大地测量观测和相对海平面联合约束的冰川均衡调整模型

利用大地测量和历史相对海平面变化数据,结合地震剪切波层析模型,联合确定了新的末次冰期冰川均衡调整（GIA）模型,其中地幔黏滞度不仅沿径向而且沿横向变化.研究思路是,先尝试性地选择比例系数β,利用与地震剪切波速异常的线性关系,计算地幔黏滞度横向扰动,并与横向均匀的黏滞度参考模型叠加给出3D地幔黏滞度模型;再利用耦合拉普拉斯方程的有限元法算法进行GIA预测;然后,重复该过程,直到预测与观测之间的吻合满意为止.主要结论有：（1）给出了横向非均匀的地幔黏滞度模型（RF3L20(β=0.4)）,发现了黏滞度显著的横向非均匀性和其对GIA预测的显著影响,指出横向非均匀不完全是由热效应引起的,可能还与化学组分等其他因素有关,该模型可用于地幔动力学研究.（2）给出了全球现今多种GIA预测速率,可为板块运动、陆地水储量、海水质量变化和冰川冰雪质量非平衡监测提供重要的改正.     

联合GRACE和ICESat数据分离南极冰川均衡调整(GIA)信号

2002年发射的GRACE重力卫星为南极冰盖质量平衡提供了一种新的测量方式,但由于南极GIA模型的不确定较大,进而影响GRACE结果的可靠性.本文联合2003-2009年的GRACE和ICESat等数据实现了南极GIA信号的分离,联合方法所分离的GIA不依赖于不确定性很大的冰负荷等假设模型,而是直接基于卫星观测数据估算而来的,具有更大的可靠性.在分离过程中,本文提出了冰流速度加权改正法和GPS球谐拟合改正法对GIA结果进行精化,同时引入了南极GPS观测站的位移数据对分离的GIA进行详细的评估和验证,GPS验证表明经过冰流速度加权和GPS球谐拟合双改正后的GIA结果精度明显得到提高.最后本文利用所分离的GIA对GRACE和ICESat结果进行了改正,得到2003-2009年南极冰盖质量变化的趋势为-66.7±54.5 Gt/a（GRACE）和-77.2±21.5 Gt/a（ICESat）,相比采用其他的GIA模型,本文的GIA结果使GRACE和ICESat这两种不同观测技术得到的南极冰盖质量变化结果更加趋于一致.     

东南极冰盖Lambert冰川流域的物质平衡研究

Lambert冰川流域是南极冰盖最大的冰流系统, 因而在整个南极冰盖的物质平衡中占有非常重要的地位. 近年来穿越该冰川流域的路线考察所获得的现场观测资料和浅冰芯研究结果显示, 该冰川东、西两侧的积累速率分布和近期变化有明显差异: 东侧积累速率较高且近几十年来呈增加趋势, 西侧积累速率较低且过去几十年为明显减小. 冰体运动速度测量和冰流通量计算表明, 该冰川东侧运动速度较快, 冰流量也较大, 说明该冰川冰量补给主要来源于东侧区域. 计算出的考察断面上游物质积累总量大于流出的冰通量约13%, 意味着该流域目前处于物质正平衡状态, 如果保持目前气候状态, 冰盖将会增厚.     

GRACE重力卫星探测南极冰盖质量平衡及其不确定性

2002年GRACE重力卫星的成功发射为南极冰盖质量平衡的研究提供了重力探测的新纪元. 本文利用美国德克萨斯大学CSR公布的2003年1月到2013年12月期间的RL05版本GRACE月重力场数据, 采用最优平均核函数法和组合滤波法两种GRACE后处理方法反演了南极冰盖质量的时空变化. 结果表明: 在2003—2013年期间南极冰盖物质平衡呈明显的负增长状态, 质量变化趋势为-163±50 Gt/a(GW13)、-129±41 Gt/a(IJ05)、-81±27 Gt/a(W12a), 加速度为-8±10 Gt/a2, 质量消融的主要区域分布在西南极阿蒙森海岸和南极半岛的北部. 另外本文还重点探讨了可能影响到估算结果的各项误差及不确定性,分析结果显示影响南极冰盖质量平衡估算结果的最大误差源为GIA改正. 通过假设检验和信息准则对时间序列分析中拟合参数的合理选取进行了探讨和分析, 在联合周年项、半年项和S2、K2、K1潮汐混频项进行拟合分析时发现K1项对拟合结果的加速度影响比其他周期项稍大, 尽管考虑该项的合理性因当前GRACE数据时间序列长度有限而无法确切证实, 但K1项的影响值得后续关注. 对比两种GRACE后处理方法的结果发现:当采用的数据时间跨度一致, 误差改正方法相同, 两种相异的后处理方法, 其估算结果也具有较好的一致性.     

