Page 65 - (DK) Ocean - The Definitive Visual Guide

Shutting Down the 63

Atlantic Conveyor

Global warming, it has been suggested, might have
CAUSES AND EFFECTS OF SHUTDOWN
the paradoxical long-term effect of lowering
temperatures in Europe. The basis on which this CHANGES IN ARCTIC ICE
COVER There is ample
could happen would be a shutdown of the Atlantic
evidence from satellite
Conveyor – a system of currents that, at present, keeps surveys that the extent of
summer sea ice in the Arctic
western Europe warm. Part of a worldwide pattern of
Ocean is diminishing rapidly
connected currents, the Atlantic Conveyor has two at a rate of about 14 percent
main components. The first is a flow of warm surface per decade. Should the
Atlantic Conveyor shut down,
water into the northeastern Atlantic in the North however, this trend would
Atlantic Drift – an extension of the Gulf Stream. The reverse—Arctic seas close
to the Atlantic, such as the
second component is the sinking of cold, salty water ARCTIC SEA ICE Greenland Sea and Barents
in the far north and the subsequent deep-ocean flow Sea, would become iced
of this water back toward the equator. over all year.
The conveyor might shut down if the Arctic seas
are flooded with fresh water as a result of melting ARCTIC MARINE LIFE Any
sea-ice and increased river run-off caused by global shutdown in the North Atlantic
Drift—the extension of the Gulf
warming. Since fresh water is less dense than salt Stream that brings warm water
water, surface waters in these regions would become to northwestern Europe—could
less likely to sink – risking disrupting the conveyor. have a major effect on life in
Arctic areas adjacent to the north
If this were to occur, Europe’s average temperature Atlantic. Changes in the currents
could fall. LIFE SUPPORT FOR THE OCEAN FLOOR would interfere with plankton
production, affecting the whole
How likely is this to happen? Computer models food chain. The likely drop in
suggest that the current increase in the flow of temperature would also drive
out some species of fish and
fresh water in the Arctic is not high enough to shut invertebrates, which include
down the conveyor. The models also suggest that crabs, starfish, and sea urchins.
the flows will not reach high enough levels for
at least a century. Although a weakening of the
conveyor could occur over the medium term,
THE MACKENZIE RIVER
the models suggest that the overall outlook in this
DELTA Increased flow in
time frame could still be warming, rather than Arctic rivers such as the
cooling, over Europe. Mackenzie—caused by
the melting of glaciers
and permafrost—might
contribute to a shutdown
Changes in the Atlantic Conveyor of the Atlantic Conveyor
by flooding fresh water into
At present, warm surface water moving north from the equator INFLOWS the Arctic Ocean.
replaces cold water that sinks in the north Atlantic. Winds
flowing over the warm ocean absorb heat and transfer it to
western Europe. An increase of fresh water in the far northern THE SCILLY ISLES Situated 30 miles (50 km) off the southwest
Atlantic could mean that cold water no longer sinks there, tip of Great Britain, the Scilly Isles sit directly in the path of the
shutting down the system and chilling Europe. North Atlantic Drift. As a result, they enjoy a subtropical climate
and are a haven for plants from all over the world. If the Atlantic
Conveyor ground to a halt, gardens such as these would become
PRESENT CIRCULATION
desolate as average temperatures plunged to about 9°F (5°C).
cold water moves
south over ocean floor
winds absorb heat
from ocean and
transfer it to Europe
warm water flows
north from equator,
THE NORTH ATLANTIC DRIFT
transferring heat
northward
END OF THE ATLANTIC
CONVEYOR
lid of less salty water
over denser, saltier water
winds absorb less heat INTRODUCTION
from ocean, and transfer
less warmth to Europe

warm Gulf Stream no longer
flows into north Atlantic