ALBERT

Description: A new image of the French continental crust between Brabant (Belgium) and the Basque province of Spain is presented on the basis of considerable recent geological and geophysical information as well as the compilation and reInterprétation of previously available data. The resulting section, which shows the main basement structures to a depth of 45 km, also is the first nonspeculative image of the westernmost part of the Variscan orogen. The French Global Geoscience Transect reveals a complete picture of this orogen between its remnant root and the surface. The divergent thrusts are bounded on the north and in the south by the old Brabant and Ebro-Aquitaine cratons, respectively; these thrusts also involve two previous plate boundaries. The lower part of the orogen is limited by a layered lower crust, probably of Permian age. Near the surface the Hercynian orogen is buried—near the northern end of the transect by the Paris Basin, which can be considered an eastward extension of the English Channel, and in the south by the South Armorican continental margin, which makes a transition between the oceanic crust of the Bay of Biscay and the axis of the Variscan orogen. In this area, the deep Parentis graben is located at the site of pronounced crustal thinning, since only 7 km of Hercynian crust are now preserved.

Description: The assessment of direct effects of anthropogenic CO2 increase on the marine biota has received relatively little attention compared to the intense research on CO2-related responses of the terrestrial biosphere. Yet, due to the rapid air–sea gas exchange, the observed past and predicted future rise in atmospheric CO2 causes a corresponding increase in seawater CO2 concentrations, [CO2], in upper ocean waters. Increasing [CO2] leads to considerable changes in the surface ocean carbonate system, resulting in decreases in pH and the carbonate concentration, [CO2−3]. These changes can be shown to have strong impacts on the marine biota. Here we will distinguish between CO2-related responses of the marine biota which (a) potentially affect the ocean's biological carbon pumps and (b) are relevant to the interpretation of diagnostic tools (proxies) used to assess climate change on geological times scales. With regard to the former, three direct effects of increasing [CO2] on marine plankton have been recognized: enhanced phytoplankton growth rate, changing elemental composition of primary produced organic matter, and reduced biogenic calcification. Although quantitative estimates of their impacts on the oceanic carbon cycle are not yet feasible, all three effects increase the ocean's capacity to take up and store atmospheric CO2 and hence, can serve as negative feedbacks to anthropogenic CO2 increase. With respect to proxies used in palaeo-reconstructions, CO2-sensitivity is found in carbon isotope fractionation by phytoplankton and foraminifera. While CO2- dependent isotope fractionation by phytoplankton may be of potential use in reconstructing surface ocean pCO2 at ancient times, CO2-related effects on the isotopic composition of foraminiferal shells confounds the use of the difference in isotopic signals between planktonic and benthic shells as a measure for the strength of marine primary production. The latter effect also offers an alternative explanation for the large negative swings in δ13C of foraminiferal calcite between glacial and interglacial periods. Changes in [CO2−3] affect the δ18O in foraminiferal shells. Taking this into account brings sea surface temperature estimates for the glacial tropics closer to those obtained from other geochemical proxies.

Description: Exposure of Fucus spiralis germlings to precise copper concentrations (0 to 844 nM Cu2+) in chemically defined medium demonstrated a relationship between urltrastructural changes and growth retardation with increasing copper concentration. Electron-translucent vesicles, present in ova, which normally disappear after fertilization, accumulated in germlings exposed to Cu2+ above 10.6 nM, suggesting that copper may inhibit a metabolic pathway involved in cell wall formation which is initiated by fertilization No membrane damage was observed during the exposure period. During a post-exposure period in copper-free medium, recovery occurred (rhizoid extension, apical hair formation) in germlings previously exposed to concentrations below 106 nM Cu2+ and electron-translucent vesicles became granular and disappeared. It is proposed that the electron-translucent vesicles contain a cell wall precursor and that copper inhibits its incorporation into the cell wall, preventing growth and development of the zygote.

