Mysterious Ocean by Peter Townsend Harris

Author:Peter Townsend Harris
Language: eng
Format: epub
ISBN: 9783030156329
Publisher: Springer International Publishing

At the time of the glacial maximum in the southern hemisphere, the Antarctic ice sheet advanced across much of the continental shelf. In South America, glaciers from the Andes extended across the shelf carving fjords and deep shelf valleys. Tierra del Fuego was joined to the mainland by a land bridge, and a thick ice sheet extended over the region. In Australia, a small ice sheet draped over the highlands of Tasmania which was joined to the mainland by a land bridge.

In the northern hemisphere, the continental shelf of Northern Canada is actually joined to northern Greenland (which is a part of the North American continental plate), and a massive ice sheet covered the archipelago, joining Greenland to Canada. In Northern Europe, ice sheets filled the Baltic Sea and smothered the Barents Sea, joining the island of Svalbard to the mainland.

In addition to the exposed shelf area were extensive floating ice shelves , essentially the floating continuation of continental ice sheets and glaciers. Examples of ice shelves exist today, and they occur along the East Antarctic margin and in the Ross Sea, in the Weddell Sea, and in Prydz Bay. These floating ice shelves are typically 1 km thick. At the point where they transition from a grounded glacier to a floating ice shelf with a cavity of seawater beneath, their bottoms drag along the seabed leaving grooves and piles of rocks and sediment that mark their passage.

During the last glacial maximum, ice shelves extended over all of the Antarctic shelf that wasn’t already under a grounded ice sheet or glacier. The Arctic Ocean was reduced in area by around 50% because of the vast area of exposed continental shelf located offshore of Siberia. Evidence suggests that the upper 1 km of the entire Arctic Ocean was frozen solid and grounded on the seabed during the late Pleistocene (probably around 130,000 years ago), but it is not certain exactly when this may have occurred.8 It may have also reached this thickness 20,000 years ago during the last glacial maximum.

Beyond the ice shelves is the sea ice zone, which grows and shrinks with the seasons. In the ice-age winter, the maximum extent of the sea ice zone around Antarctica extended close to a latitude of 45° south. Winter maximum sea ice in the northern hemisphere was located off the coast of France and extended across the North Atlantic to the coast of Maine. Sea ice extended well south of the Aleutian Islands in the North Pacific during winter. The Earth’s floating ice shelves covered an area of as much as 15 million square kilometers, and sea ice covered another 15–20 million square kilometers during winter, leaving just 300 million square kilometers of liquid ocean surface during the ice age 20,000 years ago.

The exposed continental shelves, floating ice shelves , and sea ice zones had enormous consequences for ocean currents that were diverted into different pathways. Water flow from the Pacific to the Indian Ocean through the Indonesian archipelago was greatly reduced, and the Arctic Ocean was cut off from the Pacific by the Bering land bridge.

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