Marine Ecosystems Research Department - jamstec japan agency ...

JAMSTEC 2002 Annual Report
Frontier Research System for Global Change
notion of "high latitude amplification" was introduced
in the early s. Early simulations of a xCO atmosphere
suggested that the Arctic might warm at rate twoto-four
times greater than the global average. This
notion is supported by a portion of the time series of
Arctic and global temperatures, i.e., the period -
. However, other portions of the record suggest no
amplification, e.g., the record from - shows
an Arctic warming rate of .˚C per decade compared
to the global value of .˚C per decade. In this analysis
of the -year record, we conclude "Intrinsic
Arctic variability obscures long-term changes, limiting
our ability to identify complex feedbacks in the Arctic
climate system." (Polyakov et al., )
The descending dense water along shelves/slopes differs
dynamically from the open ocean deep convection,
such as in the Labrador Sea and in the Norwegian and
Greenland seas. When the surface water loses heat to
the atmosphere or when sea-ice formation ejects salt to
the ocean surface, surface water becomes heavy enough
to become statically unstable. Along the coast of the
Arctic Ocean, seasonal variability of sea-ice cover produces
dense water on continental shelves/slopes due to
ice formation from an ice-free (or partial ice cover)
condition in summer-fall to a complete ice cover condition
in winter. Thus, the dense, cold shelf water is seasonally
supplied to the Arctic halocline layer, which
prevents sea ice from melting due to the underlying
warm Atlantic Water. Figure shows a plan-view of
the simulated dense water spreading downslope into the
deep basin using a -D primitive equation model. To
model this process, the bottom boundary layer (BBL)
must be resolved, or a BBL parameterization must be
implemented in the ocean GCMs. IARC/Frontier
researchers are working on the BBL parameterization
of the Arctic Ocean GCMs.
Dramatic changes of the Arctic atmosphere, sea-ice
and the ocean have been observed recently. Changes in
sea-ice and upper layers of liquid freshwater may
affect deep convections in the Greenland Sea and the
Labrador Sea by their export, which is believed to be
offshore deep ocean (km)
300
0 300
coast (km)
Fig.27 Horizontal salinity of bottom layer in case of surface salt
flux (-10.0 x exp (-4)[kg/s m 2 ]) forcing at day 100. Red (blue)
corresponds to high (low) salinity. This experiment shows
that turbulence of instability is developing with time integration.
Irregular turbulent flow occurs because of surface
salinity forcing at southern boundary. The turbulence reaches
the center of the model basin at day 100. Several small
scale eddies with radii of around 10km are found in the turbulence.
The growth of instability is consistent with previous
studies. The model domain is 300km x 300km.
linked to the North Atlantic Thermohaline circulation
and the associated multidecadal climate variability.
With an Arctic coupled sea-ice/ocean model for climate
study (Zhang and Zhang ), Xiangdong
Zhang, collaborating with Motoyoshi Ikeda and John
Walsh, performed modeling experiments to investigate
the Arctic sea-ice and freshwater changes driven by the
Arctic-climate-leading mode (Zhang et al. ).
IARC/Frontier scientists were developing a coupled
ice-ocean model (CIOM; Wang et al. ) that was
applied to the pan-Arctic and North Atlantic Ocean. At
m depth (Figure ), which represents the typical
Atlantic Water Layer (m), the Arctic Basin is
dynamically connected to the GIN seas, while the
northern North Atlantic Ocean is disconnected from
the Iceland-Faroe Ridge in Demark Strait, where dense
water outflow may climb the ridge and flow into the
deep ocean of the northern Atlantic.
The influence of realistic but extreme Arctic sea ice
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