Preservation conditions and the use of sediment pigments as a tool for recent ecological reconstruction in four Northern European estuaries

Down-core sediment pigment concentrations from four Northern European estuaries were measured using high-performance liquid chromatography (HPLC) to investigate phytoplankton community structure and preservation conditions over the last ca. 100 years where all sites have experienced different levels of eutrophication. Phytoplankton pigments have been shown to be useful biomarkers for phytoplankton community structure and abundance due to their taxonomic specificity. The pigment concentrations and sediment pigment inventory showed large variation between the four sites. Concentrations ranged from more than 6000 nmol/g OC to less than 100 nmol/g OC and the inventory integrated over the top 10 cm from more than 300 nmol/cm² to less than 30 nmol/cm² for total identified pigments. Good pigment preservation in Mariager Fjord (Denmark) reflected the almost permanently anoxic conditions. Pigments in Laajalahti (Finland) showed peak concentrations around the time of highest nitrogen loading events known from historical and modelled records over the past 100 years. In contrast, poor down-core preservation of pigments (especially carotenoids) was observed in the Ems-Dollard (The Netherlands) and Himmerfjärden (Sweden) estuaries. The Ems-Dollard site is an intertidal mudflat that experiences daily exposure to light and air, which enhances pigment degradation. In Himmerfjärden, resuspension is an important process affecting both the sedimentation rate and degradation properties. The different preservation conditions at the four sites were supported by the differences in two degradation indicators; the ratio of pheopigment-a to chlorophyll-a and total carotenoids to total pigments. Class-specific carotenoid pigments represented the dominant algal groups reported from each site, however, no distinct down-core changes in the pigment composition were observed at any of the four sites. This indicated that changes in plankton community structure on the group level have been limited over this time period or masked by low preservation of pigments.     

Storminess and vulnerability along the Atlantic coastlines of Europe: analysis of storm records and of a greenhouse gases induced climate scenario

Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.

An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO₂ concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO₂ concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.

The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion.     

An Ecosystem Model Coupled with Nitrogen-Silicon-Carbon Cycles Applied to Station A7 in the Northwestern Pacific

A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms; 2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO₂)—a peak in pCO₂ in winter resulting from deep winter convection, a rapid decrease in pCO₂ as a result of the spring bloom, and an almost constant pCO₂ from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that they are caused by silicate limitation of diatom growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

Jason-1: Assessment of the System Performances

On 7 December 2001, Jason-1 was successfully launched by a Boeing Delta II rocket from the Vandenberg Air Force Base, California. The Jason-1 satellite will maintain the high accuracy altimeter service provided since 1992 by TOPEX/Poseidon (T/P), ensuring the continuity in observing and monitoring the Ocean Dynamics (intraseasonal to interannual changes, mean sea level, tides, etc.). Despite one-fourth the mass and power, the Jason-1 system has been designed to have basically the same performance as T/P, measuring sea surface topography at a centimetric level. This new CNES/NASA mission also provides near real-time data for sea state and ocean forecast. The first two months of the Jason-1 mission have been dedicated to the assessment of the overall system. The goals of this assessment phase were:

1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES);

2. To verify that platform performance requirements are met with respect to Jason-1 requirements;

3. To verify that payload instruments performance requirements evaluated at instrument level are met;

4. To assess the performance of the Jason-1 Ground System.

This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products.     

Diet shifts of Caribbean grunts (Haemulidae) and snappers (Lutjanidae) and the relation with nursery-to-coral reef migrations

The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species (Haemulon sciurus and Haemulon flavolineatum) and of two snapper species (Lutjanus apodus and Ocyurus chrysurus) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus, L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodusand O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus, a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.     

Catch-quota balancing in multispecies individual fishing quotas

Individual fishery quotas (IFQs) are an increasingly prevalent form of fishery management around the world, with more than 170 species currently managed with IFQs. Yet, because of the difficulties in matching quota holdings with catches, many argue that IFQs are not appropriate for multispecies fisheries. Using on-the-ground-experience with multispecies IFQ fisheries in Iceland, New Zealand, Australia, and Canada, we assess the design and use of catch-quota balancing mechanisms. Our methodology includes a mix of interviews with fishery managers, industry representatives, and brokers, literature review, and data analysis. We find that a combination of incentives and limits on use rates for the mechanisms provide sufficient flexibility to the quota owner without the fishery manager incurring excessive levels of overexploitation risk. Contrary to some opinions, these programs are evidence that it is possible to implement IFQ programs for multispecies fisheries and that they can be profitable and sustainable.     

Effect of Pollutants on the Physical and Engineering Behavior of Lime-Treated Marine Clay

Rapid industrial growth and increasing population has resulted in the discharge of wastes into the ocean, wastes which ultimately reach the seabed and contaminate the marine sediments. The soil-contaminants interaction, and their associated physico chemical properties with sediments control the behavior of marine clays. Marine clay deposits of low strength and high compressibility are located in many coastal and offshore areas. There are several foundation problems encountered in these weak marine clays. In this study, experimental work was carried out in the laboratory to stabilize soft marine clays using the lime column technique. Also the lime-induced effects on the physical and engineering behavior of marine clays in sulfate-contaminated marine environment was investigated. Consolidation tests indicate that compressibility of the lime-treated samples was reduced to 1/2-1/3 of the virgin soil after 45 days treatment. The test results also suggest that the lime column technique can be conveniently used to improve the behavior of contaminated marine clay deposits.