The influence of island generated eddies on the carbon dioxide system, south of the Canary Islands

Measurements of surface partial pressure of CO₂ and water column alkalinity, pH_T, nutrients, oxygen, fluorescence and hydrography were carried out, south of the Canary Islands during September 1998. Cyclonic and anticyclonic eddies were alternatively observed from the northwestern area to the central area of the Canary Islands. Nutrient pumping and vertical uplifting of the deep chlorophyll maximum by cyclonic eddies were also ascertained by upward displacement of dissolved inorganic carbon. A model was applied to determine the net inorganic carbon balance in the cyclonic eddy. The fluxes were determined considering both the diffusive and convective contributions from the upward pumping and the corresponding horizontal transport of water outside the area. An increase in the total inorganic carbon concentration in the upper layers inside the eddy field of 133 mmol C m^− 2 d^− 1 was determined. The upward flux of inorganic carbon decreased the effect of the increased primary production on the carbon dioxide chemistry. The reduced fCO₂ inside the cyclonic eddy, 15 μatm lower than that observed in non-affected surface water, was explained by thermodynamic aspects, biological activity, eddy upward pumping and diffusion and air–sea water exchange effects.     

Equilibrium constants of triethanolamine in major seawater salts

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl₂ or CaCl₂), with binary mixtures of MgCl₂ and CaCl₂, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl₂, while it is increased by the other electrolytes used in this work.     

Co-variance of dissolved Fe-binding ligands with phytoplankton characteristics in the Canary Basin

Dissolved Fe and ligand concentrations and the Fe-binding strength of the organic ligands were measured in samples from the upper water column (150 m) of the oligotrophic waters of the Canary Basin (eastern North Atlantic Ocean). Concentrations of major nutrients, phytoplankton abundance and photosynthetic characteristics were also measured in the same samples.The concentrations of dissolved Fe and dissolved organic ligands were low with mean values of 0.31 ± 0.18 nM Fe and 1.79 ± 0.73 nEq of M Fe(n = 47), respectively. The conditional binding constant varied between 10^19.8–10^22.7 (n = 47). The largest variation with depth in the ligand concentrations (between 4.78 and 1.1 nEq of M Fe) was observed in the upper layer, above the Deep Chlorophyll Maximum (DCM located between 80 and 100 m), with high surface values in stations at 18 and 34.At the DCM where Fe was depleted, the ligand concentrations were still relatively high showing the same trend with depth as the amount of phytoplankton cells. Here 62% of the vertical variation in ligand concentrations can be explained by parameters describing phytoplankton cell abundance or biomass and orthosilicic acid concentration, which could reflect diatom growth. Ligand concentrations below the maximum of the DCM (n = 4) showed good linear positive relationships with the total phytoplankton biomass as well as with 2 out of 4 distinguished groups of phytoplankton (Synechococcus and pico-eukaryote I).In the maximum of the DCM and below this maximum the phytoplankton origin of the dissolved organic ligands of Fe is very probable. Data suggest a release of ligands by cell lysis and not by an active production. However, the origin in the surface layer is more difficult to explain. Although the amount of phytoplankton cells in the surface layer is reduced, it is still  25% of the cell concentration observed in the DCM. High concentrations of organic ligands could then be a remnant of past blooms or present production under nutrient depleted conditions. Input of Sahara dust can be another source of ligands.     

Characterisation and preliminary quantification of the methane reservoir in a coastal sedimentary source: San Simón Bay,Ría de Vigo,NW Spain

Ría de Vigo is a river valley flooded by the sea, with a bay (San Simón Bay) at its innermost part. The accumulation of Holocene sediment in San Simón Bay has been studied by the integration of 1) large scale high resolution seismic data, and 2) detailed geochemical analysis of a gravity core. In San Simón Bay the majority of the seismic records are obscured by acoustic turbidity which represents gassy sediments, but on records from Rande Strait it is possible to distinguish two Quaternary seismic sequences; an Upper Pleistocene sequence (SQ1) and a Holocene sequence (SQ2). Only SQ2 is recognized in San Simón Bay where it is comprised of two seismic units; the upper unit represents the HST sediment, i.e. the period of highest sea level. A gravity core taken within the gassy zone at 10 m water depth provided 3.55 m of fine-grained sediments (muds) from the youngest seismic unit (4 m thick). Geochemical analysis show high values (4 to 10%) of TOC. Sediment and porewater analyses indicate a distinct sulphate–methane transition zone (SMTZ) between 60 and 80 cm where sulphate is depleted (to <1.7 mM) and methane increases (to >0.4 mM). The top of the acoustic turbidity (the gas front) at 80 cm corresponds to the lower limit of the SMTZ. The methane cannot have been derived from the underlying metamorphic and granitic rocks, but was probably derived by microbial degradation of the organic matter in the Holocene sediments. We estimate that the sediments of the Bay contain approximately 1.8 × 10⁶ m³ of organic carbon and 275 ton of methane.     

