International Polar Year 2007–2008 - WMO

Towards a new autonomous sub-ice system
for monitoring the keel depth of sea-ice; the
collaboration between EC-DAMOCLES and the
Chinese National Arctic Research Expedition
(CHINARE) in 2008. Ice thickness is an important
parameter. The 22 ice-prediction groups that
participated in the SEARCH-for-DAMOCLES (S4D) Sea
Ice Outlook exercise concluded that an improved
measure of ice thickness in spring was the prime
requirement for improved prediction of ice extent at
the time of the late summer minimum. Supplementing
remote sensing techniques, including the laser and
radar altimetry on ICESAT and ENVISAT, and the use
of ice-surface sensors (e.g. tiltmeter buoys), a new
autonomous system based on the use of isobaric subice
floats fitted with upward-looking sonar has been
developed by EC-DAMOCLES during IPY and is now on
the point of completion. The ULS floats are designed
to drift at a constant depth of 50m beneath the arctic
ice for up to two years. The equally-new acoustic icetethered
platforms (AITP; now ‘amphibious’ rather
than ice-tethered) are designed to form the link
between ULS floats and satellite transmission, with the
EC-DAMOCLES plan calling for ten AITPs and eight ULS
floats in total. The first deployment of two ULS floats
and four AITP systems were deployed by Canadian
twin-otter aircraft above the Alpha Ridge in April
2008, together with seven PAWS weather monitors
(Broemmer, UHH) and three ice mass-balance buoys
(IMBs; Richter-Menge et al., 2006). The remainder of
the 2008 deployment, including four more AITPs,
an extensive CTD grid and a complex ice camp of
instruments was later set by the Chinese CHINARE
2008 Expedition aboard R/V Xue Long (11 July - 24
September, 2008). The full realization of data retrieval
from ULS-floats will depend on the development of
acoustic gliders as the third component of the system.
DAMOCLES began the stepwise development of such
an acoustic glider, starting in autumn 2008, followed
by trials off Svalbard in spring 2009 and leading to a
first planned deployment in spring 2010 at the North
Pole. In the meantime, data retrieval will involve ships
approaching ULS floats and forcing a download to an
acoustic modem (Gascard, pers comm). Altogether,
ten AITPs plus four ULS floats have been deployed to
date fulfilling most of the DAMOCLES plan and the
unequivocal requirement of the S4D Sea-ice Outlook
exercise for data on sea-ice thickness commends the
continued use of this technique into the IPY legacy
phase. A further four ULS floats and four new ‘hybrid’
AITPs are being constructed; in addition to having a
profiling hydrophone, the new AITPs will begin to
contribute to the ITP dataset by carrying a CTD profiler
for the first time.
The drift of the Russian Ice Island North Pole-
35 and the Arktika-2008 expedition aboard R/V
Akademik Fedorov. Since 1937–1938, the Russian
Arctic and Antarctic Research Institute (AARI) has
operated a total of 34 drift stations in the Arctic Ocean
making this type of observational platform something
of a Russian specialization. After a considerable search
for a suitable floe, NP-35 was established on September
25, 2007 at 81°26’N 103°30’E by the Akademik Fedorov
working in conjunction with the nuclear icebreaker
Russia as part of the “Arktika 2007” expedition. For
most of the following year, NP-35 was occupied by
AARI as a contribution to IPY, contributing new results
in polar oceanography, sea ice studies, processes of
greenhouses gas exchange in presence of ice cover
and polar meteorology.
During the first 7-month winter drift of NP35, the
Russian team was joined by Jürgen Graeser from the
Potsdam Research Unit in Germany and, during this
phase, the investigations of the ocean upper layer, the
characteristics of the sea ice, the snow cover and the
energy balance above the ice surface were supplemented
with further atmospheric data (temperature,
moisture, wind and air pressure) collected by ascents of
a tethered balloon up to a height of 400 metres as well
as by balloon-borne sensor ascents up to an altitude of
30 kilometres. Both contributed rarely-obtained winter
data with high temporal and spatial resolution to the
improvement of global climate models. The exchanges
of heat and moisture in the atmospheric boundary
layer to an altitude of ~400 metres, now measured for
the first time during the complete polar night, were of
especial value. As the layer that determines the lower
boundary conditions for all model calculations, a realistic
representation of the planetary boundary layer in
the Arctic is crucial for the construction of climate models;
hitherto, temperature profiles from regional climate
models have shown considerable deviation from those
measured on the floe. The data set of NP 35 will also
contribute significantly to the determination of how
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