A review of studies of ocean platform motions

In this paper various aspects of studies on the motions of ocean platforms are reviewed, with emphasis on floating and semi-submerged structures.Model experimental procedures and theoretical methods, commonly used for prediction purpose, are discussed and motion correlations are made with full scale observations. Special attention is given to the motions of platforms in the horizontal plane, where low frequency phenomena are of importance because of their being responsible for the major part of the loads in a mooring system.     

Flexural interaction and the dynamics of neogene extensional Basin formation in the Alboran-Betic region

Quantitative tectonic modelling demonstrates an interaction of flexure of the lithosphere underlying the western Betics with crustal thinning in the Alboran Basin and flank uplift in the Internal Zone. In the eastern Betics the flexural response is overprinted by post-thrusting extensional events. Lateral variations in thermal structure and rheology of the lithosphere along strike of the Betics shed light on changes in tectonic configuration and are consistent with evidence for lateral variations in the mode of extension in the Alboran Basin. Flexural modelling and subsidence analysis of Neogene basins in the Internal Zone of the Betics, with spatial development controlled by contrasts in lithosphere rheology, demonstrate that at least two extensional events have affected the orogenic evolution of the Betics. The first event appears to reflect Oligocene-Early Miocene rifting observed throughout the Western Mediterranean. The second phase, which caused the present configuration of the Betics, corresponds to Tortonian-Recent extension centered in the Alboran Basin.     

Bioaccumulation and biomarkers in the sea star Asterias rubens (Echinodermata: Asteroidea): a North Sea field study

During two North Sea field trips in March 1995 and September 1996 sea stars, Asterias rubens, were collected at various stations along pollution gradients in order to study the relation between biochemical markers and levels of accumulated contaminants. Biomarkers measured were: cytochrome P450 level, benzo[a]pyrene hydroxylase (BPH) activity, acetylcholinesterase (AChE) activity and DNA integrity. Accumulation levels of heavy metals, polychlorinated biphenyls, organochlorine pesticides and polycyclic aromatic hydrocarbons (PAHs) in the pyloric caeca of sea stars indicate different pollution gradients, influenced by rivers in The Netherlands, UK and Germany. For some contaminants, especially PAHs, relatively high levels were found in the central part of the North Sea (Dogger Bank). On the basis of multivariate statistics, stations near the mouth of the Elbe and the Rhine/Meuse were shown to have different patterns of biomarker responses. Sea stars from stations in coastal zones showed relatively high levels of cytochrome P450 and 'P418', another haemoprotein that is present in most marine invertebrates. The station nearest to the Elbe Estuary showed the lowest BPH and AChE activity. DNA integrity was lower especially in stations near the Dutch coast and in a station near the Tees/Tyne estuaries. Using these biomarkers as early warning signals of exposure and/or adverse effects, this type of monitoring can be used also in the future to study the spatial and temporal trends in the quality of coastal waters.     

Possible diagenetic mobilization of barium in sapropelic sediment from the eastern Mediterranean

In the last few years it has frequently been suggested that Ba is a useful indicator of paleoproductivity. The formation of some sapropels in the Eastern Mediterranean is considered to be related to, or to coincide with, periods of enhanced productivity. A high-resolution sampling study has been undertaken in order to investigate whether the Ba distribution in sapropels reflects a primary input signal or whether it has been altered by diagenetic processes.

On the basis of our results we suggest that three diagenetic stages determine the distribution of Ba. During deposition of the sapropel (stage 1) Ba is mobilized as anoxic conditions prograde. After deposition of the sapropel (stage 2), a progressive oxidation front develops. This front induces the formation of Mn and Fe enrichments and barite precipitation at the oxic/anoxic boundary. Barite precipitation is believed to be caused mainly by a rise in the porewater sulphate concentration after sulphides have been oxidized by the front.

Upon burial (stage 3), suboxic conditions develop as the oxygen becomes exhausted again. In contrast to Fe- and Mn-oxyhydroxides which dissolve and reprecipitate at higher levels, barite is preserved because dissolved sulphate is not depleted.

The interpretation of the Ba distribution in organic-rich sediment is not straightforward. Diagenetic reallocation of a primary Ba signal will possibly disturb the relationship between Ba and organic production. Consequently, one must be very cautious when invoking Ba as a paleoproductivity indicator.     

The expression of CYP1A, vitellogenin and zona radiata proteins in Atlantic salmon (Salmo salar) after oral dosing with two commercial PBDE flame retardant mixtures: absence of short-term responses

The short-term effects of the commercial PBDE flame retardant mixtures Penta-BDE and Octa-BDE on the expression of cytochrome P450 1A (CYP1A), vitellogenin (Vtg) and zona radiata proteins (Zrp) were investigated in juvenile salmon (Salmo salar). For this purpose, groups of fish were dosed twice (oral intake at days 1 and 4) with 10 and 50 mg/kg body weight of both commercial mixtures. The fishes were sacrificed at day 7 (n=5 for each group) and 14 (n=6 for each group), and blood, liver, fillet, and brain were collected. Blanks and positive controls were also part of the experiment. The expressions of Vtg, Zrp, and CYP1A were measured with several techniques (EROD, ELISA, Western, Northern and Slot Blot). The values in the groups of fish treated with Penta-BDE or Octa-BDE did not significantly differ from the reference group for any of the parameters tested. In contrast, the positive control groups treated with estradiol-17β for Vtg and Zrp expression, and β-naphthoflavone for CYP1A expression did show a significant response, indicating the potential sensitivity of the fishes for the parameters measured. Since the results of the chemical analyses showed concentrations of a number of PBDE congeners in liver, fillet, and brain that were about three orders of magnitude above those of fish from the North Sea, it is concluded that the short-term toxicity of both commercial PBDE mixtures for these endpoints was low.     

