Spatial complexity of ice flow across the Antarctic Ice Sheet

• Published in: Nature geoscience Vol. 8; no. 11; pp. 847 - 850
• Main Author: Ng, Felix S. L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2015; Nature Publishing Group
• Subjects: 704/106/125; 704/2151/215; Climate change; Earth science; Earth Sciences; Earth System Sciences; Flow; Geochemistry; Geology; Geophysics/Geodesy; Ice; Ice sheets; Ice shelves; letter; Rheology; Streams; Surface velocity; Topography; Tributaries; Velocity; Antarctica; PS, Antarctica
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo2532

Ice streams control the discharge of ice from the interior of the Antarctic Ice Sheet to the coast. A map of flow convergence suggests that ice-stream flow is subject to a mechanical regulation that limits flow-orthonormal strain rates. Fast-flowing ice streams carry ice from the interior of the Antarctic Ice Sheet towards the coast. Understanding how ice-stream tributaries operate and how networks of them evolve is essential for developing reliable models of the ice sheet’s response to climate change 1 , 2 , 3 , 4 , 5 , 6 . A particular challenge is to unravel the spatial complexity of flow within and across tributary networks. Here I define a measure of planimetric flow convergence, which can be calculated from satellite measurements of the ice sheet’s surface velocity, to explore this complexity. The convergence map of Antarctica clarifies how tributaries draw ice from its interior. The map also reveals curvilinear zones of convergence along lateral shear margins of streaming, and abundant ripples associated with nonlinear ice rheology and changes in bed topography and friction. Convergence on ice-stream tributaries and their feeding zones is uneven and interspersed with divergence. For individual drainage basins, as well as the ice sheet as a whole, fast flow cannot converge or diverge as much as slow flow. I therefore deduce that flow in the ice-stream networks is subject to mechanical regulation that limits flow-orthonormal strain rates. These findings provide targets for ice-sheet simulations and motivate more research into the origin and dynamics of tributarization.