"Paleo ice shelf-ocean interaction:

How we want to derive basal melt estimates

driven by ocean tides"

PhD Candidate: Ole Richter

Supervisory Team: Matt King, Ben Galton-Fenzi, David Gwyther 

PhD confirmation presentation

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

The Antarctic ice sheet is the largest potential source for future sea level rise

Future Antarctic contributions to GMSL

Deconto, R. M., & Pollard, D. (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531

Changes in glacial melt water flux impact Antarctic Bottom Water formation

Antarctic Bottom Water changes

Purkey, S. G., & Johnson, G. C. (2013). Antarctic bottom water warming and freshening: Contributions to sea level rise, ocean freshwater budgets, and global heat gain. Journal of Climate, 26

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Vertical column freshwater fluxes below 2000 m

Tide-switch "on" at major Antarctic ice shelves:

• increases net basal melt by 25% - 100%

• heavily changes basal melt magnitude and distribution

Makinson, K., Holland, P. R., Jenkins, A., Nicholls, K. W., & Holland, D. M. (2011). Influence of tides on melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica. Geophysical Research Letters, 38

Tidal currents increase ice shelf basal melting

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Tidal melting mechanisms

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

• mean circulation

• ocean mixing

• turbulent boundary layer transport

Mueller, R. D., Padman, L., Dinniman, M. S., Erofeeva, S. Y., Fricker, H. A., & King, M. A. (2012). Impact of tide-topography interactions on basal melting of Larsen C Ice Shelf, Antarctica. Journal of Geophysical Research: Oceans, 117

Griffiths, S. D., & Peltier, W. R. (2009). Modeling of polar ocean tides at the Last Glacial Maximum: Amplification sensitivity, and climatological implications. Journal of Climate, 22

M2

K1

PD

LGM

LGM GL+

Antartic paleo tides:

• have been amplified at LGM (K1 up to 70%; M2 up to 200%)

• inconsistently changed during the last deglaciation

• are sensitive to grounding line position

Antarctic MEGA tides at LGM

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

M2

M2

PD

LGM

LGM GL+

K1

K1

Background summary:

• Antarctic ice shelf basal melting is strongly dependent on tides

• Antarctic tides changed from MEGA at LGM to moderate at PD

Research scope:

• Quantification of changes in tidal melting between LGM and PD

• Identification of governing mechanisms that drive these changes

• Quantification of changes in dense shelf water export at Pliocene, the Last Interglacial and future scenarios

The missions

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Regional Ocean Modeling System (ROMS):

• 3D

• free surface

• terrain following

• ice shelf hydrostatic pressure

• ice-ocean thermodynamics (TEOS-10)

• Frazil formation (Ben)

• varying drag coefficient (Dave)

Fancy ROMS

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Domain

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Idea behind:

• captures important ocean currents
• resourceful
• FAST !

Resolution

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

St-Laurent, P., J. M. Klinck, and M. S. Dinniman (2015), Impact of local winter cooling on the melt of Pine Island Glacier, Antarctica, J. Geophys. Res. Oceans, 120

Velocity at 350 m

• 1 km resolution needed to resolve critical small eddies on continental shelf
• 10 km development -> 4 km, 1 year initial conditions -> 1 km, 1 month production runs

Sub ice shelf cavity

Southern ocean

Peltier (2014) global earth system model ICE-6G_C (VM5a)

Pollard (2016) dynamic ice sheet-shelf model

Small scale features

Schaffer (2016) Global high resolution present day topography map R-Topo

Paleo Topography

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Local tidal potential

Global ocean tides

Wilmes (2014) global paleo tide model

Paleo Tides

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Kate Hedstrom POT_Tides algorithm

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Current status

The strategy

paleo Antarctic tide-topo

ocean-ice shelf model ROMS

fate of AABW formation

ice sheet models

reduce uncertainties in

sea level rise projections

basal melt rates (LGM to PD)

dense shelf water export (PD, Pliocene, LIG, Future)

ice-ocean interaction

Knowledge

CPU POWER

PhD time

?

1. Background      2. Research scope      3.Methodology     4. Experiments, Outcomes      5. Summary

Summary

Thank you!