Thermal boundary conditions on western Greenland: Observational constraints and impacts on the modeled thermomechanical state

The surface and basal boundary conditions exert an important control on the thermodynamic state of the Greenland Ice Sheet, but their representation in numerical ice sheet models is poorly constrained due to the lack of observations. Here we investigate a land‐terminating sector of western Greenland...

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Vydané v:Journal of geophysical research. Earth surface Ročník 120; číslo 3; s. 623 - 636
Hlavní autori: Meierbachtol, Toby W., Harper, Joel T., Johnson, Jesse V., Humphrey, Neil F., Brinkerhoff, Douglas J.
Médium: Journal Article
Jazyk:English
Vydavateľské údaje: Washington Blackwell Publishing Ltd 01.03.2015
Predmet:
Ablation
Boreholes
Boundary conditions
Firn
Fluctuations
glaciology
Heat flux
Heat transfer
Ice
Ice sheets
In situ measurement
Mathematical models
modeling
Simulation
Surface temperature
Temperature
Thermodynamics
PN, Greenland, Greenland Ice Sheet
AN, Greenland
ISSN:2169-9003, 2169-9011
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Popis
Shrnutí:The surface and basal boundary conditions exert an important control on the thermodynamic state of the Greenland Ice Sheet, but their representation in numerical ice sheet models is poorly constrained due to the lack of observations. Here we investigate a land‐terminating sector of western Greenland and (1) quantify differences between new observations and commonly used boundary condition data sets and (2) demonstrate the impact of improved boundary conditions on simulated thermodynamics in a higher‐order numerical flow model. We constrain near‐surface temperature with measurements from two 20 m boreholes in the ablation zone and 10 m firn temperature from the percolation zone. We constrain basal heat flux using in situ measurement in a deep bedrock hole at the study area margin and other existing assessments. To assess boundary condition influences on simulated thermal‐mechanical processes, we compare model output to multiple full‐thickness temperature profiles collected in the ablation zone. Our observation‐constrained basal heat flux is 30 mW m−2 less than commonly used representations. In contrast, measured near‐surface temperatures are warmer than common surface temperature data sets by up to 15°C. Application of lower basal heat flux increases a model cold bias compared to the measured temperature profiles and causes frozen basal conditions across the ablation zone. Temperate basal conditions are reestablished by our warmer surface boundary. Warmer surface ice and firn can introduce several times more energy to the modeled ice mass than what is lost at the bed from reduced basal heat flux, indicating that the thermomechanical state of the ice sheet is highly sensitive to near‐surface effects. Key Points Measured thermal boundaries differ from commonly used data sets Observation‐driven basal heat flux increases numerical model cold bias Surface temperature adjustments impact modeled thermal behavior at depth
Bibliografia:NSF - No. 0909495
ArticleID:JGRF20364
Greenland Analogue Project
istex:4ED550F7965DD046C8C872E7B375B965F2D2CB11
ark:/67375/WNG-J6J3WW6B-1
ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
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ISSN:2169-9003
2169-9011
DOI:10.1002/2014JF003375