704
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
m 2 in river valleys (> 30m water depth). Gross estimates of brittle star respiration, productivity,
and organic carbon demand suggest that a substantial portion of the energy flow is channeled
through these dense brittle star assemblages (Piepenburg and Schmid, 1997). In large isopods
(Saduria entomon var. sibirica), respiration rates as indicators of metabolic activity were
significantly higher at low salinities, indicating metabolic costs of osmotic stress in a seasonally
changing brackish environment. The findings show that energy flow models of this highly
variable environment must be based on the occurrence of different biological communities,
which also represent regional differences in biomass and, therefore, most likely, productivity
and carbon demand.
Pathways of nutrients, trace elements and chlorinated biphenyls
Nutrients, trace elements, and chlorinated biphenyls were studied in sea ice, water column and
surface sediments of the Laptev Sea and in river water in order (i) to trace shelf-ocean pathways
of river discharge and sea ice, (ii) to study processes of ice formation, and (iii) to estimate the
natural and anthropogenic input into the Laptev Sea (Holemann et aI., this volume; Lara et aI.,
1998; Utschakowski, 1998; Pivovarov et aI., this volume). Input and distribution of nutrients,
trace elements, and chlorinated biphenyls are controlled by river runoff. Remarkable is a strong
increase in the content of chlorinated biphenyls and metals and a corresponding decrease in
dissolved silicon in Lena River water during the onset of spring break-up, as shown by daily
concentration measurements in 1996. As a result, approximately half of the annual discharge is
drained into the Laptev Sea during this short period of less than one month. The most important
factor controlling the transport of dissolved and suspended matter during spring break-up is the
pronounced density stratification of the water column in the Laptev Sea due to freshwater input
via river runoff. Working much like a conveyor belt driven by the intensity of river runoff,
dissolved and particulate matter are transported offshore to the north (Holemann et aI., this
volume; Ivanov and Piskin, this volume; Pivovarov et aI., this volume). Therefore, possible
depositional centers, although not clearly identified, are far away from the Lena Delta.
Another important process affecting the transport pathways of particles was studied in the
autumn of 1995. During freeze-up, particulate matter was effectively incorporated into newly
forming ice off the Lena Delta. Unexpectedly high concentrations of dissolved Fe, Mn, Zn, Cd,
and Pb were measured in the sediment laden new ice (Holemann et aI., this volume). For
instance, the concentration of Fe was up to 25 times higher as compared to the average
concentration of Lena River water. We suggest that this is caused by a redox controlled
remobilization of metals from ice-bound sediments. Further geochemical investigations of sea
ice and surface sediments from different regions in the Laptev Sea have also shown that the
chemical signature can be directly related to different fluvial sources: e.g., high Mg/AI ratios
found in sea ice sediments in the southwestern Laptev Sea reflect the geochemical signature of
flood basalts in the catchment area of the Khatanga River. Dissolved and particulate heavy
metals and chlorinated biphenyls in sediments, water column, and sea ice are at very low levels.
In particular, the content of heavy metals in sea ice and surface sediments are comparable to
those found in unpolluted marine sediment and thus give no indication of anthropogenic
pollution. High contents of As in surface sediments along the river valleys are caused by strong
sub oxic diagenesis.
Land-ocean transfer of sediments
To identify modern and past sediment transport from the Siberian hinterland across the Laptev
Sea to the Arctic Ocean, geochemical, i.e., major, trace, and rare earth element (Holemann et
aI., this volume; Rachold, this volume) and Sr isotope (Rachold et aI., 1997b), and
mineralogical, i.e., clay and heavy mineral (Behrends et aI., this volume; Rossak et aI., this
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
m 2 in river valleys (> 30m water depth). Gross estimates of brittle star respiration, productivity,
and organic carbon demand suggest that a substantial portion of the energy flow is channeled
through these dense brittle star assemblages (Piepenburg and Schmid, 1997). In large isopods
(Saduria entomon var. sibirica), respiration rates as indicators of metabolic activity were
significantly higher at low salinities, indicating metabolic costs of osmotic stress in a seasonally
changing brackish environment. The findings show that energy flow models of this highly
variable environment must be based on the occurrence of different biological communities,
which also represent regional differences in biomass and, therefore, most likely, productivity
and carbon demand.
Pathways of nutrients, trace elements and chlorinated biphenyls
Nutrients, trace elements, and chlorinated biphenyls were studied in sea ice, water column and
surface sediments of the Laptev Sea and in river water in order (i) to trace shelf-ocean pathways
of river discharge and sea ice, (ii) to study processes of ice formation, and (iii) to estimate the
natural and anthropogenic input into the Laptev Sea (Holemann et aI., this volume; Lara et aI.,
1998; Utschakowski, 1998; Pivovarov et aI., this volume). Input and distribution of nutrients,
trace elements, and chlorinated biphenyls are controlled by river runoff. Remarkable is a strong
increase in the content of chlorinated biphenyls and metals and a corresponding decrease in
dissolved silicon in Lena River water during the onset of spring break-up, as shown by daily
concentration measurements in 1996. As a result, approximately half of the annual discharge is
drained into the Laptev Sea during this short period of less than one month. The most important
factor controlling the transport of dissolved and suspended matter during spring break-up is the
pronounced density stratification of the water column in the Laptev Sea due to freshwater input
via river runoff. Working much like a conveyor belt driven by the intensity of river runoff,
dissolved and particulate matter are transported offshore to the north (Holemann et aI., this
volume; Ivanov and Piskin, this volume; Pivovarov et aI., this volume). Therefore, possible
depositional centers, although not clearly identified, are far away from the Lena Delta.
Another important process affecting the transport pathways of particles was studied in the
autumn of 1995. During freeze-up, particulate matter was effectively incorporated into newly
forming ice off the Lena Delta. Unexpectedly high concentrations of dissolved Fe, Mn, Zn, Cd,
and Pb were measured in the sediment laden new ice (Holemann et aI., this volume). For
instance, the concentration of Fe was up to 25 times higher as compared to the average
concentration of Lena River water. We suggest that this is caused by a redox controlled
remobilization of metals from ice-bound sediments. Further geochemical investigations of sea
ice and surface sediments from different regions in the Laptev Sea have also shown that the
chemical signature can be directly related to different fluvial sources: e.g., high Mg/AI ratios
found in sea ice sediments in the southwestern Laptev Sea reflect the geochemical signature of
flood basalts in the catchment area of the Khatanga River. Dissolved and particulate heavy
metals and chlorinated biphenyls in sediments, water column, and sea ice are at very low levels.
In particular, the content of heavy metals in sea ice and surface sediments are comparable to
those found in unpolluted marine sediment and thus give no indication of anthropogenic
pollution. High contents of As in surface sediments along the river valleys are caused by strong
sub oxic diagenesis.
Land-ocean transfer of sediments
To identify modern and past sediment transport from the Siberian hinterland across the Laptev
Sea to the Arctic Ocean, geochemical, i.e., major, trace, and rare earth element (Holemann et
aI., this volume; Rachold, this volume) and Sr isotope (Rachold et aI., 1997b), and
mineralogical, i.e., clay and heavy mineral (Behrends et aI., this volume; Rossak et aI., this