702
Land-Ocean Systems in the Siberian Arctic: Dvnamics and History
subsequent papers of this volume. Some of the discoveries are providing first insights into the
different processes controlling Arctic climate and linking the land and shelves to the deeper
basins.
Modern sea-ice and ocean processes
The Laptev Sea is one of the regions with the highest net-ice production rates in the Arctic
Ocean (Rigor and Colony, 1997). One of the aims of the project was to assess the spatial
patterns and variability of ice growth in the Laptev Sea including its linkage to atmospheric and
oceanic processes as well as its importance for sediment transport through the entrainment of
particulate matter.
The time period 1992 - 1996 is of particular interest since summer ice extent attained a record
minimum in 1995. As shown by meteorological data and a large-scale sea ice model, this
minimum is mostly a result of atmospheric circulation anomalies and their impact on ice
dynamics, along with enhanced ice melting due to advection of warm air masses from central
Siberia (Kolatschek et aI., 1996). As a result of advective heat transport and storage of solar
short-wave energy in the water column, the fall freeze-up 1995 was delayed by two weeks
compared to the long-term mean of ice-formation onset. This is corroborated by hydrographic
measurements which detected a warm water layer in the eastern Laptev Sea in the fall of 1995
(Kassens et aI., 1997).
Given the importance of sea ice circulation and export (Drnitrenko et aI., this volume), a more
detailed study of the ice circulation regime in the Laptev Sea was carried out in the period of
1979 to 1995. With a lack of buoy data over the shelf regions, where ice motion may be quite
complex, the ice velocity field was determined for selected years from remote-sensing data
(Russian Okean Side-looking Radar, Special Sensor Microwave/Imager (SSM/I) 85 GHz
passive microwave data, and Advanced Very High Resolution Radiometer (AVHRR) data).
This was achieved by both manual tracking of conspicuous features in the ice pack (leads,
boundaries between multi-year and first-year sea ice as visible in Okean and A VHRR data) as
well as automated tracking using maximum-likelihood correlation techniques (for SSMII
scenes). Comparison with the available buoy data showed consistent results and these were
utilized to validate and improve a large-scale dynamic-thermodynamic sea-ice model. From the
model, the areal ice flux to the Arctic Ocean and the adjacent shelf seas was derived for the
period of 1979 to 1995. Except for the summer months of 1979 and 1981, total net export
during summer and winter is positive for the entire period, ranging between 3 and 7 x 10 5 km 2
in winter (October-May). Along the northern boundary, ice was imported into the Laptev Sea
during the summer period of 12 out of 18 years. Export into the East Siberian Sea is
considerable, with mean winter values of approximately 1 x 10 5 km 2 .
Freshwater input through river discharge is an important component of the freshwater balance
of the Laptev Sea and the Arctic Ocean (Bareiss, 1996; Dmitrenko et aI., this volume; Golovin
et aI., this volume). Hydrographic surveys carried out between 1993 and 1996 have been able
to trace the influence of the plume from the Lena River throughout the eastern Laptev Sea.
Historical data indicate that salinity anomalies in the Transpolar Drift may also be directly
affected by continental runoff. While a study based on remote-sensing and hydrological data
has shown that the impact of river discharge (through its effect on short-wave radiation balance
and heat advection) on summer ice retreat is of importance only in the near-delta regions
(Bareiss, 1996), river discharge considerably affects the ice freeze-up.
We were able to show that the establishment of a fast-ice cover and its areal extent are mainly
controlled by the dispersal of river water in the eastern Laptev Sea (Dmitrenko et aI., this
volume). High resolution studies also indicate that frazil-ice production in the boundary layer
between the river plume and water of higher salinity may constitute an important component of
Land-Ocean Systems in the Siberian Arctic: Dvnamics and History
subsequent papers of this volume. Some of the discoveries are providing first insights into the
different processes controlling Arctic climate and linking the land and shelves to the deeper
basins.
Modern sea-ice and ocean processes
The Laptev Sea is one of the regions with the highest net-ice production rates in the Arctic
Ocean (Rigor and Colony, 1997). One of the aims of the project was to assess the spatial
patterns and variability of ice growth in the Laptev Sea including its linkage to atmospheric and
oceanic processes as well as its importance for sediment transport through the entrainment of
particulate matter.
The time period 1992 - 1996 is of particular interest since summer ice extent attained a record
minimum in 1995. As shown by meteorological data and a large-scale sea ice model, this
minimum is mostly a result of atmospheric circulation anomalies and their impact on ice
dynamics, along with enhanced ice melting due to advection of warm air masses from central
Siberia (Kolatschek et aI., 1996). As a result of advective heat transport and storage of solar
short-wave energy in the water column, the fall freeze-up 1995 was delayed by two weeks
compared to the long-term mean of ice-formation onset. This is corroborated by hydrographic
measurements which detected a warm water layer in the eastern Laptev Sea in the fall of 1995
(Kassens et aI., 1997).
Given the importance of sea ice circulation and export (Drnitrenko et aI., this volume), a more
detailed study of the ice circulation regime in the Laptev Sea was carried out in the period of
1979 to 1995. With a lack of buoy data over the shelf regions, where ice motion may be quite
complex, the ice velocity field was determined for selected years from remote-sensing data
(Russian Okean Side-looking Radar, Special Sensor Microwave/Imager (SSM/I) 85 GHz
passive microwave data, and Advanced Very High Resolution Radiometer (AVHRR) data).
This was achieved by both manual tracking of conspicuous features in the ice pack (leads,
boundaries between multi-year and first-year sea ice as visible in Okean and A VHRR data) as
well as automated tracking using maximum-likelihood correlation techniques (for SSMII
scenes). Comparison with the available buoy data showed consistent results and these were
utilized to validate and improve a large-scale dynamic-thermodynamic sea-ice model. From the
model, the areal ice flux to the Arctic Ocean and the adjacent shelf seas was derived for the
period of 1979 to 1995. Except for the summer months of 1979 and 1981, total net export
during summer and winter is positive for the entire period, ranging between 3 and 7 x 10 5 km 2
in winter (October-May). Along the northern boundary, ice was imported into the Laptev Sea
during the summer period of 12 out of 18 years. Export into the East Siberian Sea is
considerable, with mean winter values of approximately 1 x 10 5 km 2 .
Freshwater input through river discharge is an important component of the freshwater balance
of the Laptev Sea and the Arctic Ocean (Bareiss, 1996; Dmitrenko et aI., this volume; Golovin
et aI., this volume). Hydrographic surveys carried out between 1993 and 1996 have been able
to trace the influence of the plume from the Lena River throughout the eastern Laptev Sea.
Historical data indicate that salinity anomalies in the Transpolar Drift may also be directly
affected by continental runoff. While a study based on remote-sensing and hydrological data
has shown that the impact of river discharge (through its effect on short-wave radiation balance
and heat advection) on summer ice retreat is of importance only in the near-delta regions
(Bareiss, 1996), river discharge considerably affects the ice freeze-up.
We were able to show that the establishment of a fast-ice cover and its areal extent are mainly
controlled by the dispersal of river water in the eastern Laptev Sea (Dmitrenko et aI., this
volume). High resolution studies also indicate that frazil-ice production in the boundary layer
between the river plume and water of higher salinity may constitute an important component of