Erik R. Ivins (JPL/Caltech)

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

UNAVCO - 30th Anniversary 2

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


Southernmost South America

12 Ma 0 Ma

Breitsprecher and Thorkelson (2009)

UNAVCO - 30th Anniversary

Active Slab Windows: How ubiquitous? How Important?

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 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


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


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?


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?


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


Patagonian data and interpretation

Input for elastic model from Willis, Pritchard et al., GRL 2012


Patagonia Ice History (loss rates in Gt/yr)

Model A Model B Model C Model D0

5

10

15

20

25

30

35

40

1870-19431944-19751976-19941995-2013

Rate of loss in Gt/yr


c2 - fit

Model A versus Model B

h = 8 x 1018 Pa sec

h = 1.6 x 1018 Pa sec

c2


Antarctic Peninsula


Ice loss history

Region 1

Region 2

Region 3

Region 4

Region 5

Region 6

0

5

10

15

20

25

30

1870-19001901-19301931-19571958-19881989-20022003-2014


Why is solving for GIA important to climate change studies?

GRACE JPL Mascon 2003-2013 Corrected for GIA


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.


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


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

Documents

Erik R. Ivins (JPL/Caltech)