Sebastian Mernild - Profile on Academia.edu (original) (raw)

Papers by Sebastian Mernild

Hydrologisk og morfologisk klassifikation af vandløb og vandløbssystemer

Climate-driven fluctuations in freshwater flux to Sermilik Fjord, East Greenland, during the last 4000 years

The …, Jan 1, 2012

ABSTRACT The freshwater runoff from the glaciated and snow-covered Sermilik Fjord catchment, SE G... more ABSTRACT The freshwater runoff from the glaciated and snow-covered Sermilik Fjord catchment, SE Greenland, was estimated at annual resolution for the period 1900–2008 and at decadal resolution for the past four millennia. Our simulations were forced with available meteorological station data (1900–2008) and Greenland ice core estimated temperature data (1899 bc–ad 1980) from Dye3 and GISP2. Time series of estimated ice discharge (2000–2009) for the three major outlet glaciers Helheim, Fenris, and Midgård indicate that 53–74% of the ice discharge variations could be explained by variations in areally averaged glacier terminus surface (supraglacial) runoff. Based on these data and together with calculated subglacial geothermal and frictional melting as well as net precipitation for the fjord area, the Sermilik Fjord freshwater flux was deduced for the period 1900–2008. Our simulations indicated that during the last century surface freshwater runoff has equaled 13% of the Sermilik Fjord average freshwater flux of 33.0±5.7×109 m3/yr, covering a periodic runoff variation of 20 years. Ice discharge has accounted for 81%, with 63% of the freshwater flux originated from the Helheim glacier. This indicates that the Helheim outlet glacier plays a dominant role as a freshwater source to both Sermilik Fjord and ultimately the Irminger Sea. For the palaeorecords of the last 4000 years, simulated surface runoff has averaged 4.4±0.2×109 m3/yr. A very weak decreasing trend in runoff over the last 4 k years (1899 bc–ad 1980) is presumably associated with the general insolation-generated Northern Hemisphere cooling since the Holocene Thermal Maximum. Our simulations furthermore indicated centennial- to submillennial-scale variations in surface runoff concurrent with the well-known climate episodes such as the ‘Roman Warm Period’, the ‘Dark Ages Cold Period’, the ‘Medieval Climate Anomaly’, and the ‘Little Ice Age’. During the ‘Little Ice Age’, e.g., the average surface runoff was about 0.7×109 m3/yr lower than today, while the increase in runoff for the Modern Warming, since the late 1800s, was the second strongest and fastest for the last 4 k years.

1 Fluvial Sediment Dynamics and the Importance of Extreme Events-Glacial erosion and sediment transport in the Mittivakkat Glacier catchment, …

IAHS …, Jan 1, 2006

Greenland ice sheet surface melt extent and trends: 19602010

Journal of Glaciology, Jan 1, 2011

Page 1. Greenland ice sheet surface melt extent and trends: 19602010 Sebastian H. MERNILD,1 Thom... more Page 1. Greenland ice sheet surface melt extent and trends: 19602010 Sebastian H. MERNILD,1 Thomas L. MOTE,2 Glen E. LISTON3 1Climate, Ocean and Sea Ice Modeling Group, Computational Physics and Methods, Los ...

Eos Trans. AGU, Jan 1, 2009

Journal of …, Jan 1, 2006

A physically based snow-evolution modeling system (SnowModel) that includes four submodels-the Mi... more 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 influences, and the simulated end-of-summer location of the glacier equilibrium line altitude was confirmed by glaciological observations and digital images. The modeled test-period-averaged annual mass balance was 150 mm w.eq. yr Ϫ1 , or ϳ15%, less than the observed. Approximately 12% of the precipitation was returned to the atmosphere by sublimation. Glacier-averaged mean annual modeled surface melt ranged from 1272 to 2221 mm w.eq. yr Ϫ1 , of which snowmelt contributed from 610 to 1040 mm w.eq. yr Ϫ1 . The surface-melt period started between mid-May and the beginning of June, and lasted until mid-September; there were as many as 120 melt days at the glacier terminus. The model simulated a Mittivakkat Glacier recession averaging Ϫ616 mm w.eq. yr Ϫ1 , almost equal to the observed Ϫ600 mm w.eq. yr Ϫ1 .

Present-day climate at Zackenberg

Advances in Ecological …, Jan 1, 2008

At Zackenberg (74°30′N, 20°30′W), the polar night lasts 89 days and the polar day 106 days. Durin... more At Zackenberg (74°30′N, 20°30′W), the polar night lasts 89 days and the polar day 106 days. During the polar night, when solar energy is low or equal to zero, radiative cooling of the snow-covered surface leads to monthly mean air temperatures below −20 °C and daily ...

Snow‐distribution and melt modelling for glaciers in Zackenberg river drainage basin, north‐eastern Greenland

Hydrological Processes, Jan 1, 2007

Page 1. HYDROLOGICAL PROCESSES Hydrol. Process. 21, 32493263 (2007) Published online 12 October ... more Page 1. HYDROLOGICAL PROCESSES Hydrol. Process. 21, 32493263 (2007) Published online 12 October 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6500 Snow-distribution and melt modelling for glaciers in ...

