青藏高原北部多温型山谷冰川不同海拔处冰温变化研究 ——以祁连山老虎沟12号冰川为例

冰川温度是表征冰川物理属性和响应气候变化的关键指标。2010年7月至2011年11月在祁连山老虎沟12号冰川积累区（5 040 m）、多年平衡线处（4 900 m）和消融区（4 550 m）开展了活动层（22 m深,1 m间隔）冰温连续观测。2011年10月在冰川积累区4 971 m处钻得165 m深孔获取了115 m深层冰温廓线。研究发现：三个区域活动层下界的深度均在约17 m处,多年平衡线处冰温最低（-7.4℃）,消融区次之（-3.68℃）,积累区活动层下界冰温最高（-2.74℃）且波动最为持续,可能主要与常年积雪覆盖有关。冰温年波动随深度增加均逐渐降低,对气温变化的响应周期亦逐渐增大。与其他冰川最低温相比,老虎沟12号冰川冰温对气候变化响应敏感,过去50年来受全球变暖影响冰温显著增加。积累区深孔冰温显示50 m深度之下冰温呈线性上升,垂直增温率为0.033℃·m^-1,据此推测其底部冰温为0.02℃,主要与底部应变热有关。     

Seasonal changes in ground‐penetrating radar signature observed at a polythermal glacier,Bylot Island,Canada

In recent years, ground‐penetrating radar (GPR) has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers. The geophysical method is able to exploit the dielectric difference between water, air, sediment and ice, allowing delineation of subsurface hydrological, thermal and structural conditions. More recent GPR research has endeavoured to examine temporal change in glaciers, in particular the distribution of the cold ice zone at polythermal glaciers. However, the exact nature of temporal change that can be identified using GPR has not been fully examined. This research presents the results of three GPR surveys conducted over the course of a summer ablation season at a polythermal glacier in the Canadian Arctic. A total of approximately 30 km of GPR profiles were collected in 2002 repeatedly covering the lower 2 km of Stagnation Glacier, Bylot Island (72°58′ N 78°22′ W). Comparison between profiles indicated changes in the radar signature, including increased noise, appearance and disappearance of englacial reflections, and signal attenuation in the latter survey. Further, an area of chaotic returns in up‐glacier locations, which was interpreted to be a wet temperate ice zone, showed marked recession over the course of the ablation season. Combining all the temporal changes that were detected by GPR, results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body, including the drainage of 17 000 m³ of temporarily stored intra‐glacial meltwater. It is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydrochemistry of meltwaters draining a polythermal‐based,high‐Arctic glacier,south Svalbard: II. Winter and early Spring

The hydrochemistry of naled and upwelling water sampled from the forefields of Finsterwalderbreen, Svalbard, during spring are used for the first time to infer the hydrology of overwinter meltwaters at a polythermal‐based glacier. Hydrochemical variations in naled are explained in terms of different water sources and their chemical alteration during freezing. Two water sources to naled are identified: surficially routed snowmelt and subglacial water. Naled that results from the freezing of the former is enriched in atmospherically derived ions such as Na⁺ and Cl⁻, and is believed to be formed during winter warm periods. Naled of subglacial origin contains relatively high proportions of crustally derived solute. It reflects the freezing of subglacial meltwaters that continue to issue from a subterranean upwellling during winter. An increasing dominance of SO²⁻₄ Mg²⁺, Na⁺ and Cl⁻ in subglacial naled with increasing distance from the upwelling reflects the progressive freezing of this water body and the associated removal of Ca²⁺ and HCO by calcite precipitation. These spatial trends are accentuated by the leaching of soluble ions from the naled close to its source by subsequent upwelling waters. The chemistry of spring upwelling waters, also of subglacial origin, strongly reflects this process. Meltwater produced by geothermal heating of glacier basal ice is believed to be the principal source of water to the subglacial drainage system during winter. Solute acquisition by this meltwater is limited by a scarcity of proton suppliers. Evolution of this dilute meltwater carries an imprint of ion exchange processes. Some stored subglacial water from the end of the previous ablation season may supplement the basal meltwater component in early winter. Copyright © 2000 John Wiley & Sons, Ltd.     

