Frazil Ice Formation during the Spring Flood and its Role in
Transport of Sediments to the Ice Cover
P. Golovinl, I. Dmitrenkol, H. Kassens 2 and J.A. HOiemann 2
(1) State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226St. Petersburg.
Russia
(2) GEOMAR Forschungszentrumfiirmarine Geowissenschaften, Wischhofstrasse /- 3, D 24148, Kiel,
Germany
Received 3 March 1997 and accepted in revised form 18 November 1997
Abstract - The article describes full-scale experimental studies performed in the TransdriftIV expedition from fast ice in the near-delta of the Lena river in the Laptev Sea during the
period immediately preceding the flood (late May) and during the peak of the flood (early
and mid-June). Processing of data has revealed the presence of supercooled water layers 5 to
150 cm thick in the zone of river-sea water contact (in the upPsr part of the seasonal
pycnocline). The supercooling value was observed to be -0.8 C. Together with the
thickness of supercooled fluid it depended upon both the time (before or during the flood)
and the site of measurements (in the zone of main branches or beyond). At one of the
stations a conglomerate of frazil ice was found attached to the cable of a bottom temperature
meter at the depth of the pycnocline. Using the known conditions, the probability for
supercooling and further frazil ice formation at all stations was determined. The results of
observations have allowed the local Richardson numbers to be calculated for the river-sea
water contact zone - the layer of supercooled fluid. Based on the theory of entrainment at
the tlat turbulent jet margin and a semi-empirical turbulence theory, it was possible to
correctly relate the mean current velocity U in the upper freshened layer to the dynamic
velocity U* (root-mean-square velocity of turbulent variations) and present the entrainment
at the river-sea water boundary as a kind of entrainment at the flat turbulent jet margin.
Using ratios from laboratory studies of frazil ice formation, the actual rates of frazil ice
formation in the river/sea water contact zone were estimated. They were calculated for the
different mean motion velocities in the freshened layer during the different periods of the
tlood development in the near-mouth region of the Lena River. Based on the known
concentrations of suspended sediments in the layer freshened by river water, the tluxes of
suspended matter to the bottom ice surface, governed by the process of frazil ice formation,
were estimated.
Introduction
Many large rivers that carry a vast amount of freshwater and sediments, especially during the
spring floods, empty onto the Siberian Shelf Seas (and, in particular into the Laptev Sea). The
temperature of fresh river water during the winter-spring season is close to its freezing point.
Entering the ice-covered sea, freshwater spreads over the surface of colder, saline sea water.
Nansen (1956) found that at this contact some portion of fresh river water becames supercooled
and forms frazil ice, especially in the near-mouth sea regions. It should be noted that formation
of frazil ice is a phenomenon typical of the entire Arctic Basin, including the summer season
(Golovin et aI., 1993; Golovin et aI., 1996; Timokhov, 1989). Formation of frazil ice at the
interface of fresh and saline water leads to the growth of essentially freshwater ice crystals
(Golovin et aI., 1996). As a result, ice with a chaotic crystals orientation ice formed. This
allows us to identify the interlayers of this ice 2 cm to 2 m thick within the general structure and
texture of multiyear drifting and fast ice both in the Arctic and Antarctic (Petrov, 1971;
Cherepanov, 1972; Cherepanov and Koz]ovsky, 1972; Weeks and Ackley, 1982; Martin,
1971 ).
In: Ka:-;.'icn~, II., H.A. Buu{;h, I. Dmitrcnko, H. Eickcn, H.~W. Hubbertcn, M. Mellcs, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 125-140.
Transport of Sediments to the Ice Cover
P. Golovinl, I. Dmitrenkol, H. Kassens 2 and J.A. HOiemann 2
(1) State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226St. Petersburg.
Russia
(2) GEOMAR Forschungszentrumfiirmarine Geowissenschaften, Wischhofstrasse /- 3, D 24148, Kiel,
Germany
Received 3 March 1997 and accepted in revised form 18 November 1997
Abstract - The article describes full-scale experimental studies performed in the TransdriftIV expedition from fast ice in the near-delta of the Lena river in the Laptev Sea during the
period immediately preceding the flood (late May) and during the peak of the flood (early
and mid-June). Processing of data has revealed the presence of supercooled water layers 5 to
150 cm thick in the zone of river-sea water contact (in the upPsr part of the seasonal
pycnocline). The supercooling value was observed to be -0.8 C. Together with the
thickness of supercooled fluid it depended upon both the time (before or during the flood)
and the site of measurements (in the zone of main branches or beyond). At one of the
stations a conglomerate of frazil ice was found attached to the cable of a bottom temperature
meter at the depth of the pycnocline. Using the known conditions, the probability for
supercooling and further frazil ice formation at all stations was determined. The results of
observations have allowed the local Richardson numbers to be calculated for the river-sea
water contact zone - the layer of supercooled fluid. Based on the theory of entrainment at
the tlat turbulent jet margin and a semi-empirical turbulence theory, it was possible to
correctly relate the mean current velocity U in the upper freshened layer to the dynamic
velocity U* (root-mean-square velocity of turbulent variations) and present the entrainment
at the river-sea water boundary as a kind of entrainment at the flat turbulent jet margin.
Using ratios from laboratory studies of frazil ice formation, the actual rates of frazil ice
formation in the river/sea water contact zone were estimated. They were calculated for the
different mean motion velocities in the freshened layer during the different periods of the
tlood development in the near-mouth region of the Lena River. Based on the known
concentrations of suspended sediments in the layer freshened by river water, the tluxes of
suspended matter to the bottom ice surface, governed by the process of frazil ice formation,
were estimated.
Introduction
Many large rivers that carry a vast amount of freshwater and sediments, especially during the
spring floods, empty onto the Siberian Shelf Seas (and, in particular into the Laptev Sea). The
temperature of fresh river water during the winter-spring season is close to its freezing point.
Entering the ice-covered sea, freshwater spreads over the surface of colder, saline sea water.
Nansen (1956) found that at this contact some portion of fresh river water becames supercooled
and forms frazil ice, especially in the near-mouth sea regions. It should be noted that formation
of frazil ice is a phenomenon typical of the entire Arctic Basin, including the summer season
(Golovin et aI., 1993; Golovin et aI., 1996; Timokhov, 1989). Formation of frazil ice at the
interface of fresh and saline water leads to the growth of essentially freshwater ice crystals
(Golovin et aI., 1996). As a result, ice with a chaotic crystals orientation ice formed. This
allows us to identify the interlayers of this ice 2 cm to 2 m thick within the general structure and
texture of multiyear drifting and fast ice both in the Arctic and Antarctic (Petrov, 1971;
Cherepanov, 1972; Cherepanov and Koz]ovsky, 1972; Weeks and Ackley, 1982; Martin,
1971 ).
In: Ka:-;.'icn~, II., H.A. Buu{;h, I. Dmitrcnko, H. Eickcn, H.~W. Hubbertcn, M. Mellcs, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 125-140.