Secular gravity variations at Svalbard, Norway, from ground and satellite data: effects of glacier topography
SPIRIT Workshop 28-29/04/2010
(1)
A. Mémin(1) J. Hinderer(1) Y. Rogister(1) O.C. Omang(2)
Institut de Physique du Globe de Strasbourg, France (2) Norwegian Mapping Authority, Norway
Outline
Introduction Ground observations Satellite observations Ground/Satellite agreement Conclusions
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Outline
Introduction Ground observations Satellite observations Ground/Satellite agreement Conclusions
3
Introduction
Svalbard Archipelago ~36,000 km2 of ice => ~60% of its total area
4
Introduction
The last deglaciation at Svalbard
Present
18000 years ago
Berger (1992) 5
Introduction
Present-day ice mass change (PDIMC) at Svalbard
Midtre Lovénbreen : 2003-2005
Slakbreen : 1990-2003
Kohler & al.(2008) Ice loss at Midtre Lovénbreen: 1936-1962: 1962-1969: 1995-2003: 2003-2005:
~15 ~20 ~52 ~69
cm/yr cm/yr cm/yr cm/yr
Kääb & al.(2008) Nuth & al.(2010)
6
Introduction
Ny-Ålesund observatory, Svalbard Station - 3 GPS, VLBI, Doris, - absolute and relative gravimeters, - tige gauges. Crédit NSPO / Distribution Spot Image / Traitement CNRS-LEGOS
Ny-Ålesund
Midtre Lovénbreen
2 GPS, FG5, SG GPS
VLBI
Tides gauges
Doris
Kierulf & al.(2009)->
L&R
7
Outline
Introduction Ground observations Satellite observations Ground/Satellite agreement Conclusions
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Ground observations
Absolute gravimetry (FG5) * Corrections - Free air gradient,
*
- Polar motion, *
- Observed tides+OTL, - Pressure.
* *
Linear trend: -1,02 ± 0,48 µGal/yr
*Sato & al. (2006)9
Ground observations
Relative gravimetry (GWR) : GWR --- : -1,02 µGal/yr : FG5
Corrections and treatment -
same as AG, degree-3 polynomial filtering with a 48h windows, 5 offsets, linear drift of 1,81 µGal/yr.
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Ground observations
Glacial isostatic adjustment (GIA)
Contribution to ground observations
Ny-Ålesund: 1,88 mm/yr and -0,31 µGal/yr (Sato & al., 2006) νum = 5.1020 Pa.s, νlm = 1022 Pa.s, litho = 100 km
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Ground observations
PDIMC models Thinning rates + -
Area covered by ice
Nuth & al. Dowdeswell Uniform of Uniform of
(2010) + Kohler & al.(2007) & al.(2008), 47 cm/yr, Sato & al. (2006) 75 cm/yr.
SVAL
DCW + SPIRIT m/yr
-- SVAL (Hagedoorn & Wolf, 2003), -- Digital Chart of the World (DCW) + SPIRIT product (Korona & al., 2009).
