262
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
channel itself were nearly the same. This suggests that the stratification effectively prevents the
deposition of riverine SPM within and near the delta. This is further supported by SPM
concentrations above 70 mg/l measured at station 8 seaward off the Trofimovskaya distributary.
These high concentrations correspond well with earlier observations in the Trofimovskaya
channel during peak-draining (50-70 mg/l; Cauwet and Sidorov, 1996). The effective river-sea
transport during the breakup also has implications for the sediment budget of the Laptev Sea
because the major proportion of the annual SPM export to the Laptev Sea happens during this
short time period (Cauwet and Sidorov, 1996).
Below the pycnocline the situation only changed little. The temperature and salinity structure
of the water layer below 12 m depth was almost the same as during the first surveys. Also the
spatial distribution of oxygen saturation appeared unchanged. The concentration of suspended
matter in the near-bottom layer changed only moderately, showing SPM concentration below 5
mg/I. Sea water below the pycnocline remained transparent, although the turbidity of the
surface layer was high (20 mg/l with maximum concentrations of more than 70 mg/l at station
8).
Another important mechanism for the transport and dispersal of suspended matter in the
Laptev Sea could be observed during the last survey (Golovin et aI., this volume). Particle
loaden frazil ice aggregates formed at the contact zone of the 0 DC-freshwater and brackish water
with a temperature below 0 dc. The frazil ice rises and formed a layer of ice platelets under the
fast ice. Thus, riverine SPM is coupled to the decay, movement and melting of the fast ice
cover within the Laptev Sea.
Conclusion
The unique hydrographic regime that accompanies breakup of the Lena river is important in the
hydrologic and sedimentologic development of the SE Laptev Sea. In spring 1996, the
concentrations of dissolved oxygen, silicon, phosphorous and suspended matter during the
could be described for the first time in detail.
During the onset of the breakup, floodwater moved down the river and flushed the winter
river water to the sea. In the course of the spring thaw the floodwater formed a wedge of
freshwater within the ice covered Laptev Sea. A sharp pycnocline was established between the
spring floodwater and the underlying brackish water. During June 10-11 the freshwater layer
below the fast ice reached a thickness of 6-7 m. Silicon concentration and high suspended
matter load indicate that river water from the Lena passed nearly unchanged through the delta
and the near shore area. This spring floodwater completely filled the layer above the pycnocline
pushing out the brackish water and winter river water from the southern part of the SE Laptev
Sea. Because sedimentation of riverine SPM was impeded by a strong pycnocline, large
amounts of particulate matter can be advected far into the SE Laptev Sea.
The results presented in this study only describe the environmental conditions during spring
of 1996. The mode of freshwater discharge during the breakup depends strongly on the
hydrologic conditions, i.e. the magnitude and timing of water discharge, the duration of the
flood, the presence of ice dams in the Lena river etc .. As an example, in the pro-delta area river
water can also spread over the fast ice. Thus, different combinations of hydrologic and ice
conditions are possible. This illustrates that the conclusions drawn from the study of the 1996
breakup are only a first step towards a better understanding of the complicated processes that
shape the environment in the Siberian Arctic.
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
channel itself were nearly the same. This suggests that the stratification effectively prevents the
deposition of riverine SPM within and near the delta. This is further supported by SPM
concentrations above 70 mg/l measured at station 8 seaward off the Trofimovskaya distributary.
These high concentrations correspond well with earlier observations in the Trofimovskaya
channel during peak-draining (50-70 mg/l; Cauwet and Sidorov, 1996). The effective river-sea
transport during the breakup also has implications for the sediment budget of the Laptev Sea
because the major proportion of the annual SPM export to the Laptev Sea happens during this
short time period (Cauwet and Sidorov, 1996).
Below the pycnocline the situation only changed little. The temperature and salinity structure
of the water layer below 12 m depth was almost the same as during the first surveys. Also the
spatial distribution of oxygen saturation appeared unchanged. The concentration of suspended
matter in the near-bottom layer changed only moderately, showing SPM concentration below 5
mg/I. Sea water below the pycnocline remained transparent, although the turbidity of the
surface layer was high (20 mg/l with maximum concentrations of more than 70 mg/l at station
8).
Another important mechanism for the transport and dispersal of suspended matter in the
Laptev Sea could be observed during the last survey (Golovin et aI., this volume). Particle
loaden frazil ice aggregates formed at the contact zone of the 0 DC-freshwater and brackish water
with a temperature below 0 dc. The frazil ice rises and formed a layer of ice platelets under the
fast ice. Thus, riverine SPM is coupled to the decay, movement and melting of the fast ice
cover within the Laptev Sea.
Conclusion
The unique hydrographic regime that accompanies breakup of the Lena river is important in the
hydrologic and sedimentologic development of the SE Laptev Sea. In spring 1996, the
concentrations of dissolved oxygen, silicon, phosphorous and suspended matter during the
could be described for the first time in detail.
During the onset of the breakup, floodwater moved down the river and flushed the winter
river water to the sea. In the course of the spring thaw the floodwater formed a wedge of
freshwater within the ice covered Laptev Sea. A sharp pycnocline was established between the
spring floodwater and the underlying brackish water. During June 10-11 the freshwater layer
below the fast ice reached a thickness of 6-7 m. Silicon concentration and high suspended
matter load indicate that river water from the Lena passed nearly unchanged through the delta
and the near shore area. This spring floodwater completely filled the layer above the pycnocline
pushing out the brackish water and winter river water from the southern part of the SE Laptev
Sea. Because sedimentation of riverine SPM was impeded by a strong pycnocline, large
amounts of particulate matter can be advected far into the SE Laptev Sea.
The results presented in this study only describe the environmental conditions during spring
of 1996. The mode of freshwater discharge during the breakup depends strongly on the
hydrologic conditions, i.e. the magnitude and timing of water discharge, the duration of the
flood, the presence of ice dams in the Lena river etc .. As an example, in the pro-delta area river
water can also spread over the fast ice. Thus, different combinations of hydrologic and ice
conditions are possible. This illustrates that the conclusions drawn from the study of the 1996
breakup are only a first step towards a better understanding of the complicated processes that
shape the environment in the Siberian Arctic.