L. and Voronina, E. 2001. Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the northern North Atlantic, Arctic and sub-Arctic seas: the new 'n = 677' data base and its application for quantitative palaeoceanographic reconstruction.ABSTRACT: The distribution of dinoflagellate cyst (dinocyst) assemblages in surface sediment samples from 677 sites of the northern North Atlantic, Arctic and sub-Arctic seas is discussed with emphasis on the relationships with sea-surface parameters, including sea-ice cover, salinity and temperature of the coldest and warmest months. Difficulties in developing a circum-Arctic data base include the morphological variation within taxa (e.g. Operculodinium centrocarpum, Islandinium? cezare and Polykrikos sp.), which probably relate to phenotypic adaptations to cold and/or low salinity environments. Sparse hydrographical data, together with large interannual variations of temperature and salinity in surface waters of Arctic seas constitute additional limitations. Nevertheless, the use of the best-analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea-surface conditions at the scale of the northern North Atlantic and the Arctic domain. The error of prediction calculated from modern assemblages is ±1.3°C and ±1.8°C for the temperature of February and August, respectively, ±1.8 for the salinity, and ±1.5 months yr −1 for the sea-ice cover. Application to late Quaternary sequences from the western and eastern subpolar North Atlantic (Labrador Sea and Barents Sea) provide reconstructions compatible with those obtained using the previous dinocyst data base (n = 371), which mainly included modern data from the northern North Atlantic.

Freshwater chlorophycean algae in recent marine sediments of the Beaufort, Laptev and Kara Seas (Arctic Ocean) as indicators of river runoff Abstract Freshwater chlorophycean algae are characteristic organic-walled microfossils in recent coastal and shelf sediments from the Beaufort, Laptev and Kara seas (Arctic Ocean). The persistent occurrence of the chlorophycean algae Pediastrum spp. and Botryococcus cf. braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large Siberian and North American rivers into the Arctic shelf seas. The distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break. Sedimentary processes overprint the primary distribution of these algae. Resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break. Bottom sediments and microfossils may be incorporated into sea ice during freeze-up in autumn and winter leading to an export from the shelves into the deep sea. The presence of these freshwater algae in sea-ice and bottom sediments in the central Arctic Ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils.Keywords Arctic Ocean´Beaufort Sea´Laptev SeaḰ ara Sea´Recent sediments´Chlorophyte distribution´Freshwater discharge J. Matthiessen ( ) )´M. Kunz-Pirrung

Kunz-Pirrung, M. 2001. Dinoflagellate cyst assemblages in surface sediments of the Laptev Sea region (Arctic Ocean) and their relationship to hydrographic conditions. ABSTRACT: The occurrence and distribution of dinoflagellate cysts in surface sediments from the Laptev Sea shelf and the adjacent continental margin have been studied in relation to surface water conditions. Assemblages were interpreted by visual inspection and Q-mode factor analysis. The inner Laptev shelf is a type-area for polar environments because of the near absence of relatively warm waters from the Pacific or Atlantic oceans and an extensive seasonal sea-ice cover. Assemblages are of low diversity and are dominated by the cold water taxon Islandinium minutum and related morphotypes. The common occurrence of distinctive polykrikoid cyst morphotypes is an indicator of polar environments. Furthermore, a strong supply of fresh water in summer influences the surface water conditions, and is a major factor controlling the occurrence and distribution of dinoflagellate cysts. The dinoflagellate cysts Nematosphaeropsis labyrinthus and Operculodinium centrocarpum are restricted to the continental margin, suggesting a relation to the inflow of relatively warm Atlantic waters along the Eurasian continental margin. An abundance maximum of Brigantedinium spp. at the shelf break is related to the mean position of the marginal ice zone.

A 467-cm-long core from the inner shelf of the eastern Laptev Sea provides a depositional history since 9400 cal yr. B.P. The history involves temporal changes in the fluvial runoff as well as postglacial sea-level rise and southward retreat of the coastline. Although the core contains marine fossils back to 8900 cal yr B.P., abundant plant debris in a sandy facies low in the core shows that a river influenced the study site until ∼8100 cal yr B.P. As sea level rose and the distance to the coast increased, this riverine influence diminished gradually and the sediment type changed, by 7400 cal yr B.P., from sandy silt to clayey silt. Although total sediment input decreased in a step-like fashion from 7600 to 4000 cal yr B.P., this interval had the highest average sedimentation rates and the greatest fluxes in most sedimentary components. While this maximum probably resulted from middle Holocene climate warming, the low input of sand to the site after 7400 cal yr B.P. probably resulted from further southward retreat of the coastline and river mouth. Since about 4000 cal yr B.P., total sediment flux has remained rather constant in this part of the Laptev Sea shelf due to a gradual stabilization of the depositional regime after completion of the Holocene sea-level rise.

[1] Sediment cores from Ocean Drilling Program sites 1094 and 1093 hold the most extensive and most detailed records of carbon and nitrogen isotopes of diatom-bound organic matter in the Atlantic sector of the Southern Ocean over the past 660 ka. These records were combined with summer sea surface temperatures and winter sea ice that were deduced from diatom transfer functions to reconstruct the nutrient regime at the northern and southern boundaries of the siliceous belt at latitudes 53°S and 50°S, respectively. The strong coupling between carbon and nitrogen isotope records at site 1093 suggests that the diatom productivity was influenced mainly by changes in nutrient availability. The anticorrelation between the carbon and nitrogen isotopes at site 1094 suggests that the diatom productivity was closely linked to global temperature changes, sea ice coverage, and dissolved CO 2 concentration. A detailed comparison of the nitrogen isotope records between the two sites shows three time intervals that represent different nutrient regimes. The nutrients at site 1093, which is close to the Polar Front, were dominated by eddies and meanders that sustained relatively high productivity at times of stratification or reduced ventilation, whereas at site 1094 the nutrients were influenced by ventilation processes.Citation: Schneider-Mor, A., R. Yam, C. Bianchi, M. Kunz-Pirrung, R. Gersonde, and A. Shemesh (2008), Nutrient regime at the siliceous belt of the Atlantic sector of the Southern Ocean during the past 660 ka, Paleoceanography, 23, PA3217,