Geology Reference
In-Depth Information
bottom water streams along the sea bed for thousands of kilometres until it branches in
the abyss of the south-west Atlantic, surfacing about a thousand years later in the Indian
ocean and in the central north Pacific, releasing its hidden cargo of carbon dioxide to the
air as the waters warm once more under the hot tropical sun. The water travels through
the tropical oceans, pushed along mainly by the power of the wind, warming as it goes,
until it completes its global journey as the great Gulf Stream that brings so much warmth
to the north-east Atlantic. If our planet has an equivalent of flowing blood, this must be
it, for this vast global flow of water ably distributes dissolved gases, warmth from the
sun and vital nutrients around Gaia's great spherical living body.
Figure 26: The global thermohaline circulation in the world's oceans. (
© Science Photo Library
)
But this global circulation of ocean water is a delicate thing, highly vulnerable to
changes in the density of sea water in the downwelling regions around Greenland.
Towards the end of the last ice age, as the world warmed, huge amounts of fresh water
from the melting of the North American ice caps entered the North Atlantic, freshening
the warm salty waters of the Gulf Stream to such an extent that their sinking was pre-
vented. As a result, the downwelling weakened or shut down around 12,900 years ago,
plunging Europe and the entire North Atlantic into a dramatic cooling event known as
the Younger Dryas, that delayed the beginning of the current warm interglacial by some
1,400 years. The effects of this cooling were felt far beyond Europe. Even more dra-
matic was the end of this period of intense cold, in which an abrupt warming of around
7
0
C took place in a decade or so. Herein lies another warning for contemporary soci-
ety—it seems likely that our war on nature is set to trigger similarly abrupt, catastrophic
changes to our climate—with very little warning.
