650
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
this paper with the AMS14C-dated magnetic susceptibility record of Core PS2778 (Figure 4)
also supports a post-glacial age for Unit B (i.e., younger than Oxygen Isotope Stage 2). That
means, the alkenone signal at Core PS2471 may be used as tracer for Atlantic water inflow
along the Eurasian continental margin (cf., Figs 1 and 2) intensified during Termination I and
the early Holocene. Increased Atlantic water inflow connected with strong carbonate dissolution
and high marine organic carbon abundances during the last 12 ka has also been derived from an
organic-geochemical study of a well-dated gravity core from the northern Barents continental
margin (Knies and Stein, 1997).
Organic-carbon flux on the Laptev Sea continental margin during Oxygen Isotope Stage 1
In order to estimate the amount of total organic carbon stored in continental slope sediments of
the Laptev Sea during Oxygen Isotope Stage 1, accumulation rates of organic carbon were
calculated. The TOC accumulation rates are 0.3, 0.17, and 0.02 g C / cm 2 / ky in cores
PS2476, PS2474, and PS247l, respectively (Table 2). Assuming Unit B of Core PS2471 to
represent post-LGMlTermination I, TOC accumulation rates of Unit B would be higher by a
factor of about two than the Oxygen Isotope Stage I rates. These accumulation rates mainly
represent the flux of terrigenous organic carbon; marine organic carbon is only of secondary
importance. This is also reflected in the decrease in accumulation rates in offshore direction.
These rates are significantly higher than those calculated for the central Arctic Ocean (0.003 g C
/ cm2 / ky; Table 2; Stein et aI., 1994). That means, on the upper Laptev Sea continental slope
where maximum accumulation rates were recorded, the burial of organic matter is higher by a
factor of 100 than in the central Arctic. On the other hand, the upper slope TOC accumulation
rates are in the same order of magnitude as those calculated for coastal upwelling areas where,
however, most of the organic matter is of marine origin (cf. Stein, 1991 and further references
therein). Neverthless, the amount of organic carbon stored in the wide circum Arctic shelf and
slope areas are certainly of importance for calculation of organic carbon budgets on a global
scale.
Conclusions
I Organic geochemical bulk parameters (hydrogen index values and CIN ratios) and specific
biomarkers (n-alkanes, fatty acids, and alkenones) can be used to distinguish between
marine and terrigenous organic carbon sources. In general, terrigenous organic matter is
dominant on the Laptev Sea continental margin throughout. Marine organic carbon,
however, may occur occasionally in significant amounts.
2 The turbidites deposited during glacial Oxygen Isotope Stages 2 and/or 4 are clearly
dominated by terrigenous organic matter.
3 During Termination I (?) and the early Holocene, relatively high amounts of marine organic
matter were preserved in the sediments, as reflected be elevated hydrogen index values and
increased abundances of short-chain n-alkanes, short-chain fatty acids, and alkenones. It is
possible, however, that significant amounts of freshwater organic matter are also preserved
in this interval.
4 The alkenone signal may be used as a tracer for the inflow of Atlantic water masses along the
Eurasian continental margin, which probably started to intensify during Termination I. This
date, however, has to be proven by a more detailed stratigraphic framework.
S Oxygen Isotope Stage I accumulation rates of total organic carbon vary between 0.33 and
0.02 gC / cm 2 / ky, decreasing with increasing distance from the shelf and increasing water
depth.
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
this paper with the AMS14C-dated magnetic susceptibility record of Core PS2778 (Figure 4)
also supports a post-glacial age for Unit B (i.e., younger than Oxygen Isotope Stage 2). That
means, the alkenone signal at Core PS2471 may be used as tracer for Atlantic water inflow
along the Eurasian continental margin (cf., Figs 1 and 2) intensified during Termination I and
the early Holocene. Increased Atlantic water inflow connected with strong carbonate dissolution
and high marine organic carbon abundances during the last 12 ka has also been derived from an
organic-geochemical study of a well-dated gravity core from the northern Barents continental
margin (Knies and Stein, 1997).
Organic-carbon flux on the Laptev Sea continental margin during Oxygen Isotope Stage 1
In order to estimate the amount of total organic carbon stored in continental slope sediments of
the Laptev Sea during Oxygen Isotope Stage 1, accumulation rates of organic carbon were
calculated. The TOC accumulation rates are 0.3, 0.17, and 0.02 g C / cm 2 / ky in cores
PS2476, PS2474, and PS247l, respectively (Table 2). Assuming Unit B of Core PS2471 to
represent post-LGMlTermination I, TOC accumulation rates of Unit B would be higher by a
factor of about two than the Oxygen Isotope Stage I rates. These accumulation rates mainly
represent the flux of terrigenous organic carbon; marine organic carbon is only of secondary
importance. This is also reflected in the decrease in accumulation rates in offshore direction.
These rates are significantly higher than those calculated for the central Arctic Ocean (0.003 g C
/ cm2 / ky; Table 2; Stein et aI., 1994). That means, on the upper Laptev Sea continental slope
where maximum accumulation rates were recorded, the burial of organic matter is higher by a
factor of 100 than in the central Arctic. On the other hand, the upper slope TOC accumulation
rates are in the same order of magnitude as those calculated for coastal upwelling areas where,
however, most of the organic matter is of marine origin (cf. Stein, 1991 and further references
therein). Neverthless, the amount of organic carbon stored in the wide circum Arctic shelf and
slope areas are certainly of importance for calculation of organic carbon budgets on a global
scale.
Conclusions
I Organic geochemical bulk parameters (hydrogen index values and CIN ratios) and specific
biomarkers (n-alkanes, fatty acids, and alkenones) can be used to distinguish between
marine and terrigenous organic carbon sources. In general, terrigenous organic matter is
dominant on the Laptev Sea continental margin throughout. Marine organic carbon,
however, may occur occasionally in significant amounts.
2 The turbidites deposited during glacial Oxygen Isotope Stages 2 and/or 4 are clearly
dominated by terrigenous organic matter.
3 During Termination I (?) and the early Holocene, relatively high amounts of marine organic
matter were preserved in the sediments, as reflected be elevated hydrogen index values and
increased abundances of short-chain n-alkanes, short-chain fatty acids, and alkenones. It is
possible, however, that significant amounts of freshwater organic matter are also preserved
in this interval.
4 The alkenone signal may be used as a tracer for the inflow of Atlantic water masses along the
Eurasian continental margin, which probably started to intensify during Termination I. This
date, however, has to be proven by a more detailed stratigraphic framework.
S Oxygen Isotope Stage I accumulation rates of total organic carbon vary between 0.33 and
0.02 gC / cm 2 / ky, decreasing with increasing distance from the shelf and increasing water
depth.