ALBERT

Description: Dense Antarctic Bottom Water formed around the continent of Antarctica spreads northward in the Atlantic underneath North Atlantic Deep Water, gradually mixing and upwelling into it. This Antarctic Water forms a significant element of the meridional circulation in both directions: northward as bottom water and southward as deep water. It is important to determine the strength of each component to assess its role in ocean circulation. Such measurements are useful when made in constricted pathways because any flow is more clearly defined. A new set of fine-resolution hydrograhic measurements in the Hunter Channel of the South Atlantic Ocean has been obtained, which allow the geostrophic bottom flow there to be estimated for the first time. The northward flow through the Hunter Channel of water cooler than 2-degrees-C is thus estimated to be 0.7 X 10(6) m3 s-1.

Description: Coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the Norwegian Sea and Fram Strait. Both fossil groups are characterized by similar patterns of composition. The assemblages contain high proportions of single species. The coccolith flora is of low diversity and consists almost entirely of Coccolithus pelagicus and Emiliania huxleyi. The dinoflagellate cysts are generally dominated by Operculodinium centrocarpum and Nematosphaeropsis labyrinthus. Other species, especially Bitectatodinium tepikiense, Peridinium faeroense and Impagidinium pallidum, sometimes contribute considerably to the assemblages. Based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions. Sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10,000 yrs. B.P., indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of Atlantic water. The modern surface-water circulation pattern was reinitiated during Termination IB. The assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs B.P. Solar insolation may have caused a first temperature peak which is responsible for the early Holocene productivity maximum. A considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the Holocene climatic optimum. This change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire North Atlantic realm after the ice sheets had vanished. Since 6000 yrs B.P. the Norwegian Current with its modern oceanographic and ecological properties has been fully established.

Description: The Neogene Bolboforma zones established in the North Atlantic have been correlated with the calcareous nannoplankton stratigraphy obtained by investigation of the same samples from DSDP Sites 12–116 (44 samples), 49–408 (76 samples), 81–555 (43 samples) and 94–608 (103 samples). The absolute ages for the zonal boundaries were determined by the paleomagmetic record of Site 94–608. This correlation and the age determinations are additional useful tools to develop a precise biostratigraphy of Neogene sediments in the Northern Atlantic.

Description: An investigation was carried out on the morphology, growth and microstructure of statoliths of 833 specimens of Sthenoteuthis pteropus (Steenstrup) mantle length (ML): 2–548 mm collected in the open waters of the Gulf of Guinea in 1984–1988. Statolith morphology is similar to that of other species of the subfamily Ommastrephinae and is similar to the sibling species S. oulaniensis. Statolith development includes five stages resembling those of Illex illecebrosus and other ommastrephids. Statolith growth is characterized by negative allometry. Increments visible in ground sections of statoliths can be grouped into four main growth zones, differing mainly in colour and increment width. Age and growth rates of S. pteropus were calculated using increment counts. The life span of females of all size groups does not exceed 1 yr, that of males is 1–2 months shorter, probably due to preliminary mating. Instantaneous relative growth rage (G) of paralarvae is high (up to 16% of body weight (BW)). G values for juveniles decline, but remain relatively high (7–8% BW). Juveniles attain 100–110 mm ML by age 100–110 days. G values for adults are the lowest (1.8–2% BW), but daily growth rates reach maximum values (40–70 g per day in large females of 450–500 mm ML). Each ontogenetic phase of S. pteropus corresponds to features of morphology, growth and microstructure of the statolith.

Description: The alimentary tracts of 12 species of Antarctic squid were examined visually and serologically for the presence of Euphausia superba. Only four species, Alluroteuthis antarcticus, Galiteuthis glacialis, Martialia hyadesi and Psychroteuthis glacialis, contained material which was identifiable to species visually. Myctophid fish and euphausiids were the most common prey item. Serology showed that specimens of six species had eaten euphausiids. Where antisera showed cross-reactions with other potential prey species, biogeographical and haul data was used to determine the species of Euphausia consumed. P. glacialis (n=19) had consumed E. superba. Mastigoteuthis psychrophila (n=10) had eaten E. superba and/or E. triacantha. Brachioteuthis picta (n=6), M. hyadesi (n=27), and two Moroteuthis spp. (n=2) had consumed unidentified euphausiids. Bathyteuthis abyssicola (n=13) and Histioteuthis eltaninae (n=13) had not preyed on euphausiids. B. picta appeared to have fed in the net.

