ALBERT

Beschreibung: In Moreton Bay, Queensland, the catch obtained using monofilament polyamide (PA) otter trawl-nets with multifilament polyethylene (PE) cod ends was compared with that obtained using multifilament PE trawl-nets of identical mesh opening (38 mm). Monofilament PA otter trawl-nets retained fewer small prawns ( 〈 24 mm carapace length) than conventional multifilament PE nets, but both nets caught similar quantities of larger prawns ( 〉 24 mm carapace length). The higher retention rate of small prawns by multifilament PE gear was reflected in the greater catch weights of Peraeus plebejus, Metapenaeus bennettae and Metapenaeopsis novaeguineae in those nets. Catch weights of larger prawn species such as Penaeus esculentus and Metapenaeus endeavouri did not differ between nets. Winter whiting (Sillago maculata) and squid (Loligo spp.) were trawled in similar abundance in both nets, although the monofilament retained fewer squid 〈 50 mm mantle length. More marketable ( 〉 15 cm carapace width) sand crabs (Portunus pelagicus) were caught in the monofilament net. There was not significant difference in the trash (noncommercial component) weight caught in both nets. Over the range of towing speeds tested (1.7–2.3 kn), use of monofilament nets significantly reduced total gear drag.

Beschreibung: A total of 131 current meter records of between 6 and 24 month duration are analysed to describe the deep flow field of the eastern North Atlantic from 19° to 54°N and from the Continental Slope to the Mid Atlantic Ridge. Mean flows are weak and may be statistically indeterminate in some records and locations, but appear to indicate cyclonic circulations around the Iberia and Porcupine abyssal plains with a generally southward flow along the Mid Atlantic ridge and a deep northward slope current (where measurements exist) along the eastern boundary. The deepest inflow to the north-eastern basin that has been identified to date takes place through the Discovery Gap of 〉4,700 m sill-depth at 37° 25′N 15° 45′W in the Azores-Portugal ridge. South of that ridge, observations are sparse and no systematic circulation is yet evident. These observations are discussed in relation to recent geostrophic estimates of the deep circulation.

Beschreibung: Sediments on high Arctic shelves result from modern processes and the effect of former glaciations. Based on data from the northern Barents Sea, an area with input from large and numerous surging glaciers, we define two principal zones with different environmental regimes and corresponding sedimentary facies: (1) a glacier-proximal zone influenced by grounding-line processes and the immediately adjacent areas affected by glacial sediment input, and (2) a glacier-distal, sea-ice and current-controlled zone, which also includes a wide sediment-starved region dominated by biogenic carbonate accumulation. Characteristic of the glacier-proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea-floor morphologies. Extensive ice gouging causes a homogeneous sediment texture. In the glacier-distal zone, fine-grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes. On shallow banks, in 30–50 m of water, carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply.

Beschreibung: Molluscan fossils collected from shallow water marine sediment across NW Europe and nearby Arctic regions have been analysed for the extent of isoleucine epimerization (DL ratio) in indigenous protein residues. The DL ratios confirm that essentially all ‘classical’ Eemian sites from NW Europe are of the same age, and are correlative with the type locality near Amersfoort in the Netherlands; shells from interglacial marine sediment beneath the type Weichselian till in Poland also correlate with the type Eemian site. DL ratios in Holsteinian marine shells (0.29) are substantially higher than in their Eemian counterparts (0.17); ‘Late Cromerian’ shells yield even higher ratios (0.46). DL ratios in late glacial shells (0.06) and Middle Weichselian shells (0.09) permit differentiation from modern (0.01) and last interglacial material. Based on the position of the Matuyama-Brunhes boundary and the differences in DL ratios, the Eemian must correlate with isotope substage 5e, whereas the Holsteinian is most likely substage 7c, possibly stage 9 but certainly younger than stage 11. Intra-Saalian warm periods may be terrestrial equivalents of the younger substages of stage 7. Extensive pre-Eemian marine sediments along the SW coast of Denmark previously correlated with the Holsteinian are shown to be of ‘Late Cromerian’ age. The underlying till there is the first widespread evidence of a pre-Elsterian till in NW Europe. DL ratios in molluscs from last interglacial sites along the Arctic coast of the USSR, the Arctic Islands and eastern Greenland are substantially lower than in their European counterparts due to their low thermal histories. The combined mid- and high-latitude data are used to develop a predictive model for the expected DL ratio in any of several moderate epimerization-rate taxa for last interglacial sites with mean temperatures between −20 and +15°C. Not all sites could be unambiguously assigned to an established interglacial. The Fjøsanger (Norway) and Margareteberg (Sweden) sites previously thought to be Eemian, yield DL ratios higher than in secure nearby Eemian material. It is yet unresolved whether these are aberrant sites or if they predate the last interglacial. In situ shoreline deposits encountered in borings in SW Belgium and in exposures on the Belgium coastal plain contain molluscs that yield DL ratios intermediate between secure Eemian and Late Weichselian ratios, raising the possibility that a late stage 5 high-sea-level event attained near-modern levels in the southern North Sea basin. Resolution of these uncertainties is the focus of future work.

