The impact of internal variability in ocean-induced melting on Totten GlacierFelicity McCormack1,2, Jason Roberts3, David Gwyther2, Mathieu Morlighem4, Tyler Pelle4

1School of Earth, Atmosphere & Environment, Monash University, Victoria, Australia felicity.mccormack@monash.edu 2Institute for Marine and Antarctic Studies, University of Tasmania, Tasmania, Australia 3Australian Antarctic Division, Tasmania, Australia 4Earth Systems Science, University of California, Irvine, California, USA

This research was supported under Australian Research Council's Special Research Initiative for Antarctic Gateway Partnership (Project ID SR140300001).

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Aurora Subglacial Basin domain using the Ice Sheet System Model

ICE SHEET MODEL SETUP

How does Totten Glacier respond to constant & variable ocean forcing?

500 year simulations using ISSM with different ocean temperature forcing scenarios (PICOp parameterization):1. Mean temperatures of

-1.15, -0.95, … 0.05 °C (7 scenarios)

2. Mean temperatures as above, plus variability based on ocean model output (varying magnitude of variability; 84 scenarios)

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LIMITED STABILITY OF TOTTEN GROUNDING LINE

Constant ocean temperature forcing Variable ocean temperature forcing

1. Final grounding line stable close to present-day position for T=-0.95°C, otherwise advance or retreat

2. Variability has stabilising effect on grounding line position for T=-0.85°C, but limited impact for simulations with large-scale advance or retreat

T=-1.15T=-1.15

T=-0.95T=-0.95

T=-0.85T=-0.85

T=-0.75T=-0.75

T=-0.55T=-0.55

T=-0.35T=-0.35

T=-0.15T=-0.15

T=0.05T=0.05

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T=-0.75T=-0.75

T=-0.55T=-0.55

T=-0.35T=-0.35

T=-0.15T=-0.15

T=0.05T=0.05

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Grounding line migration more sensitive to effect of melt rate decreases than increases (Hoffman et al., 2019)

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TOTTEN EVOLUTION STRONG FUNCTION OF MEAN STATE

Constant background temperature plays a relatively more important role than variability in determining Totten’s response to ocean forcing

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PINNING POINT MODULATES GROUNDING LINE MIGRATION

Grounding line stability in simulations with ocean temperature variability is linked to the influence of the pinning point at southern end of ice shelf

Fig. 7. Schematic of the mechanism whereby the !ow of the glacier, U, can be (a) more, or (b) less impeded by theback-stress, S, resulting from variable ocean heat !ux, Q, driving basal melting of the ice shelf, M, where the size ofthe arrows show the relative in!uence of each component when compared between the two scenarios.

OCEAN FORCING OF TOTTEN GLACIER VARIABILITY 183

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Pinning point changes back stress, with feedbacks on upstream ice speed and thickness (Roberts et al., 2017)

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PINNING POINT MODULATES DISCHARGE

For variable ocean forcing simulations, nonlinear dynamics + ice shelf interaction with pinning point modify variance in ice discharge

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MODEL DETAILS

Ice Sheet System Model (ISSM; Larour et al., 2012) of Aurora Subglacial Basin• Shelfy-Stream Approximation (MacAyeal, 1989)• Time stepping every 1/2 month, and ice velocity, thickness, surface,

and grounding line are updated at each time step• 114 915 anisotropic triangular elements, with maximum resolution of

1 km near grounding line• BedMachine Antarctica bed topography (Morlighem et al., 2020)• Constant surface mass balance and atmospheric temperature

from RACMO2.3 (Lenaerts et al., 2012)• Constant geothermal heat flux of 0.55mW/m2

• Inversion for basal friction and ice shelf rigidity

PICOP ocean melt rate parameterisation (Pelle et al., 2019)• Parameterises overturning circulation in ice shelf cavity• Includes melt water plume at grounding line• Inputs are far-field temperature and salinity near ocean base

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