ALBERT

Description: Core and outcrop analysis from Lena mouth deposits have been used to reconstruct the Late Quaternary sedimentation history of the Lena Delta. Sediment properties (heavy mineral composition, grain size characteristics, organic carbon content) and age determinations (14C AMS and IR-OSL) are applied to discriminate the main sedimentary units of the three major geomorphic terraces, which form the delta. The development of the terraces is controlled by complex interactions among the following four factors: (1) Channel migration. According to the distribution of 14C and IR-OSL age determinations of Lena mouth sediments, the major river runoff direction shifted from the west during marine isotope stages 5-3 (third terrace deposits) towards the northwest during marine isotope stage 2 and transition to stage 1 (second terrace), to the northeast and east during the Holocene (first terrace deposits). (2) Eustasy. Sea level rise from Last Glacial lowstand to the modern sea level position, reached at 6-5 ka BP, resulted in back-filling and flooding of the palaeovalleys. (3) Neotectonics. The extension of the Arctic Mid-Ocean Ridge into the Laptev Sea shelf acted as a halfgraben, showing dilatation movements with different subsidence rates. From the continent side, differential neotectonics with uplift and transpression in the Siberian coast ridges are active. Both likely have influenced river behavior by providing sites for preservation, with uplift, in particular, allowing accumulation of deposits in the second terrace in the western sector. The actual delta setting comprises only the eastern sector of the Lena Delta. (4) Peat formation. Polygenetic formation of ice-rich peaty sand (''Ice Complex'') was most extensive (7-11 m in thickness) in the southern part of the delta area between 43 and 14 ka BP (third terrace deposits). In recent times, alluvial peat (5-6 m in thickness) is accumulated on top of the deltaic sequences in the eastern sector (first terrace).

Description: The marine sedimentary record in Kejser Franz Joseph Fjord and on the East Greenland continental margin contains a history of Late Quaternary glaciation and sedimentation. Evidence suggests that a middle-shelf moraine represents the maximum shelfward extent of the Greenland Ice Sheet during the last glacial maximum. On the upper slope, coarse-grained sediments are derived from the release of significant quantities of iceberg-rafted debris (IRD) and subsequent remobilization by subaqueous mass-flows. The middle-lower slope is characterized by hemipelagic sedimentation with lower quantities of IRD (dropstone mud and sandy mud), punctuated episodically by deposition of diamicton and graded sand/gravel facies by subaqueous debris flows and turbidity currents derived from the mass failure of upper slope sediments. The downslope decrease of IRD reflects either the action of the East Greenland Current (EGC) confining icebergs to the upper slope, or to the more ice-proximal setting of the upper slope relative to the LGM ice margin. Sediment gravity flows on the slope are likely to have fed into the East Greenland channel system, contributing to its formation in conjunction with the cascade of dense brines down the slope following sea-ice formation across the shelf. Deglaciation commenced after 15,300 14C years, as indicated by meltwater-derived light oxygen isotope ratios. An abrupt decrease in both IRD deposition and delivery of coarse-grained debris to the slope at this time supports ice recession, with icebergs confined to the shelf by the EGC. Glacier ice had abandoned the middle shelf before 13,000 14C years with ice loss through iceberg calving and deposition of diamicton. Continued retreat of glacier-ice from the inner shelf and through the fjord is marked by a transition from subglacial till/bedrock in acoustic records, to ice-proximal meltwater-derived laminated mud to ice-distal bioturbated mud. Ice abandoned the inner shelf before 9100 14C years and probably stabilized in Fosters Bugt at 10,000 14C years. Distinct oxygen isotope minima on the inner shelf indicate meltwater production during ice retreat. The outer fjord was free of ice before 7440 14C years. Glacier retreat through the mid-outer fjord was punctuated by topographically-controlled stillstands where ice-proximal sediment was fed into fjord basins. The dominance of fine-grained, commonly laminated facies during deglaciation supports ablation-controlled, ice-mass loss. Glacimarine sedimentation within the Holocene middle-outer fjord system is dominated by sediment gravity flow and suspension settling from meltwater plumes. Suspension sediments comprise mainly mud facies indicating significant meltwater-deposition that overwhelms debris release from icebergs in this East Greenland fjord system. The relatively widespread occurrence of fine-grained lithofacies in East Greenland fjords suggests that meltwater sedimentation can be significant in polar glacimarine environments. The ice-distal continental margin is characterized by meltwater sedimentation in the inner shelf deep, iceberg scouring over shallow shelf regions, winnowing and erosion by the East Greenland Current on the middle-outer shelf, and hemipelagic sedimentation on the continental slope.

