Spatial distribution of isotopic compositions of Globigerina bulloides and Neogloboquadrina pachyderma (dex.) and the faunal assemblages of planktic foraminifera in surface sediment samples along the Chilean continental slope between 23°S and 44°S

We report on the spatial distribution of isotopic compositions of the two planktic foraminifera species Globigerina bulloides and Neogloboquadrina pachyderma (dex.), and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the Chilean continental slope between 23°S and 44°S. Both d13C and d18O data of N. pachyderma (dex.) show little variability in the study area. North of 39°S, the isotopic values of N. pachyderma (dex.) are heavier than those of G. bulloides, whereas south of 39°S, this relation inverses. This is indicative for a change from a well-mixed, deep thermocline caused by coastal upwelling north of 39°S to well-stratified water masses in a non-upwelling environment south of 39°S. In addition, the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39°S to a high-nutrient-non-upwelling assemblage south of 39°S, which is characterized by decreased contributions of upwelling indicators such as G. bulloides, N. pachyderma (sin.), and Globigerinita glutinata. In general, we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23°S and 44°S off Chile. Our data point to higher marine productivity at upwelling centers north of 25°S and at 30-33°S. South of 39°S, significant supply of nutrients by fluvial input most likely boosts the productivity.

Grain size investigations of sediments off the coast of Istria

Composition, grain-size distribution, and areal extent of Recent sediments from the Northern Adriatic Sea along the Istrian coast have been studied. Thirty one stations in four sections vertical to the coast were investigated; for comparison 58 samples from five small bays were also analyzed. Biogenic carbonate sediments are deposited on the shallow North Adriatic shelf off the Istrian coast. Only at a greater distance from the coast are these carbonate sediments being mixed with siliceous material brought in by the Alpine rivers Po, Adige, and Brenta. Graphical analysis of grain-size distribution curves shows a sediment composition of normally three, and only in the most seaward area, of four major constituents. Constituent 1 represents the washed-in terrestrial material of clay size (Terra Rossa) from the Istrian coastal area. Constituent 2 consists of fine to medium sand. Constituent 3 contains the heterogeneous biogenic material. Crushing by organisms and by sediment eaters reduces the coarse biogenic material into small pieces generating constituent 2. Between these two constituents there is a dynamic equilibrium. Depending upon where the equilibrium is, between the extremes of production and crushing, the resulting constituent 2 is finer or coarser. Constituent 4 is composed of the fine sandy material from the Alpine rivers. In the most seaward area constituents 2 and 4 are mixed. The total carbonate content of the samples depends on the distance from the coast. In the near coastal area in high energy environments, the carbonate content is about 80 %. At a distance of 2 to 3 km from the coast there is a carbonate minimum because of the higher rate of sedimentation of clay-sized terrestrial, noncarbonate material at extremely low energy environments. In an area between 5 and 20 km off the coast, the carbonate content is about 75 %. More than 20 km from the shore, the carbonate content diminishes rapidly to values of about 30 % through mixing with siliceous material from the Alpine rivers. The carbonate content of the individual fractions increases with increasing grain-size to a maximum of about 90 % within the coarse sand fractions. Beyond 20 km from the coast the samples show a carbonate minimum of about 13 % within the sand-size classes from 1.5 to 0.7 zeta¬? through mixing with siliceous material from the alpine rivers. By means of grain-size distribution and carbonate content, four sediment zones parallel to the coast were separated. Genetically they are closely connected with the zonation of the benthic fauna. Two cores show a characteristic vertical distribution of the sediment. The surface zone is inversely graded, that means the coarse fractions are at the top and the fine fractions are at the bottom. This is the effect of crushing of the biogenic material produced at the surface by predatory organisms and by sediment eaters. lt is proposed that at a depth of about 30 cm a chemical solution process begins which leads to diminution of the original sediment from a fine to medium sand to a silt. The carbonate content decreases from about 75 % at the surface to 65 % at a depth of 100 cm. The increase of the noncarbonate components by 10 % corresponds to a decrease in the initial amount of sediment (CaC03=75 %) by roughly 30 % through solution. With increasing depth the carbonate content of the individual fractions becomes more and more uniform. At the surface the variation is from 30 % to 90 %, at the bottom it varies only between 50 % and 75 %. Comparable investigations of small-bay sediments showed a c1ear dependence of sediment/faunal zonation from the energy of the environment. The investigations show that the composition and three-dimensional distribution of the Istrian coastal sediments can not be predicted only from one or a few measurable factors. Sedimentation and syngenetic changes must be considered as a complex interaction between external factors and the actions of producing and destroying organisms that are in dynamic equilibrium. The results obtained from investigations of these recent sediments may be of value for interpreting fossil sediments only with strong limitations.

(Table 1) Calcium carbonate content of boulder clays sampled along the baltic coast of Schleswig-Holstein, Germany

The carbonate contents in the boulder clay ('Geschiebemergel') of abrasion cliffs were investigated along the Baltic coast of Schleswig-Holstein, northern West Germany. The calcareous boulder clay and stratified drift in the cliffs are interbedded with compressed thrust sheets of Cretaceous limestone, Tertiary Tarras clay, and Eemian clay. According to chemical analyses of 173 boulder clay samples, the amount of carbonate varies mostly between 6 and 17%. Owing to the small number of samples no definite conclusion could be drawn on the distribution of Danish Cretaceous limestones in the boulder clay, nor on the different directions of movement of Weichselian glaciers.

Soft-bottom macrobenthic faunal associations in the southern Chilean glacial fjord complex

Macrobenthic associations were investigated at 29 sampling stations with a semi-quantitative Agassiz trawl, ranging from the South Patagonian Icefield to the Straits of Magellan in the South Chilean fjord system. A total of 1,895 individuals belonging to 131 species were collected. 19 species belong to colonial organisms, mainly Bryozoa (17 species) and Octocorallia (2 species). The phylum Echinodermata was the most diverse in species number (47 species), with asteroids (25 species) and ophiuroids (13 species) being the best represented within this taxon. Polychaeta was the second dominant group in terms of species richness (46 species). Multidimensional scaling ordination (MDS) separated two station groups, one related to fjords and channels off the South Patagonian Icefield and the second one to stations surrounding the Straits of Magellan. 45 species account for 90% of the dissimilarity between these two groups. These differences can mainly be explained by the influence of local environmental conditions determined by processes closely related to the pres- ence/absence of glaciers. Abiotic parameters such as water depth, type of sediment and chemical features of the superficial sediment were not correlated with the numbers of individuals caught by the Agassiz trawl in each group of sampling stations.