Carbon stable isotopes in estuarine sediments and their utility as migration markers for nursery studies in the Firth of Forth and Forth Estuary, Scotland

The stable carbon isotope ratios (δ¹³C) of the organic fraction of intertidal sediments in the Forth Estuary and the Firth of Forth, Scotland, were measured to determine if terrestrially derived carbon was present in the estuarine sediments. It was hypothesised that differences in the inputs from marine vs. terrestrial sources to the organic carbon of estuarine and marine sediments, as well as differences in ambient seawater stable oxygen isotope (δ¹⁸O) ratios between the estuary and the Outer Firth, would allow the use of these two stable isotopes as habitat markers for juvenile plaice (Pleuronectes platessa), to allow determination of nursery habitats. Muddy and sandy sediments from the estuary and sandy sediments from the Outer Firth were sampled and δ¹³C measured. Juvenile plaice were caught at two estuarine sites and at two Outer Firth sites and otoliths were removed for δ¹³C and δ¹⁸O analysis. The sandy sediments in the estuary showed a strong gradient of δ¹³C enrichment with distance down the estuary, while the muddy sediments showed a much shallower gradient. δ¹³C and δ¹⁸O measured in the carbonate of juvenile plaice otoliths showed no clear difference between otoliths of fish caught at one of the estuarine sites and at the two Outer Firth sites. However, the isotope ratios of both carbon and oxygen in plaice otoliths from the other estuarine site showed the expected trend of depletion in the heavier isotopes. While the measurements recorded here did not conclusively distinguish between otoliths from juveniles caught in the estuarine site and those caught in the other three sites, they show that stable isotopes have potential to distinguish between estuarine habitats with terrestrial carbon inputs, and coastal marine habitats with predominantly marine carbon inputs.     

Detailed measurements during a transient front in a small subtropical estuary

High-resolution measurements of velocity and physio-chemistry were conducted before, during and after the passage of a transient front in a small subtropical system about 2.1 km upstream of the river mouth. Detailed acoustic Doppler velocimetry measurements, conducted continuously at 25 Hz, showed the existence of transverse turbulent shear between 300 s prior to the front passage and 1300 s after. This was associated with an increased level of suspended sediment concentration fluctuations, some transverse shear next to the bed and some surface temperature anomaly.     

Direct determination of organic carbon in modern reef sediments and calcareous organisms after dissolution of carbonate

An improved method for the direct determination of organic carbon in calcareous marine sediments, organisms and particulate matter is described. Samples are dissolved in phosphoric acid to remove carbonates, purged with oxygen to remove CO₂, and the resulting acidic solution is analysed for total (dissolved and particulate) organic carbon. The method is rapid, involves minimal sample manipulation, and is both accurate (better than ± 2%) and precise (better than ± 0.2 mg organic carbon/g sediment). The method is especially suitable for modern carbonate sediments which have low levels of predominantly acid-soluble organic carbon.     

The Rossby wave as a key mechanism of Indian Ocean climate variability

We analyze the time-longitude structure of composite cases from model-assimilated ocean data in the period 1958–1998, following on from earlier work by Huang and Kinter (J. Geophys. Res. 107(C11) (2002) 3199) that studied east–west thermocline variability in the Indian Ocean. Our analysis focuses on the Rossby wave signal along the thermocline ridge in the tropical SW Indian Ocean (10°S, 60–80°E), where wind stress curl is important. Anomalous winds in the equatorial east Indian Ocean force successive Rossby waves westward at speeds of 0.1 m s⁻¹±30%. With a wavelength of 7000 km, the period of oscillation is in the range 1.9–5.2 years. The Indian Ocean Rossby wave is partially resonant with the global influence of the El Nino–Southern Oscillation, except during quasi-biennial rhythm. The presence of the Rossby wave offers potential predictability for east–west atmospheric circulation systems and climate that affect resources in countries surrounding the Indian Ocean.     