冰川均衡调整对东亚重力和海平面变化的影响

新的全球冰川均衡调整(GIA)模型RF3L20(β=0.4)+ICE-4G考虑了地幔黏滞度沿横向的变化,其黏滞度参数得到大地测量、历史相对海平面变化观测和地震剪切波层析模型的较好约束.本文利用该模型预测了东亚现今重力变化和海平面变化,根据当前末次冰川时空变化和黏滞度参考模型中下地幔下部黏滞度认识的差异,评估了预测的不确定性.结果表明,GIA对东亚地区重力场和海平面长期变化有显著的影响:例如,在哈尔滨、长春、泰安、蓟县、郑州、武汉等测站,GIA重力影响达几十纳伽,可用超导重力仪和未来原子重力仪观测出来;在东亚大陆GIA对GRACE监测的等效水柱长期变化的影响为3%~10%,其中青藏高原西部、华北和三峡地区的影响较大.在东海—太平洋区,GIA的相对影响高达20%~40%;GIA使东亚海域绝对海平面以0.27~0.37 mm/a的速率在长期下降,在黄海、东海卫星测高监测的绝对海平面长期变化中,GIA的相对影响分别达6.9%和7.5%;在58个验潮站,平均相对海平面长期上升速率为2.22 mm/a,GIA影响为-0.17 mm/a,其中14个测站GIA的影响达-0.3~-0.4 mm/a.本文GIA预测的结果,对在东亚地区发现弱的地球动力学过程信号、监测水质量长期变化、监测海平面长期变化和分析其机制,提供精密的改正模型.     

冰川均衡调整(GIA)的研究

冰川均衡调整对固体地球物理学、大地测量学、地貌学、海洋学、冰川学、气候变化、水资源、天文学和考古学等学科具有重要的意义,通过其综述性介绍,以吸引我国地学界的注意和兴趣.本文结合作者和国内外研究成果,全方位地阐述了冰川均衡调整研究的完整内涵,首先给出了冰川均衡调整的完整概念,探讨了冰川均衡调整对冰后地壳运动、全球海平面变化、地球重力场、地球旋转运动和应力状态的影响,再分析了冰川均衡调整研究的科学目标和冰川均衡调整研究的历史与现状,最后指出了冰川均衡调整研究的未来发展方向.     

末次冰盛期中国西部冰川物质平衡线高度的模拟研究

文章使用9个气候模式的数值试验数据,研究了末次冰盛期中国西部冰川物质平衡线高度(ELA),以期加深理解冰期青藏高原地表环境以及ELA变化成因.相对于工业化革命前期这一参考时段,末次冰盛期青藏高原夏季普遍降温4-8℃,年降水量平均减少25%.在降温和降水减少的共同作用下,中国西部ELA降低,不同区域之间降幅存在差异.在青藏高原地区,其南缘和西北部下降1100m,中部腹地下降650-800m,东部下降550-800m且由西南向东北逐渐变小.中国境内天山上的ELA下降不超过650m,祁连山和阿尔泰山上的下降值在500~600m.另外,水平分辨率高的气候模式能模拟出青藏髙原中部ELA下降不超过500m的低值,这与古冰川遗迹记录一致;末次冰盛期青藏高原冰川物质积累区主要发生在边缘山地,其面积扩张至现代的2-5倍,但仍未覆盖到高原中部.     

