Calcareous dinoflagellate cycst in the mid-Cenomanian Boreal realm

A transect from the bathyal to proximal shelf facies of the Boreal Realm was investigated to compare spatial and temporal distribution changes of calcareous dinoflagellate cysts (c-dinocysts) throughout the mid-Cenomanian in order to gain information on the ecology of these organisms. Pithonelloideae dominated the cyst assemblages to more than 95% on the shelf, a prevalence that can be observed throughout most of the Upper Cretaceous. The affinity of this group with the dinoflagellates, which is still controversially discussed, can be confirmed, based on evidence from morphological features and distribution patterns. The consistent prevalence of Pithonella sphaerica and P. ovalis in c-dinocyst assemblages throughout the Upper Cretaceous indicates that they were produced more frequently than cysts of the other species and might, therefore, represent a vegetative dinoflagellate life stage. P. sphaerica and P. ovalis are interpreted as eutrophic species. P. sphaerica is the main species in a marginal-shelf upwelling area, offshore Fennoscandia. Here, sedimentary cyclicity appears to have been reduced to the strongest light/dark changes, while in the outer shelf sediments, light/dark cycles are well-developed and show pronounced temporal assemblage changes. Cyclic fluctuations in the P. sphaerica / P. ovalis ratio reflect shifts of the preferred facies zones and indicate changes in surface mixing patterns. During periods of enhanced surface mixing most parts of the shelf were well-ventilated, and nutrient-enriched surface waters led to high productivity and dominance of the Pithonelloideae. These conditions on the shelf contrasted with those in the open ocean, where more oligotrophic and probably stratified waters prevailed, and an assemblage with very few Pithonelloideae and dominance of Cubodinellum renei and Orthopithonella ? gustafsonii was characteristic. While orbitally-forced light/dark sedimentary cyclicity of the shelf sections was mainly related to surface-water carbonate productivity changes, no cyclic modulation of productivity was observed in the oceanic profile. Therefore, dark layer formation in the open ocean was predominantly controlled by the cyclic establishment of anoxic bottom water conditions. Orbitally-forced interruptions in mixing on the shelf resulted in cyclic periods of stratification and oligotrophy in the surface waters, an expansion of oceanic species to the outer shelf, and a shelfward shift of pithonelloid-facies zones, which were probably related to shelfward directed oceanic ingressions.

Reconstructed glaciation limits in Eurasia (digitized from map Fig.1)

Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17000 calendar years ago. During the Late Weichselian (25 000-10000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.

Nd concentrations and isotopic composition in the western Mediterranean Sea

The concentration and isotopic composition of Nd in water and particles collected in the western Mediterranean Sea are studied by two complementary approaches. The first examines local vertical profiles and time series; the second considers the global Nd budget of the whole western Mediterranean Sea. These two approaches are used to quantify the Nd inputs and the dissolved/particulate exchange processes in the water column. Two profiles of Nd in seawater in the Ligurian Sea taken in May and October 1992 show an average epsilon-Nd(0) = -9.6 ± 0.5. Seawater from the Strait of Sicily, representative of the eastern waters flowing into the western basin, is more radiogenic [epsilon-Nd(0) = -7.7 ± 0.6]. Profiles of particulate matter collected in sediment traps in coastal (Gulf of Lions) and offshore (Ligurian Sea) environments are also shown. Particles are enriched in Nd and are more radiogenic near the coast than offshore. Measurements of Nd concentration and epsilon-Nd(0) of external sources to the western Mediterranean Sea compared with the literature data demonstrate that particulate flux of atmospheric Saharan origin are more rich ([Nd] = 38 ± 10 µg/g) and less radiogenic [epsilon-Nd(0) = -13.0 ± 1.0] than riverine particulate discharge ([Nd] = 21.5 ± 4.4 µg/g; epsilon-Nd(0) = -10.1 ± 0.5), allowing to trace Nd particulate inputs in the water column. Nd atmospheric flux appears to be the major source into the whole western basin, although lateral advection of riverine material is the prevailing process in the coastal environment. Offshore, the vertical propagation of an important Saharan dust event has been recorded for two months in sediment traps at 80, 200 and 1000 m. The evolution of the resulting negative epsilon-Nd(0) peak along depth and time shows that the particles reach 200 m on a time scale of one week. For the first time, the Nd budget in the western Mediterranean basin is constrained by both concentrations and isotopic compositions measured in particles and seawater. Surface budget requires a remobilization of 30 ± 20% of particulate Nd input. In deep water, dissolved Nd concentrations are balanced by a scavenging of 10 ± 20% of the sinking particulate flux. On the other hand, the deep isotopic compositions suggest an exchange between 30 ± 20% of the sinking particles and the deep waters. The hypothesis of a non-stationary regime for the surface waters in the Ligurian Sea is also considered.

