHz GPR data collected over a buried Holocene coastal dune system in North Wales, UK, now reclaimed for use as an airfield. Core data from the site, reaching a maximum depth 2 m, suggest rapid vertical changes from sand to silty-organic units, and GPR profiles suggest similar lateral complexity. By applying thresholding methods to GPR depth slices, these lateral complexities are effectively and automatically mapped. Furthermore, automatic extraction of the local reflection power yields a strong correlation with the depth variation of organic content, suggesting it is a cause of reflectivity contrast. GPR-interpolated analyses away from core control thus offer a powerful proxy for parameters derived from invasive core logging. The GPR data collected at Llanbedr airfield highlight a complex dune system to a depth of 2.8 m, probably deposited in several phases over ~700 years, similar to elsewhere in North Wales.     

Geoarchaeological evidence on a Late Bronze Age earthquake,Ohrid Basin (North Macedonia)

Geoarchaeological investigations on the northeastern shore of Lake Ohrid revealed 3.5 m thick deepwater lacustrine sediments overlying terrestrial vegetation macrofossils, worked wood and abundant potsherds dated to the Late Bronze Age (LBA). Distinct contact of deepwater sediment with the sub-aerial weathered limestone bedrock point to a sudden increase in lake level. According to radiocarbon data, catastrophic flooding occurred shortly after 1214 yr bc. Because the area is located in a highly active seismic zone, we propose that this event was caused by tectonically induced, metre-scale coseismic subsidence related to faults bordering the Ohrid alluvial plain. Moreover, this event coincides well with a dramatic switch in the habitation and settlement strategy in the region. More important, however, is the finding that the age of the proposed massive tectonic event and change in habitation lies within the interval of the proposed ‘earthquake storm’ in the eastern Mediterranean dated to 1225–1175 bc. As the Ohrid-Korça zone belongs to the same tectonic province, a relationship between the abovementioned earthquakes and the proposed event can be expected. This research therefore might provide the first direct evidence of a large-scale earthquake event linkable to the LBA collapse of Europe's first urban civilisation in the Aegean.     

红原泥炭6000a以来元素异常及其可能反映甘青地区人类活动信息的初步研究

通过对红原泥炭沉积剖面Pb,Zn,Fe,Mn,Cu,Co,Ni,Ti,V,Al等10种元素和灰分的测试,发现多数元素在该剖面的变化与灰分变化较为一致,但Cu,Pb和Zn元素的变化在剖面300cm以上出现较大异常:这3种元素的变化与其他元素变化呈相反的规律,而且Pb和Zn两种元素的含量较之剖面下部出现数量级的增大。通过对比,发现元素含量的异常与位于剖面上风区的甘青地区新石器时代晚期-青铜时代文化在发生时间上较为吻合,认为这可能是人类活动环境效应的记录。用600~300cm段的元素变化作为背景值,用与Pb,Zn元素相关较好的4种元素分别计算出二者变化的自然背景值,从而分离出了人类活动强度信息与自然环境背景值,分离结果与著名的青海柳湾墓地出土人口规模对比较好。     

南极冰盖与冰川的快速变化

近10年的观测研究表明,南极冰盖和冰川存在快速的变化阿蒙森海扇区的主要冰流系统正在迅速变薄,减薄趋势可上溯至内陆150km处;罗斯冰流出现了停滞或明显减速,有的流动方向发生了改变,引发冰流袭夺;南极半岛冰架大面积崩塌,补给冰川加速,冰川出现了跃动;变暖的海水进一步侵蚀了冰架,着地线附近底部冰层融化强烈。上述发现改变了南极冰盖缓慢变化的传统观点,并对今后的冰川动力学研究,冰流模型模拟,冰盖物质平衡研究及预测具有重要意义。     

Body motion in liquid under ice plate with snow cover

The motion of a submarine in liquid under an ice plate covered with flooded snow is considered. The ice is modelled as an elastic plate and the snow cover is modelled as a viscous layer on the top of the plate. The submarine is modelled as a slender solid of revolution with scale 1:300. The experimental and theoretical study of the influence of the viscous snow layer on deflections of the floating ice plate is conducted. The viscous layer reduces the amplitudes of flexural-gravity waves. The greatest influence of the viscous layer on the plate deflections is achieved for velocities of the submarine, where the waves of maximum amplitude are generated. Theoretical results are in good qualitative and quantitative agreement with the model experiments.     

The influence of the bottom contour on the deformed state of the ice cover due to the motion of the submarine

The authors have previously determined that the effectiveness and failure pattern of the ice cover caused by flexural-gravity waves generated by a submerged body motion near the bottom ice can greatly depend on the depth of the water area. In its turn, the presence of a ledge on the ice surface may affect a wave propagation pattern. This paper presents an experimental study of the bottom contour influence on the deflection and length of flexural-gravity waves. The authors describe a numerical model for the analysis of the deformed state of ice caused by hydrodynamic loads due to a submarine motion, taking into account the bottom contour. The experiments are carried out in the ice tank. The results of calculations and experiments are compared.     

Large-time response of ice cover to a load moving along a frozen channel

Unsteady response of an ice cover in a channel with vertical walls is studied for large times. The ice deflection is caused by a load moving along the frozen channel at a constant speed. The ice cover is modelled as a thin elastic plate clamped to the walls of the channel. The time-dependent problem is solved by using the Fourier transform along the channel and the method of separating variables. In the system moving along the channel together with the load, the large-time deflection of the ice cover consists of steady deflection and standing waves in front and behind the load. The number of waves, their frequencies and wavenumbers depend on the speed of the load and the values of the critical speeds for the channel. The number of the waves and their amplitudes are calculated for a given load and its speed. The maximum stress in the ice as a function of the load speed is estimated.     

A stochastic method for the prediction of icebreaker bow extreme stresses

It is well established that the ship-ice interaction process is quite complex and associated ice loads on the icebreaker hull is a stochastic process. Obviously, novel accurate statistical methods and models should be developed and applied to estimate extreme bow stresses.This paper studies icebreaker bow stresses based on measured distribution of ice thickness in the Arctic Ocean on the way to and from the North Pole. Since the vessel route was carefully selected searching for easier ice conditions, the Arctic Ocean crossing was not a straight linear but a meandering path. Thus, the specific ship route data was biased with respect to general ice statistics in the region, but true with respect to the route specific ice data encountered by a ship navigating in that region. Therefore the route specific ice thickness data is directly needed for ship design and navigation analysis. It is assumed that captains are competent and knowledgeable, and therefore will select a route that provides the most favourable ice conditions.This paper contributes to study of the newest Chinese self-designed polar icebreaker, serving the purpose of enhancing icebreaker operational reliability. Finite Element Method software package ANSYS/LS-DYNA has been employed to simulate bow stress pattern for a particular icebreaker operating in the Arctic Ocean. Extreme bow stresses were estimated using Naess-Gaidai method. The latter is a first application of Naess-Gaidai method to a distribution with lower bound. Thus this paper aims at introducing an efficient method of estimating route-specific icebreaker extreme bow stresses.