Oceanographic Causes for Transarctic Ice Transport of River
Discharge
I. Dmitrenkol, P. Golovinl, V. Gribanov l and H. Kassens 2
(I) State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226 St. Petersburg,
Russia
(2) GEOMAR Forschungszentrumfiir marine Geowissenschaften, WischhofHrasse 1-3, D 24148 Kiel,
Germany
Received 3 March 1997 and accepted in revised fonn 8 February 1998
Abstract - The influence of river discharge on ice-hydrological conditions was investigated
during expeditions in the Laptev Sea in 1994, 1995 and 1996 during different seasons of the
year within the framework of the Russian-German project "Laptev Sea System". A
comhined analysis of both ice satellite and CTD observations has shown that the fonnation
and distribution of the fast ice edge is dependent on vertical heat exchange processes with
the wann subsurface water layer underlying river water over a depth range of 10 to 25 m. It
is formed during the summertime in areas affected by river discharge, which spreads as a
result of warm surface water converging at the discharge fronts. Calculations show that
advection of heat and double-diffusive convection are the most efficient modes of heat
transport to the growing ice at the periphery of the freshened zone. Their values are
sufficient to reduce the ice thickness at the periphery of the discharge zone hy more than
half. This leads to a fast ice edge much further south than the northern limit of the
freshened zone. As a result, a considerable amount of riverine dissolved and suspended
matter is incorporated into drifting ice and hence into transarctic ice transport.
Introduction
One of the main objectives of the Russian-German multidisciplinary research project the
"Laptev Sea System" is to investigate the pathways and mechanisms of suspended matter and
sediment transport from the Laptev Sea to the Arctic Ocean. The transarctic ice transport of
sediments and suspended matter incorporated into sea ice at freezing was suggested (e.g.
Eicken et a!., 1997). Since the Lena River is one of the main sources of dissolved and
suspended matter supply to the Laptev Sea, it is especially important to investigate the fate of
river water.
Previous expedition studies have shown that the majority of suspended matter is distributed in
accordance with the spreading of river water and that it is centered in the upper 7-9 m. In this
case, it is expected that the most intense incorporation of suspended matter coincides with
regions where river discharge was located at the onset of freezing (Dmitrenko et a!., in press).
Under the influence of river discharge, the upper sea layer is significantly diluted ("freshened,,).
The resulting strong density stratification in most regions (except in shallow water) prevents
penetration of sea water mixing processes down to the sea floor. This in turn inhibits the
transport of bottom sediments to the sea surface. However, suspended matter concentrated in
the surface freshened layer can be incorporated into the forming ice after the onset of freezing.
This ice forms a massif of fast ice or drifting first-year ice located beyond the fast ice limits
(including flaw polynyas). The latter is extremely important in terms of potential ice transport of
sediments. Drift trajectories of GPS-buoys set up on fast ice north-east of the Lena delta in the
spring of 1996 confirmed that fast ice can melt in place. However, first-year drifting ice can be
entrained to the transarctic drift. Thus, one factor determining the transarctic sea ice transport of
river discharge is the type of ice cover into which the river discharge is incorporated at freezing.
Hence, this study focuses on the influence of river discharge on the extent of the fast ice cover.
In: Kassens, H., H.A. Bauch, l. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999,73-92.
Discharge
I. Dmitrenkol, P. Golovinl, V. Gribanov l and H. Kassens 2
(I) State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226 St. Petersburg,
Russia
(2) GEOMAR Forschungszentrumfiir marine Geowissenschaften, WischhofHrasse 1-3, D 24148 Kiel,
Germany
Received 3 March 1997 and accepted in revised fonn 8 February 1998
Abstract - The influence of river discharge on ice-hydrological conditions was investigated
during expeditions in the Laptev Sea in 1994, 1995 and 1996 during different seasons of the
year within the framework of the Russian-German project "Laptev Sea System". A
comhined analysis of both ice satellite and CTD observations has shown that the fonnation
and distribution of the fast ice edge is dependent on vertical heat exchange processes with
the wann subsurface water layer underlying river water over a depth range of 10 to 25 m. It
is formed during the summertime in areas affected by river discharge, which spreads as a
result of warm surface water converging at the discharge fronts. Calculations show that
advection of heat and double-diffusive convection are the most efficient modes of heat
transport to the growing ice at the periphery of the freshened zone. Their values are
sufficient to reduce the ice thickness at the periphery of the discharge zone hy more than
half. This leads to a fast ice edge much further south than the northern limit of the
freshened zone. As a result, a considerable amount of riverine dissolved and suspended
matter is incorporated into drifting ice and hence into transarctic ice transport.
Introduction
One of the main objectives of the Russian-German multidisciplinary research project the
"Laptev Sea System" is to investigate the pathways and mechanisms of suspended matter and
sediment transport from the Laptev Sea to the Arctic Ocean. The transarctic ice transport of
sediments and suspended matter incorporated into sea ice at freezing was suggested (e.g.
Eicken et a!., 1997). Since the Lena River is one of the main sources of dissolved and
suspended matter supply to the Laptev Sea, it is especially important to investigate the fate of
river water.
Previous expedition studies have shown that the majority of suspended matter is distributed in
accordance with the spreading of river water and that it is centered in the upper 7-9 m. In this
case, it is expected that the most intense incorporation of suspended matter coincides with
regions where river discharge was located at the onset of freezing (Dmitrenko et a!., in press).
Under the influence of river discharge, the upper sea layer is significantly diluted ("freshened,,).
The resulting strong density stratification in most regions (except in shallow water) prevents
penetration of sea water mixing processes down to the sea floor. This in turn inhibits the
transport of bottom sediments to the sea surface. However, suspended matter concentrated in
the surface freshened layer can be incorporated into the forming ice after the onset of freezing.
This ice forms a massif of fast ice or drifting first-year ice located beyond the fast ice limits
(including flaw polynyas). The latter is extremely important in terms of potential ice transport of
sediments. Drift trajectories of GPS-buoys set up on fast ice north-east of the Lena delta in the
spring of 1996 confirmed that fast ice can melt in place. However, first-year drifting ice can be
entrained to the transarctic drift. Thus, one factor determining the transarctic sea ice transport of
river discharge is the type of ice cover into which the river discharge is incorporated at freezing.
Hence, this study focuses on the influence of river discharge on the extent of the fast ice cover.
In: Kassens, H., H.A. Bauch, l. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999,73-92.