Hydrology and dynamics of a polythermal (mostly cold) High Arctic glacier

To improve our understanding of the interactions between hydrology and dynamics in mostly cold glaciers (in which water flow is limited by thermal regime), we analyse short‐term (every two days) variations in glacier flow in the ablation zone of polythermal John Evans Glacier, High Arctic Canada. We monitor the spatial and temporal propagation of high‐velocity events, and examine their impacts upon supraglacial drainage processes and evolving subglacial drainage system structure. Each year, in response to the rapid establishment of supraglacial–subglacial drainage connections in the mid‐ablation zone, a ‘spring event’ of high horizontal surface velocities and high residual vertical motion propagates downglacier over two to four days from the mid‐ablation zone to the terminus. Subsequently, horizontal velocities fall relative to the spring event but remain higher than over winter, reflecting channelization of subglacial drainage but continued supraglacial meltwater forcing. Further transient high‐velocity events occur later in each melt season in response to melt‐induced rising supraglacial meltwater inputs to the glacier bed, but the dynamic response of the glacier contrasts with that recorded during the spring event, with the degree of spatial propagation a function of the degree to which the subglacial drainage system has become channelized. Copyright © 2006 John Wiley & Sons, Ltd.     

The hydrochemistry of meltwaters draining a polythermal-based,high Arctic glacier,south Svalbard: I. The ablation season

Solute and runoff time-series at Finsterwalderbreen, Svalbard, provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments. The hydrochemistry of a subglacial upwelling provides evidence for a snowmelt-fed subglacial reservoir that dominates bulk runoff during recession flow. High concentrations of Cl⁻ and crustal ions, high pCO₂ and ratios of [*SO²⁻₄/(*SO²⁻₄+HCO⁻₃)] close to 0·5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock:water ratios, prolonged residence times and restricted access to the atmosphere. At higher discharges, bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock:water ratios, short residence times and free contact with atmospheric gases. These observations suggest that icemelt is routed via a hydrological system composed of basal/ice-marginal, englacial and supraglacial components and is directed to the glacier margins by the ice surface slope. Upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system, possibly constituting flow through a sediment layer. Cold basal ice at the terminus forces it to take a subterranean routing in its latter stages. The existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal-based glaciers on Svalbard. Proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm-based glaciers. These hydrochemical characteristics of bulk runoff have not been documented on any other glacier on Svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology. © 1998 John Wiley & Sons, Ltd.     

Suspended sediment yield and transfer processes in a small High-Arctic glacier basin,Svalbard

Observations of suspended sediment concentration and discharge at two sites on the proglacial river network draining from a predominantly cold-based, High-Arctic glacier (Austre Brøggerbreen) are described. Analysis of these observations illustrates: (i) the relatively low suspended sediment yield from this basin in comparison with many other glacier basins reported in the open literature; (ii) sustained and possibly increasing availability of suspended sediment to the fluvial system as the ablation season progresses; and (iii) the role of the proglacial sandur as both a sediment source and sink. Field observations coupled with the results of the data analysis are used to make inferences concerning the changing nature and relative importance of sediment sources within the basin. © 1998 John Wiley & Sons, Ltd.     

Recurring Jökulhlaups in Sälka, Northern Sweden

An ice‐dammed lake at the margin of the glacier Sälkaglaciären, in the Kebnekaise Mountains in northern Sweden, drained suddenly in July 2003 producing a flood with a measured peak discharge of 9.5±0.25 m³s^‐1. The total lake volume of 4.55×10⁵ million³ drained within two days. The hydrograph of this event is characteristic of a jökulhlaup controlled by a single basal ice tunnel that enlarges due to melting. The jökulhlaup had an exponential rise to a peak discharge, and following the peak, a very steep fall in discharge as the water supply to the drainage system ceased. A similar jökulhlaup was observed in August 1990 with an estimated release of 8.05×10⁵ m³ water. Jökulhlaups at Sälkaglaciären are recurring events and have been indirectly observed since the 1950s.