In a significant revelation, researchers have found that the grounding line of the southern Ronne Ice Shelf in Antarctica can move up to 15 km (six miles) with changing tides.
This grounding line marks the boundary between the land-based section of the ice sheet and the floating ice shelf, playing a crucial role in ice stability. Understanding these dynamics is vital for predicting Antarctica’s response to climate change and its impact on global sea level rise.
Lead author Bryony Freer, a glaciologist at the British Antarctic Survey and the University of Leeds, emphasizes that while ice sheet changes are typically considered slow over long timeframes, this research highlights processes occurring over minutes to hours that can have significant impacts.
GROUNDING LINE’S MOVEMENT
The grounding line’s movement is influenced by the rising tide, which temporarily shifts it inland, and then it returns seaward during low tide. Earlier measurements of grounding line movement were limited in scope and duration, but this study continuously monitored a substantial portion (220 km) of the Ronne Ice Shelf grounding line for nearly five years.
Using lasers bounced off the ice by the orbiting satellite ICESat-2, the researchers measured the ice surface’s height and its daily tidal fluctuations with high precision. This data enabled them to calculate the shifting position of the grounding line.
FAST MOVING GROUNDING LINES
The study reveals that the grounding line’s shift of up to 15 km between high and low tide is one of the largest observed in Antarctica. It demonstrates that the grounding line can move at speeds exceeding 30 km per hour, allowing ocean water to penetrate several kilometres further under the ice sheet.
This exposure to seawater could accelerate ice melting from beneath the ice sheet. In less stable Antarctic regions like the Thwaites Glacier, this process has historically contributed to grounding line retreat.
The rate of grounding line movement depends on factors such as tidal range, seafloor topography, and ice strength. Importantly, the study found that in some regions, the grounding line moves inland much faster during rising tides than it retreats during falling tides. This suggests that seawater may become trapped under the ice during grounding line readvancement, potentially intensifying ice sheet melting from below.
MORE OBSERVATION
The researchers stress the need for improved observations and modelling of these tidal processes to better understand their implications for long-term ice sheet change. They recommend future satellite-derived measurements of grounding line position include timestamps, tide height, and phase data. Expanding the analysis to cover more of Antarctica is also a priority.
Helen Amanda Fricker, ICESat-2 Science Team Leader and co-author of the paper, underscores the importance of such research in utilizing advanced space-based measurements to reveal dynamic features on ice shelves and calls for continued measurements in future missions.