南极Lambert, Mellor和Fisher冰川的物质平衡及Amery冰架底部物质通量的估算

利用现场观测与遥感数据对Lambert, Mellor和Fisher冰川的物质平衡及其在Amery冰架的底部融化与冻结状况进行了估算. 结果表明, 澳大利亚组织的Lambert冰川盆地(LGB)考察路线的上游地区, Lambert与Mellor冰川分别为(3.9±2.1)和(2.1±2.4) Gt·a^-1的正平衡, 而Fisher冰川基本处于平衡状态. 上游地区总的正平衡为(5.9±4.9) Gt·a^-1. 考察路线以下, 3条冰川均处于负平衡, 总的负平衡为(-8.5±5.8) Gt·a^-1. 整个Lambert, Mellor和Fisher冰川均接近于平衡状态. 3条冰川总净平衡为(-2.6±6.5) Gt·a^-1. 前人认为GL线(1970年代初澳大利亚在LGB建立的冰川运动观测点的连线)以上的内陆盆地处于显著正平衡, 可能是因为过高地估算了总积累量, 并低估了穿过GL线的冰通量. 靠近Amery冰架南端着地线, 冰架底部的平均融化速率为(-23.0±3.5) m冰·a^-1, 向下游方向快速减小, 并在距冰架最南端约300 km处过渡为底部冻结. 沿3条冰川在Amery冰架的冰流带(flowband), 冻结速率约介于(0.5±0.1)~(1.5±0.2) m 冰·a^-1. 由于冰流带底部的融化, 流入冰架的内陆冰损失了大约80%±5%. 3条冰流带底部总融化和总冻结分别为(50.3±7.5)和(7.0±1.1) Gt 冰·a^-1, 这要比前人通过模拟和海洋观测估算的整个Amery冰架底部总融化和总冻结还要大很多.     

基于GRACE RL06数据监测和分析南极冰盖27个流域质量变化

本文基于CSR最新公布的GRACE RL06版本数据,采用Slepian空域反演法估算了南极冰盖27个流域的质量变化.Slepian空域反演法结合了Slepian空间谱集中法和空域反演法的技术优势,能够有效降低GRACE在小区域反演时信号出现的严重泄漏和衰减,进而精确获得南极冰盖在每个流域的质量变化.相对于GRACE RL05版本数据,RL06在条带误差的控制上要更加优化,获得的南极冰盖质量变化时间序列也更加平滑,但在趋势估算上差别并不明显（小于10 Gt/a）.本文的估算结果显示：在2002年4月至2016年8月期间,整个南极冰盖质量变化速率为-118.6±16.3 Gt/a,其中西南极为-142.4±10.5 Gt/a,南极半岛为-29.2±2.1 Gt/a,东南极则为52.9±8.6 Gt/a.南极冰盖损失最大的区域集中在西南极Amundsen Sea Embayment（流域20-23）,该地区质量变化速率为-203.5±4.1 Gt/a,其次为南极半岛（流域24-27）以及东南极Victoria-Wilkes Land（流域13-15）,质量变化速率分别为-29.2±2.1 Gt/a和-19.0±4.7 Gt/a,其中Amundsen Sea Embayment和南极半岛南部两个地区的冰排放呈现加速状态.南极冰盖质量显著增加的区域主要有西南极的Ellsworth Land（流域1）和Siple Coast（流域18和19）以及东南极的Coats-Queen Maud-Enderby Land（流域3-8）,三个地区质量变化速率分别为17.2±2.4 Gt/a、43.9±1.9 Gt/a和62.7±3.8 Gt/a,质量增加大多来自降雪累积,比如：Coats-Queen Maud-Enderby Land在2009年和2011年发生的大规模降雪事件,但也有来自冰川的增厚,如：Siple Coast地区Kamb冰流的持续加厚.此外,对GRACE估算的南极冰盖质量变化年际信号进行初步分析发现,GRACE年际信号与气候模型估算的冰盖表面质量平衡年际信号存在显著的线性相关关系,但与主要影响南极气候年际变化的气候事件之间却不存在线性相关关系,这说明南极冰盖质量变化的年际信号主要受冰盖表面质量平衡的支配,而气候事件对冰盖表面质量平衡的影响可能是复杂的非线性耦合过程.