Fractional abundance and indices for brGDGTs and crenarchaeol in dust samples, surface water samples and surface sediment samples

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input. Their abundance relative to marine-derived crenarchaeol, quantified in the BIT index, generally decreases offshore. However, in distal marine sediments, low relative amounts of brGDGTs can often still be observed. Sedimentary in situ production as well as dust input have been suggested as potential, though as yet not well constrained, sources. In this study brGDGT distributions in dust were examined and compared with those in distal marine sediments. Dust was sampled along the equatorial West African coast and brGDGTs were detected in most of the samples, albeit in low abundance. Their degree of methylation and cyclisation, expressed in the MBT' (methylation index of branched tetraethers) and DC (degree of cyclisation) indices, respectively, were comparable with those for African soils, their presumed source. Comparison of DC index values for brGDGTS in global soils, Congo deep-sea river fan sediments and dust with those of distal marine sediments clearly showed, however, that distal marine sediments had significantly higher values. This distinctive distribution is suggestive of sedimentary in situ production as a source of brGDGTs in marine sediments, rather than dust input. The presence of in situ produced brGDGTs in marine sediments means that caution should be exercised when applying the MBT'-CBT palaeothermometer to sediments with low BIT index values, i.e. < 0.1, based on our dataset.

Noble gases sampled from three cruises in the eastern tropical Atlantic

Oceanic upwelling velocities are too small to be measured directly. Deviations of the He-3/He-4 ratio in the mixed layer from solubility equilibrium provide an indirect means to infer vertical velocities at the base of the mixed layer. This method is applied to the Mauritanian upwelling region for data from three cruises in summer 2006 and winter 2007 and 2008. Diapycnal mixing coefficients are estimated from microstructure measurements, reaching from 10**-3 m**2/s over the shelf break to 10**-5 m**2/s in the open ocean. The resulting upwelling velocities in the onshore region (upto 50 km from the 50 m isobath) are of the order of 2 x 10**-5 m/s}, in agreement with Ekman theory. Further offshore, in some cases the vertical velocities inferred from the helium isotope disequilibrium exceed the values derived from the wind stress curl by one order of magnitude. The Mauritanian coastal area as part of the Canary Current upwelling system belongs to the most productive ocean regions in the world. Nutrient fluxes into the mixed layer (both advective and diffusive) are equivalent to a net community production of about 1 g C/d, and associated heat fluxes vary between 183 +/- 62 W/m**2 in summer and 97 +/- 25 W/m**2 in winter. Regarding the flux into the mixed layer, the contribution of diffusion and advection are of similar magnitude for both heat and nutrients. The upwelling, however, provides the supply of cold and nutrient rich water from below. The large offshore vertical velocities inferred from the helium method are associated with nutrient fluxes of the same order as for the onshore region, and may be responsible for observed patches of high productivity in that area. The offshore heat fluxes due to upwelling and diapycnal mixing are smaller than 70 W/m**2 for all cruises.

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.

