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1.
Elaboration of a modern Earth system model (ESM) requires incorporation of ice sheet dynamics. Coupling of an ice sheet model (ICM) to an AOGCM is complicated by essential differences in spatial and temporal scales of cryospheric, atmospheric and oceanic components. To overcome this difficulty, we apply two different approaches for the incorporation of ice sheets into an ESM. Coupling of the Antarctic ice sheet model (AISM) to the AOGCM is accomplished via using procedures of resampling, interpolation and assigning to the AISM grid points annually averaged meanings of air surface temperature and precipitation fields generated by the AOGCM. Surface melting, which takes place mainly on the margins of the Antarctic peninsula and on ice shelves fringing the continent, is currently ignored. AISM returns anomalies of surface topography back to the AOGCM. To couple the Greenland ice sheet model (GrISM) to the AOGCM, we use a simple buffer energy- and water-balance model (EWBM-G) to account for orographically-driven precipitation and other sub-grid AOGCM-generated quantities. The output of the EWBM-G consists of surface mass balance and air surface temperature to force the GrISM, and freshwater run-off to force thermohaline circulation in the oceanic block of the AOGCM. Because of a rather complex coupling procedure of GrIS compared to AIS, the paper mostly focuses on Greenland.  相似文献   

2.
Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet.  相似文献   

3.
研究格陵兰冰盖（GrIS）质量变化异常速率可以帮助了解异常气候事件驱动海平面变化的机制.聚焦于2010~2012年GrIS质量变化的异常速率,及其对海平面指纹（SLF）和相对海平面（RSL）变化的贡献.通过联合2003~2015年GRACE月重力场数据和表面质量平衡（SMB）数据,采用mascon拟合法及网格尺度因子恢复泄漏,获得了6个流域的质量变化时空分布.基于海平面变化方程（SLE）并考虑负荷自吸引效应估算了SLF的空间分布.结果表明,2003~2015年间GrIS总质量变化速率分别为-288±7 Gt/a及-275±1 Gt/a;而在2010~2012年间速率相应地增加至-456±30 Gt/a及-464±38 Gt/a,该时期格陵兰西北海岸及东南沿海地区呈现出大量冰盖融化,其对海平面的贡献变化呈现倒“V”型（即先升后降）,而全球平均海平面变化呈现出明显的正“V”型（即先降后升）.另外,GrIS融化对海平面的贡献约为31%,造成全球平均RSL增加了0.07 cm/a,而对斯堪的纳维亚及北欧地区的RSL贡献为-0.6 cm/a,GrIS融化造成的远海地区RSL上升速率比全球平均RSL速率高近30%.   相似文献   

4.
The marine record shows that over the last 350 ka Northern Hemisphere ice sheet volumes have fluctuated widely and only on rare short occasions have they been reduced to the present interglacial state. The fluctuations are well synchronized with hemispheric average summer insolation variations of 20 ka periodicity caused by changing orbital parameters. The development of a model which explains the varied amplitudes of the fluctuations and is consistent with the geological record embodies the following arguments: The transition from an interglacial state like today's to a glacial state is initiated when a summer insolation deficit causes a southerly extension of the North Atlantic-Arctic pack ice to 60°N latitude. The extension alters the subpolar low pressure patterns and thus causes a southward diversion of the European Gulf Stream flow. It also produces an enhanced warm West Greenland current. This current causes open seas as far north as Baffin Bay which provides moisture for rapid northern Laurentide ice sheet growth. After several glacial fluctuations driven by insolation variations, the southern Laurentide ice front may reach an extreme extension. This diverts the westerlies and the Gulf Stream thus weakening a dominant subpolar North Atlantic gyre and consequently producing a prolonged cutoff of the West Greenland current and a reduction of high latitude glacial precipitation. The subsequent high insolation can then melt back the eastern pack ice and restore the northern European Gulf Stream. This warms the high latitudes for a time sufficient to melt the continental ice, thus causing the transition back to the interglacial state.An analysis of the record in the context of model suggests that the threshold deficit in average summer insolation that is required to initiate major glacial growth is influenced by the cooling effect of the Greenland ice cap on the seas to the east. The threshold level under conditions like today's is found to lie between ?7 and ?17 ly/day relative to the present. This threshold will not be crossed for at least 54 millenia due to an interval of smaller orbital eccentricity. Probable melting of the Greenland ice cap about 30 ka AP would ensure the extension of the present interglacial beyond 120 ka AP.  相似文献   

