Geology Reference
In-Depth Information
multiyear (MY) ice. Only limited information from these
observations has been published so far. This way, the con-
tents of this chapter and in particular this section are
about the untold story of Mould Bay experiments, herald-
ing the start of the Canadian Radarsat field project, 14
years before the Earth observation satellite, Radarsat‐1,
was launched in November 1995.
Studies on engineering properties of MY ice, especially an
old rubble field, recognized as hazardous material for navi-
gation in the High Arctic, were performed in Mould Bay
only on an opportunity basis. The MY ice floes never stayed
in Mould Bay or Crozier Channel for more than one season.
These floes are mobile and move with the pack ice all over
the Arctic Ocean. Search for a “stable home” for conducting
longer term studies on MY ice led to the ice island named,
Hobsons Choice floating in the Arctic Ocean not far from
Mould Bay. This ice island was a sandwich of MY ice with a
thick layer of shelf ice as the filler. It was ideal, among many
other oceanic studies, for performing medium‐scale indenta-
tion tests for simulating ice‐ship interaction processes. The
island provided a stable base for multidisciplinary investiga-
tion for many years from 1984 to 1990. Section 5.2. of this
chapter is devoted very briefly to this topic.
surfaces of the Southern Hemisphere are in the “lower
Antarctic” (a term, introduced here, not yet popular
because there was never any population base!). Thus,
geographically, the waters of the lower Arctic and that of
the lower Antarctic are comparable except for the differ-
ences in number and size of the icebergs and ice islands.
The prevalence of shelf ice and hence the floating ice
islands in the Arctic is not acute at all in comparison to
that of the Antarctic. However, in most areas above the
Arctic Circle, often referred to as the High Arctic in
Canada, sea ice is known to survive through one or
more melt seasons. Consequently, floating sea floes can
go through a continuous aging process over a number of
years. As a result, the drifting pack ice in the polar region
of the north always contains a mixture of sea ice with
different ages. In some areas of the North Atlantic,
fragments of land‐based glacier ice (icebergs, bergy bits,
and growlers) also prevail in the shipping lanes causing
hazard to navigation of ships.
When a matured FY ice cover goes through its first
melt season, normally during the middle of July to mid-
dle of September in the Northern Hemisphere, depend-
ing on locations, the reduction in thickness occurs due to
melting from both the top and the bottom. As the remain-
ing sheet of ice enters a second season of winter freezing,
new growth occurs under the remnant FY ice. This new
growth continues until the end of the second growth sea-
son. At the end of the second growth season, the compos-
ite ice cover is called a second-year (SY) ice sheet. This
does not imply that the entire through thickness ice sheet
is 2 years old. In fact, none of this ice sheet is 2 years old.
It is the top layer of this ice sheet that has “seen” two
growth seasons (or 2GS), but this layer grew some time
during the middle of the first winter season. Thus an SY
ice cover or floe floating in the ocean during the Arctic
spring consists of a thin layer of older or 2GS ice on top
of a thick layer of new ice (of one growth season or 1GS).
When this composite (2GS + 1GS) ice sheet undergoes a
second melting season, three distinct possibilities can
develop by the end of the second summer: (1) the entire
floe may melt and disappear, (2) the top layer of 2GS ice
dissolves completely, leaving only a reduced layer of 1GS
ice of the previous season, (3) the top layer of 2GS ice
melts partially (naturally near the top surface) and the
second layer of 1GS ice also melts partially (obviously
from the bottom of the ice cover). In case of scenario 2,
the ice cover will actually consists of the remnants of
1GS ice or simply a single layer of ice that has seen only
one growth season. Strictly speaking, this ice floe should
be called as the SY ice only after the summer melt, when
a layer of new ice forms below it. The composite ice cover,
in case of scenario 3 with a layer of 2GS ice on top of a
layer of 1GS ice can be defined as the “classical SY” ice
sheet. This ice sheet eventually faces a new freezing period
5.1. Mould Bay ExpEriMEnts: BEginning
of radarsat fiEld projEct
5.1.1. Aging in Sea Ice: Transition from FY to MY Ice
Following the formation of the first cover of ice on sea
surfaces, the ice undergoes continuous processes of struc-
tural and physical changes with time. The aging occurs as
the ice thickens from “gray ice” to mature FY ice during
the first season of growth (see section 2.6.1). When a FY
ice sheet goes through the subsequent summer season,
melting occurs at both the top and the bottom surfaces of
the ice cover. The entire annual sea ice sheet may disap-
pear during the summer. This is usually the case for the
shore‐fast sea ice at latitudes less than about 50°-60° in
both the Northern and the Southern Hemispheres.
Virtually the total disappearance of the annual sea ice in
the oceans surrounding the continent of Antarctica is not
unheard. But nearly all the oceanic areas at latitudes less
than about 60° south remain ice rich in terms of disinte-
grated fragments of old land‐based ice (icebergs) and
fragments of land‐hugging shelf ice (ice islands). A
similar scenario also applies to most of the areas with
latitudes below the Arctic Circle, popularly known as the
“lower Arctic,” in the Northern Hemisphere. Actually the
lower Arctic, from the human habitat and migration, as well
as geographical point of view, can be defined as the areas
below about 70° to 68° north (see section 1.5). Since the
continent of Antarctica occupies most of the areas south
of the Antarctic Circle, practically the entire oceanic
