International Polar Year 2007–2008 - WMO

The spread of SeaGliders support of Arctic-subarctic
exchanges. The SeaGlider (usually the UW
version) has proved a versatile and effective means
of solving long-standing observational problems of
oceanic exchanges between Arctic and subarctic seas.
Drawing these uses together into a single paragraph
will underscore their versatility. On the Greenland-
Scotland Ridge, Eriksen and Rhines employed three
UW seagliders to map and measure the small, thin,
dense water overflows that have eluded measurement
by any more conventional means (see Dickson, 2008).
In the case of iAOOS-for-Norway, as we have seen, the
observational difficulty was to find some means of observing
the offshore free jet of the Norwegian Atlantic
Current where it passes north through the Svinøy
Section, carrying half the northward heat flux through
the Norwegian Sea; this was solved by the use of a UW
SeaGlider from July 2008. In the case of the Fram Strait
throughflow, the need was to resolve the filamented
two-way flow through the Strait in a way that even a
dense ‘picket fence’ of current meter moorings cannot
do; AWI introduced glider surveys for this purpose in
both 2007 and 2008 and intend, with Craig Lee’s continued
collaboration, to expand this effort westward to
recover data from the ice-covered part of the Strait. In
the case of Craig Lee’s Davis Strait Monitoring effort,
to be described below, the observational need was to
measure the totality of ocean exchanges to the west
of Greenland, in particular the freshwater flux passing
south under the seasonal ice cover in the western part
of the Strait. After first trials in December 2006, this
was solved in 2009 by a SeaGlider operating autonomously
(acoustic navigation, ice-sensing, independent
decision-making) to avoid the surface and continue
its westward transit after encountering the ice edge.
Prospectively, acoustic gliders operating under the
perennial ice of the Arctic deep basins will form the
essential third component of the DAMOCLES system
to monitor ice keel-depth, acting as the data link between
upperward looking sonar (ULS) floats and their
acoustic Ice Tethered Platforms (ITP). A first full deployment
is intended in spring 2010 at the North Pole. In
all five of these examples, a measurement of considerable
importance to our understanding of the Arctic
climate system had stalled until the unique capabilities
of SeaGliders were introduced to help solve the observational
problem. The new Deepglider development
will add a further dimension. Deepgliders are expected
to be able to survey oceanic variability autonomously
over the entire water column on deployments and recoveries
made on successive summers, making them
well-suited to observing subpolar as well as subtropical
and tropical seas. To give only one example, the
development of Deepgliders capable of cruising the
water column of the subpolar gyre has been called
for (Dickson et al., 2008) as a necessary aid to capturing
the baroclinic adjustments that cause interannual
changes in the transport of the dense water overflows
from Nordic Seas. We note that the cost of fabrication
is estimated to be less than half again that of SeaGliders,
while the cost of operation will be perhaps half that
of their upper ocean relatives (Charlie Erikson, pers.
comm., January 2009). Testing of the first full ocean
depth Deepglider took place in mid-2009.
Observing the Arctic Ocean and Circumarctic
shelves.
We need little reminding that barely a decade ago,
the Arctic Ocean was a data desert. If we did, Fig. 2.2-4
would be all that was needed to remind us. That situation
has now changed. In addition to the expanded
ship-based CTD coverage achieved during IPY (described
in Dickson, 2008; 2009), the rapid elaboration
and expansion of the ice-top observatory brought a
range of new autonomous systems to bear on the Arctic
Ocean and its ice cover that hardly existed before
the Millennium. In particular, the spectacular expansion
of CTD coverage throughout the Arctic deep basins
is principally the result of the WHOI Ice Tethered
Profiler and JAMSTEC Polar Ocean Profiler Systems. In
consequence – and probably for the first time – it is
now impractical for a summary such as this to provide
a complete accounting of what was achieved, voyage
by voyage or instrument by instrument, during IPY. Instead,
we attempt to provide a flavour of that achievement
by describing an inconsistent selection of voyages,
instruments and ideas whose novelty, difficulty,
effort, complexity, climatic importance or collaborative
nature fulfilled one aspect or another of what IPY set
out to do. In paring down our description to a few voyages,
it is important that we don’t discard all of the detail:
one suspects that it will be the multi-layered and
often internationally-provided complexity of the field
s C I e n C e P r o g r a m 159