Niels Tvis Knudsen

Snow Distribution and Melt Modeling for Mittivakkat Glacier, Ammassalik Island, Southeast Greenland

Abstract A physically based snow-evolution modeling system (SnowModel) that includes four submodels—the Micrometeorological Model (MicroMet), EnBal, SnowPack, and SnowTran-3D—was used to simulate five full-year evolutions of snow accumulation, distribution, sublimation, and surface melt on the Mittivakkat Glacier, in southeast Greenland. Model modifications were implemented and used 1) to adjust underestimated observed meteorological station solid precipitation until the model matched the observed Mittivakkat Glacier winter mass balance, and 2) to simulate glacier-ice melt after the winter snow accumulation had ablated. Meteorological observations from two meteorological stations were used as model inputs, and glaciological mass balance observations were used for model calibration and testing of solid precipitation observations. The modeled end-of-winter snow-water equivalent (w.eq.) accumulation increased with elevation from 200 to 700 m above sea level (ASL) in response to both elevation and topographic...

Dye tracer tests of water movement at the glacier Austre Okstindbreen, Norway.

Theakstone, W. H. & Knudsen, N. T. 1981. Dye tracer tests of water movement at the glacier Austre Okstindbreen, Norway. Norsk geogr. Tidsskr. Vol. 35, 21–28. Oslo. ISSN 0029-1951. Dye tracer tests of water movement through the glacier Austre Okstindbreen in three successive summers have shown that, whilst some water passes rapidly through the glacier from points of entry at the surface, considerable delays characterise throughflow from many points. The tests, together with other hydrological studies at the glacier, indicate that discrete but changeable drainage systems exist within Austre Okstindbreen during the summer. Observations suggest that the systems are well represented by the model derived by Stenborg (1969, 1973) for two Swedish glaciers. Relatively low ice permeability is indicated by the results of a test in which tracer injected into water entering a crevasse re-emerged in water overflowing from another crevase, and in which one water-filled crevasse remained tracer-free although the water in...

Snow, runoff, and mass balance modeling for the entire Mittivakkat Glacier (1998–2006), Ammassalik Island, SE Greenland

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(1):121–136, 2008 SnowModel, a physically-based snow evolution modeling system that includes four submodels—MicroMet, EnBal, SnowPack, and SnowTran-3D—was used to simulate eight full-year (1998/99 through 2005/06) evolutions of snow accumulation, blowing snow sublimation, evaporation, snow and ice surface melt, runoff, and mass changes on the entire Mittivakkat Glacier (31 km2) in southeast Greenland. Meteorological observations from two meteorological stations inside the glacier catchment were used as model input, and glaciological mass balance observations were used for model calibration (1998/99 through 2001/02) and validation (2002/03 through 2005/06) of winter snow simulations. As confirmed by observations, the spatially modeled end-of-winter snow water equivalent (SWE) accumulation increased with elevation up to 700–800 m a.s.l. in response to elevation, topography, and dominating wind direction, and maximum snow deposition occurred on the lee side of the ridge east and south of the glacier. Simulated end-of-summer cumulative runoff decreased with elevation and minimum runoff occurred on the shadowed side of the ridge east and south of the glacier. The modeled test period averaged annual mass balance was 65 mm w. eq. y−1 or ∼8% more than the observed. For the simulation period, the glacier net mass balance varies from -199 to -1,834 mm w.eq. y−1, averaging -900 (±470) mm w.eq.y−1. The glacier averaged annual modeled precipitation ranged from 1,299 to 1,613 mm w.eq. y−1, evaporation and sublimation from 206 to 289 mm w.eq., and runoff from 1,531 to 2,869 mm w.eq. y−1. The model simulated Mittivakkat Glacier net loss of900 mm w.eq. y−1 contributes approximately 42% to the average simulated runoff of 2,140 mm w.eq. y−1, indicating a mean specific runoff of 67.8 l s−1 km−2.

