ALBERT

Description: Distribution of recent, benthic foraminifera in the silled, partly anoxic Drammensfjord, reflects the prevailing hydrographic conditions, and reveals different intra basin responses to depleted oxygen conditions. The redox cline dips from about 35 m in the northern to about 60 m in the southern part of the fjord. Sediment surface samples are strongly dominated by agglutinated taxa except in the most oxygen depleted areas (O2 〈2 ml/1) in middle and southern parts. The water masses are subdivided into three units: 1) Brackish surface layer dominated by Miliammina fusca; 2) Transitional water masses with Astrammina sphaerica, Eggerelloides scabrus, Spiroplectammina biformis, and Ammodiscus? gullmarensis as frequently occurring species; and 3) Oxygen depleted water masses (salinity max. 31.2 ‰) dominated by Stainforthia fusiformis. The thin-shelled S. fusiformis shows adaption to low oxygen (〈2 ml/1) conditions and muddy, organic rich substrate as long as salinity exceeds about 30 ‰. Species diversity decreases towards the redox cline, and no foraminifera are found in oxygen depleted areas with salinities less than about 30 ‰

Description: Six sediment cores from the Eurasian Basin were studied to determine and understand climatically driven changes of Arctic Ocean basins. Detailed time control of sediments for the last 45 kyr is based on accelerator mass spectrometry (AMS) C14-dating of biogenic carbonate (N. pachyderma, left coiling). The most important results from our study are summarized as follows. From 45 to 13.5 ka low sedimentation rates prevailed (0.35 cm/kyr). They increased drastically at the transition from the last glacial to interglacial (Termination Ia, 13.5 ka) leading into high Holocene sedimentation rates (1.06 cm/kyr). Low carbonate concentrations (〈 4%) prevailed from 13.5 to 9 ka at Termination I. Decreased salinities can be expected for Termination la (Zahn et al., 1985, Jones & Keigwin, 1988, Mienert et al., 1989) due to glacial meltwater influence possibly accompanied by sea ice melting. As a result of the freshwater influence, productivity of planktic foraminifers decreased and this, in turn, resulted in a drastic decrease in carbonate concentration during Termination Ia. Although carbonate concentration varies only between 0 and 9%, it distinctly changes both the compressional-wave velocity (from 1485 to 1510 m/s) and the wave attenuation (from 0.1 to 0.45 dB/m/kHz) in the sediment. Climatically driven changes in magnetic susceptibility have proved to be a valuable paleoclimatic tool for intercore correlations. Our results indicate that the same general conclusions are valid for pelagic environments of both Atlantic and Arctic Ocean basins.

Description: Based on organic carbon accumulation rates, nine time slices of oceanic export paleoproductivity (Pnew) are presented which depict the variability of Pnew on a global scale through the last 30,000 years and document that the basic distribution patterns did not change through glacial and interglacial times. However, the glacial ocean shows an increased contrast of high- versus low-productivity zones. δ13C values of near-surface-dwelling planktonic foraminifera Globigerinoides ruber suggest that the same contrast applies to the glacial nutrient inventories of the ambient surface waters, with a significant glacial transfer of PO4 from low- to high-productivity zones. In this way, glacial Pnew increased by a global average of about 2–4 Gt Cyr−1 and led, via an enhanced CaCO3 dissolution and alkalinity in the deep ocean, to a significant extraction of CO2 from the surface water and the atmosphere.

Description: Unicellular protozoans are among the oldest fossils which we can recognize from the Precambrian. Presumably, foraminiferal ancestors were among the earliest of them, but had not yet benefitted from being sheltered by a biomineralized test. During the earliest Cambrian the first agglutinating foraminifera made their first appearance in the geologic record. These “primitive” forms built their test of foreign particles held together by an organic cement. This organic cement may have been secreted by the foraminifer in cytoplasmic vacuoles as is the case with Recent agglutinating foraminifera. Yet, the capability to biomineralize calcite did not evolve until after another 60 million years when the fusulinids developed their microgranular wall. Calcitic cemented agglutinates occur even later, at the base of the Carboniferous. Thus, in the fossil record the agglutinated foraminifera occur as a twofold group with a rather distinct evolution.

Description: Based on accumulation rates of the bulk sediment and some pelagic components (carbonate, total organic carbon, and biogenic opal fractions) major changes in the paleoceanography of the northern North Atlantic from Miocene to Recent are discussed. Interactions of various processes could have created a stepwise evolution of cold climates in the northern hemisphere. Prominent events were the onset of deep water export across the Greenland-Scotland Ridge with the first significant overflow across the Iceland-Scotland segment occurring most probably between 13 – 11 Ma and at about 7 Ma across the Denmark Strait. Oscillations of sea-level around the critical sill depth in the early phases of the subsidence may have influenced the oceanic circulation in the North Atlantic as well as in the Norwegian-Greenland Sea. Furthermore the potential of the Norwegian-Greenland Sea to form and export dense deep water, increased the meridionality in the northern hemisphere. During 10.2 – 9.3, 8.7 – 8.2, 5.8 – 5.4 and 4.8 – 3.2 Ma representing times of increased water mass exchange to the central North Atlantic, carbonate deposition occurred. On the other hand, higher opal accumulation rates and decreased water mass exchange (9.3 – 8.7 and 5.4 – 4.8 Ma) may be correlated with sea-level oscillations around the critical sill depth of the Greenland-Scotland Ridge. The build-up of northern hemisphere cooling can probably traced back to late Miocene times with modest ice-rafted debris input. A significant stepwise increase of northern hemisphere cooling occurred around 4 Ma and finally resulted in the first large extension of sea ice and ice-rafting in the entire North Atlantic at ca. 2.6 Ma.

Description: A stable oxygen isotope stratigraphy for the last 150.000 yr is established in sedimentary cores from the central Fram Strait. Radiometric ages obtained by the U/Th method in one core provide an absolute time framework for the oxygen isotope stratigraphy. The oxygen isotope record from substage 5a in the central Fram Strait is represented by lighter oxygen isotope ratios than substage 5e. This probably reflects lower salinities of the uppermost water column due to intense melting of icebergs and/or the supply of meltwater from adjacent landmasses rather than higher sea surface temperatures.

Description: Much of Arctic sea ice forms over the shallow continental shelves along the perimeter of the basin. Ice which escapes the shelf is transported several years within the Beaufort Gyre and Transpolar Drift stream, before exiting the Arctic Basin through Fram Strait. This ice, and especially that in the Siberian branch of the Transpolar Drift stream in the Eurasian Basin, may incorporate large quantities of particulate matter during formation on the shelf. Subsequent seasonal surface melting and winter freezing on the ice underside results in surface accumulation of particulate matter. Rafting of floes over and under each other results in a complex ice stratigraphy and redistribution of sediment accumulations. In contrast, Antarctic sea ice has only limited sources for sediment incorporation, and most of the ice-cover melts each year. These variations in Arctic and Antarctic ice characteristics are illustrated by analyses of ice crystal texture, c-axis orientations, salinity, δ 18O on ice cores and discussion of potential sediment input.

Description: We live in a world of ever increasing complexity. In the 25 years since the publication of the Treatise volumes by Loeblich and Tappan (1964), the number of validly described foraminiferal genera has more than doubled from 1192 in 1964, to at least 2455 in 1988. Agglutinated foraminifera (including the proteinaceous allogromiids) occupy about 180 pages of the recently revised version (Loeblich and Tappan, 1988). From the astrorhizids to the chrysalidinids, there are now at least 624 valid agglutinated genera, nearly as many genera as in the hyaline calcareous benthic suborder Rotaliina.