Microzooplankton herbivory in the Ross Sea, Antarctica

Microplankton abundances and phytoplankton mortality rates were determined at six stations during four cruises spanning three seasons in the Ross Sea polynya, Antarctica (early spring, Oct.–Nov. 1996; mid-late summer, Jan.–Feb. 1997; fall, Apr. 1997; mid-late spring, Nov.–Dec. 1997). Rates of microzooplankton herbivory were measured using a modified dilution technique, as well as by examining the rate of disappearance of phytoplankton (chlorophyll) in samples incubated in the dark (i.e. grazing in the absence of phytoplankton growth). Strong seasonal cycles of phytoplankton and microzooplankton abundance were observed during the study. Microzooplankton abundance varied by more than three orders of magnitude during the four cruises, and was positively correlated with phytoplankton biomass over the entire data set. Nevertheless, microzooplankton grazing was insufficient to impact significantly phytoplankton standing stocks during most of the experiments performed in this perenially cold environment. Only thirteen out of a total of 51 experiments yielded phytoplankton mortality rates that were significantly different from zero. The highest mortality rate observed in this study (0.26 d⁻¹) was modest compared with maximal rates that have been observed in temperate and tropical ecosystems. Results from twenty experiments examining the rate of decrease of phytoplankton biomass during incubations in the dark agreed quite well with the results of the dilution experiments performed at the same time. The range of mortality rates for the dark incubations was −0.09–0.06 d⁻¹, and the average was essentially zero (−0.01 d⁻¹). That is, chlorophyll concentration was virtually unchanged in samples incubated in the dark for 3 d. A number of factors appeared to contribute to the very low rates of microbial herbivory observed, including low water temperature, and the size and taxonomic composition of the phytoplankton assemblage. Based on our results we conclude that the seasonal, massive phytoplankton blooms observed in the Ross Sea are due, in part, to low rates of removal by microbial herbivores.     

Reconstruction of contaminant trends in a salt wedge estuary with sediment cores dated using a multiple proxy approach

The Taunton River is a partially mixed tidal estuary in southeastern Massachusetts (USA) which has received significant contaminant inputs, yet little information exists on the history of discharge and the subsequent fate of these contaminants. Three sediment cores taken along a transect were analyzed, reconstructing the spatial and temporal trends of pollution in the estuary. A combination of radiometric dating, contaminant markers, and storm layers from major hurricanes were used to establish age models and sedimentation rates. Age estimates obtained from the different dating methods compared well, establishing an accurate history of contaminant release to the estuary. Polycyclic aromatic hydrocarbons (PAHs) were present in one core at depths corresponding to the early 1860s, earlier than previously established dates of introduction. Temporal and spatial trends of Cr, Cu, Hg and Pb indicated multiple sources of varying input to the river. Polychlorinated biphenyls (PCBs) were present in each of the cores from the 1930s onward, with elevated levels still present in surficial sediments at several sites. A unique organic compound, Topanol, which was produced locally was used as a tracer to track contaminant transport in the river. Tracer data indicates that contaminants are still being transported and deposited to surficial sediments at high concentrations well after their discharge. This reconstruction demonstrates the utility of using multiple dating proxies where often the sole use of radiometric dating techniques is not an option and provides insights into the fate of contaminants discharged decades ago but continue to represent environmental risks.     

Guidelines for navigation and overflight in the exclusive economic zone

Several significant international incidents in Asian exclusive economic zones (EEZs) have underscored the ambiguity and lack of agreement regarding the regime governing foreign military activities in coastal States’ EEZs. A group of senior officials and analysts participated in their personal capacities in a dialogue from 2002–2005 that discussed the issues with a view to improving mutual understanding of the regime and finding areas of agreement. The Tokyo meeting in September 2005 reached consensus on some voluntary, non-binding guidelines that are presented here. The guidelines are based selectively on the 1982 UNCLOS, State practice and emerging ‘soft’ law, and attempt to balance the interests of coastal States and user States. It is hoped that they may serve as the basis for discussion and eventual agreements between governments.     

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.     

Marine renewable energy: The ecological implications of altering the hydrodynamics of the marine environment

Many countries now recognise the need for mitigation of climate change induced by human activities and have incorporated renewable energy resources within their energy policy. There are extensive resources of renewable energy within the marine environment and increasing interest in extracting energy from locations with either large tidal range, rapid flow with and without wave interaction, or large wave resources. However, the ecological implications of altering the hydrodynamics of the marine environment are poorly understood. Ecological data for areas targeted for marine renewable developments are often limited, not least because of the considerable challenges to sampling in high energy environments. In order to predict the scale and nature of ecological implications there is a need for greater understanding of the distribution and extent of the renewable energy resource and in turn, of how marine renewable energy installations (MREIs) may alter energy in the environment. Regional ecological implications of a MREI need to be considered against the greater and global ecological threat of climate change. Finally, it is recommended that the identification of species and biotopes susceptible to the removal of hydrokinetic energy could be a suitable strategy for understanding how a MREI may alter flow conditions.