Suspended sediment transport in glacial meltwater during the initial quiescent phase after a major surge event at Kuannersuit Glacier, Greenland

Abstract This paper describes a rough estimate of the suspended sediment transport in the bulk meltwater evacuated from Kuannersuit Glacier during the summers of 2000 and 2001. In 1995–98, an 11 km terrestrial surge of Kuannersuit Glacier, an outlet glacier of the largest ice cap on Disko Island, West Greenland, affected the catchment dramatically. The results show that in 2000, the daily sediment discharge was about 32,500 t day−1, corresponding to a specific sediment load of 19,000 t km-2 year−1. In 2001 the diurnal suspended sediment load was about 26,000 t day−1, corresponding to a specific sediment load of 15,000 t km−2 year−1. There was only a poor relation between meltwater discharge and suspended sediment transport, indicating that the drainage system was highly unstable. In 2001 the discharge and the sediment transport on several occasions was affected by collapse within the glacial drainage system and at the glacier margin. Assuming that suspended sediment transport and bedload is equal, the effective mechanical erosion is about 15 mm year−1. Compared to the sediment transport from other parts of Greenland and High Arctic regions the transport during the surge event and in the early quiescent phase is significantly higher. This indicates the importance of glacier surge in initiating sediment transport pulses in cold regions.

Radio-echo Sounding at the Mittivakkat Gletscher, Southeast Greenland

Profiles along sounding lines and maps are presented of the glacier surface, bottom topography, and ice thickness of Mittivakkat Gletscher. The maps are the result of the use of monopulse radio-echo sounding of ice thickness in about 450 points along profiles across the glacier. The position of most points was surveyed using a theodolith together with Electrooptic Distance Measurement. The Mittivakkat Gletscher consists of several accumulation basins which combine into a single ice tongue. There is a marked relief underneath the glacier, and it is possible to identify two major subglacial depressions, which probably strongly influence the subglacial drainage of water from the glacier. The bottom topography is reflected in the surface topography and in the position of crevassed areas. The following data were extracted: area: 17.6 km2; volume: 2024 × 106 m3; ice thickness, Hmean: 115 m; ice thickness, Hmax: 245 m.

Geochemistry of groundwater in front of a warm-based glacier in Southeast Greenland

Abstract Groundwater in front of warm‐based glaciers is likely to become a more integrated part of the future proglacial hydrological system at high latitudes due to global warming. Here, we present the first monitoring results of shallow groundwater chemistry and geochemical fingerprinting of glacier meltwater in front of a warm‐based glacier in outheast reenland (ittivakkat letscher, 65° 41′ , 37° 48′ ). The groundwater temperature, electrical conductivity and pressure head were monitored from ugust 2009 to ugust 2011, and water samples were collected in 2009 and analyzed for major ions and water isotopes (δD, δ18O). The 2-yrs of monitoring revealed that major outbursts of glacier water during the ablation season flushed the proglacial aquifer and determined the groundwater quality for the next 2–8 weeks until stable chemical conditions were reached again. Water isotope composition shows that isotopic fractionation occurs in both groundwater and glacier meltwater, but fractionation due to evaporation from near‐surface soil moisture prior to infiltration has the most significant effect. This study shows that groundwater in ow rctic reenland is likely to possess a combined geochemical and isotopic composition, which is distinguishable from other water sources in the proglacial environment. However, the shallow groundwater composition at a given time is highly dependent on major outbursts of glacier water in the previous months.

Mass balance observations at Mittivakkat Glacier, Ammassalik Island, Southeast Greenland 1995–2006

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(1):111–120, 2008 Measurements of mass balance were made at Mittivakkat Glacier, Ammassalik Island, Southeast Greenland during the period 1995–2006 using the stake method, usually called the direct glaciological method, for determining the net accumulation and ablation of snow and ice during the accumulation(September—May) and ablation (June-August) period, and the net mass balance year (September—August). For the period 1995–2006, mean values of measured winter, summer and net balance were 1.19 m, -1.96 m and–0.78 m, respectively. The measurements showed that 9 out of 11 balance years had a negative balance and 2 balance years had a slightly positive balance. The cumulative mass balance during the period 1995—2006 was -8.1 m w. eq., corresponding to a mass loss of about 7% of the total glacier ice volume determined in 1994. The observations also showed that during 4 balance years the mass balance was negative on the entire glacier. A comparison between modelled surface mass balance of the Greenland Ice Sheet (GrIS) and mass balance at Mittivakkat Glacier showed the same tendency during individual years for the period 1991–2004.

