Temporal changes in subglacial meltwater activity: field evidence from the late Devensian in the north of Ireland

Temporal changes in meltwater abundance, distribution and characteristics (controlling subglacial processes and ice sheet dynamics) can be inferred from subglacial sediment successions. Field evidence for changes in subglacial meltwater characteristics over time is presented from two sites (Doonan, Drummee) near a former late Weichselian (Devensian) ice centre in the north of Ireland. On a macroscale, both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms. In more detail, primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice/bed interface (IBI). Sedimentary evidence suggests sediment transport and deposition took place by low-viscosity subglacial slurries (mobile sediment–meltwater admixtures), which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding. Subtle changes in meltwater abundance and distribution at the IBI controlled slurry rheology, mechanisms of particle support and detailed sediment depositional processes.     

Snow and stream-water chemistry of the Ganga headwater basin,Garhwal Himalaya,India

Abstract

Studies of the chemical composition of snowpack and stream water were carried out in a catchment having an area of 53km² (31°03′-30°55′N and 78°40′-78°51′E) in the Garhwal Himalaya, India. The dominant ions in the snowpack and stream water were Ca²⁺, Na⁺, NO^? ₃, SO^2- ₄ and HCO^? ₃. Solute patterns in the snowpack show preferential elution. Investigation of the chemical composition of stream water shows that meltwater changes its composition substantially as it passes through soil pathways to the stream. The groundwater flushing perhaps controls the chemical composition of meltwater in the early spring. However, in the period from July to September, the stream water carries the chemical signature of monsoonal precipitation.     

LINKS BETWEEN PROGLACIAL STREAM SUSPENDED SEDIMENT DYNAMICS,GLACIER HYDROLOGY AND GLACIER MOTION AT MIDTDALSBREEN,NORWAY

Two-hourly suspended sediment concentration variations observed during the summer of 1987 in the proglacial stream draining Midtdalsbreen, Norway are modelled using multiple regression and time series techniques. Suspended sediment fluctuations are influenced by stream discharge variations, diurnal hysteresis effects, medium-term sediment supply and transport variations and the recent suspended sediment concentration history of the stream. They do not appear to be influenced by seasonal exhaustion or rainfall variations. Possible reasons for this are discussed. Large positive residuals from the fitted models are major pulses of suspended sediment unrelated to discharge variations; these sediment flushes correlate with periods of enhanced glacier motion. They cannot be explained by enhanced sediment production by subglacial erosion, but are probably due to the tapping of subglacially stored sediment during sudden changes in the hydraulics and/or configuration of the subglacial hydrological system. Seasonal changes in the lag between glacier motion peaks and suspended sediment flushes suggest that the subglacial hydrological system evolves over the summer from a distributed to a more channelized configuration.     

Routing of canopy drip in the snowpack below a spruce crown

Snow that is retained by a forest canopy may either sublimate or evaporate directly from the crown or drop as snow clumps or meltwater to the ground. Redistributed snow and meltwater affect the snow structure and prevent the formation of mechanically weak layers, which is the prerequisite for avalanche formation in forests. In this paper we describe the results of dye tracer experiments conducted in a subalpine forest near Davos, Switzerland. Before a snowfall event we stained snow‐free branches of a spruce with a dye tracer solution. After snowfall the coloured meltwater dripping from the branches down on to the snowpack stained the percolation pathways of the meltwater in the snowpack. Photographs of the snow profiles indicate that the meltwater seeped almost vertically through the isothermal snowpack to the soil surface not exceeding the projected crown edge. Meltwater of different events moves along different preferential flow channels in the snow suggesting that old channels are not non‐conducting and additional meltwater fronts create new channels. Copyright © 1999 John Wiley & Sons, Ltd.     

Seasonal controls of meltwater runoff chemistry and chemical weathering at Urumqi Glacier No.1 in central Asia

Temporal variation of runoff chemistry and its seasonal controls relating to chemical weathering processes and drainage system evolution were examined at Urumqi Glacier No.1 in Xinjiang, China, over a full melt season. The dominant ions in meltwater runoff are HCO₃^?, Ca²⁺, and SO₄^2?; and Fe, Sr, and Al are dominant elements. Concentrations of major ions and some elements show periodic variations with seasons and negatively correlate with discharge, whereas other elements (e.g., Al, Ni, Cu, Zn, Cd, and Pb) show a random change, providing insights into the hydrological and physicochemical controls. HCO₃^? and Ca²⁺ are primarily derived from calcite, SO₄^2? and Fe mainly come from pyrite, and Sr and Al principally originate from silicate. Hydrochemical fluxes of solutes exhibit strong seasonality but are positively related to discharge, suggesting an increasing release of solutes during higher flow conditions. Solute yields, cation denudation rate, and chemical weathering intensity observed at Urumqi Glacier No.1 are higher than those at most basins worldwide. This suggests that chemical weathering in central Asia may be stronger than at other glacial basins with similar specific discharge. Concentrations of some elements (e.g., Fe, Al, As, Pb, and Zn) are close to or exceed the guidelines for drinking water standards in meltwater‐fed rivers. These rivers may face future challenges of water quality degradation, and relationships between changing flow and water quality conditions should be established soon, given that development of channelized flow is expected to be earlier over a melt season in a warming climate.     

