Stable carbon and oxygen isotope ratios of foraminifera in surface sediments of the South China Sea

The relationship between planktonic and benthic foraminiferal stable-isotope values and oceanographic conditions and factors controlling isotopic variations are discussed on the basis of oxygen and carbon isotopic analyses of 192 modern surface and Last Glacial Maximum (LGM) samples from the South China Sea (SCS). The harmonic variation of benthic delta18O in surface sediments with water depth and temperature implies that the temperature is the main factor influencing benthic delta18O variations. Planktonic delta18O fluctuates with sea surface temperature (SST) and salinity (SSS). The N-S temperature gradient results in planktonic delta18O decreasing from the northeast to the south. Cool, saline waters driven by the winter monsoon are interpreted to have been responsible for the high delta18O values in the northeast SCS. The East Asian monsoons not only bring nutrients into the South China Sea and maintain high nutrient concentration levels at the southwestern and northeastern ends, which cause depleted delta13C both in planktonic (surface) and benthic (bottom) samples but also reduce planktonic/benthic delta18O differences. The distribution of delta18O and delta13C in the surface and LGM samples are strikingly similar, indicating that the impact of SST and SSS has been maintained, and nutrient inputs, mainly from the northeastern and southwestern ends, have been controlled by monsoons since the LGM. Comparisons of the modern and LGM delta18O indicate a difference of about 3.6 °C in bottom-water temperature and a large surface-to-bottom temperature gradient during the LGM as compared to today.

Distribution of organic-walled dinoflagellate cysts in surface sediments of the Benguela upwelling system

To obtain insight in the relationship between the spatial distribution of organic-walled dinoflagellate cysts (dinocysts) and local environmental conditions, fifty-eight surface sediment samples from the coastal shelf off SW Africa were investigated on their dinocyst content with special focus on the two main river systems and the active upwelling that characterise this region. To avoid possible overprint by species-selective preservation, samples have been selected mainly from shelf sites where high sedimentation rates and/or low bottom water oxygen concentrations prevail. Multivariate ordination analyses have been carried out to investigate the relationship between the distribution patterns of individual species to environmental parameters of the upper water column and sediment transport processes. The main oceanographical variables at the surface (temperature, salinity, nutrients chlorophyll-a) in the region show onshore-offshore gradients. This pattern is reflected in the dinocyst associations with high relative abundances of heterotrophic dinocyst species in neritic regions characterised by high chlorophyll-aand low salinity conditions in surface waters. Phototrophic dinocyst species, notably Operculodinium centrocarpum, dominate in the more oceanic area. Differences in the distribution of phototrophic dinocyst species can be related to sea surface salinity and sea surface temperature gradients and to a lesser extent to chlorophyll-a concentrations. Apart from longitudinal gradients the dinocyst distribution clearly reflects regional environmental features. Six groups of species can be distinguished, characteristic for (1) coastal regions (cysts of Polykrikos kofoidii and Selenopemphix quanta), (2) the vicinity of active upwelling (Brigantedinium spp., Echinidinium aculeatum, Echinidinium spp. and Echinidinium transparantum), (3) river mouths (Lejeunecysta oliva, cysts of Protoperidinium americanum, Selenopemphix nephroides and Votadinium calvum), (4) slope and open ocean sediments (Dalella chathamense, Impagidinium patulum and Operculodinium centrocarpum, (5) the southern Benguela region (south of 24°S) (Spiniferites ramosus) and (6) the northern Benguela region (north of 24°S) (Nematosphaeropsis labyrinthus and Pyxidinopsis reticulata). No indication of overprint of the palaeo-ecological signal by lateral transport of allochthonous species could be observed.

Distribution of benthic foraminifera in surface sediments on the continental margin off North-West Africa

The benthic foraminiferal populations along three traverses across the Northwest African continental margin were analyzed on the base of ca. 60 surface sediment samples. Depth ranges of 213 species were established and the main trends of vertical distribution are compared with those known from adjacent regions. Main faunal breaks occure at 100/200 m and 1000/1500 m depth of water. Some species show latitudinal distribution boundaries and the same applies to population density (standing stock), reflecting the regional distribution of nutrients supply by river discharge and upwelling processes. - High proportions of Bolivina test at the lower slope indicate extended downslope transport.

Total organic carbon in surface sediments of the Ob and Yenisei estuaries and adjacent coastal areas, appendix 1

Two main mechanisms are controlling the accumulation of organic matter in the sediments of the Kara Sea. The large rivers Ob and Yenisei supply significant quantities of freshwater onto the shelf (Lisitsyn and Vinogradov, 1995; Bobrovitskaya et al., 1996; Johnson et al., 1997) and deliver terrigenous organie matter and aquatic algae. Additionally, marine organic matter is produced in the water column. In order to distinguish between the different sources of the organic material maceral analysis, organic-geochemical bulk Parameters and biomarkers (short- and long-chain D-alkanes, fatty acids and pigments) were used to determine the quality (marine vs. terrigenous) and quantity of the organic carbon fraction in the surface sediments taken during the 28th cruise of RV Akademik Boris Petrov (Matthiessen and Stepanets, 1998) (Fig. 1). Previous organic-geochemical investigations (i.e., total organic-carbon content (TOC), hydrogen indices (Hl), CIN-ratios) indicate the importance of terrigenous input of organic matter (Galimov et al., 1996; Stein, 1996). Studies of lipid biomarkers in surface sediments in the Ob estuary show also a predominance of terrestrial constituents and an increase in planktonogenic and bacterial lipids further offshore (Belyaeva and Eglinton, 1997). In complex systems such as the Eurasian continental margin characterized by high input of terrestriallaquatic organic matter and strong seasonal variation in sea-ice Cover and primary productivity, the Interpretation of the organic geochemical data is much more complicated and restricted in comparison to similar data Sets from low-latitude open-ocean environments (Fahl and Stein, 1998). Microscopical studies (maceral analysisl palynology), however, allow a direct visual inspection of the particulate organic matter and allow to differentiate particles of different biological sources. Thus, a combination of both methods as shown in this study, yields a more precise identification of organic-carbon sources.

