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International Polar Year 2007–2008 - WMO

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Fig. 3.2-4. Fresh water<br />

content (FWC, meters)<br />

variability and<br />

trends for moorings<br />

A-D (locations in<br />

inset map). FWC is<br />

calculated relative to<br />

34.8 salinity at depths<br />

below 65m and 95m<br />

down to depth where<br />

salinity is less or equal<br />

to 34.8.<br />

(Image: Andrey Proshutinsky,<br />

WHOI pers. comm.)<br />

376<br />

IPY 20 07–20 08<br />

seasonal transformations of liquid FWC due to the<br />

seasonal cycle of sea ice melt and growth. A first peak<br />

(June-July) is observed when the sea ice thickness<br />

reaches its minimum (maximum fresh water release<br />

from sea ice to the ocean) when Ekman pumping is<br />

very close to its minimum (maximum wind curl). The<br />

second maximum is observed in November-January<br />

when wind curl reaches its minimum (maximum<br />

Ekman pumping) and the salt flux from the growing<br />

sea ice has not reached its maximum.<br />

The most important BGOS finding however, is the<br />

fact that the Beaufort Gyre freshwater content is a<br />

field in rapid transition with strongly increasing trends<br />

in FWC between 2003-2008 at mooring locations (Fig.<br />

3.2-4) along Ice-Tethered Profiler trajectories and at<br />

the standard BGOS summer CTD sites. According to<br />

Proshutinsky et al., (2009), the spatially integrated<br />

FWC of the gyre increased by >1000 km 3 post-1990<br />

relative to climatology.<br />

Q: What is the effect on climate of the recent transition<br />

from stable multi-year land-fast ice to free ice along the<br />

Canadian Arctic Margin?<br />

A: Warm Pacific Summer Water (PSW) inflow through<br />

the Bering Strait plus the creation of a Near Surface<br />

Temperature Maximum (NSTM) in the Canada Basin<br />

through the albedo feedback mechanism (Jackson<br />

et al., 2009) thins the ice against the Canadian Arctic<br />

coast. Once the multi-year ice breaks free of the coast,<br />

intensive Japanese investigations by Koji Shimada<br />

(Univ. Tokyo) suggest that the clockwise gyre circulation<br />

is able to rotate the ice out over what might now be<br />

termed the ‘hotplate’ of the Chukchi Borderland. The<br />

melting ice joins the transpolar drift and exits through<br />

Fram Strait. The now ice-free ocean stimulates the<br />

development of anomalously low pressure and the<br />

resulting formation of an atmospheric dipole further<br />

speeds the clockwise circulation of the Beaufort Gyre.<br />

Satellite remote sensing of sea-surface height appears<br />

to support a recent rapid intensification of the Gyre

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