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Ground observations
Altitude of thinning areas
SVAL Sign of Δg Mass loss Mass accumulation
m
+
+ -
DCW + SPIRIT + GTOPO30 13
Ground observations
Deformation and gravity variation
the last deglaciation
present-day ice mass change
Uplift velocity:
uv
Gravity variation:
gv
ge + gn
gv/uv = -0.15 μGal/mm (Wahr & al., 1995)
(ge + gn)/ue = -0.26 μGal/mm (de Linage & al., 2007)
Ratio:
Observations: n=96
ue
uv + ue = uobs gv + ge + gn = gobs 14
Ground observations
Modeling and observations
GIA -0,15 µGal/mm
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Ground observations
Modeling and observations
GIA -0,15 µGal/mm
-0,26 µGal/mm
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Ground observations
Modeling and observations SVAL no topo
GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
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Ground observations
Modeling and observations SVAL no topo DCW no topo GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
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Ground observations
Modeling and observations SVAL no topo DCW no topo SVAL + TOPO GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
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Ground observations
Modeling and observations SVAL no topo DCW no topo SVAL + TOPO DCW + SPIRIT + GTOPO30
GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
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Ground observations
Modeling and observations SVAL no topo DCW no topo SVAL + TOPO DCW + SPIRIT + GTOPO30
GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
Observation Uplift velocity from Sato & al. (2006)
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Ground observations
Modeling and observations SVAL no topo DCW no topo SVAL + TOPO DCW + SPIRIT + GTOPO30
GIA -0,15 µGal/mm
Thinning 75 cm/yr 47 cm/yr Non uniform
-0,26 µGal/mm
Observation Uplift velocity from Sato & al. (2006)
Ice loss: ~25 km3/yr 22
Outline
Introduction Ground observations Satellite observations Ground/Satellite agreement Conclusions
23
Satellite GRACE trends January 2003/January 2008
CSR
GRGS
*Swenson & Wahr, 2006
Cosine taper (30-50) Destriping filter*
observations
GFZ
n = 50
Mean
µGal/yr
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Satellite observations
Glacial isostatic adjustment (GIA) Contribution to satellite data from SELEN (Spada & Stocchi, 2007) νum = 5.1020 Pa.s, νlm = 1022 Pa.s, litho = 100 km
(Sato & al., 2006) ICE-3G
GRACE-GIA
µGal/yr 25
Satellite observations
PDIMC and GRACE
m/yr
-75 cm/a
µGal/yr
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Satellite observations
~13 km3/yr
GRACE - GIA - PDIMC CSR
GFZ
Ice loss
~25 km3/yr
~15 km /yr 3
µGal/yr
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Outline
Introduction Ground observations Satellite observations Ground/Satellite agreement Conclusions
28
Ground/Satellite agreement
Ice basins (DCW+SPIRIT)
Ice thickness variation Nuth Kohler Moholdt Kierulf
& & & &
al. al. al. al.
(2010) (2007) (2009) (2009)
Ground/Satellite agreement
Modeling and observations SVAL no topo DCW no topo SVAL + TOPO DCW + SPIRIT + GTOPO30
GIA
Thinning 75 cm/yr 47 cm/yr
Ice loss: ~15.7 km3/yr
Non uniform Observation Uplift velocity from Sato & al. (2006)
Ice loss: ~25 km3/yr 30
Outline
Introduction Ground observations Satellite Observations Ground/Satellite agreement Conclusions
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Conclusions
Ground Gravity observations Good agreement between absolute and relative gravity measurements: -1.02 +/- 0.48 µGal/yr. => Modeled ice loss: ~25 km3/yr. Satellite Gravity observations GIA must be considered to study PDIMC in Svalbard from GRACE data. => Modeled ice loss: ~13-15 km3/yr. Topography of glaciers Need to be taken into account to estimate gravity variations due to ice mass change. Can lead to better agreement between ground and satellite data. 32
Thank you
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More…
More... On GRACE solutions On the uplift observed at Ny-Alesund
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GRACE trends January 2003/January 2008 CSR
GRGS
Cosine taper (30-50)
n = 50
µGal/yr
On GRACE solutions
GFZ
GFZ Mean
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On the uplift observed at Ny-Alesund
GPS, VLBI, Doris Sato & al. (2006)
5.2 mm/yr VLBI : 1994-2004 NYA1 : 1998-2004 NALL : 1991-2004
Keirulf & al. (2009) D’après Altamimi & al. (2007)
36
On the uplift observed at Ny-Alesund Keirulf & al. (2009)
Inst.
Période
PPP
DD
NYAL
-2003
8
6,5
NYA1
-2003
8,6
4,7
NYALES20
-2003
NYAL
2003-
13,3
8,9
NYA1
2003-
13,2
9,1
NYALES20
2003-
7,3
9,9
Doris Ign09wd01 : 1993-1999: 6.2 +/- 0.6
mm/yr
1999-2003: -0.3 +/- 0.9 mm/yr 2003-2009: 6.2 +/- 0.3
mm/yr
Up (mm/yr) 37