Description: The 10Be records of four sediment cores forming a transect from the Norwegian Sea at 70°N (core 23059) via the Fram Strait (core 23235) to the Arctic Ocean at 86°N (cores 1533 and 1524) were measured at a high depth resolution. Although the material in all the cores was controlled by different sedimentological regimes, the 10Be records of these cores were superimposed by glacial/interglacial changes in the sedimentary environment. Core sections with high 10Be concentrations ( 〉1 * 10**9 at/g) are related to interglacial stages and core sections with low10Be concentrations ( 〈0.5 * 10**9 at/g) are related to glacial stages. Climatic transitions (e.g., Termination II, 5/6) are marked by drastic changes in the 10Be concentrations of up to one order of magnitude. The average 10Be concentrations for each climatic stage show an inverse relationship to their corresponding sedimentation rates, indicating that the 10Be records are the result of dilution with more or less terrigenous ice-rafted material. However, there are strong changes in the 10Be fluxes (e.g., Termination II) into the sediments which may also account for the observed oscillations. Most likely, both processes affected the 10Be records equally, amplifying the contrast between lower (glacials) and higher (interglacials) 10Be concentrations. The sharp contrast of high and low 10Be concentrations at climatic stage boundaries are an independent proxy for climatic and sedimentary change in the Nordic Seas and can be applied for stratigraphic dating (10Be stratigraphy) of sediment cores from the northern North Atlantic and the Arctic Ocean.

Description: Results from a detailed sedimentological investigation of surface sediments from the eastern Arctic Ocean indicate that the distribution of different types of sediment facies is controlled by different environmental processes such as sea-ice distribution, terrigenous sediment supply, oceanic currents, and surface-water productivity. In comparison to other open-ocean environments, total organic carbon contents are high, with maximum values in some deep-basin areas as well as west and north of Svalbard. In general, the organic carbon fraction is dominated by terrigenous material as indicated by low hydrogen index values and high C/N ratios, probably transported by currents and/or sea ice from the Eurasian Shelf areas. The amount of marine organic carbon is of secondary importance reflecting the low-productivity environment described for the modern ice-covered Arctic Ocean. In the area north of Svalbard, some higher amounts of marine organic matter may indicate increased surface-water productivity controlled by the inflow of the warm Westspitsbergen Current (WSC) into the Arctic Ocean and reduced sea-ice cover. This influence of the WSC is also supported by the high content of biogenic carbonate recorded in the Yermak Plateau area. The clay mineral distribution gives information about different source areas and transport mechanisms. Illite, the dominant clay mineral in the eastern central Arctic Ocean sediments, reaches maximum values in the Morris-Jesup-Rise area and around Svalbard, indicating North Greenland and Svalbard to be most probable source areas. Kaolinite reaches maximum values in the Nansen Basin, east of Svalbard, and in the Barents Sea. Possible source areas are Mesozoic sediments in the Barents Sea (and Franz-Josef-Land). In contrast to the high smectite values determined in sea-ice samples, smectite contents are generally very low in the underlying surface sediments suggesting that the supply by sea ice is not the dominant mechanism for clay accumulation in the studied area of the modern central Arctic Ocean.