Iron concentration and fluxes in the water column during POLARSTERN cruises in the Southern Ocean

In large parts of the Southern Ocean, primary production is limited due to shortage of iron (Fe). We measured vertical Fe profiles in the western Weddell Sea, Weddell-Scotia Confluence, and Antarctic Circumpolar Current (ACC), showing that Fe is derived from benthic Fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography. Our data together with literature data reveal an exponential decrease of dissolved Fe (DFe) concentrations with increasing distance from the continental shelves of the Antarctic Peninsula and the western Weddell Sea. This decrease can be observed 3500 km eastward of the Antarctic Peninsula area, downstream the ACC. We estimated DFe summer fluxes into the upper mixed layer of the Atlantic sector of the Southern Ocean and found that horizontal advection dominates DFe supply, representing 54 ± 15% of the total flux, with significant vertical advection second most important at 29 ± 13%. Horizontal and vertical diffusion are weak with 1 ± 2% and 1 ± 1%, respectively. The atmospheric contribution is insignificant close to the Antarctic continent but increases to 15 ± 10% in the remotest waters (>1500 km offshore) of the ACC. Translating Southern Ocean carbon fixation by primary producers into biogenic Fe fixation shows a twofold excess of new DFe input close to the Antarctic continent and a one-third shortage in the open ocean. Fe recycling, with an estimated 'fe' ratio of 0.59, is the likely pathway to balance new DFe supply and Fe fixation.

Elements and mineralogical compostions from different sediment cores off the southern China Sea

The mineralogy, major and trace elements, and neodymium and strontium isotopes of surface sediments in the South China Sea (SCS) are documented with the aim of investigating their applicability in provenance tracing. The results indicate that mineralogical compositions alone do not clearly identify the sources for the bulk sediments in the SCS. The Nd isotopic compositions of the SCS sediments show a clear zonal distribution. The most negative epsilon-Neodymium values were obtained for sediments from offshore South China (-13.0 to -10.7), while those from offshore Indochina are slightly more positive (-10.7 to -9.4). The Nd isotopic compositions of the sediments from offshore Borneo are even higher, with epsilon-Neodymium ranging from -8.8 to -7.0, and the sediments offshore from the southern Philippine Arc have the most positive epsilon-Neodymium values, from -3.7 to +5.3. This zonal distribution in epsilon-Neodymium is in good agreement with the Nd isotopic compositions of the sediments supplied by river systems that drain into the corresponding regions, indicating that Nd isotopic compositions are an adequate proxy for provenance tracing of SCS sediments. Sr isotopic compositions, in contrast, can only be used to identify the sediments from offshore South China and offshore from the southern Philippine Arc, as the 87Sr/86Sr ratios of sediments from other regions overlapped. Similar zonal distributions are also apparent in a La-Th-Sc discrimination diagram. Sediments fromthewestmargin of the SCS, such as those fromBeibuwan Bay, offshore fromHainan Island, offshore from Indochina, and from the Sunda Shelf plot in the same field, while those offshore from the northeastern SCS, offshore from Borneo, and offshore from the southern Philippine Arc plot in distinct fields. Thus, the La-Th-Sc discrimination diagram, coupledwith Nd isotopes, can be used to trace the provenance of SCS sediments. Using this method, we re-assessed the provenance changes of sediments at Ocean Drilling Program (ODP) Site 1148 since the late Oligocene. The results indicate that sediments deposited after 23.8 Ma (above 455 mcd: meters composite depth) were supplied mainly from the eastern South China Block, with a negligible contribution from the interior of the South China Block. Sediments deposited before 26 Ma (beneath 477 mcd) were supplied mainly from the North Palawan Continental Terrane, which may retain the geochemical characteristics of the materials covered on the late Mesozoic granitoids along the coastal South China. For that the North Palawan Continental Terrane is presently located within the southern Philippine Arc but was located close to ODP Site 1148 in the late Oligocene. The weathering products of volcanic material associated with the extension of the SCS ocean crust also contributed to these sediments. The rapid change in sediment source at 26-23.8 Ma probably resulted from a sudden cessation of sediment supply from the North Palawan Continental Terrane. Wesuggest that the North Palawan Continental Terrane drifted southwards alongwith the extension of the SCS ocean crust during that time, and when the basin was large enough, the supply of sediment from the south to ODP Site 1148 at the north slope may have ceased.

