Controls on circum-Antarctic grounding line sinuosity

Mapping of modern and paleo-grounding lines of the Antarctic Ice Sheet elucidates changes in grounding line positions, extent of grounding zones and grounding line processes. Positional differences across individual grounding lines conceptually result in portions that are farther retreated or advanced, manifested as longitudinal (plan-view) grounding line sinuosity. We explore the causes and significance of such sinuosity by coupling observations of contemporary Antarctic grounding lines and paleo-grounding lines expressed as ice-marginal landforms. We find that there is little geographic (i.e., regional tectonic and geologic) control on grounding line sinuosity except for larger ranging sinuosity for grounding lines situated on sediment(ary) beds. Surprisingly, grounding line sinuosity is highest on low sloping beds and lower on rougher beds with few exceptions where grounding lines are presumably pinned on topographic highs. For contemporary systems, sinuosity is higher and more variable for grounding lines near floatation and with zero to low buttressing by floating ice. Additionally, higher ice-flow velocities are associated with lower grounding line sinuosity. From paleo-grounding lines, sinuosity increases with ice-marginal landform size, suggesting that greater sinuosity develops through increased grounding line sediment flux and/or occupation time. Retreat magnitude is larger and more variable for more sinuous paleo-grounding lines, perhaps indicating that sinuosity sensitizes grounding lines for retreat. With sinuosity relationships to contemporary ice-flow velocities and paleo-retreat magnitudes, we argue that sinuosity is a product of spatiotemporal changes in grounding line behavior. Increased grounding line sinuosity fundamentally increases grounding lines to ocean exposure and potentially amplifies tidal-influence processes, both of which may lead to larger retreat events particularly on low-sloping beds.