The Pechora Sea: Past,recent, and future

The main stages in the development of the Pechora Sea are discussed. It is established that, during the high sea level stand corresponding to the warmest epoch of the Mikulino Interglacial, the Pechora Sea represented a more spacious, as compared with its present-day size, basin owing to the flooded valleys of river lower reaches. No sea in its present-day configuration existed during the last (Valdai) glaciation. At that time, the sea could have occupied only a narrow area along the southern coast of Novaya Zemlya, where marine sedimentation was in progress during the Late Pleistocene and Holocene. During the glaciation and postglacial time, the dried bottom of the former Pechora Sea accumulated large volumes of sand that are now concentrated largely in the accretion structures along its southern coast. In the current century, changes will occur mainly in the coastal zone of the Russkii Zavorot Peninsula, Pesyakov Island, the Varandei Settlement area, and the Medynskii Zavorot Peninsula, where a shoreline retreat for a distance of 0.5 km is expected.     

A comparative mineralogical study of gas-related sediments of the Gulf of Cádiz

The Gulf of Cádiz area has been extensively surveyed in recent years and several gas-related fluid escape seafloor structures have been identified. In this study, gravity cores, collected during the ANASTASYA/00 and ANASTASYA/01 cruises, on mud volcanoes, hemipelagic sediments and dredged material from diapiric structures, have been studied. A comparative mineralogical analysis by XRD and SEM of samples from different areas has been performed in order to determine whether there is a characteristic mineralogy related to these fluid escape structures, and also to determine the origin of the mud matrix and constrain the depth of the parent units. The mineralogical analysis reflects the different origins of the different units described in the cores: hemipelagic material of the slope, clays that underlie the mud volcanoes and are discharged at the sea bottom surface, and authigenic and diagenetic minerals possibly involved in the anaerobic oxidation of methane in the mud volcano sediments.     

Supply and precipitation of hydrothermal iron in the rift valley of the Mid-Atlantic Ridge at 26° and 29° N

This publication considers the probing data on aquatic anomalies (hydrothermal plumes) in the areas of 26° and 29° N of the Mid-Atlantic Ridge (MAR). The mass of the hydrothermal iron supply and the intensity of the iron sedimentation onto the bottom were estimated by means of sediment traps. It was found that the plume of the TAG hydrothermal vent 6 km³ in volume contained about 67 t of suspended Fe; the plume of the Broken Spur field (up to 8.24 km³ in volume) contained 23.5 t or less because of the lower concentration. The data on the sedimentary matter fluxes showed that 0.3–0.5% of the hydrothermal iron was precipitated immediately from a plume of neutral buoyancy onto the bottom; the bulk of the iron was dissipated into the environment. From the dimensions of the plumes, the flow dynamics, the iron concentrations in the plumes, and the amounts of iron supplied by hydrothermal vents, it was found that the resident time of the plumes considered was from 5 to 10 days.     

Intense Arctic mesocyclones

Characteristics of polar mesoscale cyclones (PMCs) over the North European Basin are analyzed using cloud cover distribution data for 1981–1995. Special features of the annual cycle and interannual variations in characteristics of Arctic mesocyclones with a spiral and comma-shaped cloud structure are discussed. Against the background of large interannual variations, no statistically significant trends were found in the characteristics of Arctic mesocyclones over the North European Basin in the late 20th century. It is shown that the cumulative frequency distribution of PMCs is well approximated by an exponential function in a size range for Arctic mesocyclones from 50 to 400 km. The applicability of the Weibull distribution as an approximation of the PMC size distribution of the number of cyclone days is analyzed. It is shown that the correspondence between the real distribution and the Weibull distribution became worse in the 1990s than in the 1980s, especially the first half of the 1980s. Much of this was due to an increased local maximum in the 1990s in the distribution of polar mesocyclones with diameters about 400 km. This local maximum was found for all types of mesoscale vortices and for all analyzed five-year subperiods during 1981–1995. A large discrepancy between the frequency distribution functions for PMCs depending on their diameters was shown to exist for different types of Arctic mesocyclones.     

The impact of the M2 internal tide on data-assimilative model estimates of the surface tide

We use a synthetic data experiment to assess the accuracy of ocean tides estimated from satellite altimetry data, with emphasis on the impact of the phase-locked internal tide, which has a surface expression of several centimeters near its sites of genesis. Previous tidal estimates have regarded this signal as a random measurement error; however, it is deterministic and not scale-separated from the barotropic (surface) tide around complex bathymetric features. The synthetic data experiments show that the internal tide has a negligible impact on the barotropic tidal fields inferred under these circumstances, and the barotropic dissipation (a quadratic functional of the tidal fields) is in good agreement with the energetics of the three-dimensional regional primitive equations model which is the source of the synthetic data.     

Response behaviour of triangular tension leg platforms under impact loading

Excellent station keeping characteristics and relative insensitivity with increasing water depth make triangular tension leg platforms (TLPs) a proven concept in deep water oil exploration. TLPs are often subjected to less probable forces which arise due to collision of ships, icebergs or any other huge sea creature. Dynamic analysis of two triangular TLP models at water depths 1200 and 527.8 m is performed under regular waves along with impulse load acting at an angle of 45 degrees at the TLP column. Hydrodynamic forces on these TLPs are evaluated using modified Morison equation, based on water particle kinematics arrived at using Stokes’ fifth order wave theory. Based on numerical studies conducted, it is seen that impulse loading acting on corner column of TLP significantly affect its response while that acting on pontoons dose not affect TLPs behaviour.     

Mixed layer variability in Northern Arabian Sea as detected by an Argo float

Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April - May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.3 °C and ocean gained an average of 99.8 Wm⁻². Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained abnormally low ∼18 Wm⁻² and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm⁻². Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively. Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided well with short term variability of surface forcing.     

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.     

Stress Sharing Behavior and Its Mechanism during Consolidation Process in Composite Ground Improved by Sand Compaction Piles with Low Replacement Area Ratio

In order to accurately design a sand compaction pile (SCP) with low replacement area ratio, it is important to understand the mechanical interaction between the sand pile and clay ground and its mechanism during consolidation process in composite ground. In this article, therefore, a series of numerical analyses on composite ground improved by SCP with low replacement area ratio were carried out. The applicability of numerical analyses, in which an elasto-viscoplastic consolidation finite element method was applied, were confirmed by comparing the results obtained from a series of laboratory model tests with the composite ground improved by SCP. Through the results of the numerical analyses, mechanical behavior of the sand pile and clay in composite ground during consolidation is elucidated, together with a stress sharing mechanism between sand pile and clay.     

Estimating the underwater light field from remote sensing of ocean color

We present a new approach that incorporates two models to estimate the underwater light field from remote sensing of ocean color. The first employs a series of analytical, semi-analytical, and empirical algorithms to retrieve the spectrum of inherent optical properties (IOPs), including the absorption and the backscatter coefficients, from the spectrum of remote sensing reflectance. The second model computes the profile of photosynthetically available radiation E _0,PAR (z) for a vertically homogeneous water column using the information of the retrieved IOPs and the ambient optical environment. This computation is based on an improved look-up table technology that possesses high accuracy, comparable with the full solution of the radiative transfer equation, and meets the computational requirement of remote sensing application. This new approach was validated by in situ measurements and an extensive model-to-model comparison with a wide range of IOPs. We successfully mapped the compensation depth by applying this new approach to process the SeaWiFS imagery. This research suggests that E _0,PAR (z) can be obtained routinely from ocean-color data and may have significant implications for the estimation of global heat and carbon budget.