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: We reconstructed changes of temperature, salinity, and productivity within the southern Peru-Chile Current during the last 8000 years from a high-resolution sediment core recovered at 41°S using alkenones, isotope ratios of planktic foraminifera, biogenic opal, and organic carbon. Paleotemperatures and paleosalinities reached maximum values at ~5500 years ago and thereafter declined to modern values, whereas paleoproductivity continuously increased throughout the last 8000 years. We ascribe these long-term Holocene trends primarily to latitudinal shifts of the Antarctic Circumpolar Current (ACC). The concurrence with shifts in the position of the Southern Westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern Chile. Millennial- to centennial-scale fluctuations of paleotemperatures and paleosalinities, on the other hand, lag displacements in the position of the Southern Westerlies but reveal a significant correlation to short-term temperature changes in Antarctica, indicating a high-latitude control of the ACC at these timescales.

Description: The Atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite lysocline. However, calculations and models that attribute the calcite lysocline to the critical undersaturation depth (hydrographic or chemical lysocline) and not to the depth at which significant calcium carbonate dissolution is observed (sedimentary calcite lysocline) strongly overestimate the preservation potential of calcareous deep-sea sediments. Significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep Guinea and Angola Basin and below 4400 m in the Cape Basin. Our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera Globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the South Atlantic Ocean. In particular, coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic CO2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic lysocline.

Description: Thirty-two surface sediment samples from the Southern Ocean (eastern Atlantic sector), between the Subtropical Front and the Weddell Gyre, were investigated to provide information on the distribution of modern organic-walled dinoflagellate cysts in relation to the oceanic fronts of the Antarctic Circumpolar Current (ACC). A clearly distinguishable distribution pattern was observed in relation to the water masses and fronts of the ACC. The dinoflagellate cysts of species characteristic of open oceanic environments, such as Impagidinium species, are highly abundant around the Subtropical Front, whereas south of this front, cosmopolitan species such as Nematosphaeropsis labyrinthus and the cysts of Protoceratium reticulatum characterise the transition from subtropical to subantarctic surface waters. The subantarctic surface waters are dominated by the cysts of heterotrophic dinoflagellates, such as Protoperidinium spp. and Selenopemphix antarctica. The cysts of Protoperidinium spp. form the dominant part of the assemblages around the Antarctic Polar Front, whereas S. antarctica concentrations increase further to the south. The presence of S. antarctica in sediments of the Maud Rise, a region of seasonal sea-ice cover, reflects its tolerance for low temperatures and sea-ice cover. A previously undescribed species, Cryodinium meridianum gen. nov. sp. nov., has a restricted distribution pattern between the Antarctic Polar Front and the ACC-Weddell Gyre Boundary.