Benthic macrofauna changes in areas of Venice lagoon populated by seagrasses or seaweeds.

Two areas of the Venice lagoon populated by seagrasses (three stations covered by Cymodocea nodosa (Ucria) Asherson, Zostera marina Linnaeus, Zostera noltii Hornemann) or seaweeds (two stations: one covered by Ulva rigida C. Agardh and another at present without seaweed biomass) were monitored by means of six surveys over a year in order to study macrofaunal composition and seasonal changes. The seagrass stations showed a mean species richness (28-30 S m(-2)), individual abundance (1854-4018 N m(-2)) and biomass (22.3-37.7 g m(-2) ash-free-dry-weight, AFDW) ca. 3-8 times higher than those populated by seaweeds (10-15 S m(-2), 494-1395 N m(-2) and 5.6-13.7 g m(-2) AFDW). Differences among seagrass or seaweed stations were much lower. The Ulva-dominated station showed a macrofauna completely different both from the other stations and the communities recorded ca. 30 years ago, before the prolific growth of Ulva. In this station, frequent biomass decompositions and anoxic crises created critical conditions for life favouring organisms with reduced life cycles, younger individuals and the epifaunal species instead of the infaunal ones. In particular, Ulva grazers and scrapers such as Gammarus aequicauda Stock and Gibbula adriatica Philippi were found to be by far the most abundant species, whereas the taxa characteristic of the associations found in the past, in the presence of seagrasses or seaweeds and typical of low eutrophicated environments, appear strongly reduced. Marked differences in the macrophyte dominance and in the bio-physico-chemical variables which characterise the main environmental conditions of the Venice lagoon support the different distribution and composition of macrofaunal communities. Seaweed stations appear mainly governed by the seasonal cycles of these un-rooted macrophytes which, by alternating periods of production and decomposition, are responsible for the drastic reduction of macrofauna biodiversity and biomass. Conversely, seagrass stations exhibit a better oxidisation of the environment and show conditions more favourable for macrofauna colonisation, especially in the presence of macrophytes which are characterised by very well developed below-ground systems such as Cymodocea nodosa.     

Turbulent structure of the subsurface layer of the sea according to the data of the <Emphasis Type="Italic">Sigma-1</Emphasis> measuring complex

We present the results of experimental investigations of the characteristics of turbulence in the layer of wave-induced mixing. The data on the fluctuations of velocity, temperature, and conductivity are obtained with the help of a Sigma-1 measuring complex. The computed values of the dissipation rate of turbulent energy are compared with different models proposed for the subsurface layer. It is shown that the available models fail to guarantee satisfactory agreement of the numerical results with the experimental data for the layer of active wave action and, in particular, in the presence of swell. This leads us to the conclusion concerning the necessity of parametrization and assimilation of more complete data on the state of the sea surface, the structure of currents, and the surface layer of the atmosphere in the models. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 15–28, March–April, 2007.     

Trends in the solubility of iron,aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean

The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO₄²⁻, NO₃⁻) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean.     

Treatment of Hydrodynamic Loading for Random Sea State

- In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques.     

Mechanism of the seasonal transport variation through the Tokara Strait

To investigate an mechanism of the seasonal variation of transport through the Tokara Strait, two numerical experiments with real geometry and wind forcing were carried out. The models are linear barotropic models which are a North Pacific Ocean model and a limited-area model with a fine grid. The seasonal variation of volume transport with a maximum in the summer and a minimum in the autumn could be well reproduced by both models. The results demonstrate the wind stress component normal to a gradient vector of bottom topography is crucial for determining the seasonal variation. The similar seasonal variation widely covers the East China Sea and has a large amplitude near the Tokara Strait. Finally, it can be concluded that winds north of 35°N have little influence on the seasonal response of our model at the Tokara Strait.     

Deep ocean fluxes and their link to surface ocean processes and the biological pump

Intense studies of upper and deep ocean processes were carried out in the Northwestern Indian Ocean (Arabian Sea) within the framework of JGOFS and related projects in order to improve our understanding of the marine carbon cycle and the ocean’s role as a reservoir for atmospheric CO₂. The results show a pronounced monsoon-driven seasonality with enhanced organic carbon fluxes into the deep-sea during the SW Monsoon and during the early and late NE Monsoon north of 10°N. The productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer-deepening. Deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the NE Monsoon. Nevertheless, deep mixing and strong upwelling during the SW Monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone. When silica concentrations fall below 2 μmol l⁻¹, diatoms lose their dominance in the plankton community. During diatom-dominated blooms, the biological pathway of uptake of CO₂ (the biological pump) appears to be more efficient than during blooms of other organisms, as indicated by organic carbon to carbonate carbon (rain) ratios. Due to the seasonal alternation of diatom and non-diatom dominated exports, spatial variations of the annual mean rain ratios are hardly discernible along the main JGOFS transect.Data-based estimates of the annual mean impact of the biological pump on the fCO₂ in the surface water suggest that the biological pump reduces the increase of fCO₂ in the surface water caused by intrusion of CO₂-enriched subsurface water by 50–70%. The remaining 30 to 50% are attributed to CO₂ emissions into the atmosphere. Rain ratios up to 60% higher in river-influenced areas off Pakistan and in the Bay of Bengal than in the open Arabian Sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fCO₂ in the surface water by supporting diatom blooms. Consequently, it is assumed that reduced river discharges caused by the damming of major rivers increase CO₂ emission by lowering silica inputs to the Arabian Sea; this mechanism probably operates in other regions of the world ocean also.     

On the application of the units of measurement of the amount and composition of matter in oceanology

We consider the procedures of conversion of the conventional and out-of-system units of measurement of the amount and composition of matter used in oceanology to the International System of Units (SI). The coefficients of conversion are presented in the form of a table. We present the data on the units of measurement of mineralization (scales of salinity) of seawater for the oceanic range of its variability, freshened waters of internal seas, and brines. The contemporary concept of salinity as a dimensionless quantity is discussed.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 61–72, July–August, 2004.