Geographic distribution of dinoflagellate cysts in surface sediments

Dinoflagellate cysts are useful for reconstructing upper water conditions. For adequate reconstructions detailed information is required about the relationship between modern day environmental conditions and the geographic distribution of cysts in sediments. This Atlas summarises the modern global distribution of 71 organicwalled dinoflagellate cyst species. The synthesis is based on the integration of literature sources together with data of 2405 globally distributed surface sediment samples that have been preparedwith a comparable methodology and taxonomy. The distribution patterns of individual cyst species are being comparedwith environmental factors that are knownto influence dinoflagellate growth, gamete production, encystment, excystment and preservation of their organic-walled cysts: surface water temperature, salinity, nitrate, phosphate, chlorophyll-a concentrations and bottom water oxygen concentrations. Graphs are provided for every species depicting the relationship between seasonal and annual variations of these parameters and the relative abundance of the species. Results have been compared with previously published records; an overview of the ecological significance as well as information about the seasonal production of each individual species is presented. The relationship between the cyst distribution and variation in the aforementioned environmental parameters was analysed by performing a canonical correspondence analysis. All tested variables showed a positive relationship on the 99% confidence level. Sea-surface temperature represents the parameter corresponding to the largest amount of variance within the dataset (40%) followed by nitrate, salinity, phosphate and bottom-water oxygen concentration, which correspond to 34%, 33%, 25% and 24% of the variance, respectively. Characterisations of selected environments as well as a discussion about how these factors could have influenced the final cyst yield in sediments are included.

(Table 2) Composition of polycyclic aromatics in bottom sediments from the Weddell Sea

Distribution, composition and genesis of organic matter in recent bottom sediments of the Weddell Sea (Western Antarctic) are discussed. Geochemical background levels of bitumen, organic matter, and polycyclic aromatics in the sediments are respectively 0.01-0.1%, 0.003-0.005%, and 0.0001-0.0002%. Deviations from the background level, probably caused by secondary processes, are found. Organic matter has characteristic properties resulting from distinctive character of aquatic biota organic matter, from which it has been formed.

(Table 1) Lipid biomarkers in surface sediments from the Gulf of Genoa

A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C29 and n-C31 alkanes, n-C26 and n-C28 alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, aeolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C37 alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1 to 30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based UK'37 index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEXH86-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa.

(Table 1) Organic carbon isotopic composition in Cretaceous sediments at DSDP Hole 75-530A

Cretaceous sediments from DSDP Site 530 have been analyzed for organic carbon isotopic composition. The d13C values in the sediments decrease from -22.7 per mil to -27.5 per mil in the following order: light-olive green mudstone/claystone, dark brown-red mudstone/siltstone/claystone, and black shale. This large range is primarily the result of variation in the relative amounts of terrestrial organic carbon superimposed on that derived from marine organisms. The black shales have an average d13C value of -25.9 per mil (range is from -23.7 per mil to -27.5 per mil). These values indicate that they originated primarily in terrigenous organic materials. The average d13C value present throughout the Cretaceous suggests that a large amount of terrestrial organic matter was supplied into this paleoenvironment, except during the Campanian, when an average d13C of -23.9 per mil is found near the marine end of the range.

Long chain 1,13- and 1,15-diols in surface sediments ans SST reconstruction for sediment core GeoB6518-1

Although commonly reported in marine and freshwater environments, little is known about the biological sources of long chain alkyl 1,13- and 1,15-diols, and factors controlling their distributions. Here we analyzed the occurrence and distribution of these lipids in a comprehensive set of marine surface sediments and compare their distributions with environmental conditions like sea surface temperature (SST), salinity and nutrient concentrations. Fractional abundances of the C28 1,13-, C30 1,13- and C30 1,15-diols show a strong correlation with SST and based on these results, we propose the Long chain Diol Index (LDI), which expresses the C30 1,15-diol abundance relative to those of C28 1,13-, C30 1,13- and C30 1,15-diols. The LDI shows a strong linear correlation with SST (LDI = 0.033 × SST + 0.095; R2 = 0.969, n = 162) over a temperature range of -3 to 27 °C. Long chain diol distributions in sediments from the South Atlantic close to the Congo River outflow (West Africa) provided a 43 kyr LDI SST record. This record reflects several known climatic events and shows similarities with an alkenone-derived SST record obtained using the same suite of sediments, both in trend and in terms of absolute SST. This confirms the potential of the LDI as a proxy for palaeo-SST reconstruction.

Grain size distribution in surface sediments samples of the continental shelf and slope of southeast Greenland

During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.