Trust relationships between fishers and government: New challenges for the co-management arrangements in the Dutch flatfish industry

Until the 1990s fisheries were largely managed by the state. Since then, Dutch government and the sector increasingly recognized that a fishing industry cannot be managed effectively without the cooperation and participation of fishers to formulate policy and to implement and enforce laws and regulations. As a result, in the nineties, the existing neo-corporatist arrangement was replaced by a co-management system in the Dutch flatfish fishery. Co-management is often seen as leading to greater procedural legitimacy and subsequently compliance. However, constructing an effective co-management arrangement is not only a matter of building institutions but also a matter of building trust relations between the government and industry. Institutional arrangements such as co-management can contribute to these trust building processes; however, a too strong reliance on institutional arrangements can lead to distrust when new challenges are being faced and institutional arrangements fail to adapt to these changes.     

Impact of mega-scale sand extraction on tidal dynamics in semi-enclosed basins: An idealized model study with application to the Southern North Sea

Long-term considerations of repeated and increasing sand extraction on the Netherlands Continental Shelf (North Sea) may lead to the creation of a mega-scale extraction trench in front of the Dutch coast (length hundreds of km, width over 10 km, depth several m). We investigate the impact of such a huge topographic intervention on tidal dynamics, which is a key aspect in hydrodynamics, and indirectly also affecting morphodynamics and ecology.     

Deep-sea Fe-Mn Crusts from the Northeast Atlantic Ocean: Composition and Resource Considerations

Eighteen deep-sea ferromanganese crusts (Fe-Mn crusts) from 10 seamounts in the northeast Atlantic were studied. Samples were recovered from water depths of ～1,200 to ～4,600 m from seamounts near Madeira, the Canary and Azores islands, and one sample from the western Mediterranean Sea.

The mineralogical and chemical compositions of the samples indicate that the crusts are typical continental margin, hydrogenetic Fe-Mn crusts. The Fe-Mn crusts exhibit a Co + Cu + Ni maximum of 0.96 wt%. Platinum-group element contents analyzed for five samples showed Pt contents from 153 to 512 ppb.

The resource potential of Fe-Mn crusts within and adjacent to the Portuguese Exclusive Economic Zone (EEZ) is evaluated to be comparable to that of crusts in the central Pacific, indicating that these Atlantic deposits may be an important future resource.     

Distribution and ecology of Nectocarcinus antarcticus and N. bennetti (Brachyura: Portunidae) in the New Zealand region

The distributions of two swimming crabs endemic to the New Zealand region are described, mostly from material obtained at 118 of 2544 New Zealand Oceanographic Institute benthic stations sampled.

Nectocarcinus antarcticus (Jacquinot) was found within the geographic limits 34°S‐51°S and 166° E‐176° W, with concentrations around Cook Strait, the Chatham Rise, Foveaux Strait, and the Auckland Is. N. bennetti (Takeda & Miyake) occurred between 44° S and 53° S, and 165° E and 180°, most frequently in the south and west, on the ‘highs’ of the Campbell Plateau. Although the distributions overlap between 44° S and 51° S, and this overlap zone produced most of the available material, only one joint occurrence of the two species was noted. This apparent separation was not satisfactorily explained by any of the ecological factors recorded. The depth ranges of both species were broadly similar (0–550 m for TV. antarcticus, 20–474 m for JV. bennetti); both were most frequently obtained at depths less than 200 m. Both occurred primarily on the coarser sediment grades, though N. antarcticus occupied a broader range of grades than N. bennetti.

The size ranges of the two species were similar; carapace lengths were 8.0–62.0 mm for N. antarcticus and 5.8–68.0 mm for N. bennetti. The larger specimens of both species were found towards the southern limits of distribution. Larger specimens of N. antarcticus were absent from depths greater than 120 m; smaller N. antarcticus and all N. bennetti occurred throughout their respective depth ranges. Ovigerous N. antarcticus (smallest, 8.8 mm carapace length) were obtained at depths of 17–263 m from May to October; ovigerous N. bennetti (smallest 36.1 mm) were from depths of 150–183 m in May only.     

Relationship between turbidity and fish diets in Lakes Waahi and Whangape,New Zealand

Abstract

Stomach contents of Gobiomorphus cotidianus,Retropinna retropinna, Gambusia affinis, and Anguilla australis were compared between two shallow lakes in the lower Waikato River basin, to examine the relationship between turbidity and diet. Lake Waahi and the south arm of Lake Whangape had been turbid (20–40 g suspended solids (SS) m^?3) and devoid of submerged macrophytes since the late 1970s and early 1980s, respectively. The main basin of Lake Whangape had been generally clearer (5 g SS m^?3) with dense beds of submerged macrophytes, but at the time of sampling (1987) water clarity had deteriorated (> c. 10 g SS m³) and submerged macrophytes had declined. The mysid Tenagomysis chiltoni was an important prey for all species of fish from turbid water bodies but was less important in stomachs of fish in the main basin of Lake Whangape. Apparently, mysids were not an important prey in Lake Waahi before it became turbid. Chironomid larvae and pupae dominated the diets of small fish in the main basin of Lake Whangape. Fish and mysids were the most important prey of shortfinned eels in both lakes, with mysids most important in Lake Waahi. High mysid densities in the turbid water bodies provide an alternative food resource apparently compensating for those lost by fish when water clarity declined and submerged macrophytes collapsed.