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
Century-scale continent-to-ocean ice mass transport and measurement of lithospheric thickness and mantle viscosity using GPS. Focus: Little Ice Age & Modern “ Anthropogene ” Glacier Demise. Erik R. Ivins (JPL/Caltech). Climate and Tectonics. Slab-window environs of the Eastern Pacific Rim - PowerPoint PPT Presentation
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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.
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 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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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