The 1999 Flatfish Symposium: where to go from now?

A summary report of the 1999 Flatfish Symposium is presented. The Symposium was built on the themes of the previous Symposia, whereby the link is through processes related to recruitment. As in the previous Symposia, the papers presented have a strong focus on temperate species and basic information on (sub)tropical species is still lacking. The lack of insight into (sub)stock structure is still a problem and more insight is necessary into the methodologies for determining and describing stock structure. Another important unresolved issue concerns the quantitative understanding of the physical processes that affect the cross-shelf transport and exchange of eggs and larvae. Finally, there is a need for bioenergetic approaches to habitat quality and quantity both at the individual and population level to assess the qualitative and quantitative use of habitats in space and time. Applying global information systems (GIS) might be promising in this respect. With respect to management issues two items are of utmost importance: the collapse and recovery of stocks and the problems relating to re-stocking.     

Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment

ABSTRACT

Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42?mg?m^?3 vs. 8.32?mg?m^?3) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62?m vs. 6.48?m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment.     

The effect of bedforms (crest and trough systems) on sediment erodibility on a back-barrier tidal flat of the East Frisian Wadden Sea, Germany

The erosion potential over bedforms in a tidal flat of the East Frisian Wadden Sea was studied by conducting erosion and physical and biological sediment property measurements on the crests and troughs of bedforms. Five stations along a cross-shore transect of 1.5 km length from immediately below the salt marsh to the mid tide-level of the tidal flat were visited during two field campaigns in June and September 2002. Measurements of sediment erodibility were made on both crests and troughs using an EROMES erosion device and quantified in terms of critical erosion shear stress and erosion rate. Surface sediment scrape samples (upper 1 mm layer) were taken from crests and troughs to determine various physical and biological properties of the sediment. The results show that crests are generally more stable (i.e. higher critical erosion shear stresses and lower erosion rates) than troughs. In general, crests contained more chlorophyll a, colloidal carbohydrate, and EPS (extracellular polymeric substance) than troughs. Median grain-size, water content and wet bulk density of the crests showed no statistically significant difference from those of the troughs with the exception at the most landward station immediately below the salt marsh margin, where crests had significantly lower water content and higher wet bulk density than troughs.Two different processes were identified for the difference in erodibility between crests and troughs: (1) At stations with emersion times less than 6 h, the higher benthic diatom biomass (measured as chlorophyll a concentration) on the crests increases the amount of EPS, which is likely to stabilize the sediment surface of these features; (2) in a saltmarsh transition area (most landward station), physical processes such as surface drying and compaction seem to enhance in a synergistic way the sediment stability on the crests.     

Inputs of iron,manganese and aluminium to surface waters of the Northeast Atlantic Ocean and the European continental shelf

Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in March 1998, surface concentrations were enhanced up to 4 nmol L^− 1 dFe, 3 nmol L^− 1 dMn and 40 nmol L^− 1 dAl and returned to 0.6 nmol L^− 1 dFe, 0.5 nmol L^− 1 dMn and 10 nmol L^− 1 dAl towards the end of the cruise three weeks later. A simple steady state model (MADCOW, [Measures, C.I., Brown, E.T., 1996. Estimating dust input to the Atlantic Ocean using surface water aluminium concentrations. In: Guerzoni. S. and Chester. R. (Eds.), The impact of desert dust across the Mediterranean, Kluwer Academic Publishers, The Netherlands, pp. 301–311.]) was used which relies on surface ocean dAl as a proxy for atmospheric deposition of mineral dust. We estimated dust input at 1.8 g m^− 2 yr^− 1 (range 1.0–2.9 g m^− 2 yr^− 1) and fluxes of dFe, dMn and dAl were inferred. Mixed layer steady state residence times for dissolved metals were estimated at 1.3 yr for dFe (range 0.3–2.9 yr) and 1.9 yr for dMn (range 1.0–3.8 yr). The dFe residence time may have been overestimated and it is shown that 0.2–0.4 yr is probably more realistic. Using vertical dFe versus Apparent Oxygen Utilization (AOU) relationships as well as a biogeochemical two end member mixing model, regenerative Fe:C ratios were estimated respectively to be 20 ± 6 and 22 ± 5 μmol Fe:mol C. Combining the atmospheric flux of dFe to the upper water column with the latter Fe:C ratio, a ‘new iron’ supported primary productivity of only 15% (range 7%–56%) was deduced. This would imply that 85% (range 44–93%) of primary productivity could be supported by regenerated dFe. The open ocean surface data suggest that the continental shelf is probably not a major source of dissolved metals to the surface of the adjacent open ocean. Continental shelf concentrations of dMn, dFe, and to a lesser extent dAl, were well correlated with salinity and express mixing of a fresher continental end member with Atlantic Ocean water flowing onto the shelf. This means probably that diffusive benthic fluxes did not play a major role at the time of the cruise.