5.
The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 ka), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 ka in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice-free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and regional climate data and climate reconstructions.  相似文献   

6.
冰架是南极冰盖物质损失的主要出口。南极冰架动态变化和物质平衡的研究对揭示南极地区的气候变化具有重要的参考价值。本文从表面融化、冰流速、前缘崩解、底部融化和物质平衡五个方面入手,对近些年来南极冰架变化监测的研究进展进行梳理和归纳总结,综述了它们的观测方法、观测结果、机制分析及当前面临的问题。极地观测卫星和现场观测网络的发展、冰架多维度综合分析及数值模拟研究的推进,将有助于进一步揭示冰架变化因子之间的耦合作用及其演变机制,为全球增温影响南极冰盖/冰架的物理机制研究及其变化预测提供重要依据。  相似文献   

7.
格陵兰冰盖表面消融研究进展   总被引：3，自引：1，他引：2  
杨康 《冰川冻土》2013,35(1):101-109
冰盖表面消融是格陵兰冰盖物质平衡的重要组成部分, 已成为近年来格陵兰冰盖研究的热点. 格陵兰冰盖表面消融研究的关键在于理解冰盖融水的产生、 运移和释放等水文过程, 需要解决如下关键科学问题: 1) 冰盖表面产生了多少融水;2)冰盖表面水文系统具有什么特征; 3)冰盖表面融水如何影响冰盖运动; 围绕这些科学问题, 总结了格陵兰冰盖表面消融的研究进展. 冰盖表面消融建模、 冰盖表面湖的信息提取与面积特征变化、 深度反演与体积量算等是目前研究冰盖表面融水量的主要途径, 冰盖表面湖、 冰盖表面径流、 锅穴与冰裂隙等表面水文要素的空间分布规律研究则可用于揭示冰盖表面水文系统特征, 冰盖表面融水与冰盖运动速率的关系、 表面融水进入冰盖内部与底部的水文过程是目前揭示表面融水如何影响冰盖运动的主要手段.  相似文献   

8.
We suggested a relatively simple model describing changes in the total balance of the ice sheet mass due to global climate change. Taking into account the basic mechanisms behind change in the ice sheet mass and their relations with temperature, we obtained a nonlinear analytical dependence of the ice sheet thickness on the global near-surface temperature. The behavior of the ice sheet can be split into six regimes. Implementation of some regime or another depends essentially on the initial (present-day) value of the mass balance and the sensitivity parameters of precipitation and ice melt to the temperature. Based on this model, we obtained an analytical estimate of the critical level in global warming, in excess of which the regime of the Antarctic ice sheet gain due to snow accumulation changes to sheet degradation due to more intense growth in ice melting.  相似文献   

9.
We constrain a three-dimensional thermomechanical model of Greenland ice sheet (GrIS) evolution from the Last Glacial Maximum (LGM, 21 ka BP) to the present-day using, primarily, observations of relative sea level (RSL) as well as field data on past ice extent. Our new model (Huy2) fits a majority of the observations and is characterised by a number of key features: (i) the ice sheet had an excess volume (relative to present) of 4.1 m ice-equivalent sea level at the LGM, which increased to reach a maximum value of 4.6 m at 16.5 ka BP; (ii) retreat from the continental shelf was not continuous around the entire margin, as there was a Younger Dryas readvance in some areas. The final episode of marine retreat was rapid and relatively late (c. 12 ka BP), leaving the ice sheet land based by 10 ka BP; (iii) in response to the Holocene Thermal Maximum (HTM) the ice margin retreated behind its present-day position by up to 80 km in the southwest, 20 km in the south and 80 km in a small area of the northeast. As a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka BP, which corresponds to a deficit volume (relative to present) of 0.17 m ice-equivalent sea level. Our results suggest that remaining discrepancies between the model and the observations are likely associated with non-Greenland ice load, differences between modelled and observed present-day ice elevation around the margin, lateral variations in Earth structure and/or the pattern of ice margin retreat.  相似文献   

