(Table 1) Estimated e-Nd(0) input calculated using the relative fraction of ODP Hole 105-647A amphibole grains originated from different provinces of the North America

Many marine radiogenic isotope records show both spatial and temporal variations, reflecting both the degree of mixing of distinct sources in the oceans and changes in the distribution of chemical weathering on the continents. However, changes in weathering and transport processes may themselves affect the composition of radiogenic isotopes released into seawater. The provenance of physically weathered material in the Labrador Sea, constrained through the use of Ar-Ar ages of individual detrital minerals, has been used to estimate the relative contributions of chemically weathered terranes releasing radiogenic isotopes into the Labrador Sea. A simple box-model approach for balancing observed Nd-isotope variations has been used to constrain the relative importance of localised input in the Labrador Sea, and the subsequent mixing of Labrador Sea Water into North Atlantic Deep-Water. The long-term pattern of erosion and deep-water formation around the North Atlantic seems to have been a relatively stable feature since 1.5 Ma, although there has been a dramatic shift in the nature of physical and chemical weathering affecting the release of Hf and Pb isotopes. The modelled Nd isotopes imply a relative decrease in water mass advection into the Labrador Sea between 2.4 and 1.5 Ma, accompanied by a decrease in the rate of overturning, possibly caused by an increased freshwater input into the Labrador Sea.

(Table 3) Observations of Mediterranean water lenses in the Eastern North Atlantic

Spreading pattern and mesoscale structure of Mediterranean water outflow in the eastern North Atlantic are studied on the basis of historical hydrographical records. Effect of bottom topography on Mediterranean water distribution is revealed. It is shown that the Mediterranean water outflow is divided into two streams after leaving the Gulf of Cadiz. These are northwestern and southwestern ones; the former is more intensive and spreads in more regular and continuous way. West of the Tejo (Tagus) Plateau it splits into three branches; the most intense of them keeps continuity up to 14°W. The less intensive southwestern stream passes south of the Gettysburg Bank and splits into two branches immediately after the Gulf of Cadiz. From 11°W, this stream has lenticular, intermittent character. West of 14°-15°W all Mediterranean water branches are represented mainly by isolated salty patches. As a result of historical data analysis in the 32°-44°N, 8°-22°W area, 30 Mediterranean water lenses have been found; 12 of them had not been previously mentioned in publications. A table of main parameters of Mediterranean water lenses is presented. It includes data of 108 observations from 1911 to 1993.

Planktic foraminiferal populations and test flux in the eastern North Atlantic Ocean

Planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties, between water masses, and after periodical changes and episodic events (e.g. reproduction, storms). Distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data. In this paper we discuss the short-term impacts on interannual flux rates based on data from opening-closing net hauls obtained between the ocean surface and 500 m water depth. Data were recorded during April, May, June, and August at around 47°N, 20°W (BIOTRANS) in 1988, 1989, 1990, 1992, 1993, and during May 1989 and 1992 at 57°N, 20-22°W. Species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column. In addition, species assemblages >100 µm are almost indistinguishable from assemblages that are >125 µm in test size. The standing stock of planktic foraminifers at BIOTRANS can vary by more than one order of magnitude over different years; however, species assemblages may be similar when comparing corresponding seasons. Early summer assemblages (June) are distinctly different from late summer assemblages (August). Significant variations in the species composition during spring (April/May) are independent of the mixed layer depth. Spring assemblages are characterized by high numbers of Globigerinita glutinata. In particular, day-to-day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations. This appears to be independent of the reproduction cycle. Species assemblages at 47°N and 57°N are similar during spring, although surface water temperatures and salinities differ by up to 10°C and 0.7 (PSU). We suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer. Planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations, a quasi-annual periodicity in flux levels, and substantial differences in timing and magnitude of peak fluxes. At the BIOTRANS station, the average annual planktic foraminiferal CaCO3 fluxes at 100 and 500 m depth are estimated to be 22.4 and 10.0 g/m**2/yr, respectively.