Description: The Recent distribution of living and dead benthic foraminifera of the Arctic Ocean proper has been examined in surface sediments that were sampled during the International Arctic Ocean Expedition 1991 (Arctic 91). The samples represent the Amundsen and Nansen Basins, the Morris Jesup Rise, and the Yermak Plateau from 90°N to 79°42.4'N, 05°15.6'E. Due to the technical difficulties of deep-sea drilling in the Arctic Ocean these areas have, until now, been investigated only in very low density sampling. The Arctic 91 sites of this study cover a water depth range between 552 and 4375 m and represent three sites which are seasonally ice-free, although not yearly, while the other sites are characterized by permanent sea-ice. There is a Recent production of benthic foraminifera in the whole investigation area and all surface samples contain both benthic and planktonic foraminifera. Abyssal assemblages are recorded in the Amundsen and Nansen Basins where Stetsonia arctica dominates with high abundances. It is, however, also possible to distinguish these two basins by the use of diagnostic species. At intermediate water depths (500 to 2000-2500 m) the faunas show higher diversities and higher abundances of Atlantic species than the deep-sea sites. Mixing of North Atlantic water down to approximately 2500 m, is suggested to explain the influx of Atlantic species on the Yermak Plateau and the Morris Jesup Rise. The foraminiferal tests are well preserved within the investigation area and dissolution does not seem to be very obvious in the deeper areas. There is no evidence from the Recent foraminiferal faunas that the bottom waters of the eastern, central Arctic Ocean are undersaturated with respect to calcium carbonate and the deep-sea areas appear, therefore, to lie above the present CCD.

Description: A high-resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents, has been performed on undisturbed near-surface (0-40 cm) sediment sequences taken in the eastern Arctic Ocean during the international Arctic 91 Expedition. Based on the oxygen stable isotope records measured on Neogloboquadrina pachyderma (sin.) and AMS 14C dating, the upper 10 to 20 cm of the sediment sequences represent isotope stage 1, and the base of Termination I (15.7 ka) can be identified very well. Stage 1 sedimentation rates vary between 0.4 and 〉2.0 cm/kyr. In general, glacial stage 2 sedimentation rates are probably lower and vary between 0.4 and 0.7 cm/kyr. The glacial-interglacial shifts in delta18O values of N. pachyderma sin. may reach values of 1.3 to 2.5 per mil indicating (1) that, in addition to the glacial-interglacial global ice-volume signal, changes in surface-water salinity have effected the isotope records and (2) that these salinity changes have varied laterally. Glacial-interglacial differences in salinity were small in the Lomonosov Ridge area (0-0.4 per mil) and relatively high in the Morris-Jesup-Rise area (up to 1.4 per mil). This implies that the supply of low-saline waters onto the Eurasian shelves and its further transport into the central Arctic Ocean via the Transpolar Drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central Arctic. On the Morris-Jesup-Rise, on the other hand, the glacial low-saline-water signal at that time was strongly reduced in comparison to the modern situation. At the glacial-interglacial stage 1/2 boundary, a strong meltwater signal is recorded in a sharp depletion in delta18O as well as delta13C. This central Arctic Ocean meltwater event can be correlated from the Makarov Basin through the Lomonosov Ridge and Amundsen Basin to the eastern Gakkel Ridge. The beginning of this event is AMS 14C dated at 15.7 ka, i.e., significantly older than the major decrease in the global ice-volume signal which occurs between 9 and 13.5 ka. Large amounts of freshwater/meltwater were probably supplied from the Eurasian continent due to the decay of the Barents-Sea-Ice-Sheet, causing this distinct early meltwater anomaly in the central Arctic Ocean. The extension of a well-oxygenated surface-near water mass in the Arctic Ocean and (at least seasonal) open-ice conditions and some increased bioproductivity were probably established at the end of Termination I, as indicated by the increase in delta13C to modern values as well as increased carbonate (i.e., foraminifers, coccoliths, ostracodes) and total organic carbon contents.