1 kg m
À3
. Most Antarctica icebergs discharge their load
near the place of their origin; here submarine moraines
are formed.
Fine material of icebergs is formed in bottom layers of
glaciers as a result of the detachment of rock fragments
from the glacier bed and their breaking up and abrasion
(up to glacier milk).
Sea-ice sedimentation
The average time of life of sea ice in the Northern Hemisphere is 1.3 years (here the center of existence of
multiyear ice is situated). There is no multiyear ice in the
Southern Hemisphere. Sea ice is developed at the area of
26 Æ 3 *10
6 km
2
; 13.1 *10
6 km
2 of them are in the Arctic
Ocean (Lisitzin, 2002). The average thickness of sea ice is
about 1.5 m, though in the area of multiyear ice, it reaches
4–6 m. The thickness of ice in water determines its carrying capacity – it is sufficient to carry coarse material
including boulder with weight of tens to hundreds of kg
(for icebergs the weight of boulders can be many tons).
In the main area of modern multiyear ice distribution in
the Arctic, the average area of ice cover changes during a
year from 11.4 * 10
6 km
2 in March to 7 * 10
6 km
2 in September. In the last years the area of ice cover considerably
decreased as a result of climate warming.
Sea ice could be divided into one-year ice (which melts
in summer and loses sedimentary matter included in it)
and multiyear (packs) that could exist in a few years
(up to 10–15 years in the Beaufort Gyre).
Correspondingly, one-year ice is the agent of nearby
and middle-range transport of sedimentary matter, while
multiyear ice is the agent of long-range transport (for
100–1,000 km). Major routes of their drift and horizontal
fluxes according to satellite data and drifting station observations are demonstrated in Figure 2. One-year ice fields
and pack ice fields discharge sedimentary matter differently. For one-year ice fields the spring melting along
the outer periphery takes place at large area and sedimentary matter deposits as a result of the so-called carpet-like
discharge. The discharge runs differently for pack ice. The
melting occurs along the contact with warm waters
(temperature from 0
C to 1–2
C above zero) in the Fram
Strait (meeting with the North Atlantic Current) and in
confluence of the Kuroshio and Oyashio currents
(northwestern Pacific Ocean) (Lisitzin, 1968, 1996).
The distribution of ice-rafted material is analyzed in
comparison with data on ice exposition (time of ice covering at this bottom part). After that the granulometric composition of ice-rafted material is studied by sieve method,
roundness index is determined in comparison with standard samples, and fouling by organisms and concretions
(for ancient samples) is estimated.
The most important part of the study of ice-rafted
stones is petrographic analysis with selection of typical
samples of standard collection and with looking through
thin sections under a microscope. It allows to judge about
complexes of rocks and to sort out provinces of ice-rafted
material distribution in bottom sediments (the same as
sorting out results of mineralogical analysis of aleuritic
fraction).
In some cases, for example, in the Kara Sea, an unusual
wide distribution of basalt stones is registered (Lisitsin
et al., 2004; Lisitsyn et al., 2004). Their source is situated
in the catchment area at the Putorana Plateau. Comparative petrochemical analyses and determination of age confirmed marker value of this type of rocks. The preparation
of maps of distribution of different types of rocks
(generally few tens) in the upper layer of bottom sediments in the Sea of Okhotsk, Bering Sea, and northern
Pacific Ocean made possible to establish areas of each
rock type distribution and places of their supply from the
continent (according to growth of concentrations). It
became possible to determine the sources of these rocks
as a result of comparison of collected rocks with rocks in
the catchment area and to reveal ways of migration of
ice fields marked by rock material (according to their contents in bottom sediments) (Lisitzin, 1968, 1972, 1996,
2001, 2002, 2010; Lisitsin et al., 2004; Lisitsyn et al.,
2004).
Coarse waste material is an impressive indication of ice
rafting, but it is not sole. The study of finer fractions
(sand-aleuritic and politic) and biogenic material gives
important data. Analysis of sedimentary matter
obtained by melting of sea ice gives important materials
also. These studies made possible to reveal one unexpected source of glacial sediments – aeolian (Darby
et al., 1974; Lisitzin, 2002; Shevchenko et al., 2002; Shevchenko, 2010; Chewings et al., 2014; Miller et al., 2015).
The main feature of aeolian supply here is that
aeolian material is deposited mostly during polar winter
at low temperatures. In summer aeolian material is washed
out rapidly from the atmosphere by rains. In winter most
part of catchment area is covered by snow and frozen.
The sedimentary aeolian matter in winter is supplied
mainly as a result of long-range (often more than
1,000 km) transport of matter in the atmosphere at levels
higher than clouds.
Lastly, it is important to say about the new mechanism
of fine sediment supply by sea-ice fields, which originated
in polynyas along the boundary between fast ice and drift
ice. Polynyas formation is related to strong winds separating the drift ice from the fast ice; the winds are particularly
strong along the periphery of the east Siberian anticyclone
(Kara, East Siberian, and Laptev seas) and accompanied
by very low temperatures (À30 to À40
C). The extent
of some polynyas from time to time reaches 1–3,000
km. This giant freezing plant combines open water of
polynyas with strong wind and very low temperature. This
leads to overcooling of both the surface layer and a significant part of the water column. Frazil ice and sometimes
bottom ice are formed around centers of crystallization
represented by suspended particles. The tiny freshwater
ice crystals become even less dense compared to the host
marine water (the process of cold distillation) and appear
as hanging to the suspended particles; like floats, they
290
GLACIAL-MARINE SEDIMENTATION
À3
. Most Antarctica icebergs discharge their load
near the place of their origin; here submarine moraines
are formed.
