Glacial Discharge Research Articles

Monsoonal control on glacier discharge and hydrograph characteristics, a case study of Dokriani Glacier, Garhwal Himalaya, India

Stream discharge from Dokriani Glacier, Garhwal Himalaya was monitored during the ablation months (May–October) of 1994, 1998, 1999 and 2000. Contributions from the monsoon rainfall, coincided with the peak ablation period, were quantified by using a water balance. Calculated monsoonal component in 1994 and 1998 was 10–11% of the bulk glacier runoff where as in 1999 and 2000 it was 24–26%. The increase in rainfall component in 1999 and 2000 was due to enhancement of rainfall area rather than an increase in rainfall. The increase in rainfall area was result of a lower temperature lapse rate during these two years. This study suggests that the discharge-rainfall correlation is a questionable method to study the rainfall influence in glacier discharge. Analysis of monthly monsoonal component of bulk glacier discharge and rainfall-discharge correlation are presented and ambiguities discussed. This observation is further supported by the detailed analysis of daily hydrograph which suggests that the rainfall over the glacier produces different responses on discharge hydrograph depending on the season of occurrence, intensity, duration and distribution characteristics. Study suggests that the rainfall with intensity >20 mm d −1 influenced the shape of daily discharge hydrograph, which experienced only on 20% of rainfall days of monsoon season. Comparative study of diurnal hydrograph of rainy days and non-rainy days with the mean daily temperature and sunshine hours highlights the flaws in the use of rainfall-discharge correlation as an indicator of rainfall influence on glacial discharge.

New insights into the subglacial and periglacial hydrology of Vatnajökull, Iceland, from a distributed physical model

AbstractWe apply a time-dependent distributed glaciohydraulic model to Vatnajökull ice cap, Iceland, aiming to determine the large-scale subglacial drainage structure, the importance of basally derived meltwater, the influence of a permeable glacier bed and Vatnajökull’s discharge contribution to major rivers in Iceland. The model comprises two coupled layers that represent the subglacial horizon perched on a subsurface aquifer in the western sector and bedrock in the eastern sector. To initialize and drive the simulations, we use digital elevation models of the ice surface and bed, the 1999/2000 measured mass balance and an estimate of subglacial geothermal heat fluxes. The modelled subglacial flow field differs substantially from that derived by hydraulic-potential calculations, and the corresponding distribution of basal effective pressure shows a strong correlation between low effective pressure and surge-prone areas in northeastern and southern sectors of Vatnajökull. Simulations suggest that geothermally derived basal melt may account for up to ∼5% of the annual glacial discharge, and buried aquifers may evacuate up to ∼30% of subglacialwater.Time-dependent tests yield estimates of the glacial discharge component in various outlet rivers and suggest a possible seasonal migration of subglacial hydraulic divides. This study of present-day Vatnajökull hydrology forms the starting point for investigations of its future evolution.

The distribution of juvenile benthic invertebrates in an arctic glacial fjord

The distribution of juvenile benthic invertebrates with respect to their abiotic environment was investigated at four locations along a gradient in Kongsfjorden (79°N, 12°E), Spitsbergen, in September 1997. Heavy discharge of inorganic sediments released by the three glaciers was expected to be one of the main structuring factors of benthic communities in the fjord. Juveniles of 76 species/families are identified. Total abundance increases with distance from the fjord head due to the dominance of opportunistic polychaetes, while diversity is highest close to the glacier. Juvenile polychaetes are the most abundant taxon over all stations (92%), followed by bivalves, crustaceans and others. Polychaetes also provide most species (55%) and are the dominant taxon at every station. Their abundance is highly correlated with total organic carbon, indicating that most of them are deposit feeders. Young crustaceans rapidly decrease towards the fjord mouth, probably due to stronger bottom currents. Even though young oligochaetes are exclusively found near the glacier, no species seem to be well adapted to the high sedimentation rate close to the glacier. Juvenile suspension-feeding bivalves seem to be less disturbed by glacial discharge but appear to be more vulnerable to currents on the more exposed sites. The importance of deposit feeders and carnivores increases towards the outer stations. Non-metric multidimensional scaling confirms the distinct gradient in community composition along the fjord. Coupling the biotic data to abiotic factors (depth, bottom-water salinity, bottom-water temperature, sediment grain size and sedimentation rate) using canonical correspondence analysis revealed that hydrographic factors are more responsible for the structuring of the benthic juvenile community at the shallow stations close to the glacier (except the station directly at the glacier). At the outer deeper stations, sediment grain size and related properties may play a more important role.

Sedimentology of proglacial rivers in eastern Scotland during the Late Devensian

ABSTRACTThis paper reconstructs the characteristics of rivers which deposited proglacial fluvial sediments in east-central Scotland during the Late Devensian. Sediment depositional architecture and geometry, together with the relationship between high-stage and falling and low-stage depositional elements, were used to relate the proglacial sediments to the glacial meltwater discharge regime. The proglacial river systems studied were dominated by ‘normal’ ablation controlled discharge, rather than by high magnitude flood events. Consequently there is a great deal of spatial and vertical variability. Deposition occurred during short intervals of rapid aggradation, so that relatively fine-grained falling-stage sediments, as well as coarser, bar-core sediments are well preserved. Models relating the characteristics of the final deposit to the nature of the river are presented. These emphasise the role of stage changes and aggradation rates in controlling sediment architecture in braided fluvial deposits.

