Geochemical studies of surface sediment samples off North-West Africa

One hundred and twenty-eight surface-sediment samples collected off North-West Africa were studied geochemically to detect the expressions of different meridional climate regimes and zonal productivity gradients in the surface sediments. This geochemical multi-tracer approach, coupled with additional information on the bulk carbonate and TOC contents makes it possible to characterise the sedimentological regime in detail. Typical terrigenous elements like Al, K and Fe mirror the importance of the humid (fluvial) influence in the north of the study area and the dominance of aeolian input in the south. Furthermore, the distributions of Ti and Fe in the surface sediments serve as tracers for the supply of eolian volcanic material from the Canary Islands. The spatial variability of the TOC contents in the surface sediments closely follows the ocean surface productivity patterns, whereas the CaCO3 contents are mainly controlled by dilution with terrigenous matter. The potential productivity proxy Ba is not a reliable tracer for productivity in this region, since it is mainly supplied by terrigenous input (coupled with aluminosilicates).

Magnetic properties, grain sizes, XRF Scanner Data of sediment core GeoB9307-3

Geochemical and mineralogical proxies for paleoenvironmental conditions have the underlying assumption that climate variations have an impact on terrestrial weathering conditions. Varying properties of terrigenous sediments deposited at sea are therefore often interpreted in terms of paleoenvironmental change. Also in gravity core GeoB9307-3 (18° 33.99' S, 37° 22.89' E), located off the Zambezi River, environmental changes during Heinrich Stadial 1 (HS 1) and the Younger Dryas (YD) are accompanied by changing properties of the terrigenous sediment fraction. Our study focuses on the relationship of variability in the hydrological system and changes in the magnetic properties, major element geochemistry and granulometry of the sediments. We propose that changes in bulk sedimentary properties concur with environmental change, although not as a direct response of climate driven pedogenic processes. Spatial varying rainfall intensities on a sub-basin scale modify sediment export from different parts of the Zambezi River basin. During humid phases, such as HS 1 and the YD, sediment was mainly exported from the coastal areas, while during more arid phases sediments mirror the hinterland soil and lithological properties and are likely derived from the northern Shire sub-basin. We propose that a de-coupling of sedimentological and organic signals with variable discharge and erosional activity can occur.

25 Years of Polarstern Hydrography (1982-2007)

Since her commissioning in 1982 RV Polarstern has been operating in the Arctic and Antarctic to carry out scientific research. Between November and March she usually sails to and around the waters of the Antarctic, while the northern summer months are spent in Arctic waters. But also during transits between Bremerhaven and South Africa or South America long-term observations have regularly been performed by using a.o. XBT (Expendable Bathythermograph), CTD (Conductivity, Temperature, Depth), and Thermosalinograph which are standard instruments to carry out hydrographic measurements and are part of the standard instrumentation on board Polarstern. This report presents XBT and CTD profiles as well as sea surface temperature and salinity data recorded with Thermosalinograph during Polarstern cruises. In the framework of physical oceanographic studies the measurements were performed as part of international projects (e.g. like WOCE) or to support multidisciplinary studies.

Multi-sensor global compilation of mid-Holocene sea surface temperatures, based on Mg/Ca and alkenone palaeothermometry and reconstructions obtained using planktonic foraminifera and organic-walled dinoflagellate cyst

We present and examine a multi-sensor global compilation of mid-Holocene (MH) sea surface temperatures (SST), based on Mg/Ca and alkenone palaeothermometry and reconstructions obtained using planktonic foraminifera and organic-walled dinoflagellate cyst census counts. We assess the uncertainties originating from using different methodologies and evaluate the potential of MH SST reconstructions as a benchmark for climate-model simulations. The comparison between different analytical approaches (time frame, baseline climate) shows the choice of time window for the MH has a negligible effect on the reconstructed SST pattern, but the choice of baseline climate affects both the magnitude and spatial pattern of the reconstructed SSTs. Comparison of the SST reconstructions made using different sensors shows significant discrepancies at a regional scale, with uncertainties often exceeding the reconstructed SST anomaly. Apparent patterns in SST may largely be a reflection of the use of different sensors in different regions. Overall, the uncertainties associated with the SST reconstructions are generally larger than the MH anomalies. Thus, the SST data currently available cannot serve as a target for benchmarking model simulations.

Geo-referenced photo-mosaics of the Menez Gwen Hydrothermal Vent (Mid-Atlantic Ridge)

The Menez Gwen hydrothermal vents, located on the flanks of a small young volcanic structure in the axial valley of the Menez Gwen seamount, are the shallowest known vent systems on the Mid-Atlantic Ridge that host chemosynthetic communities. Although visited several times by research cruises, very few images have been published of the active sites, and their spatial dimensions and morphologies remain difficult to comprehend. We visited the vents on the eastern flank of the small Menez Gwen volcano during cruises with RV Poseidon (POS402, 2010) and RV Meteor (M82/3, 2010), and used new bathymetry and imagery data to provide first detailed information on the extents, surface morphologies, spatial patterns of the hydrothermal discharge and the distribution of dominant megafauna of five active sites. The investigated sites were mostly covered by soft sediments and abundant white precipitates, and bordered by basaltic pillows. The hydrothermally-influenced areas of the sites ranged from 59 to 200 m**2. Geo-referenced photomosaics and video data revealed that the symbiotic mussel Bathymodiolus azoricus was the dominant species and present at all sites. Using literature data on average body sizes and biomasses of Menez Gwen B. azoricus, we estimated that the B. azoricus populations inhabiting the eastern flank sites of the small volcano range between 28,640 and 50,120 individuals with a total biomass of 50 to 380 kg wet weight. Based on modeled rates of chemical consumption by the symbionts, the annual methane and sulfide consumption by B. azoricus could reach 1760 mol CH4 yr**-1 and 11,060 mol H2S yr**-1. We propose that the chemical consumption by B. azoricus over at the Menez Gwen sites is low compared to the natural release of methane and sulfide via venting fluids.

Element concentration and GDGT fractional abundances of sediment core GeoB3910-2

In dieser Arbeit wurde das Zeitintervall zwischen 20 und 10 ka vor heute einschließlich des Heinrichevent 1 und der Younger Dryas am Kern GeoB 3910-2 neu untersucht. An organischen Parametern, basierend auf der Verteilung von bakteriellen GDGTs, und Elementkonzentrationen wurde eine Rekonstruktion der klimatischen Bedingungen und Veränderungen im Hinterland von NO Brasilien durchgeführt. Es zeigt sich, dass sich die durchschnittliche Landtemperatur gleich der Oberflächenwassertemperatur verhält und im Gegensatz zu den Phasen von H6 bis H2 dem antarktischen Erwärmungstrend ab 17 ka vor heute folgt. Weiterhin konnte gezeigt werden, dass durch die südwärts Verlagerung der ITCZ während H1 und der YD die Niederschläge in NO Brasilen intensiviert wurden, was eine Ausbreitung der Flüsse und Änderung der Erosionsgebiete zur Folge hatte.