The researchers of the Grantham Institute and Department of Earth Science and Engineering, Imperial College London, UK and Universiti Malaysia Terengganu, together with colleagues from Newcastle University UK, University of Exeter UK, University of Kansas USA, University of Alabama USA, University of California USA, Stanford University USA and University of Bristol UK have published an article in Nature Communication, a prominent scientific journal, on the 1st of November 2018 (Nature Communication 9, Article number : 4576 - 2018)
HARD ROCK LANDFORMS GENERATE 130 KM ICE SHELF CHANNELS THROUGH WATER FOCUSING IN BASAL CORRUGATIONS
Synopsis: Sea level rise poses a major socio-economic problem for hundreds of millions of people living in close proximity to the ocean, in particular Southeast Asia. While there are many factors effecting sea level rise, the principle cause comes from the collapse and melting of large glaciers around the world. Over the years, the instability of polar ice-sheets caused by atmospheric and ocean warming has been a major concern regularly discussed in conjunction with the climate change issue. There are two very large ice-sheets on Earth: the Greenland and Antarctic ice-sheet. Antarctica is located at the southernmost latitude and is divided into two distinct regions: East and West Antarctica. Although West Antarctic Ice Sheet (WAIS) is smaller in size relative to its eastern counterpart, it is thought that the WAIS is much more unstable. This instability is caused by the WAIS resting on a bed approximately ~2 km below sea level, where the ice is in direct contact with the warm ocean water.
Ice-sheet is a block of ice which is still grounded on a bedrock, whereasice shelf is a freely floating body of ice still attached to the ice-sheet. The boundary between ice-sheet and ice shelf is known as grounding line (GL). A fraction of ice shelf which has been split from the grounded ice-sheet is known as an iceberg. Ice shelves play an important role in the stability of an ice-sheet by providing mechanical ‘back force’ support to the ice-sheet. In other words, the breakdown of an ice shelf would result in the ice-sheet becoming unstable. Given the importance of maintaining ice shelf integrity in support of ice-sheet stability, it is crucial to understand processes which could potentially cause ice shelf collapse.
This study looks into the internal ice-sheet and ice shelf processes at the Foundation Ice Stream located at the northern grid of the WAIS. Satellite images reveal flow stripes parallel to ice sheet flow on Foundation Ice Stream and meandering features on the ice shelf which are thought to be formed by water exiting the grounded ice-sheet. These meandering features are referred to as M-channels. Ice-penetrating radar data shows flow-parallel hard-bed landforms beneath the grounded ice-sheet and channels incised upwards into the ice shelf base, known as U-channels, located directly beneath the M-channels. Radar reflectivity and abruptness analyses reveal the presence ofsub glacial water alongside the landforms, indicating a well-organized drainage system. The landforms dictate the exit location of the sub glacial water from the ice-sheet and into the ocean water beneath the ice shelf (ice shelf cavity). Since the sub glacial water is fresher relative to ocean water, the water rises upwards. Warm cavity water mixes with the sub glacial water and erodes the ice shelf base causing an upward incised basal channel extending 130 km downstream of the GL. Hard-bedded landforms influence both sub glacial water system and ice shelf structure on formerly glaciated regions which indicate that they could be more widespread than thought previously.