ALBERT

Description: In large areas of the world's oceans, there is a relationship between the mass flux of particulate matter and the unsupported 231Pa/230Th (xs231Pa/xs230Th) activity ratio of recent sediments. This observation forms the basis for using the xs231Pa/xs230Th ratio as a proxy for past changes in export productivity. However, a simple relationship between xs231Pa/xs 230Th ratio and particle flux requires that the water residence time in an ocean basin is far in excess of the scavenging residence time of 231Pa, and that the composition of sinking particles maintains a strong preference for the adsorption of 230Th over 231Pa with a constant 230Th/231Pa fractionation factor (F). The best correlation between xs231Pa/xs230Th ratio and mass flux is found in the Pacific Ocean. In the Atlantic, the contrast in the xs231Pa/xs230Th ratios between open ocean (low flux regions) and ocean margins (high flux regions) is much less pronounced due to the shorter residence time of deep water, resulting in less effective boundary scavenging of 231Pa. In the Southern Ocean, south of the Polar Front, there is no more a simple relationship between xs231Pa/xs230Th and particle flux. This is a result of a southward decrease in F, probably reflecting the increased opal content of sinking particles. Opal does not fractionate 231Pa and 230Th significantly. This lack of fractionation results in high xs231Pa/xs230Th ratios in opal-dominated regions, even in areas of very low particle fluxes such as the Weddell Sea. The xs231Pa/xs230Th ratio can therefore only be used as a paleoproductivity proxy if, in the time interval of interest, changes in the basin ventilation rate and differential scavenging of both radionuclides due to changes in the chemical composition of particulate matter can be excluded.

Description: Glacial landforms in northern Russia, from the Timan Ridge in the west to the east of the Urals, have been mapped by aerial photographs and satellite images supported by field observations. An east-west trending belt of fresh hummock-and-lake glaciokarst landscapes has been traced to the north of 67°N. The southern boundary of these landscapes is called the Markhida Line, which is interpreted as a nearly synchronous limit of the last ice sheet that affected this region. The hummocky landscapes are subdivided into three types according to the stage of postglacial modification: Markhida, Harbei and Halmer. The Halmer landscape on the Uralian piedmont in the east is the freshest, whereas the westernmost Markhida landscape is more eroded. The west- east gradient in morphology is considered to be a result of the time-transgressive melting of stagnant glacier ice and of the underlying permafrost. The pattern of ice-pushed ridges and other directional features reflects a dominant ice flow direction from the Kara Sea shelf. Traces of ice movement from the central Barents Sea are only discernible in the Pechora River left bank area west of 50°E. In the Polar Urals the horseshoe-shaped end moraines at altitudes of up to 560 m a.s.l. reflect ice movement up-valley from the Kara Ice Sheet, indicating the absence of a contemporaneous ice dome in the mountains. The Markhida moraines, superimposed onto the Eemian strata, represent the maximum ice sheet extent in the western part of the Pechora Basin during the Weichselian. The Markhida Line truncates the huge arcs of the Laya-Adzva and Rogovaya ice-pushed ridges protruding to the south. The latter moraines therefore reflect an older ice advance, probably also of Weichselian age. Still farther south, fluvially dissected morainic plateaus without lakes are of pre-Eemian age, because they plunge northwards under marine Eemian sediments. Shorelines of the large ice-dammed Lake Komi, identified between 90 and 110 m a.s.l. in the areas south of the Markhida Line, are radiocarbon dated to be older than 45 ka. The shorelines, incised into the Laya-Adzva moraines, morphologically interfinger with the Markhida moraines, indicating that the last ice advance onto the Russian mainland reached the Markhida Line during the Middle or Early Weichselian, before 45 ka ago.

Description: The marine-lacustrine transition (isolation contact) in sediment cores from eight lake basins situated 13.5–72 m a.s.l., in the Norwegian-Russian border area north of Nikel, northwest Russia, was identified based on lithological and diatom analysis, radiocarbon dated, and used to construct a relative sea-level (RSL) curve for the Holocene. All the lakes except one (interpreted as having an unconformable slumped transition) show a regressive I-II-III (marine-transitional-lacustrine) facies succession, indicating a postglacial history of continuous emergence. The RSL curve shows rapid emergence between 10 000 and 8000 BP, very slow emergence between 7000 and 5000 BP, increased rate of emergence between 4500 and 4000 BP, and a moderate rate of emergence after 3500 BP. The low rate of emergence around 6000 BP correlates with the Tapes transgression of more coastal regions, but corresponding sea level, at 25–26 ma. present s.l., lies 5–10 m lower than the elevation predicted based on existing isobase maps for the region. The discrepancy suggests a need for further work in order to more rigorously define and map the Tapes transgression and associated shoreline complex in the northern Fennoscandian-Kola region.

Description: In this paper the relationship between whole-core compressional wave velocities and gamma-ray attenuation porosities of sediments cored at CRP-2/2A is examined, and compared with results from CRP-1, CRP-2/2A core-plug samples, and global models for velocity/porosity relationships of marine sediments. The high degree of data scatter observed in the velocity/porosity relationship of CRP-1 core is even larger in CRP-2/2A core. The general pattern of the velocity/porosity relationship is similar in CRP-2/2A whole core and core plug measurements. Despite scatter, all data indicate a strong primary dependence of velocity on porosity. This relationship appears to be independent of lithology except for sections with zero porosity and porosity 〉0.6, which are attributed to large lonestones and lapillistones, respectively. Core velocity/porosity patterns of CRP-1 and CRP-2/2A are very similar for sediments from the same age interval (19-23 Ma), both characterized by relatively low velocities (mostly between 2 and 3 km s-1) compared to porosity (0.1 - 0.4). Within this range of porosity, core velocities increase significantly up to more than 4 km s-1 below ca 440 mbsf. The change in the velocity/porosity relationship as a function of core depth is attributed to down-core increase in intergrain coupling enhanced by carbonate cementation. This is confirmed by a positive correlation of carbonate content with velocities higher or lower than empirically predicted from porosity. After removing first-order compaction control from the whole-core porosity record, no significant control by clay content can be identified (R = 0.3). This is different to the results for core from CRP-1 (R = 0.6) which is not cemented.

Description: The mineralogy of the lower Oligocene to Quaternary sediments of core CRP-2/2A drilled on the continental shelf of McMurdo Sound in Ross Sea, Antarctica, was examined by the X-ray diffraction method. Quartz, plagioclase feldspar and K-feldspar are the most important non-clay minerals. Pyroxene and amphibole occur in minor amounts throughout the core. The composition of the sediments points to an origin in the Transantarctic Mountains for the majority of the detrital components. There, the plutonic and metamorphic rocks of the basement, the sediments of the Beacon Supergroup and the volcanic rocks of the Ferrar Group could serve as possible source lithologies. The distribution of the detrital minerals reflects a long-term history of successive erosion and valley incision. During the deposition of the lower part of the core, the detrital minerals were probably mainly derived from the sediments of the Beacon Supergroup, as indicated by the high quartz but relatively low feldspar abundances. In the upper c. 350 m of the core, the influence of a source in the basement became stronger and results in lower quartz contents but increasing abundance of feldspar. Some diagenetic alteration of the sediments is indicated by the occurrence of zeolites below c. 320 mbsf and of opal-CT above c. 320 mbsf.