Moving the Waters - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 97

Currents during benthic storms are quite sufficient to erode the
sea floor and carry and deposit sediment (and could, we suspect,
be enough to knock off their feet any deep-sea diver incautious
enough to venture into one). Over the millions of years that these
currents have operated they have built up masses of sediment
hundreds of metres thick. Geologists call these deposits contour-
ite drifts, and recognized them as thick sediment blankets on the
lower parts of continental slopes long before they managed to get
their hands on the sediments themselves by drilling down into
them. They used to think that contourites would retain a distinct
layering that would reflect successive benthic storms, but the bore-
hole cores showed that, between storms, the sea floor creatures so
burrowed through and chewed up the sea floor sediments that the
original stratification was entirely lost. (Contourites, because of
this thorough biological reworking, are difficult to recognize in
ancient rock strata.)
This deep current continues southwards, reaching Antarctica,
swinging round the continent into the Pacific where it journeys north,
then surfaces and heads back, now as a warm surface current, through
the Indian Ocean and into the Atlantic. It is not, of course, a simple
loop—there are bifurcations, junctions, partings—but in outline it
can be so represented. It has been termed the 'great ocean conveyor
belt', and it controls much that is in the air as well as the sea, for it is a
prime influence on climate (Fig. 8).
The final leg of the journey starts around the Gulf of Mexico, not
far off the tip of Florida. It is hot—usually too hot to be pleasant for
humans in the summer. The surface water here is also warm, having
absorbed energy from the Sun's rays. The whole surface layer is less
dense than the deeper waters beneath, and will not sink down into
them. The buoyancy caused by this warmth will keep this water near
the ocean surface for the next 8,000 kilometres.