Hitching a Ride on the Global Ocean Conveyor Belt
Susan Lozier Studies How Currents Deep Below the Ocean's
Surface Can Affect Our Climate
By Lisa M. Dellwo
IT'S JUNE, and Susan
Lozier is gearing up for her summer research
voyage. In her spacious office atop West Campus’s Old
Chemistry building, she scans the controlled clutter on her
desk for a Coast Guard advisory on a new motion sickness medication.
Yes, even oceanographers can get seasick.
Seasick pills are just one of the hundreds of details Lozier
must attend to before embarking on the first cruise in a three-year
project to map North Atlantic ocean currents. What she learns
will have important implications for understanding the role
of the world’s oceans in global climate.
Lozier is the Truman and Nellie Semans/Alex Brown & Sons
Associate Professor of Earth and Ocean Sciences in the Nicholas
School. A member of the Duke faculty since 1992, she is a
physical oceanographer who is increasingly recognized for
her research into the system of ocean currents known as the
global ocean conveyer belt.
“Here’s the ocean floor,” Lozier says,
sketching a basin-like shape on the back of a computer printout.
She points to one end of the basin—“this is the
North Pole”—and the other—“this is
the South Pole.”
Rapidly penciling arrows into her sketch, Lozier explains
that water from the higher latitudes—the subpolar regions—becomes
very cold over the winter and sinks, in a process called convection,
moving roughly in the direction of the equator, where it pushes
warmer, less dense waters up to the surface. Thus, waters
that are on the surface at high latitudes become deep waters
when they reach the tropics, and they are still cold. Meanwhile,
those warmer waters have to go somewhere, so they head back
in the direction of the poles.
This multi-dimensional system of ocean currents, the global
ocean conveyer belt, has long been understood to be an important
regulator of the world’s climate. Without the fluid
movement of the ocean, Lozier says, our poles would be much
colder and our tropics much warmer. One well-known current,
for instance, the Gulf Stream, brings heat from the tropics
up the North American East Coast to the North Atlantic region,
where prevailing winds carry its warmth to western Europe
and moderate the climate there.
Although surface waters are mixed by wind and waves, deeper
waters stay together as a unit, Lozier explains. So as the
cold waters travel the conveyer belt, they retain a set of
characteristics that amount to a fingerprint. “If you
steamed offshore of Cape Hatteras,” says Lozier, “and
dropped an instrument and started measuring temperature and
salinity at a depth of about 1,000 meters, you could say,
‘these waters came from the Mediterranean Sea.’
And if you went down further, you’d find waters from
the Labrador Sea, then the Norwegian-Greenland Sea. And in
the deepest waters, you’d find a water mass from Antarctica.”
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