     

1961～2006年塔里木河流域冰川融水变化及其对径流的影响

以国家气象台站的月降水与月气温资料为驱动数据、90m分辨率的数字高程模型(DEM)和第一次冰川编目的冰川分布矢量数据为基础,利用月尺度的度日模型重建了塔里木河流域各水系冰川物质平衡、融水径流序列,并应用冰川物质平衡、融水径流和平衡线高度等资料对模型进行了对比验证,表明模拟结果具有较高的可信度.对冰川物质平衡和融水径流的特征、变化趋势以及其对河流径流的贡献进行的分析表明,塔里木河流域1961～2006年平均冰川物质平衡为?139.2mm·a?1,46a冰川物质一直在加剧亏损,同期升温对冰川的影响超过降水增加的影响.塔里木河冰川融水径流的年际变化主要受控于流域内冰川的物质平衡波动,46a冰川融水径流的持续增加主要是由温度升高引起的.1961～2006年整个塔里木河流域年平均冰川融水径流量为144.16×108m3,冰川融水对河流径流的平均补给率为41.5%,并且与多年平均值相比冰川融水对河流径流的贡献在1990年之后明显增大.塔里木河流域出山径流年际变化与冰川融水径流年际变化过程基本一致,总体上呈上升趋势,并且河流径流量的增加约3/4以上源于冰川退缩的贡献.     

High-harmonic geoid signatures related to glacial isostatic adjustment and their detectability by GOCE

The Earth’s asthenosphere and lower continental crust can regionally have viscosities that are one to several orders of magnitude smaller than typical mantle viscosities. As a consequence, such shallow low-viscosity layers could induce high-harmonic (spherical harmonics 50–200) gravity and geoid anomalies due to remaining isostasy deviations following Late-Pleistocene glacial isostatic adjustment (GIA). Such high-harmonic geoid and gravity signatures would depend also on the detailed ice and meltwater loading distribution and history.ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission, planned for launch in Summer 2008, is designed to map the quasi-static geoid with centimeter accuracy and gravity anomalies with milligal accuracy at a resolution of 100 km or better. This might offer the possibility of detecting gravity and geoid effects of low-viscosity shallow earth layers and differences of the effects of various Pleistocene ice decay scenarios. For example, our predictions show that for a typical low-viscosity crustal zone GOCE should be able to discern differences between ice-load histories down to length scales of about 150 km.One of the major challenges in interpreting such high-harmonic, regional-scale, geoid signatures in GOCE solutions will be to discriminate GIA-signatures from various other solid-earth contributions. It might be of help here that the high-harmonic geoid and gravity signatures form quite characteristic 2D patterns, depending on both ice load and low-viscosity zone model parameters.     

Glacial isostatic adjustment at the Laurentide ice sheet margin: Models and observations in the Great Lakes region

Glacial Isostatic Adjustment (GIA) modelling in North America relies on relative sea level information which is primarily obtained from areas far away from the uplift region. The lack of accurate geodetic observations in the Great Lakes region, which is located in the transition zone between uplift and subsidence due to the deglaciation of the Laurentide ice sheet, has prevented more detailed studies of this former margin of the ice sheet. Recently, observations of vertical crustal motion from improved GPS network solutions and combined tide gauge and satellite altimetry solutions have become available. This study compares these vertical motion observations with predictions obtained from 70 different GIA models. The ice sheet margin is distinct from the centre and far field of the uplift because the sensitivity of the GIA process towards Earth parameters such as mantle viscosity is very different. Specifically, the margin area is most sensitive to the uppermost mantle viscosity and allows for better constraints of this parameter. The 70 GIA models compared herein have different ice loading histories (ICE-3/4/5G) and Earth parameters including lateral heterogeneities. The root-mean-square differences between the 6 best models and the two sets of observations (tide gauge/altimetry and GPS) are 0.66 and 1.57 mm/yr, respectively. Both sets of independent observations are highly correlated and show a very similar fit to the models, which indicates their consistent quality. Therefore, both data sets can be considered as a means for constraining and assessing the quality of GIA models in the Great Lakes region and the former margin of the Laurentide ice sheet.     

