Mega-epibenthos at Bouvet Island (South Atlantic)

Mega-epibenthic diversity was analysed using a seabed photography at four stations off Bouvet Island and one station at the Spiess Seamount in the South Atlantic. Surprisingly, the intermediate-scale diversity within the area of investigation was not lower compared to that on the Patagonian shelf and only moderately lower than that on the Antarctic continental shelf. This result is incompatible with Mac Arthur and Wilson's Island Biogeography Theory describing species richness as a function of immigration of new species into an area and its extension. The relatively high species number and the very small extension of the Bouvet shelf compared to the much larger continental shelves of the other two areas can be explained by long-range dispersal of marine benthic animals in the Antarctic Circumpolar Current and high habitat heterogeneity. The observed uncoupling of intermediate-scale from large-scale background species diversity on the Antarctic shelf raises the question whether in these benthic systems an upper capacity limit for diversity exists.

Occurrence of Inoceramus in the South Atlantic and oxygen isotopic paleotemperatures in DSDP Hole 75-530A

Inoceramus occurs in every DSDP hole that penetrated Cretaceous sediments in the South Atlantic Ocean, and specimen occurrence has been mapped in detail for each core. Oxygen and carbon isotope measurements were completed on 18 Inoceramus specimens from Hole 530A. Textural evidence of diagenesis is accompanied by depletion in 18O. Paleotemperature results were obtained from 11 well-preserved specimens. Bottom water temperatures in the Angola Basin decreased from 23°C during the Coniacian to 13°C near the end of the Campanian.

Zn/Sr record of the Last Interglacial Transition in South Atlantic Ocean sediments

We examined the zinc content of diatom frustules as an indicator of past changes in surface seawater Zn2+ concentration. Zn/Si data of samples from three cores located in the South Atlantic sector of the Southern Ocean spanning the last interglacial-glacial transition are presented. Changes in the Zn/Si record are linked to changes in the surface water Zn2+ concentration. The source of variation in Zn2+ concentration appears to be via changes in deep water upwelling and circulation. We rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the Zn/Si record. Likewise, the Zn/Si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects. The Zn/Si results presented do not support the zinc hypothesis. There is no link between the uptake of CO2 by phytoplankton, as inferred from the d13C record, and the Zn/Si record.

Sample locations, stratigraphic information and listing of carbon and oxygen isotope data of the measured planktonic foraminifera of surface sediments in the western South Atlantic Ocean (Table 1)

We explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the Brazil-Malvinas Confluence (BMC) in the Argentine Basin. For this purpose, we measured the oxygen and carbon isotopic compositions of Globigerinoides ruber (pink and white varieties measured separately), Globigerinoides trilobus, Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides (left- and right-coiling forms measured separately) from a latitudinal transect of 56 surface sediment samples from the continental slope off Brazil, Uruguay and Argentina between 20 and 48°S. Lowest oxygen isotopes values were found in G. ruber (pink), followed by G. ruber (white) and G. trilobus reflecting the highly stratified near surface water conditions north of the BMC. Globigerina bulloides was present mainly south of the BMC and records subsurface conditions supporting earlier plankton tow studies. Globorotalia inflata and G. truncatulinoides (left and right) were both available over the whole transect and calcify in the depth level with the steepest temperature change across the BMC. Accordingly, the delta18O of these species depict a sharp gradient of 2? at the confluence with remarkably stable values north and south of the BMC. Our data show that the oxygen isotopic composition of G. inflata and G. truncatulinoides (left and right) are the most reliable indicators for the present position of the BMC and can therefore be used to define the past migration of the front if appropriate cores are available.

Magnetic susceptibility dataset from the early Givetian to early Frasnian in the La Thure section

Recent advances in radiometric dating result in significant improvements in the geological timescale and provide better insight into the timing of various processes and evolutions within the Earth's system. However, no radiometric ages are contained within the Givetian. Consequently, the absolute ages of the Givetian Stage boundaries, as well as the stage's duration, remain poorly constrained. As an alternative, the analysis of sedimentary cycles allows for the estimation of the duration of this stage. We examined the high-resolution magnetic susceptibility signals of four Givetian outcrops in the Givet area for a possible astronomical imprint, to fully understand the rates of evolutionary and environmental change. All four sections are firmly correlated and wavelet analyses of the magnetic susceptibility signals reveal the imprint of astronomical eccentricity forcing. The highly stable 405 kyr cycles constrain the duration of the Givetian Stage at 4.35±0.45 Myr, which is in good agreement with the International Chronostratigraphic Chart (5.0 Myr). The studied sections also exhibit an imprint of obliquity, suggesting a climatic teleconnection between low and high latitudes. The corresponding microfacies curves demonstrate similar astronomical imprint, and thereby indicate that the observed 10**5 year-scale cyclicity is the result of climatic and environmental change.