Fine material of icebergs is formed in bottom layers of
glaciers as a result of the detachment of rock fragments
from the glacier bed and their breaking up and abrasion
(up to glacier milk).
Sea-ice sedimentation
The average time of life of sea ice in the Northern Hemisphere is 1.3 years (here the center of existence of
multiyear ice is situated). There is no multiyear ice in the
Southern Hemisphere. Sea ice is developed at the area of
26 Æ 3 *10
6 km
2
; 13.1 *10
6 km
2 of them are in the Arctic
Ocean (Lisitzin, 2002). The average thickness of sea ice is
about 1.5 m, though in the area of multiyear ice, it reaches
4–6 m. The thickness of ice in water determines its carrying capacity – it is sufficient to carry coarse material
including boulder with weight of tens to hundreds of kg
(for icebergs the weight of boulders can be many tons).
In the main area of modern multiyear ice distribution in
the Arctic, the average area of ice cover changes during a
year from 11.4 * 10
6 km
2 in March to 7 * 10
6 km
2 in September. In the last years the area of ice cover considerably
decreased as a result of climate warming.
Sea ice could be divided into one-year ice (which melts
in summer and loses sedimentary matter included in it)
and multiyear (packs) that could exist in a few years
(up to 10–15 years in the Beaufort Gyre).
Correspondingly, one-year ice is the agent of nearby
and middle-range transport of sedimentary matter, while
multiyear ice is the agent of long-range transport (for
100–1,000 km). Major routes of their drift and horizontal
fluxes according to satellite data and drifting station observations are demonstrated in Figure 2. One-year ice fields
and pack ice fields discharge sedimentary matter differently. For one-year ice fields the spring melting along
the outer periphery takes place at large area and sedimentary matter deposits as a result of the so-called carpet-like
discharge. The discharge runs differently for pack ice. The
melting occurs along the contact with warm waters
(temperature from 0
C to 1–2
C above zero) in the Fram
Strait (meeting with the North Atlantic Current) and in
confluence of the Kuroshio and Oyashio currents
(northwestern Pacific Ocean) (Lisitzin, 1968, 1996).
The distribution of ice-rafted material is analyzed in
comparison with data on ice exposition (time of ice covering at this bottom part). After that the granulometric composition of ice-rafted material is studied by sieve method,
roundness index is determined in comparison with standard samples, and fouling by organisms and concretions
(for ancient samples) is estimated.
The most important part of the study of ice-rafted
stones is petrographic analysis with selection of typical
samples of standard collection and with looking through
thin sections under a microscope. It allows to judge about
complexes of rocks and to sort out provinces of ice-rafted
material distribution in bottom sediments (the same as
sorting out results of mineralogical analysis of aleuritic
fraction).
In some cases, for example, in the Kara Sea, an unusual
wide distribution of basalt stones is registered (Lisitsin
et al., 2004; Lisitsyn et al., 2004). Their source is situated
in the catchment area at the Putorana Plateau. Comparative petrochemical analyses and determination of age confirmed marker value of this type of rocks. The preparation
of maps of distribution of different types of rocks
(generally few tens) in the upper layer of bottom sediments in the Sea of Okhotsk, Bering Sea, and northern
Pacific Ocean made possible to establish areas of each
rock type distribution and places of their supply from the
continent (according to growth of concentrations). It
became possible to determine the sources of these rocks
as a result of comparison of collected rocks with rocks in
the catchment area and to reveal ways of migration of
ice fields marked by rock material (according to their contents in bottom sediments) (Lisitzin, 1968, 1972, 1996,
2001, 2002, 2010; Lisitsin et al., 2004; Lisitsyn et al.,
2004).
Coarse waste material is an impressive indication of ice
rafting, but it is not sole. The study of finer fractions
(sand-aleuritic and politic) and biogenic material gives
important data. Analysis of sedimentary matter
obtained by melting of sea ice gives important materials
also. These studies made possible to reveal one unexpected source of glacial sediments – aeolian (Darby
et al., 1974; Lisitzin, 2002; Shevchenko et al., 2002; Shevchenko, 2010; Chewings et al., 2014; Miller et al., 2015).
The main feature of aeolian supply here is that
aeolian material is deposited mostly during polar winter
at low temperatures. In summer aeolian material is washed
out rapidly from the atmosphere by rains. In winter most
part of catchment area is covered by snow and frozen.
The sedimentary aeolian matter in winter is supplied
mainly as a result of long-range (often more than
1,000 km) transport of matter in the atmosphere at levels
higher than clouds.
Lastly, it is important to say about the new mechanism
of fine sediment supply by sea-ice fields, which originated
in polynyas along the boundary between fast ice and drift
ice. Polynyas formation is related to strong winds separating the drift ice from the fast ice; the winds are particularly
strong along the periphery of the east Siberian anticyclone
(Kara, East Siberian, and Laptev seas) and accompanied
by very low temperatures (À30 to À40
C). The extent
of some polynyas from time to time reaches 1–3,000
km. This giant freezing plant combines open water of
polynyas with strong wind and very low temperature. This
leads to overcooling of both the surface layer and a significant part of the water column. Frazil ice and sometimes
bottom ice are formed around centers of crystallization
represented by suspended particles. The tiny freshwater
ice crystals become even less dense compared to the host
marine water (the process of cold distillation) and appear
as hanging to the suspended particles; like floats, they
290
GLACIAL-MARINE SEDIMENTATION