From accumulation to discharge: modification of stable isotopes during glacial and post-glacial processes

The isotopes of the water molecule (tritium, deuterium and oxygen-18) are considered to be ideal tracers of the water cycle, an isobalance of accumulation and discharge from glaciated areas is therefore challenging. In this article we review data from the Alps concerning both the isotopic information of accumulated snow and ice and the relevant information of glacial discharge on a local to regional scale. In the Alps the seasonal distribution of accumulated snow is governed by small-scale meteorology and exposition and distribution of cold and temperate glaciers. From comparison with direct precipitation measurements it follows that uncontrolled erosive loss of parts of the seasonal (mainly winter) snow cover is more important for input-output considerations of glacial discharge, reconstruction of mean accumulation rates and palaeotemperatures by means of isotopes, than occasional melting or even rainfall events. The order of magnitude of the latter is controlled by laboratory and field experiments. Sublimation and evaporation turn out to be of minor influence if only the absolute values and not the deuterium excess (the relationship of both stable isotopes, deuterium and oxygen-18) is considered. Nevertheless, during warming periods a pronounced increase of deuterium excess caused by intensive melting and evaporation may be used as an additional climate indicator. The different isotopic signature of the seasonal snow cover, old glacier ice and groundwater stored in the glacier bed enables a quantitative separation of the individual water components discharging at a given time of the day or the season. Although several detailed isotope studies are reported, a complete isobalance from glaciated areas based on an interdisciplinary approach, including hydrology and glaciology, is still missing. The hydroclimatic imprint of the discharge from glaciated areas remains even on a regional scale. Snowmelt shifts the more negative isotope values from winter precipitation to the summer months. Interannual climatic variability and changes in seasonal distribution of precipitation (for instance reduced winter precipitation during the late 1980s) are recorded by the stable isotopes in precipitation and discharge as well indicating that the modification of the isotopic information during glacial and post-glacial processes does not override climatic trends.

Analysis of fluid pressure propagation in heterogeneous rocks: Implications for hydrologically‐induced earthquakes

Mathematical models are developed to study the propagation of excess pore pressure in heterogeneous and fractured rocks. For a homogeneous rock, the time needed for a pore pressure front to migrate downward is directly proportional to the square of the depth, and inversely proportional to the permeability of the rock. Variational studies show that pore pressure propagation is highly influenced by the permeability heterogeneity of the crust. The results argue for the importance of accounting for geologic complexity when using mathematical models to estimate the extent of downward transmission of increases in hydraulic heads. The models presented in the paper are used to estimate a range of possible hypocentral depths of periodic seismicity observed near Mt. Ogden on the Alaska‐British Columbia border. The time lag between these earthquakes and hydrologic loading is on the order of days or weeks, indicating a quick response of seismicity to the increased surface water input from rainfall or glacial discharge, if such a causal relationship exists. Our models estimate that the hypocentral depths of these earthquakes could be on the order of several kilometers, if a high degree of vertical interconnectivity of fractures exists.

The Black Sea: A Freshwater Lake?

The Black Sea: A Freshwater Lake?

Geomorphology of a Degrading Arctic Delta, Sermilik, South-East Greenland

Niels Nielsen: Geomorphology of a Degrading Arctic Delta, Sermilik, South-East Greenland. Geografisk Tiddskrift, Danish Journal of Geography 94:xx–xx. Copenhagen, Dec. 1994. An arctic delta at the Sermilik Station (65°41′ N., 37°49′ W.), Ammassalik Island, S-E Greenland has been studied including its geomorphology, sediments, dynamics and evolution. The fluvial system is fed by a retreating glacier (30 km2) and compraises an alluvial valley (1.6 km long) and a lobate delta (0.8 km2). The river discharges into a polar sea, which is ice-bound for about 7–8 months a year and with abundant icebergs during the summer. Albeit exposed to the very stormy Denmark Strait, low wave energy conditions prevail, because of the presence of floating ice. Yet major wave-built coastal structures: barriers, tombolos and swash bars, strongly influenced by macro tidal conditions, are superimposed on the delta flat. Recent investigations indicate that the alluvial valley now acts as a sink for glacial discharge of coarse clasti...