基于GRACE/GRACE-FO和Swarm卫星研究2002—2020年南极和格陵兰岛冰盖质量时空变化

两极冰盖消融及其质量变化作为全球气候变化的重要指标之一,一直是联合国政府间专门气候委员会IPCC(Intergovernmental Panel on Climate Change)报告的重点关注内容.GRACE(Gravity Recovery and Climate Experiment,2002年4月—2017年6月)和GRACE-FO(GRACE Follow-on,2018年5月至今)重力卫星,作为监测两极冰盖质量变化最直接和有效的手段,存在近一年的观测间断期.因此本文提出联合Swarm三颗低轨卫星观测资料(2015年1月—2019年6月)和ARIMA-MC(Autoregressive Integrated Moving Average Model-Monte Carlo)预测方法来填补两组重力卫星间断期两极冰盖消融质量变化观测的时间序列,从而基于完整时间序列来研究两极冰盖质量时空变化规律.研究结果表明：(1)利用Swarm卫星反演得到的时变重力场信号和ARIMA-MC预测方法可以有效填补间断期两极冰盖消融质量变化的时间序列,但两种方法得到的结果也存在一定的差异;(2)在2002年4月—2020年3月期间,GRACE/GRACE-FO探测到南极和格陵兰岛冰盖质量变化速率分别为-119±23 Gt·a^-1和-259±20 Gt·a^-1,等效于全球平均海平面每年约上升0.33 mm和0.72 mm;(3)南极威尔克斯地区在2010—2020年期间的冰盖融化速率较2002—2009年期间增加了10倍,Swarm结果也证实了该地区近年来的加速消融;(4)2019年夏季格陵兰岛冰盖明显的加速消融与夏季北大西洋涛动有关.

     

Mass balance of the Lambert Glacier basin, East Antarctica

Since it is the largest glacier system in Antarctica, the Lambert Glacier basin plays an important role in the mass balance of the overall Antarctic ice sheet. The observed data and shallow core studies from the inland traverse investigations in recent years show that there are noticeable differences in the distribution and variability of the snow accumulation rate between east and west sides. On the east side, the accumulation is higher on the average and has increased in the past decades, while on the west side it is contrary. The ice movement measurement and the ice flux calculation indicate that the ice velocity and the flux are larger in east than in west, meaning that the major part of mass supply for the glacier is from the east side. The mass budget estimate with the latest data gives that the integrated accumulation over the upstream area of the investigation traverse route is larger than the outflow ice flux by 13%, suggesting that the glacier basin is in a positive mass balance state and the ice thickness will increase if the present climate is keeping.     

Glacial isostatic adjustment in 3-D earth models: Implications for the analysis of tide gauge records along the U.S. east coast

Tide gauge records of recent sea-level change along the U.S. east coast have received significant attention within the literature of glacial isostatic adjustment (GIA). Geographic trends in these tide gauge rates are not reduced by a GIA correction based on a commonly adopted radial viscosity profile (characterized, in particular, by a lower mantle viscosity 1−2×10²¹ Pa s), and this has led to speculation that the residual trends reflect contributions from neotectonics or oceanographic processes. While the trends can be significantly reduced by adopting an Earth model with a stiffer lower mantle, such a model appears to be incompatible with independent constraints from post-glacial decay times in Hudson Bay. We use a finite-element model of the GIA process to investigate whether 3-D viscosity variations superimposed onto the “common” radial viscosity profile may provide a route to reconciling the east coast sea-level trends. We find that the specific 3-D structure we impose has little impact on the geographic trends in the GIA-corrected rates. However, we do find that the imposed lateral variations in lower mantle viscosity introduce a nearly uniform upward shift of 0.5 mm/yr in GIA-induced sea-level rates along the U.S. east coast. Thus, inferences of regional (U.S. east coast) sea-level rise due to modern melting of ice reservoirs, based on tide gauge rates corrected using 1-D GIA models, may be significantly biased by this simplifying assumption.     

Axial and equatorial rotations of the Earth's cores associated with the Quaternary ice age

