ALBERT

Description: A study of the echo peak amplitudes from known nodule areas is initiated to observe the acoustic response for varying nodule abundances and number densities. A statistical study of the peak amplitudes from different nodule areas confirms that the coefficient of variation is the highest for medium nodule abundance and number density. Echo fluctuation study based on the Rician probability density function (PDF) establishes that the non‐nodule sediment bottom contributes to less scattering, i.e., it is a microtopographic type, whereas scattering is dominant in the nodule‐bearing areas. The spectral studies are conducted on depth data of different areas. This study ensures that the signal scattering in the nodule bottom area is due to the nodules lying on the seabed rather than the large / small‐scale topographic variations. The study based on Poisson PDF for nodule area confirms this fact again. Agreement between the nodule distribution and the Poisson distribution parameter is clearly seen. Such a relation is not observed in the case of Rician density functions.

Description: Plastic debris accumulates in the marine environment following its use in agricultural, industrial and social activities. Its ultimate fate is accomodation in sediments where it may persist for times up to centuries or longer. There appears to be an increasing flux of materials with time and an increased areal coverage of the benthos. Impacts upon bottom organisms can take many forms. Systematic monitoring tactics for the extent of seafloor coverage by plastics are yet to be incorporated into national programs.

Description: The ability to monitor the heat content of oceans over long distances is becoming increasingly important for understanding the role of oceans in climate change, for determining the variability of the state of the oceans, for operational ocean observing systems, and for studying large-scale ocean processes such as water-mass formation. Although the properties of the upper layers of the ocean can be routinely measured on large scales by satellite remote sensing (providing altimetric and infrared data) and with expendable probes dropped from commercial vessels, the deep interior of the ocean is more difficult to monitor. Ocean acoustic tomography1 is a promising technique for such applications, as it has the potential to provide systematic, instantaneous and repeated measurements of the ocean interior over large parts of an ocean basin. Here we demonstrate the capability of this technique for measuring the heat content across an entire (albeit small) ocean basin—the western Mediterranean Sea.

Description: Newly hatched Baltic cod Gadus morhua larvae are typically found at depths 〉60 m. This is a region of low light and prey availability, hence generating the hypothesis that larvae have to migrate from hatching depth to the surface layer to avoid starvation and improve their nutritional condition. To test this hypothesis, Baltic cod larvae were sampled during the spawning seasons of 1994 and 1995 with depth-resolving multiple opening/closing nets. Each larva was aged by otolith readings and its RNA/DNA ratio was determined as a measure of nutritional condition. The RNA/DNA ratios of these larvae aged 2-25 days (median 10 days) ranged from 0.4 to 6.2, corresponding to levels exhibited by starving and fast-growing larvae in laboratory calibration studies (starvation, protein growth rate, Gpi= -12.2% day−1; fastgrowing larvae, Gpi=14.1%day−1) respectively. Seventy per cent of the field caught larvae had RNA/DNA ratios between the mean values found for starving and fed laboratory larvae. Only larvae aged 8-11 days had higher mean RNA/DNA ratios above 45 m than below (t-test, P〈0.05). However, the instantaneous protein growth rates were significantly higher for all larval age groups in the surface layers (t-test, P〈0.05). Starving larvae were found in all depths sampled (10-85 m), whereas growing larvae (positive Gpi) were restricted to samples taken shallower than 45 m. These superior growth rates above 45 m corroborate the hypothesis and imply that migration to the shallow water layers is a prerequisite for good nutritional condition, growth and survival of Baltic cod larvae. The frequent occurrence of cod larvae older than 8 days in the deep water in poor condition suggests that a proportion of the larvae will die from Starvation in the deep layers of the Baltic Sea.

