Hitching a Ride on the Global Ocean Conveyor Belt
Susan Lozier Studies How Currents Deep Below the Ocean's
Surface Can Affect Our Climate p.2
The fingerprints that help identify the individual water
masses, or what she calls “climate signals,” are
of special significance to Lozier. In particular, she is interested
in salinity and temperature, and whether changes in those
signals might tell us something about global climate change.
For instance, if icemelt or riverflow caused polar waters
to freshen or if the polar waters warmed, these surface waters
wouldn’t sink. Scientists believe the implications of
such a development for the earth’s climate could be
dramatic. In fact, evidence suggests that those conditions
might be on the verge of occurring. In 2000, scientists at
the National Oceanographic Data Center in Maryland published
a paper suggesting that the world’s oceans have been
warming over the last half-century. But while all of the oceans
are warming at the surface, they reported, in the North Atlantic
the deeper waters are also warming.
Having studied the dynamics of the North Atlantic basin since
her postdoctoral days at Woods Hole Oceanographic Institute
(WHOI), Lozier finds this trend disturbing. Water has a huge
heat capacity, she says, so it takes a tremendous amount of
heat to raise the temperature of water just a small amount.
Because of that property, the deep ocean serves as a sort
of storage locker for excess heat generated by our climate
system. If deep waters (those below 700-1000 meters from the
surface) are getting warmer in the North Atlantic, does that
mean the storage space is filling up more quickly than in
the past?
In order to understand this scenario better, Lozier believes
we need to learn more about how climate signals are distributed
in the ocean, particularly the deep ocean. With frequent collaborator
Amy Bower, a scientist at Woods Hole Oceano-graphic Institute,
she was awarded a five-year National Science Foundation grant
to verify the circulation pathways of newly formed water masses
as they leave the North Atlantic near Newfoundland and spread
to the rest of the ocean basin.
In July, Lozier, Bower, Duke graduate students Jaime Palter
and Ana Grappold, and four other scientists boarded the R/V
Oceanus, a WHOI research vessel, to launch the project.
Embarking on a two-week cruise from St. John’s, Newfoundland,
they deployed six instruments called RAFOS floats along the
Deep Western Boundary Current, believed to be the major southern
pathway used by waters from the Labrador Sea to reach the
tropics.
RAFOS floats resemble test tubes on steroids—four-foot-long
glass cylinders loaded with ballast that will enable them
to sink to the desired depth and containing instruments that
will record their position and the water’s temperature
and salinity. Although fragile in appearance (the glass is
less than a quarter inch thick), these floats have at least
a 90 percent survival rate, withstanding the buffeting sea
waters on their downward journey and the cold temperatures
in the deep waters that are their destination. They are most
vulnerable at the moment of their release, an awkward two-person
procedure that requires split-second timing to prevent the
35-pound instruments from shattering against the side of the
ship.
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