Geology Reference
In-Depth Information
has been commonly accepted. It states that MIZ is the “part
of the ice cover which is close enough to the open ocean
boundary to be affected by its presence.” In other words,
MIZ is defined as the area where open ocean processes, par-
ticularly ocean waves, alter the physical and dynamical
properties of the sea ice cover. Ocean waves are the primary
source of energy that break up the ice, determine the size of
the broken floes, their concentration, and mobility. The cat-
egories of ocean wave in terms of their origin, wavelength,
and amplitude are presented in section 7.7.2. The two rele-
vant categories in this context are gravity waves (a few
meters wavelength) and swell (hundreds of meters wave-
length), which propagates from the large ocean basins. As
the waves encroach on the ice cover, they leave significant
impacts that determine the main features of the MIZ.
According to the earlier definition, MIZ always exists
in open ocean where wave action and interaction with ice
cover is strong. On the other hand, they are less likely to
exist in enclosed seas. Geographic regions that feature
MIZ include Greenland Sea, Bering Sea, Labrador Sea,
Barents Sea, and the Southern Ocean around the
Antarctica [ Wadhams , 2000]. The MIZ plays an increas-
ingly important role in governing the evolution of sea ice
and the upper layer of the ocean. Its coupled interaction
with the ocean and atmosphere in terms of energy fluxes
is yet to be fully understood.
The most visible impacts of ocean wave on ice cover
include bending and potentially breaking the ice floes (or
sheets) into smaller floes that can eventually be reduced
to small ice fragments or a slurry. Swell can break ice
floes into many smaller floes of different sizes within a
few hours. Smaller floes are expected to be closest to the
open water side while larger floes are usually concen-
trated near the pack ice. The floe size distribution in the
MIZ impacts ice strength and roughness as well as the
exchanges of heat, energy and moisture between ocean
and air through ice. The penetration of the ocean waves
into ice also enhances the ice floe mobility and therefore
alters their shape, size, and deformation. Consequently, it
reduces the resistance of the ice to the wind and ocean
current stresses. This allows more wave penetration fol-
lowed by more disintegration of the ice, that is, a positive
feedback cycle. By breaking up the ice cover into small
and scattered floes, ocean waves can accelerate lateral
melting of the ice when temperature rises above the melt-
ing point. New ice is formed between ice floes when
atmospheric temperature decreases. It should be men-
tioned that the ice cover acts as a dampener of ocean
wave. These mutual effects act simultaneously to modify
the spectrum of the wave travelling through the ice and
determine the main properties of the MIZ.
The interest in studying the MIZ has gained momentum
under two thrusts. The first is the incomplete understanding
of the processes that govern the ocean‐ice‐air interactions in
the MIZ. Despite the information that has been acquired
about ice characteristics in the MIZ a few questions still
need to be answered. Examples are the surface energy bal-
ance, propagation of ocean wave into the ice, and the mixing
of water density and salinity under the ice cover. Descriptions
of key processes in ice and oceanic processes related to the
MIZ are presented in Lee et al . [2012]. The second thrust is
related to the recent decline of sea ice in the Arctic. As the
Arctic ice has been shrinking at a fast rate during the past
decade, the ice edge has retreated away from the coast and
continental shelf to be located closer to the center of the
Arctic basin above the deep ocean. This has produced MIZ
in areas that have always been covered with consolidated ice
such as Beaufort Sea and the Canada basin north of Alaska.
New locations and ice conditions of MIZ are predicted at a
variety of temporal and spatial scales as the trend of Arctic
ice decline continues. These changes have affected the ocean‐
ice‐atmosphere interactions significantly and caused pro-
found impacts on the sea ice evolution. This new situation
warrants further field studies of MIZ.
In response to this need, the US Office of Naval Research
(ONR) has launched a 5‐year program starting in late 2012
called MIZ DRI (Departmental Research Initiative). The
program aims at addressing a few scientific questions that
include (i) What are the processes that govern the spatial
and temporal evolution of the MIZ? (ii) What are the roles
of ocean wave, solar radiation, and extra heat release in
governing the MIZ evolution and how do these processes
couple? (iii) What are the current modeling capabilities
that predict the MIZ and how can it be improved? (iv)
What is the ice floe response to ocean wave, and what are
the short‐scale flexural variations across the floe?
The extent of the MIZ is determined by the distance to
which waves and swell penetrates the ice cover. Swell can
penetrate great distances into the ice. It may extend to
tens or even a few hundreds of kilometers and move at a
speed of more than 50 km/day [ Perrie and Hu , 1997].
Aspline et al . [2012] reported that 200-300 m wavelength
swell penetrated the ice pack in the eastern Beaufort Sea
in September 2009 to as much as 250 km. Statistics of ice
floe size, geometry, and the spacing between floes are
important parameters in modeling the dynamics, wave
characteristics, energy balance, and flux exchanges in the
MIZ. Lu et  al . [2008] suggested that the distribution of
floe sizes in the MIZ follows a zone‐based pattern with
small floes in the outer area, medium size floes in the inte-
rior area and large floes near the solid ice pack. The
authors also suggested a distribution of ice floe size and
geometry given by the following equation:
NL
N
L
L
(2.44)
1exp
0
0
where N is the cumulative number of floes with size smaller
than L ; N 0 is the total number of floes, L 0 and γ are scale
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