Going with the Flow

Wind and gravity aren't the only forces that move the
oceans water there's also a conveyor belt at work.

The Great Ocean Conveyor works by thermohaline
circulation water movement caused by density
differences. The oceans are layered in water masses
that differ in temperature and salt content. Lower
temperatures and higher salinity translate to greater
density.

The densest water in the ocean is formed at high
latitudes, in the Arctic and Antarctic regions. In the
North Atlantic, for example, cold Arctic air cools the
salty surface water until it becomes dense enough to
sink.

This deep water slowly flows southward as the first
leg of the conveyor belt. It eventually gets swept
up with other deep water moving eastward around
the Antarctic continent. Here, strong winds on the
sea surface gradually mix the deep frigid water with
warmer layers above it. This mixing continues as the
water flows into the Indian and Pacific oceans, where
some of it finally returns to the surface up to 1,000
years later! Surface currents drive the conveyor belt
from here on, sweeping the now-warm water into the
southern Atlantic, then back toward Greenland to
complete the circuit.

The ocean conveyor moves huge amounts of heat
around the globe, making it a key regulator of Earth's
climate. Scientists have linked some major climate
shifts in Earth's history to conditions that prevented
water from getting cold enough or salty enough to
sink, bringing the conveyor to a halt. They're also
investigating whether mankind's impact on the oceans
could affect the conveyor and thus, the world climate
in the future.