Variations in turbulent energy dissipation and water column stratification at the entrance of a tidally energetic strait

We observed tidal currents, turbulent energy dissipation and water column stratification at the entrance of a narrow strait (Neko Seto) in the Seto Inland Sea, Japan, using a free-falling turbulent microstructure profiler (TurboMAP) and acoustic Doppler current profiler (ADCP). The variation in turbulent energy dissipation at the entrance of the strait was not at quarter-diurnal frequency but at semi-diurnal frequency; turbulent energy dissipation was enhanced during the ebb tide, although it was moderate during the flood tide. This result is consistent with the results of Takasugi (1993), which showed the asymmetry of tidal energy loss during a semidiurnal tidal cycle using control volume analysis. It is suggested that significant turbulent energy dissipation is generated in the strait, which influences the properties of water outside the strait when tidal currents flow out from the strait.     

The WOCE-era 3-D Pacific Ocean circulation and heat budget

To address questions concerning the intensity and spatial structure of the three-dimensional circulation within the Pacific Ocean and the associated advective and diffusive property flux divergences, data from approximately 3000 high-quality hydrographic stations collected on 40 zonal and meridional cruises have been merged into a physically consistent model. The majority of the stations were occupied as part of the World Ocean Circulation Experiment (WOCE), which took place in the 1990s. These data are supplemented by a few pre-WOCE surveys of similar quality, and time-averaged direct-velocity and historical hydrographic measurements about the equator.An inverse box model formalism is employed to estimate the absolute along-isopycnal velocity field, the magnitude and spatial distribution of the associated diapycnal flow and the corresponding diapycnal advective and diffusive property flux divergences. The resulting large-scale WOCE Pacific circulation can be described as two shallow overturning cells at mid- to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal waters from the Southern Ocean into the Pacific where they upwell across isopycnals and are returned south as deep waters. Upwelling is seen to occur throughout most of the basin with generally larger dianeutral transport and greater mixing occurring at depth. The derived pattern of ocean heat transport divergence is compared to published results based on air–sea flux estimates. The synthesis suggests a strongly east/west oriented pattern of air–sea heat flux with heat loss to the atmosphere throughout most of the western basins, and a gain of heat throughout the tropics extending poleward through the eastern basins. The calculated meridional heat transport agrees well with previous hydrographic estimates. Consistent with many of the climatologies at a variety of latitudes as well, our meridional heat transport estimates tend toward lower values in both hemispheres.     

Long-term numerical evolution of the nitrogen bulk content in the Mediterranean Sea

The behavior of the Mediterranean ecosystem in response to realistic riverine inputs and dissolved matter exchange is investigated. The strategy is to evaluate the stability of the ecosystem subjected to various atmospheric inputs.     

Infaunal burrow ventilation and pore-water transport in muddy sediments

The ventilation of burrows by tube-dwelling benthos is understood to be important in determining rates of exchange of solutes between the sediment and overlying water. However, few models have attempted to link the burrow ventilation behavior of tube-dwelling organisms with their geochemical consequences. The classic cylinder model of bioirrigation in muddy sediments (Aller, R.C., 1980. Quantifying solute distributions in the bioturbated zone of marine sediments by defining an average microenvironment. Geochimica et Cosmochimica Acta 44, 1955–1965) links pore-water processes and burrow sizes and distributions in the sediment by assuming that burrows are fully flushed. The equivalence between the cylinder model and the more commonly used one-dimensional non-local exchange model depends upon this assumption. However, this assumption has seldom been tested in the field. We have extended the cylinder model of bioirrigation to include burrow ventilation activities of organisms. Burrow ventilation is modeled as a simple non-local exchange of burrow water with overlying water. Model simulations indicate that burrow ventilation has a large effect on vertical profiles and fluxes of solute tracers. We collected data on burrow geometry in the field by CT-scanning freshly collected sediment cores. At the same study sites, we measured activity profiles of ²²²Rn, a naturally occurring radionuclide tracer of pore-water transport. With model geometry independently constrained, we tested the model by comparing our model-predicted profiles with measured profiles. Our results demonstrate that burrows in the field are not fully flushed. Our estimated burrow ventilation rates compare favorably with previous laboratory measurements. The inclusion of realistic burrow ventilation in this pore-water transport model strongly affects modeled solute profiles and fluxes. We demonstrate how model parameters can be determined from field samples and present a model that more realistically simulates pore-water transport processes in muddy sediments.     

Differential reproductive strategies of two bivalves in the Dutch Wadden Sea

Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria.     

