Page 194 - (DK) Ocean - The Definitive Visual Guide

192 POLAR OCEANS

Ice Shelves

AN ICE SHELF IS A HUGE FLOATING ice platform, PEOPLE
formed where a glacier, or group of glaciers, extends SIR JAMES CLARK ROSS
from a continental ice sheet over the sea. The landward
side of an ice shelf is fixed to the shore, where there is The British naval officer Sir James Clark
Ross (1800-1862) spent his early adulthood
a continuous inflow of ice from glaciers or ice streams exploring the Arctic. In 1839, he set off
that flow down from the ice sheet. At its front edge, to find the south magnetic pole, and on
January 11, 1840 reached Antarctica, near
there is usually an ice cliff, from which massive chunks the western side of what is now called
of ice break off (calve) periodically, forming icebergs. the Ross Sea. Later, Ross and his crew
discovered an ice cliff 165 ft (50 m) high.
Ice shelves are almost entirely an Antarctic phenomenon, This was later named the Ross Ice Shelf.
with only a few small ones in the Arctic.

Antarctic Ice Shelves ICE CLIFF
This massive ice cliff was photographed at
Fimbul Ice Shelf the seaward edge of the Riiser-Larsen Ice
Ice shelves surround about 44 percent of the continent
Lazarev Ice Shelf Shelf. In front of it, emperor penguins line
of Antarctica and cover an area of some 600,000 square
Ekstrom Ice Shelf miles (1.5 million square km). The largest is the Ross up to enter the water at Atka Bay,
Weddell Sea Riiser Larsen Ice Shelf Ice Shelf, also called the Great Ice Barrier, discovered on the Weddell Sea.
Larsen Ice Shelf Brunt Ice Shelf
Amery by Sir James Clark Ross (see panel, above). It is as large
Ice Shelf
Filchner Ice Shelf as mainland France, with an area of about 190,000 square miles
Wilkins Ronne
Ice Shelf Ice Shelf West (500,000 square km) and is fed by seven different ice streams.
Antarctic Peninsula
Ice
George VI Shelf The second largest, the Ronne–Filchner Ice Shelf, covers about
Sound ANT ARCTICA
Abbot 160,000 square miles (430,000 square km). About 15 or so other
Ice Shelf
ice shelves are dotted around the edge of the continent. Since 1995,
a few of the smaller ice shelves around the Antarctic Peninsula,
Shackleton
Ice Shelf
Ross Ice including parts of the Larsen Ice Shelf, have disintegrated, most
Shelf probably as a result of ocean warming (see p.487).
Getz Ice Shelf
Ross Sea
Sulzberger Voyeykov ICE-SHELF LOCATIONS
Ice Shelf Ice Shelf
The two largest ice shelves—the Ross
Cook and Ronne–Filchner ice shelves—sit
Ice Shelf
on either side of west Antarctica.
Structure and Behavior
Every ice shelf is anchored to the sea floor (ending at a point called
the grounding line) and has a front part that floats. The front part is
usually 330–3,300 ft (100–1,000 m) thick, though only about one-ninth
protrudes above water. The back of an ice shelf is fixed while the front
part moves up and down with the tides, creating stresses that can lead
to the formation of cracks. Overall, there is a gradual movement of
ice from the rear to the front of an ice shelf, from where large tabular
icebergs occasionally calve. There is sometimes also a slow upward
migration of ice, due to seawater freezing
to the bottom of a shelf and the ice on the CALVING SHELF
upper surface melting and evaporating in The front part of an ice shelf will
sometimes break up and the pieces
summer. Even deposits from the sea floor
drift off as tabular icebergs. Each
under an ice shelf are sometimes brought piece visible here has a surface Gains in ice
OCEAN ENVIRONMENTS GAINS AND LOSSES Sea Inflow from Antarctic ice-sheet Cracks Floating ice shelf Freezing of seawater onto
to the surface by this mechanism.
area of several square miles.
Summer evaporation
From ponds on surface
Losses of ice
S
n
o
Iceberg calving
Tide
w f a l l
An ice shelf gains ice from
Icebergs
glaciers flowing into its
landward end, from new
Level
snowfall, and from seawater
freezing to its undersurface.
1000m
Sea level rises
(3280ft)
and falls with tide
It loses ice by iceberg calving,
by some summer melting of
Grounded ice
2000m
underside of ice shelf
its upper surface and through
(6560ft)
Melting of ice at depth
evaporation, and by melting
Grounding line
of part of on its undersurface.