10.
《Quaternary Science Reviews》2005,24(1-2):155-171
Polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models. The stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent. We describe a coupled model of ice and tracer dynamics that is realized by adding a semi-Lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model. Model skill is demonstrated by using ice core data from the GRIP site near Summit Greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites. The success of this effort indicates that, when compensated for the effects of ice flow and elevation, all the deep cores relate a coherent glacial history over the past 120,000 years. According to the simulation results, the oldest Greenland ice lies beneath the GRIP, GISP2 and NorthGRIP sites although comparably old ice may also be found in North Greenland and East Central Greenland.  相似文献   

11.
冰盖数值模拟是一种基于多源观测数据,通过构建并求解冰流动力学方程组,理解冰流运动物理机制以及诊断和预估其演化过程的方法,目前已被广泛应用于冰盖变化研究。本文简要介绍了极地冰盖数值模拟方法,归纳综述了近十余年我国学者在极地冰盖数值模拟方面的研究进展,厘清我国在冰盖数值模拟领域遇到的瓶颈和关键问题。阐述了如何与我国的极地冰盖科考优势区域深度结合,协同多源强化观测和数值模拟,研发和改进冰盖模式,提高冰盖模拟能力,对定量估算极地冰盖的物质平衡及其对未来海平面上升的影响做出实质贡献。通过逐步发展冰盖模式的研究能力,有望将来在冰盖关键动力过程和机制的科学认识上有所突破。  相似文献   

12.
The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The ‘zero order’ (Shallow Ice Approximation, SIA)-, ‘higher order’-, and ‘full Stokes’ ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheet-ice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model.  相似文献   

13.
The basal ice of many glaciers contains debris structures that reflect subglacial processes. Presented here is an unusually clear photograph of ice and debris in the lowest 2 m of the basal layer at the margin of the Greenland ice sheet. The photograph shows ice-debris relationships and deformation structures that reflect entrainment processes and flow history.  相似文献   

14.
The influence of glacier hydrology on the time-dependent morphology and flow behaviour of the late Weichselian Scandinavian ice sheet is explored using a simple one-dimensional ice sheet model. The model is driven by orbitally induced radiation variations, ice-albedo feedback and eustatic sea-level change. The influence of hydrology is most marked during deglaciation and on the southern side of the ice sheet, where a marginal zone of rapid sliding, thin ice and low surface slopes develops. Such a zone is absent when hydrology is omitted from the model, and its formation results in earlier and more rapid deglaciation than occurs in the no-hydrology model. The final advance to the glacial maximum position results from an increase in the rate of basal sliding as climate warms after 23000 yr BP. Channelised subglacial drainage develops only episodically, and is associated with relatively low meltwater discharges and high hydraulic gradients. The predominance of iceberg calving as an ablation mechanism on the northern side of the ice sheet restricts the occurrence of surface melting. Lack of meltwater penetration to the glacier bed in this area means that ice flow is predominantly by internal deformation and the ice sheet adopts a classical parabolic surface profile.  相似文献   