Hydrochemical appraisal of ice‐ and rock‐glacier meltwater in the hyperarid Agua Negra drainage basin,Andes of Argentina

The Agua Negra drainage system (30 12′S, 69 50′ W), in the Argentine Andes holds several ice‐ and rock‐glaciers, which are distributed from 4200 up to 6300 m a.s.l. The geochemical study of meltwaters reveals that ice‐glaciers deliver a HCO₃^?? Ca²⁺ solution and rock‐glaciers a SO₄^2?? HCO₃^?? Ca²⁺ solution. The site is presumably strongly influenced by sublimation and dry deposition. The main processes supplying solutes to meltwater are sulphide oxidation (i.e. abundant hydrothermal manifestations), and hydrolysis and dissolution of carbonates and silicates. Marine aerosols are the main source of NaCl. The fine‐grained products of glacial comminution play a significant role in the control of dissolved minor and trace elements: transition metals (e.g. Mn, Zr, Cu, and Co) appear to be selectively removed from solution, whereas some LIL (large ion lithophile) elements, such as Sr, Cs, and major cations, are more concentrated in the lowermost reach. Daily concentration variation of dissolved rare earth elements (REE) tends to increase with discharge. Through PHREEQC inverse modelling, it is shown that gypsum dissolution (i.e. sulphide oxidation) is the most important geochemical mechanism delivering solutes to the Agua Negra drainage system, particularly in rock‐glaciers. At the lowermost reach, the chemical signature appears to change depending on the relative significance of different meltwater sources: silicate weathering seems to be more important when meltwater has a longer residence time, and calcite and gypsum dissolution is more conspicuous in recently melted waters. A comparison with a non‐glacierized semiarid drainage of comparable size shows that the glacierized basin has a higher specific denudation, but it is mostly accounted for by relatively soluble phases (i.e. gypsum and calcite). Meltwater chemistry in glacierized arid areas appears strongly influenced by sublimation/evaporation, in contrast with its humid counterparts. Copyright © 2007 John Wiley & Sons, Ltd.     

Modified passive capillary samplers for collecting samples of snowmelt infiltration for stable isotope analysis in remote,seasonally inaccessible watersheds 2: field evaluation

Twelve modified passive capillary samplers (M‐PCAPS) were installed in remote locations within a large, alpine watershed located in the southern Rocky Mountains of Colorado to collect samples of infiltration during the snowmelt and summer rainfall seasons. These samples were collected in order to provide better constraints on the isotopic composition of soil‐water endmembers in the watershed. The seasonally integrated stable isotope composition (δ¹⁸O and δ²H) of soil‐meltwater collected with M‐PCAPS installed at shallow soil depths < 10 cm was similar to the seasonally integrated isotopic composition of bulk snow taken at the soil surface. However, meltwater which infiltrated to depths > 20 cm evolved along an isotopic enrichment line similar to the trendline described by the evolution of fresh snow to surface runoff from snowmelt in the watershed. Coincident changes in geochemistry were also observed at depth suggesting that the isotopic and geochemical composition of deep infiltration may be very different from that obtained by surface and/or shallow‐subsurface measurements. The M‐PCAPS design was also used to estimate downward fluxes of meltwater during the snowmelt season. Shallow and deep infiltration averaged 8·4 and 4·7 cm of event water or 54 and 33% of the measured snow water equivalent (SWE), respectively. Finally, dominant shallow‐subsurface runoff processes occurring during snowmelt could be identified using geochemical data obtained with the M‐PCAPS design. One soil regime was dominated by a combination of slow matrix flow in the shallow soil profile and fast preferential flow at depth through a layer of platy, volcanic rocks. The other soil regime lacked the rock layer and was dominated by slow matrix flow. Based on these results, the M‐PCAPS design appears to be a useful, robust methodology to quantify soil‐water fluxes during the snowmelt season and to sample the stable isotopic and geochemical composition of soil‐meltwater endmembers in remote watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

高寒流域同位素径流分割研究进展

径流分割是应用水文学中的一个基本问题,同位素径流分割则是采用同位素进行分割的方法,其应用范围已从产流理论研究拓展至地下水地表水相互作用、生态水文过程等多个领域.评述了高寒流域同位素径流分割方法原理及其应用研究进展,突出其对全球变化的指示意义.详细介绍了雪融水稳定同位素变化特征机理,以及加权平均值(VWA)、即时值(CMW)及径流校正(RunCE)等误差处理方法及其优缺点.最后,阐述了高寒流域同位素径流分割的应用前景,指出同位素径流分割可以与GIS软件等结合拓宽其研究的空间尺度、与水化学及人工试验等方法相结合拓展其研究手段,可以结合高寒流域独特地形研究山区产流机制.