Century-scale continent-to-ocean ice mass transport and
measurement of lithospheric thickness and mantle viscosity using
GPS
Erik R. Ivins
(JPL/Caltech)
Focus: Little Ice Age &
Modern “Anthropogene”
Glacier Demise
Climate and Tectonics
• Slab-window environs of
the Eastern Pacific Rim
• Patagonian and Antarctic
Peninsula Glacier Change
Little Ice Age and Constraints on Upper
Mantle Viscosity of Slab Windows
• Who cares about slab window mantle viscosity?
• What do we know about the Little Ice Age above slab
windows?
• How ubiquitous are slab windows?
• Are there independent estimates of the viscosity?
• We use GPS uplift data – robust (non-elastic)
correction for GRACE mass balance 2003-2014 – to
derive new estimates for two active slab windows.
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Central America: example of ongoing
slab window tectonics
From Johnston and Thorkelson
(EPSL 146, 465-474, 1997).
The physics of determining the mantle viscosity
o
o
Little Ice Age spatial
scales: 100’s km
Little Ice Age time scales:
100’s years
GIA is measured with GPS geodesy
Southernmost South America
Breitsprecher and Thorkelson (2009)
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Active Slab Windows: How ubiquitous?
How Important?
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Thorkelson et al. Geology 2012
What do geodesists have to say?
• Model by Pollitz and Nyst (2005)
o Strain-rate and velocity using PBO GPS data
o h= 1.2 x 1019 Pa sec
• Zandt and Carrigan (1993) (seismic tomographic
flow model)
o h < 5 x 1019 Pa sec
• Studies Pertinent to Window south of Mendicino
Triple Junction
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What do the climate
scientists have to say?
• Importance of trend in the
Atlantic Multi-decadal
Oscillation
• Two competing hypotheses
1.
2.
Rapid rates of land ice loss begin
only after ~ 1989
Loss initiated at times coincident
with LIA terminating conditions –
at substantial mass rates during
1870 -1900
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Little Ice Age to modern-day Patagonia
• How much mass at LIA
max?
• 2003-2013 mass loss rate
via GRACE (26 ± 8 Gt/yr)
• History of the rate of landocean mass transport. Do
we know it?
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Little Ice Age to modern-day Antarctic
Peninsula
• Observations:
i.
ii.
iii.
iv.
Outlet glacier height changes
since 1948
9 Ice shelf catastrophic breakups since 1989
Surface atmospheric
temperature rising since 1900
GRACE & ICESat ice loss rate -37
± 10 Gt/yr
• Question: When does
land ice mass loss begin?
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What do geodesists have to say?
• Observe GPS uplift
• Southern Patagonian network: Heiner Lange PhD
thesis
• Antarctic Peninsula: IGS stations – Reinhard
Dietrich (TU Dresden) network has legacy to early
1990s – NSF & BAS effort (LARISA)
SPI 31 stations – max uplift rate at 39 ± 2.5 mm/yr
AP 11 stations – max uplift rate at 14 ± 3 mm/yr
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Patagonian data and interpretation
Input for
elastic
model
from
Willis,
Pritchard
et al., GRL
2012
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Patagonia Ice History (loss rates in Gt/yr)
40
35
30
Rate of
loss in
Gt/yr
25
1870-1943
20
1944-1975
1976-1994
15
1995-2013
10
5
0
Model A
Model B
Model C
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Model D
13
2
c
- fit
h = 1.6 x 1018 Pa sec
Model A
versus
Model B
h = 8 x 1018
Pa sec
c2
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Antarctic Peninsula
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Ice loss history
30
25
20
15
10
5
1870-1900
1901-1930
1931-1957
1958-1988
1989-2002
2003-2014
0
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Why is solving for GIA important to
climate change studies?
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Antarctic Peninsula GRACE corrected mass loss
Conclusions: GPS station uplift data
• Determine 2 of 5 slab-window upper
mantle viscosity values: 0.6 – 3 x 1019 Pa
sec --- consistent with Pollitz and Nyst
(2005).
• Sensitivity to both LIA ice history & to
space era loss is demonstrated – But
independent constraints are unlikely
• Data + model derive a 10-15 Gt/yr level
GIA correction for GRACE mass balance.
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What do climate scientists have to say?
• Antarctic Peninsula & Southern Patagonia
o Sea Surface & Atmospheric surface temperatures rise (SST & SAT) – trend since
AD 1900
o Sea Ice Concentration (SIC) around Antarctica during 1900-2014
o Atlantic Multi-decadal Oscillation (AMO) serves as a dominant teleconnection
mechanism for LIA – to ‘modern’ glacier demise in Antarctic Peninsula & S.
Patagonia (Li, Holland, Gerber & Yoo, Science 2014) (CAM4 & GFDL)
• Two hypotheses:
o Global warming and ice mass loss are post-1960’s phenomenon – e.g.
Greenland, etc., are ‘stable’ until about late 1980’s
o Mass transport (ice-to-ocean) is better characterized by the tide-gauge record
– sustained ice losses traced back to the late 1880’s
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Ice Losses and Slab Windows – Overview of this talk
• Slab windows
• What parts of the climate are responsible for
Little Ice Age demise?
• Patagonian GPS Network
• Antarctic Peninsula GPS Networks
• GIA model Results – GRACE JPL Mascon Solutions
2003-2014
• Speculations – Cryosphere
• Speculations – Mantle - Lithosphere
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