Geografisk Tidsskrift-Danish Journal of …, Jan 1, 2006

neath the glacier in different flow paths, e.g., through snow and firn cover (porous medium), sup... more neath the glacier in different flow paths, e.g., through snow and firn cover (porous medium), supraglacial ponds and channels, crevasses and moulins, englacial pockets, englacial and subglacial drainage system and fractures, subglacial cavities, and in basal subglacial sediment

Surface Melt Area and Water Balance Modeling on the Greenland Ice Sheet 1995-2005

Journal of …, Jan 1, 2008

... SnowTran-3D simulations have previously been compared against observations in glacier and gla... more ... SnowTran-3D simulations have previously been compared against observations in glacier and glacier-free alpine, Arctic, and Antarctic ... Few quality observations for spatial in situ snow evolution, snow and ice surface melt, and glacier net mass balance are available. ...

Hydrological …, Jan 1, 2009

The freshwater flux from the Greenland Ice Sheet (GrIS) to the ocean is of considerable importanc... more The freshwater flux from the Greenland Ice Sheet (GrIS) to the ocean is of considerable importance to the global eustatic sea level rise. A physical modelling approach using SnowModel, a state-of-the-art snow-evolution modelling system that includes four submodels (MicroMet, EnBal, SnowPack,, was used to quantify the 1995-2007 GrIS surface massbalance (SMB), including freshwater flux. Meteorological observations from 26 meteorological stations located on the GrIS (Greenland Climate Network; GC-Net stations) and in coastal Greenland (Danish Meteorological Institute (DMI) WMOstations) were used as model inputs. The GrIS minimum surface melt extent of 29% occurred in 1996, while the greatest extent of 51% was present in 2007. The 2007 melt extent was 20% greater than the average for 1995-2006. The year 2007 had the highest GrIS surface runoff (523 km 3 y 1 ) and the lowest SMB ( 3 km 3 y 1 ); the only year with a negative GrIS SMB. Runoff in 2007 was approximately 35% greater than average for 1995-2006. From 1995 through 2007 overall,

Hydrological Processes, Jan 1, 2008

A spatially distributed, physically based, hydrologic modeling system (MIKE SHE) was applied to q... more A spatially distributed, physically based, hydrologic modeling system (MIKE SHE) was applied to quantify intra-and interannual discharge from the snow and glacierized Zackenberg River drainage basin (512 km 2 ; 20% glacier cover) in northeast Greenland. Evolution of snow accumulation, distribution by wind-blown snow, blowing-snow sublimation, and snow and ice surface melt were simulated by a spatially distributed, physically based, snow-evolution modelling system (SnowModel) and used as input to MIKE SHE. Discharge simulations were performed for three periods 1997-2001 (calibration period), 2001-2005 (validation period), and 2071-2100 (scenario period). The combination of SnowModel and MIKE SHE shows promising results; the timing and magnitude of simulated discharge were generally in accordance with observations (R 2 D 0Ð58); however, discrepancies between simulated and observed discharge hydrographs do occur (maximum daily difference up to 44Ð6 m 3 s 1 and up to 9% difference between observed and simulated cumulative discharge). The model does not perform well when a sudden outburst of glacial dammed water occurs, like the 2005 extreme flood event. The modelling study showed that soil processes related to yearly change in active layer depth and glacial processes (such as changes in yearly glacier area, seasonal changes in the internal glacier drainage system, and the sudden release of glacial bulk water storage) need to be determined, for example, from field studies and incorporated in the models before basin runoff can be quantified more precisely. The SnowModel and MIKE SHE model only include first-order effects of climate change. For the period 2071-2100, future IPCC A2 and B2 climate scenarios based on the HIRHAM regional climate model and HadCM3 atmosphere-ocean general circulation model simulations indicated a mean annual Zackenberg runoff about 1Ð5 orders of magnitude greater (around 650 mmWE year 1 ) than from today 1997-2005 (around 430 mmWE year 1 ), mainly based on changes in negative glacier net mass balance.

IAHS Publications-Series of …, Jan 1, 2004

The arctic alpine landscape on Ammassalik Island features catchments with varying glacier coverag... more The arctic alpine landscape on Ammassalik Island features catchments with varying glacier coverage. Climatic data from three stations were analysed, water balances were calculated, and the problems in estimating the water balance in this type of catchment are discussed. Potential évapotranspiration according to varies from 379 mm year' 1 to 400 mm year" 1 ; cor rected precipitation varies between 1036 mm year" 1 and 1255 mm year" 1 ; and modelled runoff from 702 mm year" 1 to 1708 year" 1 on a 4-year average. Comp arisons of modelled runoff with measured values indicate that the higher runoff values, based on corrected precipitation, are in the right order of magnitude. The high measured runoff values can partly be explained by excess runoff from glaciers in the area having a negative annual mass balance.

Climate, glacier mass balance and runoff (1993-2005) for the Mittivakkat Glacier catchment, Ammassalik Island, SE Greenland, and in a long term perspective (1898- …

Hydrology …, Jan 1, 2008

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Meltwater flux and runoff modeling in the ablation area of Jakobshavn Isbræ, West Greenland

Journal of …, Jan 1, 2010

Observed runoff, jokulhlaups and suspended sediment load from the Greenland ice sheet at Kangerlussuaq, West Greenland, 2007 and 2008

Journal of Glaciology, Jan 1, 2009

The influence of air temperature inversions on snowmelt and glacier mass balance simulations, Ammassalik Island, southeast Greenland

Journal of Applied Meteorology and …, Jan 1, 2010

… Tidsskrift-Danish Journal …, Jan 1, 2008

… Journal of Geography, Jan 1, 2004

Meteorological stations have been operating at Sermilik (65°40'N, 38°10'W), southeast Greenland, ... more Meteorological stations have been operating at Sermilik (65°40'N, 38°10'W), southeast Greenland, since June 1993. The physical environment and meteorological stations are described and meteorological parameters presented and discussed, using 2002 as an example.