Stable isotopes, Mg/Ca ratios and sea surface temperatures on foraminifera from sediment cores off equatorial Peru during the last ~17kyr

The complex deglacial to Holocene oceanographic development in the Gulf of Guayaquil (Eastern Equatorial Pacific) is reconstructed for sea surface and subsurface ocean levels from (isotope) geochemical proxies based on marine sediment cores. At sea surface, southern sourced Cold Coastal Water and tropical Equatorial Surface Water/Tropical Surface Water are intimately related. In particular since ~10 ka, independent sea surface temperature proxies capturing different seasons emphasize the growing seasonal contrast in the Gulf of Guayaquil, which is in contrast to ocean areas further offshore. Cold Coastal Water became rapidly present in the Gulf of Guayaquil during the austral winter season in line with the strengthening of the Southeast Trades, while coastal upwelling off Peru gradually intensified and expanded northward in response to a seasonally changing atmospheric circulation pattern affecting the core locations intensively since 4 ka BP. Equatorial Surface Water, instead, was displaced and Tropical Surface Water moved northward together with the Equatorial Front. At subsurface, the presence of Equatorial Under Current-sourced Equatorial Subsurface Water was continuously growing, prominently since ~10-8 ka B.P. During Heinrich Stadial 1 and large parts of the Bølling/Allerød, and similarly during short Holocene time intervals at ~5.1-4 ka B.P. and ~1.5-0.5 ka B.P., the admixture of Equatorial Subsurface Water was reduced in response to both short-term weakening of Equatorial Under Current strength from the northwest and emplacement by tropical Equatorial Surface Water, considerably warming the uppermost ocean layers.

Pore pressure measurements on IODP Exp308 sites

Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML source) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.

Pollen analysis of surface sediments from the Gulf of Guinea and offshore NW-Africa

The areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes, whereas wind transport is much more important than river transport. Pollen distribution patterns of Pinus, Artemisia, Chenopodiaceae-Amaranthaceae, and Asteraceae Tubuliflorae trace atmospheric transport by the northeast trades. Pollen transport by the African Easterly Jet is reflected in the pollen distribution patterns of Chenopodiaceae-Amaranthaceae, Asteraceae Tubuliflorae, and Mitracarpus. Grass pollen distribution registers the latitudinal extension of Sahel, savannas and dry open forests. Marine pollen distribution patterns of Combretaceae-Melastomataceae, Alchornea, and Elaeis reflect the extension of wooded grasslands and transitional forests. Pollen from the Guinean-Congolian/Zambezian forest and from the Sudanian/Guinean vegetation zones mark the northernmost extension of the tropical rain forest. Rhizophora pollen in marine sediments traces the distribution of mangrove swamps. Only near the continent, pollen of Rhizophora, Mitracarpus, Chenopodiaceae-Amaranthaceae, and pollen from the Sudanian and Guinean vegetation zones are transported by the Upwelling Under Current and the Equatorial Under Current, where those currents act as bottom currents. The distribution of pollen in marine sediments, reflecting the position of major climatic zones (desert, dry tropics, humid tropics), can be used in tracing climatic changes in the past.

Age model and stable isotopes of sediment cores from north-central Chile and south-central Chile

Terrigenous sediment supply, marine transport, and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings. Sequence stratigraphic models predict coarse-grained sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves. To decipher the controls on Holocene highstand turbidite deposition, we analyzed 12 sediment cores from spatially discrete, coeval turbidite systems along the Chile margin (29° - 40°S) with changing climatic and geomorphic characteristics but uniform changes in sea level. Sediment cores from intraslope basins in north-central Chile (29° - 33°S) offshore a narrow to absent shelf record a shut-off of turbidite deposition during the Holocene due to postglacial aridification. In contrast, core sites in south-central Chile (36° - 40°S) offshore a wide shelf record frequent turbidite deposition during highstand conditions. Two core sites are linked to the Biobío river-canyon system and receive sediment directly from the river mouth. However, intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies. High sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control Holocene turbidite sedimentation and distribution. Shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment-mass balances.