Erik R. Ivins (JPL/Caltech)
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Transcript of Erik R. Ivins (JPL/Caltech)
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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 DemiseClimate and Tectonics
• Slab-window environs of the Eastern Pacific Rim
• Patagonian and Antarctic Peninsula Glacier Change
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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).
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The physics of determining the mantle viscosity
o Little Ice Age spatial scales: 100’s km
o Little Ice Age time scales: 100’s years
GIA is measured with GPS geodesy
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Southernmost South America
12 Ma 0 Ma
Breitsprecher and Thorkelson (2009)
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UNAVCO - 30th Anniversary
Active Slab Windows: How ubiquitous? How Important?
Thorkelson et al. Geology 2012
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What do geodesists have to say?
• Model by Pollitz and Nyst (2005)o Strain-rate and velocity using PBO GPS datao 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 hypotheses1. Rapid rates of land ice loss begin
only after ~ 19892. 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 land-ocean mass transport. Do we know it?
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Little Ice Age to modern-day Antarctic Peninsula
• Observations:i. Outlet glacier height changes
since 1948ii. 9 Ice shelf catastrophic break-
ups since 1989iii. Surface atmospheric
temperature rising since 1900iv. 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)
Model A Model B Model C Model D0
5
10
15
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25
30
35
40
1870-19431944-19751976-19941995-2013
Rate of loss in Gt/yr
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c2 - fit
Model A versus Model B
h = 8 x 1018 Pa sec
h = 1.6 x 1018 Pa sec
c2
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Antarctic Peninsula
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Ice loss history
Region 1
Region 2
Region 3
Region 4
Region 5
Region 6
0
5
10
15
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25
30
1870-19001901-19301931-19571958-19881989-20022003-2014
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Why is solving for GIA important to climate change studies?
GRACE JPL Mascon 2003-2013 Corrected for GIA
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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 Patagoniao Sea Surface & Atmospheric surface temperatures rise (SST & SAT) – trend since
AD 1900o Sea Ice Concentration (SIC) around Antarctica during 1900-2014o 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’so 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