Interactions and relations between mountain permafrost, glaciers, snow and water

AbstractThere are problems in determining the amount of precipitation at a given site in mountain permafrost areas, because snow can be redistributed by wind or avalanches. Both snow and rain greatly affect permafrost distribution. Surface soil conditions also affect permafrost distribution. Dry blocky surfaces, peaty soils and soils with a thick organic mat tend to favour permafrost development. Active layers are deepest on dry mineral soils at low latitudes. Moist soils have thin active layers which exhibit the zero curtain effect during freezing and thawing. Meteoric H2O enters permafrost in response to thermal gradients. The H2O content may reach 80% by volume in its upper layers in some rock glaciers. In Kazakhstan a perched water table occurs above the thawing front in the active layer and provides a reliable supply of water to plants, so that the permafrost lands have a lush meadow tundra in summer. The physical and chemical properties of the discharge from mountain permafrost areas can be used to differentiate it from glacial discharge and groundwater. There is an antipathetic relationship between the lower limit of permafrost and the equilibrium line on glaciers. Gorbunov's Continentality Index is the only system for classifying the climate of mountain permafrost areas that indicates their great climatic variability.

High-Resolution Stable Isotope and Microfossil Record from the Gulf of Mexico

ODP Site 625B was hydraulically piston cored in the northeastern Gulf of Mexico providing an apparently complete sedimentary record for the last 5.35 my. A high-resolution chronology was derived by tuning the oxygen isotope record to variations in orbital obliquity. Ages for calcareous nannofossil and planktonic foraminiferal datums were determined. Eight of the 11 nannofossil last appearances occur during glacials or during the onset of glacial periods. Of the eight foraminiferal last appearances, half occur during glacials. Results from open-ocean records also show a preponderance of last appearances within glacial intervals for the last 2.5 my. The higher frequency of last appearances during glacial intervals may result from greater environmental stress. Late Pliocene (2.30-1.66 Ma) and early Pleistocene (1.66-0.73 Ma) oxygen isotope anomalies with magnitudes of {minus}1.4 to {minus}2.0{per thousand} indicate glacial meltwater discharge from the Mississippi River implying that an ice sheet has been present at midlatitudes in North America periodically since 2.3 Ma.

Regional hydrogeology of agricultural drainage wells in Iowa

In Iowa, agricultural drainage wells (ADW9s) represent the largest deliberate transfer of degraded water into major aquifers. An estimated 700 ADW9s remove tile and surface waters from level farmland and inject it into underlying aquifers. Of 174 field-identified ADW9s, 165 were grouped into 3 clusters in north-central Iowa (17 in Floyd County, 44 in Wright County, and 104 in Humbolt-Pocahontas Counties). Geologically, most of the identified ADW9s penetrate the Des Moines glacial lobe and discharge into carbonate aquifers. These aquifers are in the intermediate ground-water flow regime, with recharge mainly from the overlying landscape and discharge mainly to rivers. A graphic flow net model indicates a progressive increase in recharge down gradient, providing increased dilution for contaminants. Modeling suggests that tile-line drainages have averaged about 10-12 ppm nitrate-N during the past decade, mostly derived from fertilizer applications. ADW effluents measured during Spring 1983 ranged between 10 and 20 ppm nitrate-N. Plumes associated with ADW9s would contain nitrate-N in concentrations approaching 20 ppm near the source, decreasing down gradient to 2-6 ppm with ground-water mixing. Joint and bedding-plane openings in the carbonate aquifer formations were measured in quarries, and the effective porosities were about 1%. If it is assumed that diffuse flow approximates isotropic and homogeneous conditions, ground-water flow velocities range from 500 to 26,000 ft/yr. Residence times for ground water in the carbonate aquifers range from a few months to a few decades, depending on the ground-water velocity and the length of individual flow paths.

Mantle rheology and satellite signatures from present‐day glacial forcings

We study the changes of the long‐wavelength portion of the Earth's gravity field as a result of present‐day glacial discharges and the possible growth of the Antarctic ice sheet. We employ both Maxwell and Burgers' body rheologies and find that there are significant differences in the responses between the two rheologies for time spans less than a century. Both present‐day glacial forcing and the ice buildup on Antarctica can cause non‐negligible perturbations in j2 of about one‐third the observed amount. The contributions from the two mechanisms have opposite signs in j2. Only for l = 3 and 6 do these cryospheric contributors act in concert with one another in disturbing the gravity field. All other degree harmonics, up to l = 9, have opposite signs from these two excitations. For a steady‐state lower‐mantle viscosity of 1022 Pa s, j3 can attain a maximum value of around 1.5×10−11 yr−1 and j6 a value of −1.3×10−11 yr−1 for current forcings. These have signs opposite to those predicted for Pleistocene deglaciation. All harmonics, up to l = 9, are sensitive to variations of the steady‐state viscosity in the lower mantle, even for time scales shorter than 100 years. It is proposed that detailed satellite monitoring of present‐day ice movements in conjunction with geodetic satellite missions will eventually provide a viable alternative for estimating deep mantle viscosity, useful in mantle convection models.

Excitation of the Earth's rotational axis by recent glacial discharges

We study the effects of present‐day glacial discharges and the growth of the Antarctic ice sheet on exciting the Earth' rotational axis. Glacial forcing could cause a maximum change in J2 of about one‐third of the observed amount, for the Maxwell rheology and for Burgers’ body models with a long‐term, lower‐mantle viscosity greater than about 1023P. For transient rheologies the amount of excitation due to glacial melting decreases. Polar wander is not much excited by recent glacial melting for the various types of rheologies examined.