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| The author loads an XCTD into the hand-held launcher and then
initializes the data acquisition computer program.
Photo by Rick Krishfield, WHOI. |
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| While the XCTD and launcher are carried out to the stern, Terry
Rhyno feeds the serial communications cable through the passage.
Photo by Rick Krishfield, WHOI. |
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| The XCTD is launched by pulling a restraining pin, and descends
quietly into the ocean. The thin wire must be kept clear of nearby icefloes
to ensure that it is not broken prematurely, so that all of the data down to
1000 m may be received. Photo by Rick Krishfield, WHOI. |
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Cruise - 2006 Dispatches
Calendar
Dispatch 21, August 25, 2006
By Shigeto Nishino, JAMSTEC
Tiny Torpedoes
So far this cruise, nearly 60 expendable
conductivity-temperature-depth probes (XCTDs) shaped like tiny torpedoes
have been launched from the stern of the Louis into the Arctic Ocean, with
perhaps another 40 more to go. The probe measures the seawater temperature
and salinity while sinking to a depth of 1000 m (over 3000 ft) in only about
10 minutes. The data is communicated back to a deck unit and computer
onboard the ship by a fine wire which breaks when the probe reaches its
maximum depth.
One advantage of the XCTD observation is the short amount of ship
time that it takes to make a measurement (compared to a CTD rosette cast
which takes several hours). Consequently, it is suitable to capture fine
scale ocean structure between CTD casts, such as mesoscale eddies and
frontal boundaries. Sometimes, the XCTD is also a powerful tool for a
preliminary survey for the CTD (which measures not only temperature and
salinity but also oxygen, turbidity, and fluorescence in the sea water). The
XCTD data may suggest the best location where a CTD cast should be
conducted.
Combining the XCTD with the CTD observations, we investigate ocean
circulation and water mass distributions to understand the relationships of
those variables to recent climate change, which appears to be most prominent
in the Arctic region. Recent sea ice retreat in summer in the Pacific sector
of the Arctic Ocean could be related to the inflow of warm water that
originates from the Pacific and enters via the Bering Strait. Furthermore,
this so-called Pacific Water carries nutrients to the Arctic Ocean, and
therefore, influences the Arctic ecosystem. Cold water formed in winter in
polynya (open water) regions of the Arctic shelf sinks into the deep basins
accompanied by the transport of nutrients and carbons, which are important
for biogeochemical element cycles (biogeochemistry describes the
interactions between biological primary production, ocean chemistry, and
geological particle deposition). In addition, a significant warm anomaly of
Atlantic water has been observed in the Canada Basin far from the Fram
Strait source where the Atlantic water flows into the Arctic Ocean.
Scientists from JAMSTEC have been conducting XCTD
surveys (and other work) from the Louis (and other vessels) over the past
several years to address these issues in collaboration with IOS/DFO under
the JWACS (Joint Western Arctic Climate Studies) project.
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