Description: The “rugophilic”; behaviour (e.g. the preference for settling in concavities) of barnacles is well documented. In contrast, little is known about settlement preferences of other species with regard to surface microtopography. In a randomized block design, five different rugosities (smooth, 0.1 mm, 0.5 mm, 1 mm, 5 mm) were exposed to natural fouling in the Baltic Sea. In four experiments, test panels were colonized by Mytilus edulis, Polydora dliata, Balanus improvisus, diatoms, hydrozoa, bryozoa, and several ciliates. Settlement densities and microtopographical preferences for pits or elevations as a function of grain size were evaluated. Rugosities influenced settlement densities and the microtopographical preferences of almost all investigated species. Settlement densities were generally lowest on smooth panels, with most species showing distinct preferences for different rugosities. While a preference for pits was frequent, in some species the proportion of individuals settling on elevations significantly increased with roughness. These data on microtopographical preferences of different species give new insights into interactions between settlement behaviour, surface roughness, boundary layer hydrodynamics and community structure.

Description: A quantitative relationship between observed sea-ice roughness and simulated large-scale deformation work is established in order to provide new means for model validation and a better representation of the sea-ice component in climate modelling. Sea-ice roughness is introduced as an additional prognostic variable in a dynamic–thermodynamic sea-ice model with a viscous-plastic rheology. It is defined as the accumulated work of internal forces acting upon an ice volume, given in energy per area. A fraction of this total deformation work is transferred to the potential energy stored in pressure ridges. Using ridge geometries and distribution functions from observations, observable quantities like mean pressure ridge height, ridge frequency as well as volumetric and areal fractions of deformed ice are derived from the simulated ice roughness. Comparisons of these simulated quantities with measurements (submarine-borne sonars, laser altimeters on helicopters) show good agreement. Satellite-borne observations of sea-ice roughness now under development will provide an even larger data set which will be used for model verification. Additionally roughness-dependent drag coefficients are introduced to account for the effect on the momentum exchange between ocean and atmosphere due to the form drag of roughness elements. The simulations indicate that the inclusion of sea-ice roughness provides for a more realistic representation of the boundary layer processes in climate models.

Description: To study the variability of the thermohaline circulation in the North Atlantic on decadal time scales, the atmospheric regional model REMO is currently investigated as a component of a fully-coupled atmosphere–ice–ocean model for the Arctic/North Atlantic. A comparison of a 5-year uncoupled simulation of the regional model with a 5-year NCEP/NCAR reanalysis period is carried out in order to assess the performance of the regional model in polar and subpolar regions. The model simulates basic structures realistically. It performs well in middle latitudes but shows some problems in the region of the marginal ice zone and in continental regions with extreme temperature amplitudes. The high elevations of Greenland in the central part of the model domain give rise to problems in the model dynamics, resulting in moderate deviations from NCEP/NCAR reanalysis.

Description: Application of a neural network to ERS-SAR images to retrieve pressure ridge spatial frequencies is presented. For an independent dataset, the rmserror between the retrieved and the true ridge frequency as determined by means of laser profiling was about 5 ridges per kilometre, or 30%. The network is trained with results from in situ laser profiling of ridge distributions and coincident SAR backscatter properties. The study focuses on summer data from the Bellingshausen, Amundsen and Weddell Seas in Antarctica, which were gathered in February 1994 and 1997. Pressure ridge frequencies varied from 3 to 30 ridges per kilometre between different regions, thus providing a wide range of training and test data for the algorithm development. From ERS-SAR images covering the area of the laser flights with a time difference of a few days at maximum, histograms of the backscatter coefficient sigma0 were extracted. Statistical parameters (e.g. mean, standard deviation, tail-to-mean ratio) were calculated from these distributions and compared with the results of the laser flights. Generally, the mean backscatter increases with a growing ridge frequency, and the signal range becomes narrower. However, these correlations are only poor, and improved results are obtained when the statistical parameters are combined to train the neural network.