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EGU 2017: New atlas shows polar seabeds

by Liz Kalaugher

Frost polygons: This polygonal or geometric patterns on the shallow seafloor (10-17 m water depth) here shown on a side-scan sonar image, were formed when the area was emergent (land) during the last glacial and was permanently frozen but not covered by glaciers.

Frost polygons: This polygonal or geometric patterns on the shallow seafloor (10-17 m water depth) here shown on a side-scan sonar image, were formed when the area was emergent (land) during the last glacial.

Wednesday saw a team of geophysicists at the EGU meeting present their new Atlas of Submarine Glacial Landforms. Four years in preparation, the atlas is the work of more than 250 marine geologists and glaciologist and is the most comprehensive and high-resolution atlas to date of the seafloor of both polar regions. The last such atlas was created 20 years ago.

Kelly Hogan, one of the Atlas editors, detailed at a press conference how the atlas reveals how ice has shaped the sea floor. Scientists will use the atlas to interpret the history of Earth’s large ice sheets and examine how environmental change reshaped continents.

Iceberg ploughmark showing rotation amongst a field of pockmarks from the central Barents Sea. Red 240 m water depth, purple 252 m.

Iceberg ploughmark showing rotation amongst a field of pockmarks from the central Barents Sea. Red 240 m water depth, purple 252 m.

The atlas assembles images of the sea floor that together cover an area the size of Great Britain. Modern acoustic mapping from onboard ship can image glacial landforms that are as much as five times smaller than earlier methods. Multibeam bathymetry, for example, creates a fan of sound and measures the return time of each ping to measure water depth across the fan. The researchers also used seismic reflection to look at sediment and remotely operated vehicles to take pictures from the seafloor.

These techniques revealed permafrost patterns on the floor of the Laptev Sea that became submerged when sea-level rose. The patterns are well-preserved because of the absence of weathering and human activities like road-building. In the Barents Sea the atlas shows ploughmarks on the seabed caused by the keel of an iceberg, in what’s one of Hogan’s favourite pictures.

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