Beschreibung: Marine geophysical surveys employing Seabeam, multi- and single-channel seismic reflection, gravity and magnetic instruments were conducted at two locations along the continental slope of the Peru Trench during the Seaperc cruise of the R/V “Jean Charcot” in July 1986. These areas are centered around 5°30′S and 9°30′S off the coastal towns of Paita and Chimbote respectively. These data indicate that (1) the continental slope off Peru consists of three distinct morpho-structural domains (from west to east are the lower, middle and upper slopes) instead of just two as previously reported; (2) the middle slope has the characteristics of a zone of tectonic collapse at the front of a gently flexured upper slope; (3) the upper half of the lower slope appears to represent the product of mass wasting; (4) thrusting at the foot of the margin produces a continuous morphologic feature representing a deformation front where the products of mass-wasting are overprinted by a compressional tectonic fabric; (5) a change in the tectonic regime from tensional to compressional occurs at the mid-slope-lower slope boundary, the accretionary prism being restricted to the very base of the lower slope in the Paita area. The Andean margin off Peru is an “extensional active margin” or a “collapsing active margin” developing a subordinated accretionary complex induced by massive collapse of the middle slope area.

Beschreibung: Piston cores from fiords, shelf troughs, and the deep-sea off eastern Baffin Island, N.W.T., Canada, have been sampled for texture and detrital carbonate in the 〈2 mm fraction. The sediments consist primarily of silty clays usually containing 〈5% sand. Estimates are made for sediment accumulation (kg/m**2/ka) over the last ca. 10 ka. Three sets, of two cores each, lie on a fiord-shelf transect and thus define variations in sediment accumulation gradients. These continental margin data are compared with cruder estimates of Holocene sediment accumulation at three sites farther offshore in Baffin Bay, Davis Strait and the northern Labrador Sea. Minimum accumulation in a 2 ka interval was 200 kg/m2 with a maximum estimate of 8,800 kg/m2. Detrital carbonate accumulation varies between 0 and 1,300 kg/m**2. Median accumulation for a typical fiord-shelf-deep-sea transect over the last 10 ka have been 10,340, 3493 and 820 kg/m**2. At DSDP Leg, site 645 in central Baffin Bay, the sedimentation rate ranged between 40 and 130 m/Ma (ca. 400 and 1200 kg/m**2/2ka); that is, comparable with the Late Quaternary input into Baffin Bay.

Beschreibung: Clay- and silt-size mineral assemblages are described from eight piston cores from the fiords and shelf on the western margin of Baffin Bay, Arctic Canada. Radiocarbon dates indicate that all the cores extend back in time to the last local glacial/interglacial transition (i.e. 8–10 ka); four extend back to between 10 and 12 ka, and HU77-021-156, located on the Southeast Baffin Island shelf, includes the entire late Foxe glacial stage. Silt- and clay-size particles constitute ca 40 and 55%, respectively, by weight of the bulk sediment. The clay-size fraction is dominated by mica; feldspars and quartz are the main constituents of the silt fraction. The fiord sediments are mainly composed of local mineralogies, but on the shelf, and at times in the fiords, exotic mineral species occur. The most important of these are detrital carbonates, derived from erosion of the Paleozoic basins in Arctic Canada and/or northwest Greenland. Both calcite and dolomite occur; calcite is the major carbonate mineral in the “southern” cores, whereas dolomite is the most abundant in cores north of 66°N. Higher inputs of carbonate species occur during regional deglaciation, 7–10 ka, and during the last 5 ka (probably reflecting increased iceberg production from northwest Greenland). Thus variations in the precentages of the carbonate minerals indicate significant shifts in Late Quaternary glacial-sediment source areas and oceanographic regimes.

Beschreibung: Changes in composition of modern benthic ostracod faunas across the continental margin of southwestern Africa occur at boundaries between and within major water masses: a Mixed Layer-Antarctic Intermediate Water (AAIW) boundary at 200 m, an AAIW salinity minimum zone at 650 m, an AAIW bathyal thermocline at 1000 m, and the AAIW/North Atlantic Deep Water (NADW) boundary at 1500 m. In addition, two population changes occur within the NADW at 1.8–2.0 km and 2.0–3.0 km. The Antarctic Bottom Water assemblage is sparse and poorly preserved.