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 This area has proved particularly troublesome for researchers to
study, as scientific instruments are typically designed to either
sink to the ocean floor or float on the surface. But this elusive
region is teeming with ocean life that plays a key role in keeping
atmospheric carbon-dioxide (CO2) levels 30 percent lower than it
otherwise would be, according to the scientists from NOC.
"Just like the plants in your garden, phytoplankton - the plants in
the ocean - absorb carbon dioxide from the atmosphere. The
difference is when these guys sink they can go down into the deep
ocean. And then the deep ocean of course isn't in contact with the
air anymore and so it's captured and it's stored down there for long
periods of time," ocean biochemist Dr. Stephanie Henson told
Reuters, adding that understanding what processes are involved in
carbon transport in the ocean could lead to better predictions of
global environmental change.
 Professor Richard Sanders is leading a project to develop a
scientific instrument that can gather samples of these organisms. At
the NOC headquarters in Southampton, Sanders and his team are
testing a device they've built called PELAGRA, or the 'pelagic
lagrangian sediment trap'.
"This is specifically designed to attack and sample the key unknown
part of the ocean; we call it the 'twilight zone', where there's
just a little bit of light. So what this does is it samples the bit
between about 50 and 500 meters, that's where a lot of the action
is. We've got stuff sinking and there's lots of organisms that live
there eating it. And what we want to know is what they're doing.
What this device does is it captures the flux at different depths in
that depth range, so we can work out what the organisms that live
there are doing," explained Sanders.
PELAGRA's sediment traps will help scientists calculate the carbon
entering the oceans by providing a sample of the volume of sediment
that sinks in a given period of time. Known as 'marine snow' for its
appearance as it falls through the ocean, this sediment consists of
flakes of marine detritus - dead plant and animal plankton, and
plankton faeces.
 "Marine snow is composed of dead phytoplankton which sort of clump
together to form flakes and then they're heavy enough to sink down
into the deep ocean. It can also be formed of little animals which
eat the little plants and then they poop out that carbon, and then
their fecal pellets are very heavy and they sink down to the bottom
of the ocean, also carrying lots of carbon with them," said Henson.
She added that scientists have known about marine snow as a
mechanism for getting carbon out of the atmosphere and down into the
ocean for about 50 years, but it's only recently that technology has
evolved to a degree that allows for accurate measurements.
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But building a scientific instrument capable of effectively
collecting samples of marine snow presented a multitude of
challenges for Sanders' team, who had to get the 100 kilogram
PELAGRA device to drift in the 'twilight zone' without sinking or
rising to the surface.
"If we can get the density of this instrument just right, it will
sit neither sinking nor floating. Now that's easy to say but it's
actually a considerable challenge to do... They weigh about 100
kilograms and we need to ballast them to approximately better than
one gram. So that's a considerable challenge. The way that we do
that is by putting them in tanks of water... and adding weights
until they're just sinking; at which point we know they have the
same density as the water that they're sitting in," said Sanders.
The team is preparing to embark on two missions to the south
Atlantic Ocean in a bid to understand why marine snow is more
prevalent in some areas than others and to collect enough samples to
determine how important it is in removing CO2 from the air. The
research, Henson said, will also lead to more advanced computer
climate models that could more accurately predict future climate
change.
"This new project that we're working on is going to try and figure
out what kind of things control when and where we get this marine
snow occurring, how much carbon it takes down into the deep ocean
and, ultimately, with the data we collect, we're going to build new
models which are going to help us to better predict the ocean
storage of carbon and its impact on the climate."
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