Erik R. Ivins (JPL/Caltech)

1. 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 • Patagonian and Antarctic Peninsula Glacier Change

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? • Howubiquitous 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. UNAVCO - 30th Anniversary

3. Central America: example of ongoing slab window tectonics From Johnston and Thorkelson (EPSL 146, 465-474, 1997).

4. The physics of determining the mantle viscosity • Little Ice Age spatial scales: 100’s km • Little Ice Age time scales: 100’s years GIA is measured with GPS geodesy

5. Southernmost South America Breitsprecher and Thorkelson (2009) 0 Ma 12 Ma UNAVCO - 30th Anniversary

6. Active Slab Windows: How ubiquitous? How Important? Thorkelson et al. Geology 2012 UNAVCO - 30th Anniversary

7. What do geodesists have to say? • Model by Pollitz and Nyst (2005) • Strain-rate and velocity using PBO GPS data • h= 1.2 x 1019 Pa sec • Zandt and Carrigan (1993) (seismic tomographic flow model) • h < 5 x 1019 Pa sec • Studies Pertinent to Window south of Mendicino Triple Junction UNAVCO - 30th Anniversary

8. What do the climate scientists have to say? • Importance of trend in the Atlantic Multi-decadal Oscillation • Two competing hypotheses • 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 UNAVCO - 30th Anniversary

9. 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? UNAVCO - 30th Anniversary

10. Little Ice Age to modern-day Antarctic Peninsula • Observations: • Outlet glacier height changes since 1948 • 9 Ice shelf catastrophic break-ups 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? UNAVCO - 30th Anniversary

11. 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 UNAVCO - 30th Anniversary

12. Patagonian data and interpretation Input for elastic model from Willis, Pritchard et al., GRL 2012 UNAVCO - 30th Anniversary

13. Patagonia Ice History (loss rates in Gt/yr) Rate of loss in Gt/yr UNAVCO - 30th Anniversary

14. c2 - fit Model A versus Model B h = 1.6 x 1018 Pa sec h = 8 x 1018 Pa sec c2 UNAVCO - 30th Anniversary

15. Antarctic Peninsula UNAVCO - 30th Anniversary

16. Ice loss history UNAVCO - 30th Anniversary

17. Why is solving for GIA important to climate change studies? GRACE JPL Mascon 2003-2013 Corrected for GIA UNAVCO - 30th Anniversary

18. 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. UNAVCO - 30th Anniversary

19. What do climate scientists have to say? • Antarctic Peninsula & Southern Patagonia • Sea Surface & Atmospheric surface temperatures rise (SST & SAT) – trend since AD 1900 • Sea Ice Concentration (SIC) around Antarctica during 1900-2014 • Atlantic Multi-decadal Oscillation (AMO) serves as a dominant teleconnectionmechanism for LIA – to ‘modern’ glacier demise in Antarctic Peninsula & S. Patagonia (Li, Holland, Gerber & Yoo, Science2014) (CAM4 & GFDL) • Two hypotheses: • Global warming and ice mass loss are post-1960’s phenomenon – e.g. Greenland, etc., are ‘stable’ until about late 1980’s • Mass transport (ice-to-ocean) is better characterized by the tide-gauge record – sustained ice losses traced back to the late 1880’s UNAVCO - 30th Anniversary

20. 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 UNAVCO - 30th Anniversary