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.3
Each season for the next three years, Lozier and her colleagues
will release six floats at carefully calculated points along
the Deep Western Boundary Current, three at a depth of 700
meters and three at 1,500 meters.
For this summer’s inaugural cruise, the researchers
also spent 10 days distributing sound sources in a wide arc
from the coast of Labrador to points south of Greenland. Previous
researchers have used floats that rise to the surface periodically
and beam their data to a satellite, but concerns have been
raised that these floats can lose their position in the deep
current during their time at the surface. So Lozier and Bower
chose to use passive acoustic floats that remain at the designated
depth for two years. Each day the sound sources emit a low-amplitude
sound that the floats “listen” for and use to
calculate their position. These data will be used to map the
current upon which the floats are traveling and calculate
the speed at which they are moving. The floats also take daily
measurements of temperature, salinity, and other data.
Although a research cruise sounds like a pleasant way to
spend a summer, the scientific team encountered temperatures
that averaged in the 40s—typical for the chilly Labrador
waters—and fogs that resulted from the collision of
warm air coming off the nearby land masses with the cold air
over the ocean. Hats and gloves were part of the scientists’
gear most days, and waterproof clothing was required when
the floats were deployed.
But most of the 14 days at sea were calm, so the Coast Guard’s
seasick medicine didn’t get a workout. And the team
was rewarded on their last day at sea when the Oceanus unexpectedly
broke through a fogbank and entered a feeding ground for finback
whales. At least 50 of the marine mammals were spouting nearby,
recalls Lozier. “It was one of the most amazing things
I’ve ever seen.”
The scientists will also be releasing floats in November
and May, when the Labrador Sea can be even less hospitable.
“We’ll probably be drawing straws for those trips,”
Lozier laughs. Because ships don’t ply those waters
in the winter, an annual February release will be handled
by a float park established each November: a batch of floats
anchored to the sea floor is programmed to detach from their
anchors on a set date and drift upward to their target depth.
Patience is a virtue scientists must cultivate, and it is
called for in this project. The floats will remain underwater
for two years each, faithfully collecting data every day.
They are programmed to then drop their ballast and return
to the surface, beaming two years’ worth of measurements
to a satellite, from where it will be retrieved by the scientific
team for analysis. It will be five years before the last data
are available.
The team will map the pathway each float followed and analyze
the variability of these tracks from season to season and
year to year. This information will be matched with climatological
data so that the researchers can demonstrate, for instance,
how the current’s pathway changes depending on the severity
of the winter.
The scientists will also learn more about the trajectory
of subpolar waters—do they go on a direct path to the
tropics or do they recirculate for awhile? This information
will help Lozier ascertain how quickly the ocean could adapt
in the event that heavy icemelt or riverflow or surface warming
created subpolar waters so fresh or warm that they didn’t
sink. Scientists have surmised that such shutdowns of the
ocean conveyer have occurred episodically in the geologic
past; by studying today’s ocean, Lozier and Bower hope
to shed light on the consequences of these past events.
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