15.
In this study, we present new information on the glacial history of the Greenland Ice Sheet (GrIS) and a local ice cap in Qaanaaq, northwest Greenland. We use geomorphological mapping, 10Be exposure dating of boulders, analysis of lake cores, and 14C dating of reworked marine molluscs and subfossil plants to constrain the glacial history. Our 14C ages of reworked marine molluscs reveal that the ice extent in the area was at or behind its present‐day position from 42.2 ± 0.4 to 30.6 ± 0.3k cal a BP after which the GrIS expanded to its maximum position during the Last Glacial Maximum. We find evidence of early ice retreat in the deep fjord (Inglefield Bredning) at 11.9 ± 0.6 ka whereas the Taserssuit Valley was deglaciated ~4 ka later at 7.8 ± 0.1k cal a BP. A proglacial lake record suggests that the local ice cap survived the Holocene Thermal Maximum but moss kill‐dates reveal that it was smaller than present for a period of time before 3.3 ± 0.1k until 0.9 ± 0.1k cal a BP, following which the ice in the area expanded towards its Little Ice Age extent. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

16.
An estimate of the sliding velocity and basal meltwater discharge of the Puget lobe of the Cordilleran ice sheet can be calculated from its reconstructed extent, altitude, and mass balance. Lobe dimensions and surface altitudes are inferred from ice limits and flow-direction indicators. Net annual mass balance and total ablation are calculated from relations empirically derived from modern maritime glaciers. An equilibrium-line altitude between 1200 and 1250 m is calculated for the maximum glacial advance (ca. 15,000 yr B.P.) during the Vashon Stade of the Fraser Glaciation. This estimate is in accord with geologic data and is insensitive to plausible variability in the parameters used in the reconstruction. Resultant sliding velocities are as much as 650 m/a at the equilibrium line, decreasing both up- and downglacier. Such velocities for an ice sheet of this size are consistent with nonsurging behavior. Average meltwater discharge increases monotonically downglacier to 3000 m3/sec at the terminus and is of a comparable magnitude to ice discharge over much of the glacier's ablation area. Palcoclimatic inferences derived from this reconstruction are consistent with previous, independently derived studies of late Pleistocene temperature and precipitation in the Pacific Northwest.  相似文献   

17.
The deglaciation at the end of the Weichselian in the Danish area has previously been considered to occur as a frontal wastage. Since the glacier ice was assumed to be debris-free, the wasting should be characterized by outwash plains and successions of end-moraines. The almost complete lack of sandur plains in the eastern part of the area and indications from recent investigations of widespread occurrence of flow till justify a re-evaluation of the mentioned deglaciation model.
Two morphological features have a general occurrence: the plains and the 'tunnel' valleys. The plains appear stepwise in the landscapes, and are frequently limited by steep slopes. Topmost is a subcircular kame-like hill. Sedimentologically, the plains mainly consist of melt water deposits, and the scattered occurrences of till are interpreted as flow till. The plains continue from the open landscape into the 'tunnel' valleys where they appear as terraces.
These features are considered to have been formed during the deglaciation. The almost horizontal surface of the ice sheet over large areas caused a sensitivity to changes in the climate. The wasting of the ice may therefore be expected to affect large areas almost simultaneously. On the assumption that the ice contained debris, an increasing amount of clastic matter was released on the ice surface. This material was concentrated in the depressions. If such a depression perforated the ice, the content of sediments settled on the substratum and a plain was established. During continued wasting the thickness of the ice decreased and the depressions were enlarged. They assumed the character of sandur plains. As still larger areas of these supraglacial sandurs rested on the basement the successive lower situated plains were formed. The latest ice was preserved where the 'tunnel' valleys are situated to-day.  相似文献   

