Distribution and transport of organic matter along a filament-eddy system in the Canaries – NW Africa coastal transition zone region

The distribution and transport of chlorophyll a (Chla), particulate (POC) and dissolved (DOC) organic carbon, and the respiratory ETS activity of the microplankton community were studied along a filament-eddy system located in the transition zone between the NW Africa upwelling and Canary Islands waters. Two independent filaments (F1 and F2) stemming from the coastal jet, between Cape Juby and Cape Bojador, merged about 100 km offshore, turning southward and onshore forced by the circulation of a recurrent oceanic cyclonic eddy. In general, the coastal upwelling waters presented higher Chla, but lower POC, DOC and ETS activity than filament waters. However, differences in organic carbon distribution and respiratory activity were observed among stations from the two filaments. The bio-chemical fields were strongly influenced by a complex sub-mesoscale hydrography resulting from the interaction of cyclonic and anticyclonic island eddies with the filaments. The combined F1 + F2 filament system transported 97.1 kg s⁻¹ of excess (non-refractory) total organic carbon (e-TOC), a value comparable to other published estimates from upwelling filaments in the NE Atlantic. About 90% of e-TOC was exported as DOC, since eddy re-circulation precluded the offshore transport of POC. Assuming that the calculated transport of e-TOC is representative of the annual average, the yearly offshore transport (3.1 x 10⁹ kg C) would represent about 25% of the upwelling primary production of the region of study.     

Variations of antioxidant efficiency and presence of endosymbiotic diatoms in the Antarctic porifera Haliclona dancoi

The role of endosymbiotic diatoms as pro-oxidant stressors in porifera has been investigated in the Antarctic sponge Haliclona dancoi in which the presence of diatoms is influenced by marked seasonal variations during the austral summer. Both chlorophaeopigments and frustules were absent in sponge tissues sampled in early November at the beginning of the summer and increased from the mid of December with slightly shifted temporal trends. The efficiency of antioxidant defenses in the sponge showed a marked response to symbionts with clearly enhanced values corresponding to the peak of diatoms.     

The wadic project: A comprehensive field evaluation of directional wave instrumentation

The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results.     

The Feni Drift: The importance and meaning of slump deposits on the eastern slope of the Rockall Bank

Sedimentary facies of cores from the eastern side of the Rockall Bank and the Feni Drift (55°–58°N) have been studied. They confirm the existence of slumping which contributes only in small part to drift build-up.

These slumps occurred at different episodes during last Glacial and early Post-Glacial periods. They are sandwiched in between more important turbidites, and are found in places where the drift lies against the slope and so is acted upon by continental-rise sedimentary processes. The sea level rise periods with ice melting seems to favour gravity flow release.     

The effect of copper pollution on mitochondrial degeneration

The authors describe the effect of copper pollution on the mitochondria from various areas of the Torpedo marmorata central nervous system. A high percentage of swollen mitochondria has been observed in neurons from animals experimentally exposed to high level of copper (4 ppm). The correlation with age pigment granules is discussed.     

Nitrate assimilation by zooxanthellae maintained in laboratory culture

The ability of cultured zooxanthellae to use ammonium and nitrate was tested. The zooxanthellae were initially isolated from the anemone Aiptasia pulchella. The zooxanthellae were able to grow on media supplemented with either form of dissolved inorganic nitrogen (DIN) although ammonium was inhibitory above 300 μM. In accord with the intact symbiosis and freshly isolated algae, the cultured zooxanthellae took up ammonium. In contrast, the cultured algae demonstrated nitrate uptake and utilization. This was enhanced with DIN deprivation. Nitrate reductase was found in the algae and appeared to be inducible. Within the animal host, excretory ammonium may repress this induction.     

Advances in the fatigue assessment of wire ropes

This paper presents the findings from an in-depth analysis of the (axial) stiffness data recorded during tension–tension fatigue tests on wire ropes, particularly in relation to how changes in stiffness during testing relate to changes in rope strength. A linear relationship between stiffness and strength is shown to exist and a methodology presented for quantifying residual strength with applied cycles. New lower bound fatigue lines for six-strand rope and spiral strand are presented which are based on a 10% loss of strength. These new lines have the advantage of having been established using a common discard criterion for wire ropes.     

White-light promoted degradation of leucopterin and related pteridines dissolved in seawater, with evidence for involvement of complexation from major divalent cations of seawater

The photochemical instability of several related pteridines in seawater was investigated by aseptic incubation of solutions at 20–22°C under illumination from cool-white light of intensity 6 kerg cm⁻² sec⁻¹, and the chemical changes were spectrophotometrically monitored. All the pteridines showed markedly accelerated degradation from this illumination relative to their behaviour in total darkness.Pterin and lumazine were degraded very slowly with zero-order reaction kinetics, while the other pteridines photolysed rapidly (according to first-order kinetics) with decomposition rates increasing in the order dioxylumazine (2,4,6,7-tetrahydroxypteridine) < leucopterin < isoxanthopterin < xanthopterin < oxylumazine (2,4,6-trihydroxypteridine). Excepting leucopterin and dioxylumazine, the photolysis rates were attributable to the pH of seawater and not its salt content; this was also the case with oxylumazine which required the salt content of seawater for decomposition in darkness. Leucopterin and dioxylumazine (both 6,7-dihydroxylated pteridines) gave evidence of complexation with the major divalent cations (Ca²⁺, Mg²⁺) of seawater, by virtue of which their photolytic degradation rates were enhanced to magnitudes obtained in pH-10 buffer without seawater. It is proposed that such complexation produces structural forms of these pteridines analogous to their normal ionic forms at pH 10–12.The photolysis of the 6-hydroxylated pteridines (xanthopterin, oxylumazine) proceeded via intermediate formation of their corresponding 7-hydroxylated derivatives (leucopterin, dioxylumazine).