ALBERT

Description: We present a method for objectively characterizing a swath of digitally sampled seafloor topography. Our method analyzes the distribution of surface slopes by compiling surface-normal vectors into a two-dimensional histogram using an equal-area projection. The direction of maximum variance (first principal axis) of the histogram is used to determine the azimuth of lineations in the topography, and the variance is used as a measure of seafloor roughness. We apply the method to short sections of Sea Beam swath data and find that the histogram parameters are effective in describing the behavior of the topography. In particular, similar patterns are observed for a sequence of histograms derived from data collected over the Mendocino and the Surveyor fracture zones in the northeast Pacific. Because the method does not require any data modification and is suitable for irregularly-shaped sample regions, it lends itself to real-time analysis.

Description: 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.

Description: The renewal of the deep water of the East Atlantic and its large-scale internal circulation are studied on the basis of the distributions of potential temperature, silicate, ΣCO2, and 14C. An isopycnal multibox model including advection, mixing, and sources and sinks is set up and described. Tracer data are input for the model, and balance equations for the various properties for the boxes of the model serve as constraints for the determination of water fluxes, mixing coefficients, and source parameters. Extremal values for various model parameters that are consistent with the tracer data (satisfy the balance equations within the estimated tolerances) are calculated by linear programming techniques. 14C data are seen to be valuable in determining absolute flow rates. Model results confirm the importance of the Romanche Facture Zone for the renewal of east Atlantic deep water. Eastward flows through the Romanche Fracture Zone were found to be between 2.6 and 5.1 Sv. Flows through the Vema Fracture Zone amount to at most 20% of the Romanche Fracture Zone inflow. Contributions of Antarctic Bottom Water at the southern end of the East Atlantic (Walvis Ridge) and of Iceland Scotland Overflow Water at the northern end are very small (〈 5% of equatorial inflow). Diapycnal mixing coefficients are between 1 and 10 cm2/s, and values for the dissolution rates of silicate and carbon are in the expected range.

Description: Reducing the large volume of TIROS-N series advanced very high resolution radiometer-derived data to a practical size for application to regional physcial oceanographic studies is a formidable task. Such data exist on a global basis for January 1979 to the present at approximately 4-km resolution (global area coverage data, ≈2 passes per day) and in selected areas at high resolution (local area coverage and high-resolution picture transmission data, at ≈1-km resolution) for the same period. An approach that has been successful for a number of studies off the east coast of the United States divided the processing into two procedures: preprocessing and data reduction. The preprocessing procedure can reduce the data volume per satellite pass by over 98% for full-resolution data or by ≈84% for the lower-resolution data while the number of passes remains unchanged. The output of the preprocessing procedure for the examples presented is a set of sea surface temperature (SST) fields of 512 × 1024 pixels covering a region of approximately 2000 × 4000 km. In the data reduction procedure the number of SST fields (beginning with one per satellite pass) is generally reduced to a number manageable from the analyst's perspective (of the order of one SST field per day). This is done in most of the applications presented by compositing the data into 1- or 2-day groups. The phenomena readily addressed by such procedures are the mean position of the Gulf Stream, the envelope of Gulf Stream meandering, cold core Gulf Stream ring trajectories, statistics on diurnal warming, and the region and period of 18°C water formation. The flexibility of this approach to regional oceanographic problems will certainly extend the list of applications quickly.

Description: A suit of sediment cores close to and south of the Strait of Gibraltar (12°-36°N, 500–2800 m water depth) were analyzed for stable isotopes in epibenthic foraminifers Cibicidoides wuellerstorfi and Planulina ariminensis. During peak glacial times, the data exhibit higher δ13C values of up to 1.6‰ at intermediate depths near the Strait of Gibraltar (36°N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38°N (in Duplessy et al. [1987]). Thus, the distribution pattern of δ13C provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the δ18O fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5°C. During glacial times and during Termination I the maximum δ13C values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and vice versa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.

Description: Of about 20,000 modern fish species, only about 200 are found south of the Antarctic Convergence. The ichthyofauna is dominated by small species up to 40 cm long. The majority are bottom dwelling forms which belong mostly to the suborder Notothenioidei. Antarctic pelagic fishes are descendants from several faunal groups of different origins: bathypelagic and mesopelagic species, and species originating from demersal families which are secondarily adapted to temporary or permanent midwater life. More than 30 species of squid are so far known from the Southern Ocean. The majority are obviously meso-and bathy-pelagic dwellers. Several adaptations, including stenothermy, freezing resistance, aglomerular kidneys, and neutral buoyancy, enable Antarctic coastal fish to live successfully in the harsh environment. Growth rates of coastal fish are comparable to those found in Newfoundland cod. Most coastal fish do not spawn until they are 5 year old. Three reproductive strategies occur in coastal fish: autumn/early winter spawners with few, but yolky, eggs of 3–6 mm diameter; late winter/spring spawners with many, but smaller, eggs of 1.5–2 mm diameter; and species which guard their nests. Based on their food spectra, fish species can roughly be divided into three groups: fish and krill feeders, plankton feeders, and benthos feeders. Krill consumption by coastal fish around South Georgia and in West Antarctic waters was probably in the order of 5–6 × 106 tonnes before the onset of exploitation. Overall euphausiid consumption may have been about 20 × 106 tonnes. Fish, particularly mesopelagic fish, appear to be more important krill predators than squid. The role of squid as krill predators may have been overestimated in the past. Squid seem to be more important as a food resource for top level predators, particularly sperm whales and birds, than fish appear to be. All estimates of food consumption—krill as well as fish—are still subject to many uncertainties, and so it can be expected that increasing knowledge in the future may alter the given figures quite substantially. Exploitation of Antarctic finfish started at the end of the 1960s. The main fishing grounds are South Georgia and Kerguelen Islands. So far about 2.3 × 106 tonnes have been harvested from the Southern Ocean and the stocks particularly around South Georgia are heavily depleted. Conservation measures adopted by the Commission for the Conservation of Antarctic Marine Living Resources in 1984 and 1985 are probably not sufficient to support the recovery of the stocks.

Description: The upper part of the Deccan Traps sequence (Bushe to Mahabaleshwar Formations) shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials. This is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation (AFC). The observed correlations (e.g. between Mg-number and Sr isotope initial ratios) are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence, while contaminant availability declines in the upper part. It is probable, however, that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes, a process during which fractional crystallisation is suppressed by magmatic turbulence. The absence of AFC relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber. Other continental flood basalt provinces such as the Parana and Etendeka do show AFC relationships, and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent.