Thiede et al.: Dvnamics and History (Jfthe Laptev Sea and its Continental Hinterland
703
the ice-mass balance and playa role in sediment entrainment and transport (Dmitrenko et aI.,
1998; Golovin et aI., this volume). Given the variability on decadal and in particular on longer
timescales, the dispersal and the fate of river discharge and its impact on the ice regime are a
central issue in understanding the long-term changes in the Laptev Sea and the Arctic Ocean.
Ice export from the Laptev Sea is of great importance for sedimentation processes on the
shelf, in the central Arctic Ocean and the Nordic Seas (e.g. Wollenburg, 1993; Niirnberg et aI.,
1994; Pfirman et aI., 1995; Eicken et aI., 1997). Field studies have shown that substantial
quantities of sediments are entrained into sea-ice growing over the broad, shallow Siberian
shelves. Part of this ice grows throughout the winter season in a system of coastal polynyas and
flaw leads (Dethleff et aI., 1993; 1995; Rigor and Colony, 1997). To date, the relative
contribution of polynyas, both to total ice export and transport of sediments, has not yet been
fully understood, however. These sediments are transported with the ice and released during ice
melting, most of which occurs in the Greenland Sea area. A major entrainment event was
identified in the eastern Laptev and western East Siberian Sea in 1994. Through a combination
of remote-sensing and field measurements, the evolution and drift of this ice field were studied.
Estimates of the total sediment load from this single event, surviving ice melt in 1995 and hence
exported to the Arctic Basin, amount to between 7 and 10 million tons. In conjunction with
entrainment of sediments over the remaining shelf areas, sea ice transport may represent an
important component of the Laptev Sea sediment budget, in particular with respect to shortterm, long-range transport.
The marine ecosystem
Biological studies focused on the abundance and community structure of phytoplankton
(Juterzenka and Knickmeier, this volume; Cremer, this volume), on zooplankton and benthos
(Abramova, this volume; Petryashov et aI., this volume; Bauch, this volume) as well as on
benthic life in relation to environmental changes (Grahl et aI., this volume). Three distinct
faunal and floral provinces have been identified by multivariate analysis in the central, the
northern, and the southeastern part of the Laptev Sea. The overall phytoplankton biomass
during the summer period (August/September 1993) given by carbon content of the different
taxa was relatively low compared to other Arctic shelf regions, despite a maximum of
chlorophyll a, revealing the influence of the Lena river runoff. The late freezing period in
autumn 1995 was characterized by a locally high chlorophyll a biomass, which can be used by
zooplankton as a last food source before the winter period.
In newly formed sea ice, pigment concentrations varied considerably. However, total algal
biomass within the new and young ice was relatively high and within the range of the water
column standing stock in October 1995. Therefore, this algal biomass may serve as food for the
developing micro- and meiofaunal ice community. Endoscopic observations showed significant
differences in the three-dimensional small-scale ice morphology as well as enclosures of biotic
and abiotic origin, which are characterizing the habitat.
Zooplankton on the Laptev Sea Shelf is dominated by Calanus glacialis and C. finmarchicus,
but in areas of freshwater influence in the south and east, brackish water taxa contributed as
much as 27% of the total biomass. The export of Calanus species from the Nansen Basin onto
the Laptev Shelf appears to be of great importance for the shelf communities. On the other
hand, the eastern outer shelf and slope area of the Laptev Sea are thought to have a pronounced
effect on the deep basin, modifying the populations entering the central Arctic Ocean
(Kosobokova et aI., 1998).
Benthic faunas can be abundant but show little diversity. Except for some shallow areas «
20m) with low bottom water salinity « 30), the brittle star Ophiocten sericeum dominates the
megabenthic shelf assemblage and reaches a maximum density of more than 500 individuals per
703
the ice-mass balance and playa role in sediment entrainment and transport (Dmitrenko et aI.,
1998; Golovin et aI., this volume). Given the variability on decadal and in particular on longer
timescales, the dispersal and the fate of river discharge and its impact on the ice regime are a
central issue in understanding the long-term changes in the Laptev Sea and the Arctic Ocean.
Ice export from the Laptev Sea is of great importance for sedimentation processes on the
shelf, in the central Arctic Ocean and the Nordic Seas (e.g. Wollenburg, 1993; Niirnberg et aI.,
1994; Pfirman et aI., 1995; Eicken et aI., 1997). Field studies have shown that substantial
quantities of sediments are entrained into sea-ice growing over the broad, shallow Siberian
shelves. Part of this ice grows throughout the winter season in a system of coastal polynyas and
flaw leads (Dethleff et aI., 1993; 1995; Rigor and Colony, 1997). To date, the relative
contribution of polynyas, both to total ice export and transport of sediments, has not yet been
fully understood, however. These sediments are transported with the ice and released during ice
melting, most of which occurs in the Greenland Sea area. A major entrainment event was
identified in the eastern Laptev and western East Siberian Sea in 1994. Through a combination
of remote-sensing and field measurements, the evolution and drift of this ice field were studied.
Estimates of the total sediment load from this single event, surviving ice melt in 1995 and hence
exported to the Arctic Basin, amount to between 7 and 10 million tons. In conjunction with
entrainment of sediments over the remaining shelf areas, sea ice transport may represent an
important component of the Laptev Sea sediment budget, in particular with respect to shortterm, long-range transport.
The marine ecosystem
Biological studies focused on the abundance and community structure of phytoplankton
(Juterzenka and Knickmeier, this volume; Cremer, this volume), on zooplankton and benthos
(Abramova, this volume; Petryashov et aI., this volume; Bauch, this volume) as well as on
benthic life in relation to environmental changes (Grahl et aI., this volume). Three distinct
faunal and floral provinces have been identified by multivariate analysis in the central, the
northern, and the southeastern part of the Laptev Sea. The overall phytoplankton biomass
during the summer period (August/September 1993) given by carbon content of the different
taxa was relatively low compared to other Arctic shelf regions, despite a maximum of
chlorophyll a, revealing the influence of the Lena river runoff. The late freezing period in
autumn 1995 was characterized by a locally high chlorophyll a biomass, which can be used by
zooplankton as a last food source before the winter period.
In newly formed sea ice, pigment concentrations varied considerably. However, total algal
biomass within the new and young ice was relatively high and within the range of the water
column standing stock in October 1995. Therefore, this algal biomass may serve as food for the
developing micro- and meiofaunal ice community. Endoscopic observations showed significant
differences in the three-dimensional small-scale ice morphology as well as enclosures of biotic
and abiotic origin, which are characterizing the habitat.
Zooplankton on the Laptev Sea Shelf is dominated by Calanus glacialis and C. finmarchicus,
but in areas of freshwater influence in the south and east, brackish water taxa contributed as
much as 27% of the total biomass. The export of Calanus species from the Nansen Basin onto
the Laptev Shelf appears to be of great importance for the shelf communities. On the other
hand, the eastern outer shelf and slope area of the Laptev Sea are thought to have a pronounced
effect on the deep basin, modifying the populations entering the central Arctic Ocean
(Kosobokova et aI., 1998).
Benthic faunas can be abundant but show little diversity. Except for some shallow areas «
20m) with low bottom water salinity « 30), the brittle star Ophiocten sericeum dominates the
megabenthic shelf assemblage and reaches a maximum density of more than 500 individuals per