Particle analysis in the Kara Sea

In September 1999 two short-term moorings with cylindrical sediment traps were deployed to collect sinking particles in bottom waters off the Ob and Yenisei river mouths. Samples were studied for their bulk composition, pigments, phytoplankton, microzooplankton, fecal material, amino acids, hexosamines, fatty acids and sterols and compared to suspended matter and surface sediments in order to collect information about the nature and cycling of particulate matter in the water column. Results of all measured components in sinking particles point to an ongoing seasonality in the pelagic system from blooming diatoms in the first phase to a more retention system in the second half of trap deployment. Due to a phytoplankton bloom observed north of the Ob estuary, flux rates were generally higher in the trap deployed off the Ob than off the Yenisei. The Ob trap collected fresh surface-derived particulate matter. Particles from the Yenisei trap were more degraded and resembled deep water suspension. This material may partly have been derived from resuspended sediments.

(Table 3) Contents of P2O5 and total REE in phosphorites from Pacific seamonts

Changes in concentration levels and speciation of heavy metals during sedimentation on example of a typical semi-closed bay, where bottom sediments have formed due to river run-off, are under consideration. It is shown that due to desorption of mobile manganese, zinc and copper entered the bay with river suspended matter, their total contents in bottom sediments decrease and percentages of lithogenic forms increase. Contents and speciation of iron in bottom sediments are determined by its participation in coagulation of river colloids in the mixing zone and by mechanical differentiation of sedimentary material.

Pollen record and age determination of a sediment core from the Kara Sea

AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon. A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.