18.
The position of the Inland Ice margin during the late Wisconsin-Würm glaciation (ca. 15,000 yr BP) is probably marked by offshore banks (submarine moraines?) in the Davis Strait. The history of the Inland Ice since the late Wisconsin-Würm can be divided into four principal phases: (1) Relatively slow retreat from the offshore banks occurred at an average rate of approximately 1 km/100 yr until ca. 10,000 yr BP (Younger Dryas?) when the Taserqat moraine system was formed by a readvance. (2) At ca. 9500 yr BP, the rate of retreat increased markedly to about 3 km/100 yr, and although nearly 100 km of retreat occurred by ca. 6500 yr BP, it was punctuated by frequent regional reexpansions of the Inland Ice that formed extensive moraine systems at ca. 8800-8700 yr BP (Avatdleq-Sarfartôq moraines), 8400-8100 yr BP (Angujârtorfik-Fjord moraines), 7300 yr BP (Umîvît moraines), and 7200-6500 yr BP (Keglen-Mt, Keglen moraines). (3) Between 6500 and 700 yr BP, discontinous ice-margin deposits and ice-disintegration features were formed during retreat, which may have continued until the ice margin was near or behind its present position by ca. 6000 yr BP. Most of the discontinuous ice-margin deposits occur within 5–10 km of the present ice margin, and may have been formed by two main phases of readvance at ca. 4800-4000 yr BP and 2500-2000 yr BP. (4) Since a readvance at ca. 700 yr BP, the Inland Ice margin has undergone several minor retreats and readvances resulting in deposition of numerous closely spaced moraines within about 3 km of the present ice margin. The young moraines are diffieulto to correlate regionally, but several individual moraines have the following approximate ages: A.D. 1650, 1750, and 1880–1920.Inland Ice fluctuations in West Greenland were very closely paralleled by Holocene glacial events in East Greenland and the eastern Canadian Aretic. Such similarity of glacier behavior over a large area strongly suggests that widespread climatic change was the direct cause of Holocene glacial fluctuations. Moreover, historical advances of the Inland Ice margin followed slight temperature decreases by no more than a few decades, and 18O data from Greenland ice cores show that slight temperature decreases occurred frequently throughout the Holocene. Therefore, we conclude that construction of the major Holocene moraine systems in West Greenland was caused by slight temperature decreases, which decreased rates of ablation and thereby produced practically immediate advances of the ice sheet margin, but did not necessarily affect the long-term equilibrium of the ice sheet.  相似文献   

19.
《Quaternary Science Reviews》2005,24(1-2):173-194
The climate history and dynamics of the Greenland Ice Sheet are studied using a coupled model of the depositional provenance and transport of glacier ice, allowing simultaneous prediction of the detailed isotopic stratigraphy of ice cores at all the major Greenland sites. Adopting a novel method for reconstructing the age–depth relationship, we greatly improve the accuracy of semi-Lagrangian tracer tracking schemes and can readily incorporate an age-dependent ice rheology. The larger aim of our study is to impose new constraints on the glacial history of the Greenland Ice Sheet. Leading sources of uncertainty in the climate and dynamic history are encapsulated in a small number of parameters: the temperature and elevation isotopic sensitivities, the glacial–interglacial precipitation contrast and the effective viscosity of ice in the flow law. Comparing predicted and observed ice layering at ice core sites, we establish plausible ranges for the key model parameters, identify climate and dynamic histories that are mutually consistent and recover the past depositional elevation of ice cores to ease interpretation of their climatic records. With the coupled three-dimensional model of ice dynamics and provenance transport we propose a method to place all the ice core records on a common time scale and use discrepancies to adjust the reconstructed climate history. Analysis of simulated GRIP ice layering and borehole temperature profiles confirms that the GRIP record is sensitive to the dynamic as well as to the climatic history, but not enough to strongly limit speculation on the state of the Greenland Ice Sheet during the Eemian. In contrast, our study indicates that the Dye 3 and Camp Century ice cores are extremely sensitive to ice dynamics and greatly constrain Eemian ice sheet reconstructions. We suggest that the maximum Eemian sea-level contribution of the ice sheet was in the range of 3.5–4.5 m.  相似文献   

20.
Alun Hubbard 《Geology Today》2011,27(6):212-215
In September 2011 two Greenland stories hit the press, by far the bigger of which was the widespread misreporting (and consequent backlash) that Greenland had apparently lost 15 per cent of its ice cover since 1999. The public are used to an annual press bombardment of record temperatures, ever increasing melt and ice retreat in polar regions but a 15 per cent loss in 12 years does seem fanciful.  相似文献   

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