Atmospheric and oceanic influence on mass balance of northern North Atlantic region land‐terminating glaciers

Abstract In this study, observed annual mass‐balance data series from 1970 to 2009 for 29 land‐terminating glaciers and ice caps in the northern orth tlantic region are presented to highlight their spatio‐temporal variability. The glaciers and ice caps mass‐balance data are compared with various zonal latitude bands of regional near‐surface air temperature time series, large‐scale atmospheric and oceanic circulation indices, as well as with orth celandic sea‐surface temperature records, since variations in mass‐balance conditions are related both to variations in surface weather conditions and to atmospheric and oceanic circulations. The purpose is to explore statistical and physical relations based on the hypothesis that the general atmospheric and sea‐surface warming trends are potential drivers of the ongoing regional glaciers and ice caps mass change. Our analysis shows that the mean observed northern orth tlantic glaciers and ice caps annual mass balance was mostly negative during the first decade of the twenty‐first century, with a variability in glaciers and ice caps loss from c. 860 mm water equivalent yr–1 for outheast reenland and celand to c. 380 mm water equivalent yr–1 for valbard and candinavia. For celand and candinavia, variations in the orth tlantic oscillation seem to be important for mass‐balance conditions, whereas overall for the entire northern orth tlantic region the mass‐balance time series was significantly correlated with both s oddard nstitute for Space Studies regional near‐surface air temperature and tlantic multidecadal oscillation time series, individually.

Land-terminating glacier volume changes in different Circum-Arctic areas, mid-1980s to late-2000s/2011

Glaciology and Climate Change Laboratory, Center for Scientific Studies/Centro de Estudios Cientificos (CECs), Valdivia, Chile; Climate, Ocean, and Sea Ice Modeling Group, Computational Physics and Methods, Los Alamos National Laboratory, Los Alamos, NM, USA; Faculty of Science and Technology, Sogn og Fjordane University College, Sogndal, Norway; Department of Geoscience, Aarhus University, Aarhus, Denmark

Ice-dammed lake and ice-margin evolution during the Holocene in the Kangerlussuaq area of west Greenland

ABSTRACT There is a lack of detailed information on the Holocene evolution of the west Greenland ice margin, not least because it was farther inland than at present and thus at present is covered by ice. Suggestions have been put forward, both of relatively quick ice-margin retreat and of relatively stable ice-margin positions. This study presents the first exploitation of sediments from an ice-dammed basin. Sediment that is rich in organic material records a period of time sufficient for vegetation to thrive; thus, without a lake and with a distal and diminished ice mass relative to the present. In contrast, sediment composed of suspension-settling deposits and with drop stones records an ice-dammed lake and a proximal calving ice-margin. Overall, we evidence relatively coarse-grained glacifluvial sedimentation predominantly from an ice-marginal delta and/or a proglacial, braided river soon after the early Holocene deglaciation of this area. Subsequent mid-Holocene aeolian activity deposited leaves, some vegetation (roots) developed in the basin, and ponding of water formed organic-rich “gyttja” sediments and thin layers of peat. The lake then became ice marginal, and ice advances are interpreted to have occurred at approximately 4000 cal. yr BP, and between 2776 ± 26 cal. yr BP and 2440 ± 45 cal. yr BP. The Little Ice Age ice-margin advance at Russell Glacier apparently reached its maximum extent after 147 ± 39 cal. yr BP, whereas at Isunnguata Sermia the maximum could have been as early as 245 ± 26 cal. yr BP. Given that ice-marginal lakes are becoming globally ubiquitous, improved resolution and new geological data on lake and ice-margin dynamics and interactions, such as ice-dammed lake-basin sediments, will be important for numerical models for assessing past and future ice-mass evolution.