A nonsteady-state firn-densification model for the percolation zone of a glacier

Niels Reeh

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

A simple steady state firn-densification model is modified to account for short-term time variations of accumulation rate and surface temperature. The temporal surface-elevation- and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined. It is shown that a straight-forward translation of observed short-term ice-sheet surface-elevation variations into mass changes may be completely misleading, particularly for the percolation zone of the ice sheet, where temperature driven variations of melting/re-freezing rates have a strong impact on near surface density. In the lower percolation zone, the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed, simultaneous surface elevation change. Moreover, significant surface elevation change may occur even in periods of constant surface climate, and consequently unchanged mass balance, as a delayed response to previous changes of the local surface climate. Forcing the model with cyclic temperature variations mimicking fluctuations of West Greenland instrumental temperature records during the past hundred years, shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all. In the lower percolation zone, temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short-term surface elevation changes in contrast to the situation in the higher percolation zone, where short-term surface-elevation change is dominated by fluctuations of accumulation rate.
Original languageEnglish
JournalJournal of Geophysical Research - Oceans
Volume113
Issue number3
ISSN2169-9380
DOIs
Publication statusPublished - 2008

Keywords

  • Greenland
  • mass/volume change
  • Ice sheet

Cite this

@article{96fdbccde50644779c90d6ab7239be6f,
title = "A nonsteady-state firn-densification model for the percolation zone of a glacier",
abstract = "A simple steady state firn-densification model is modified to account for short-term time variations of accumulation rate and surface temperature. The temporal surface-elevation- and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined. It is shown that a straight-forward translation of observed short-term ice-sheet surface-elevation variations into mass changes may be completely misleading, particularly for the percolation zone of the ice sheet, where temperature driven variations of melting/re-freezing rates have a strong impact on near surface density. In the lower percolation zone, the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed, simultaneous surface elevation change. Moreover, significant surface elevation change may occur even in periods of constant surface climate, and consequently unchanged mass balance, as a delayed response to previous changes of the local surface climate. Forcing the model with cyclic temperature variations mimicking fluctuations of West Greenland instrumental temperature records during the past hundred years, shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all. In the lower percolation zone, temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short-term surface elevation changes in contrast to the situation in the higher percolation zone, where short-term surface-elevation change is dominated by fluctuations of accumulation rate.",
keywords = "Greenland, mass/volume change, Ice sheet",
author = "Niels Reeh",
year = "2008",
doi = "10.1029/2007JF000746",
language = "English",
volume = "113",
journal = "Journal of Geophysical Research",
issn = "0148-0227",
publisher = "American Geophysical Union",
number = "3",

}

A nonsteady-state firn-densification model for the percolation zone of a glacier. / Reeh, Niels.

In: Journal of Geophysical Research - Oceans, Vol. 113, No. 3, 2008.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - A nonsteady-state firn-densification model for the percolation zone of a glacier

AU - Reeh, Niels

PY - 2008

Y1 - 2008

N2 - A simple steady state firn-densification model is modified to account for short-term time variations of accumulation rate and surface temperature. The temporal surface-elevation- and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined. It is shown that a straight-forward translation of observed short-term ice-sheet surface-elevation variations into mass changes may be completely misleading, particularly for the percolation zone of the ice sheet, where temperature driven variations of melting/re-freezing rates have a strong impact on near surface density. In the lower percolation zone, the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed, simultaneous surface elevation change. Moreover, significant surface elevation change may occur even in periods of constant surface climate, and consequently unchanged mass balance, as a delayed response to previous changes of the local surface climate. Forcing the model with cyclic temperature variations mimicking fluctuations of West Greenland instrumental temperature records during the past hundred years, shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all. In the lower percolation zone, temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short-term surface elevation changes in contrast to the situation in the higher percolation zone, where short-term surface-elevation change is dominated by fluctuations of accumulation rate.

AB - A simple steady state firn-densification model is modified to account for short-term time variations of accumulation rate and surface temperature. The temporal surface-elevation- and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined. It is shown that a straight-forward translation of observed short-term ice-sheet surface-elevation variations into mass changes may be completely misleading, particularly for the percolation zone of the ice sheet, where temperature driven variations of melting/re-freezing rates have a strong impact on near surface density. In the lower percolation zone, the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed, simultaneous surface elevation change. Moreover, significant surface elevation change may occur even in periods of constant surface climate, and consequently unchanged mass balance, as a delayed response to previous changes of the local surface climate. Forcing the model with cyclic temperature variations mimicking fluctuations of West Greenland instrumental temperature records during the past hundred years, shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all. In the lower percolation zone, temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short-term surface elevation changes in contrast to the situation in the higher percolation zone, where short-term surface-elevation change is dominated by fluctuations of accumulation rate.

KW - Greenland

KW - mass/volume change

KW - Ice sheet

U2 - 10.1029/2007JF000746

DO - 10.1029/2007JF000746

M3 - Journal article

VL - 113

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

SN - 0148-0227

IS - 3

ER -