Nanoplanktonic assemblages in the upwelling area off Concepción (∼36°S), central Chile: Abundance, biomass, and grazing potential during the annual cycle

The structure and functioning of nanoplanktonic assemblages in coastal upwelling areas have usually been overlooked in explorations of the productivity of these areas. As part of a multidisciplinary, time-series station in the coastal area off Concepción, seasonal variations (upwelling and non-upwelling) in the abundance and biomass of these assemblages were investigated. Hydrographic measurements and biological samples were taken monthly over a 2-year period (18 August 2004-28 July 2006). Nanoflagellates dominated the total integrated abundance (3-317 × 10⁹ cells m⁻²; 0-80 m). Diatoms and dinoflagellates usually contributed to a lesser degree (<20%) but sporadically made important contributions to the total integrated nanoplankton biomass (0.02-10.6 g C m⁻²). Most of the nanoplankton was concentrated in surface waters (<30 m) during all the samplings and no seasonal differences in abundance or biomass were found in this layer, although the mean values and dispersions around them were highest during the upwelling period along with maximum integrated (0-80 m) chlorophyll-a values, as total or in the <20 μm fraction. Changes in nanoplankton abundance were significantly but weakly (r < 0.4) correlated with changes in the hydrographic variables; the highest correlation values were positive for temperature and oxygen, factors that varied with depth and date. The potential grazing rates of heterotrophic nano-predators (flagellates and dinoflagellates) on prokaryotic prey, estimated with a generic model, ranged from 3 to 242 bacterioplankton predator⁻¹ h⁻¹ and from 0.1 to 14 cyanobacteria predator⁻¹ h⁻¹. Our results imply a small impact of seasonal hydrographic variability on the abundance and biomass of nanoplanktonic assemblages and suggest that grazing by nanoheterotrophs might control the prokaryotic picoplankton populations in the upwelling area off Concepción.     

Understanding El Niño — The importance of Grey Literature in Coastal Ecosystem Research and Management

Access to information about past states of the environment and social systems is fundamental to understand, and cope with, the challenges of climate change and over-exploitation of natural resources at the onset of the 21st century. The loss of (old) data is a major threat to understanding better and mitigating long-term effects of human activities and anthropogenic changes to the environment. Although this is intuitively evident for old and local literature of any kind, even present-day international publishing of papers without the underlying raw data makes access to basic information a crucial issue. Here, we summarise experience resulting from a EU-funded International Science & Technology Cooperation (INCO) project (CENSOR) addressing Coastal Ecosystem Research and Management in the El Niño Southern Oscillation (ENSO) context. We show that indeed “Grey Literature” is still one of the most important sources of knowledge about natural science research and management of natural resource systems in Latin American countries. We argue that public archiving of original data of present-day research and old (Grey) Literature and easy public access are important for appreciating today's global environmental challenges caused by human activities, both past and present.     

Offshore marine conservation policies in the North East Atlantic: Emerging tensions and opportunities

An inherent tension exists between legal approaches to nature conservation and fisheries management in the European Union, as the former remains the remit of Member States while the latter is under the exclusive legislative jurisdiction of the European Community (EC). This tension is of particular importance when addressing the conservation of habitats or species that are under threat from fishing activities. This article examines recent developments in offshore marine conservation in the North-East Atlantic in light of the legislative developments and political frameworks that are currently evolving. By analysing the emergency closure of the Darwin Mounds area of cold-water corals and the UK pair-trawl ban, it becomes evident that the precautionary principle is a key factor in the tension between fisheries management and marine nature conservation, and is not always taken into account.     

Assessment of a Sr isotope vital effect (87Sr/86Sr) in marine taxa from Lee Stocking Island, Bahamas

 Data from Lee Stocking Island, Bahamas, confirms the hypothesis that there are no vital effects with the uptake of Sr isotopes (⁸⁷Sr/⁸⁶Sr) at the present mass spectrometer resolution [±2×10^-5 (2σ)]. Our data set contains analyses of 40 samples derived from 37 different calcareous taxa inhabiting a wide range of carbonate subenvironments (i.e., reefal, intertidal, supratidal, mangrove). The mean value of our analyses was 0.709179 with a standard deviation of 2.4×10^-5 (2σ) which was very close to the long-term uncertainty of the strontium isotope methodology [±2.0×10^-5 (2σ)] and to the widely reported ⁸⁷Sr/⁸⁶Sr value of seawater, which clusters around 0.709175. Received: 14 October 1997 / Revision received: 20 March 1998