Description: Sixteen samples (588 individuals) of the Argentine shortfin squid Illex argentinus were collected by commercial vessels from Falkland and surrounding waters (42°06–51°17S) between February and May 1990 and subjected to starch gel electrophoresis. Levels of electrophoretically detectable generic variability and the extent of population differentiation were determined from allele frequencies at 25 enzyme-coding loci. Low levels of genetic variability were detected, with the overall proportion of polymorphic loci, P = 0.28, mean heterozygosities per locus, H1 = 0.011, and the average effective number of alleles, Nc = 1.23. Marked population differentiation was indicated by significant differences in allele frequency among samples, and unbalanced genotypic distributions with heterozygote deficits at most loci. Nei's mean genetic distances (D) and identities (I) ranged from 0.000 to 0.130 and 1.000 to 0.878, respectively, underlining the marked genetic divergence detected. Some evidence of microgeographic differentiation (between replicates within sites) was observed. Individuals collected from northerly limits of the sampled area (42: 06 S, 58:09 W) were most genetically distinct (I = 0.878−0.904), suggesting the existence of a hitherto unrecognised subspecies or species of Illex. Emphasis is placed on the need to delimit putative stock boundaries, and develop appropriate population models to ensure conservation of genetic resources.

Description: Nine gravity cores collected on the East Greenland continental margin off Kangerdlugssuaq Fjord reveal a drastic decrease in average sedimentation rates from the cross-shelf through the continental slope (from 43.2 cm/kyrs to 2.2 cm/kyrs, respectively). Since the last deglaciation, beginning at 〈15, 000 yrs B.P., both carbonate and non-carabonate accumulation rates have been controlled by the decrease in glaciers and sea ice and the increase in surface-water circulation. CaCo3 and non-CaCO3 accumulation rates at about 14,000 yrs B.P. were high on the outer shelf, followed by high values at the inner shelf about 9000 yrs B.P., suggestive or rapid glacier retreat. About 9000 yrs B.P., the northerly flowing Irminger Current and the southerly flowing East Greenland Current may have increased intensity leading to distinct increases in CaCO3 accumulation (〉2g/cm2kyrs). At 4000 yrs B.P., both CaCO3 and non-CaCO3 accumulation rates became high (〈g/cm2kyrs); since 3000 yrs B.P. these rates distinctly decreased. Melting of glaciers and current activity, which drastically changed in space and time controlled the terrigenous sediment input, and thus the grain-size distribution and the physical properties of sediments, across the shelf. These observations suggest that current winnowing on sediments is one of the dominant processes at present. This is seen in the acoustic reflectivity and in the acoustically hard seafloor, particularly at the upper continental slope. In addition, icebergs transported southward along the continental margin, have scoured the sediment surface in water depths 〈350m.

Description: The concentration of 230Th in Mn crust VA13-2 (146°W, 9°25′S, 4830 m) from the Pacific Ocean was measured with high depth resolution (0.02 mm) to a depth of 1.4 mm corresponding to an age of ∼226 ka B.P. The mean growth rate estimated from these results is 6.2 ± 0.4 mm/Ma. However, the exponential curve obtained shows two drastic events in the 230Th concentration record with durations of41 ± 4 ka and 37 ± 6 ka which are interpreted as growth standstills. The decay-corrected 230Th concentration is inversely correlated with those of Mn, Fe and Co indicating that the 230Th flux into the crust has been constant throughout time and that the observed fluctuations in 230Th are due to dilution by the main components. By applying a constant 230Th flux model, high-resolution growth rates were derived from every sample investigated. A detailed comparison of the growth pattern with the SPECMAP time table reveals that the VA13-2 growth rates tend to be higher during interglacial than during glacial periods. In particular, the observed growth standstills are associated with glacial stages 6 and 8. Further investigation of Mn crust 72 DK 9 taken from shallower water (170°35′W, 20°13′N, 1550 m) tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the Late Quaternary.

Description: Condensed pelagic deposits characterize the uppermost sediment sequence of the Maud Rise in the eastern Weddell Sea. The comparison of subbottom profiling data with the sediments drilled at two ODP sites shows that Lithologic Unit Ib deposited during late Miocene to late Pliocene times is generally characterized by acoustic transparency. A prominent reflector with strongly increased amplitude (called Reflector “Pc”) occurs within this mainly homogeneous diatom ooze unit and is correlated with the porcellanite horizon found at ODP Site 689. As evidenced by sediment findings, Reflector “Pc” marks a distinct stratigraphic layer of early Pliocene age. The development of the Reflector “Pc” and its amplitude of reflection in the echosounding records is most likely caused by the silica cementation of porcellanite within this layer. The analyses of the sediment echosounder profiles from five R.V. Polarstern cruises make it possible to map the regional distribution of Reflector “Pc”. In large areas of the central Maud Rise, a patchy but also continuous distribution of Reflector “Pc” was found. The reflector does not occur in sediments below 3000 meters of water. On average Reflector “Pc” is detected around 11 and 12 meters below seafloor, but depth occurrence is highly variable within the range of 8 m to more than 18 m. The apparent amplitude of Reflector “Pc” is higher in those areas where the diatom ooze Unit Ib reaches greater thicknesses, which may be caused by local enhanced tectonic subsidence. In general a good correlation of Reflector “Pc” amplitude and thickness of lithologic Unit Ib is observed. This may imply that the diatom ooze Unit Ib serves as a silica source, since the extent of silica cementation of the porcellanite layer is controlled by the amount of dissolved silica supply. Other possible interpretations for silica sources include silica-rich interstitial water ascending from deeper sediment levels using tectonic structures for migration.