Description: The ocean stores and transports vast quantities of heat, fresh water, carbon and other materials, and its circulation plays an important role in determining both the Earth's climate and fundamental processes in the biosphere. Understanding the development of climate and important biological cycles therefore requires detailed knowledge of ocean circulation and its transport properties. This cannot be achieved solely through modelling, but must involve accurate observations of the spatio-temporal evolution of the global oceanic flow field. Estimates of oceanic flow are currently made on the basis of space-borne measurements of the sea surface, and monitoring of the ocean interior. Satellite altimetry and acoustic tomography are complementary for this purpose1, as the former provides detailed horizontal coverage of the surface, and the latter the requisite vertical sampling of the interior. High-quality acoustic-tomographic2 and altimetric3 data are now available to test the combined power of these technologies for estimating oceanic flows. Here we demonstrate that, with the aid of state-of-the-art numerical models, it is possible to recover from these data a detailed spatio-temporal record of flow over basin-scale volumes of fluid. Our present results are restricted to the Mediterranean Sea, but the method described here provides a powerful tool for studying oceanic circulation worldwide.

Description: A description of egg masses from Gonatus frabricii (Lichtenstein) caught with pelagic trawl in the Norwegian Sea is given. The eggs were kept together in a single layer between two mucous membranes, and the pieces collected appeared to be fragments of more extensive structures torn apart by wear from the sampling gear. No embryos were observed in the eggs, and none of the eggs showed any staining for five enzyme systems analyzed by isoelectric focusing. Either the eggs were caught shortly after spawning and fertilization, or the lack of embryonic tissue reflects the fact that most of the eggs were caught in water colder than 0°C. The development rate at this temperature is expected to be very slow.

Description: The South Tasman Rise is a large submarine plateau of continental origin, located south of Tasmania. In the light of satellite‐derived gravity data and shipboard swath‐bathymetry and magnetic data collected in 1994 in the South Tasman Rise region, this paper re‐examines the sea‐floor spreading history of the surrounding ocean basins (northeastern Australian‐Antarctic Basin and southwestern Tasman Sea). This information is synthesised in seven plate tectonic reconstructions of the South Tasman Rise region from the mid‐Cretaceous (95 Ma) to the Early Oligocene (34 Ma). Our interpretation and model confirm that the South Tasman Rise is composed of two distinct terranes. A western domain, limited to the west by a transform margin along the Tasman Fracture Zone and to the east by a N170°E oriented boundary at 146.5°E, was initially attached to Antarctica. The western terrane rifted away from Antarctica in the Late Paleocene/Early Eocene and underwent severe wrench deformation as the Antarctic plate moved southward relative to the Australian plate. Shear motion continued to shape the Tasman Fracture Zone transform margin until the Early Miocene (chron 6B, 23 Ma) after which the Southeast Indian Ridge axis cleared from the western edge of the South Tasman Rise. An eastern domain limited to the east by a boundary at 146.5°E, rifted off from Tasmania and the East Tasman Plateau. After an initial phase of stretching between Tasmania, the East Tasman Plateau and the Lord Howe Rise that lasted until the mid‐Cretaceous, sea‐floor spreading in the Tasman Sea started in the Late Cretaceous (chron 34y) north of the East Tasman Plateau. Seismic, magnetic and gravity profiles between the eastern South Tasman Rise and the East Tasman Plateau suggest that sea‐floor spreading began between the two microcontinental blocks in the Late Cretaceous (ca chron 33y) and failed shortly after (chron 30y).

Description: Recent captures of two female giant squid ( Architeuthis ) off southern Australia have provided the first record of a mated female specimen of these almost mythical deepsea creatures. We found sperm packages (spermatophores) embedded within the skin of both ventral arms of the larger of the two specimens. It seems that male giant squids may use their muscular elongate penis to ‘inject’ sperm packages under pressure directly into the arms of females.

Description: The female of the harpacticoid Cholidya polypi Farran, 1914, is redescribed and the male is described for the first time. This copepod parasite of octopuses, reported previously only from Benthoctopus (= Polypus) ergasticus off Ireland, is here documented from the North Atlantic east of Florida on Tetracheledone spinicirrus and off North Carolina and New Jersey on Bathypolypus anticus, and from the northeastern Pacific west of Oregon and Washington on Graneledone pacifica and off central California on Graneledone spp.