The differential axial and equatorial rotations of both cores associated with the Quaternary glacial cycles were evaluated based on a realistic earth model in density and elastic structures. The rheological model is composed of compressible Maxwell viscoelastic mantle, inviscid outer core and incompressible Maxwell viscoelastic inner core. The present study is, however, preliminary because I assume a rigid rotation for the fluid outer core. In models with no frictional torques at the boundaries of the outer core, the maximum magnitude of the predicted axial rotations of the outer and inner cores amounts to ∼2° year⁻¹ and ∼1° year⁻¹, respectively, but that for the secular equatorial rotations of both cores is ∼0.0001° at most. However, oscillating parts with a period of ∼225 years are predicted in the equatorial rotations for both cores. Then, I evaluated the differential rotations by adopting a time-dependent electromagnetic (EM) torque as a possible coupling mechanism at the core-mantle boundary (CMB) and inner core boundary (ICB). In a realistic radial magnetic field at the CMB estimated from surface magnetic field, the axial and equatorial rotations couple through frictional torques at the CMB, although these rotations decouple for dipole magnetic field model. The differential rotations were evaluated for conductivity models with a conductance of 10⁸ S of the lowermost mantle inferred from studies of nutation and precession of the Earth and decadal variations of length of day (LOD). The secular parts of equatorial rotations are less sensitive to these parameters, but the magnitude for the axial rotations is much smaller than for frictionless model. These models, however, produce oscillating parts in the equatorial rotations of both cores and also in the axial rotations of the whole Earth and outer and inner cores. These oscillations are sensitive to both the magnitude of radial magnetic field at the CMB and the conductivity structure. No sharp isolated spectral peaks are predicted for models with a thin conductive layer (∼200 m) at the bottom of the mantle. In models with a conductive layer of ∼100 km thickness, however, sharp spectral peaks are predicted at periods of ∼225 and ∼25 years for equatorial and axial rotations, respectively, although these depend on the strength of radial magnetic field at the CMB. While the present study is preliminary in modelling the fluid outer core and coupling mechanism at the CMB, the predicted axial rotations of the whole Earth may be important in explaining the observed LOD through interaction between the equatorial and axial rotations.     

Estimation of mass and energy balance of glaciers using a distributed energy balance model over the Chandra river basin (Western Himalaya)

The ongoing glacier shrinking in the Himalayan region causes a significant threat to freshwater sustainability and associated future runoff. However, data on the spatial climatic contribution of glacier retreat is scanty in this region. To investigate the spatially distributed glacier surface energy and mass fluxes, a two-dimensional mass balance model was developed and applied to the selected glaciers of the Chandra basin, in the Upper Indus Basin, Western Himalaya. This model is driven by the remote sensing data and meteorological variables measured in the vicinity of the Chandra basin for six hydrological years (October 2013 to September 2019). The modelled variables were calibrated/validated with the in-situ observation from the Himansh station in the Chandra basin. We have derived air temperature (T_a ) spatially using the multivariate statistical approach, which indicates a relative error of 0.02–0.05°C with the observed data. Additionally, the relative error between the modelled and observed radiation fluxes was <10.0 W m⁻². Our study revealed that the Chandra basin glaciers have been losing its mass with a mean annual mass balance of −0.59 ± 0.12 m w.e. a⁻¹ for the six hydrological years. Results illustrated that the mean surface melt rate of the selected glaciers ranged from −5.1 to −2.5 m w.e. a⁻¹ that lies between 4500 and 5000 m a.s.l. The study revealed that the net radiation (R_N) contributes ~75% in total energy (F_M ) during the melt season while sensible heat (H_S) , latent heat (H_l) , and ground heat (H_G) fluxes shared 15%, 8%, and 2%, respectively. Sensitivity analysis of the energy balance components suggested that the mass balance is highly sensitive to albedo and surface radiations in the study area. Overall, the proposed model performed well for glacier-wide energy and mass balance estimation and confirms the utility of remote sensing data, which may help in reducing data scarcity in the upper reaches of the Himalayan region.     

末次冰期冰盖消融对东亚历史相对海平面的影响及意义

基于新的末次冰期冰川均衡调整(GIA)模型,利用有限元算法模拟了盛冰期以来东亚相对海平面的变化,并与观测数据进行比较分析.研究表明,早期相对海平面上升由盛冰期后全球冰盖消融控制,后期的变化则由地壳黏性均衡调整控制;每个时期的结果均具有显著的区域性差异,与地壳均衡作用及远场均衡效应的区域性差异有关;模拟的不确定性主要来自冰盖消融模型差异的影响,量级在观测误差范围内.此外,利用本文的GIA模拟结果,对东亚海岸历史相对海平面观测进行改正,揭示了华南全新世以来不同阶段的地壳垂直运动,其中3—8 kaBP地壳以较稳定的速率(1~4 mm/a)下沉,之后则以较小速率下降或隆升,推测可能与东南部菲律宾板块的俯冲有关;揭示近千年来粤东海岸和珠江三角洲地壳垂直运动有长期隆升趋势,而近三十年的观测结果则显示下沉,推测该差异与人类活动导致的沉降有关.