Neodymium isotopes in benthic foraminifera from the South Atlantic

Records of the past neodymium (Nd) isotope composition of the deep ocean can resolve ambiguities in the interpretation of other tracers. We present the first Nd isotope data for sedimentary benthic foraminifera. Comparison of the epsilon-Nd of core-top foraminifera from a depth transect on the Cape Basin side of the Walvis Ridge to published seawater data, and to the modern dissolved SiO2- epsilon-Nd trend of the deep Atlantic, suggests that benthic foraminifera represent a reliable archive of the deep water Nd isotope composition. Neodymium isotope values of benthic foraminifera from ODP Site 1264A (Angola Basin side of the Walvis Ridge) from the last 8 Ma agree with Fe-Mn oxide coatings from the same samples and are also broadly consistent with existing fish teeth data for the deep South Atlantic, yielding confidence in the preservation of the marine Nd isotope signal in all these archives. The marine origin of the Nd in the coatings is confirmed by their marine Sr isotope values. These important results allow application of the technique to down-core samples. The new epsilon-Nd datasets, along with ancillary Cd/Ca and Nd/Ca ratios from the same foraminiferal samples, are interpreted in the context of debates on the Neogene history of North Atlantic Deep Water (NADW) export to the South Atlantic. In general, the epsilon-Nd and delta13C records are closely correlated over the past 4.5 Ma. The Nd isotope data suggest strong NADW export from 8 to 5 Ma, consistent with one interpretation of published delta13C gradients. Where the epsilon-Nd record differs from the nutrient-based records, changes in the pre-formed delta13C or Cd/Ca of southern-derived deep water might account for the difference. Maximum NADW-export for the entire record is suggested by all proxies at 3.5-4 Ma. Chemical conditions from 3 to 1 Ma are totally different, showing, on average, the lowest NADW export of the record. Modern-day values again imply NADW export that is about as strong as at any stage over the past 8 Ma.

Stable isotope composition of Holocene benthic foraminifers from the Eastern Mediterranean Sea

Temporal and regional changes in paleoproductivity and paleoceanography in the eastern Mediterranean Sea during the past 12 kyr were reconstructed on the basis of the stable oxygen and carbon isotope composition of the epibenthic Planulina ariminensis and the shallow endobenthic Uvigerina mediterranea from three sediment cores of the Aegean Sea and Levantine Basin. The Younger Dryas is characterized by high d18O values, indicating enhanced salinities and low temperatures of deep water masses at all investigated sites. With the onset of the Holocene, d18O records show a continuous decrease towards the onset of sapropel S1 formation, mainly caused by a freshening and warming of surface waters at deep water formation sites. In the middle and late Holocene, the similarity of d18O values from the southern Aegean Sea and Levantine Basin suggests the influence of isotopically identical deep water masses. By contrast, slightly higher d18O values are observed the northern Aegean Sea, which probably point to lower temperatures of North Aegean deep waters. The epifaunal d13C records reveal clear changes in sources and residence times of eastern Mediterranean deep waters associated with period of S1 formation. Available data for the early and late phase of sapropel S1 formation and for the interruption around 8.2 kyr display drops by 0.5 and 1.5 per mil, indicating the slow-down of deep water circulation and enhanced riverine input of isotopically light dissolved inorganic carbon from terrestrial sources into the eastern Mediterranean Sea. The decrease in epifaunal d13C signals is particularly expressed in the southern Aegean Sea and Levantine Basin, while it is less pronounced in the northern Aegean Sea. This points to a strong reduction in deep water exchange rates in the southern areas, but the persistence of local deep water formation in the northern Aegean Sea. The d13C values of U. mediterranea records reveal temporal and regional differences in paleoproductivity during the past 12 kyr, with rather eutrophic and mesotrophic conditions in the North Aegean Sea and southeast Levantine Basin, respectively, while the South Aegean Sea is characterized by rather oligotrophic conditions. After S1 formation, increasing d13C values reflect a progressive decrease in surface water productivity in the eastern Mediterranean Sea during the middle and late Holocene. In the northern Aegean Sea, this time interval is marked by repetitive changes in organic matter fluxes documented by significant fluctuations in the d13C signal of U. mediterranea on millennial- to multi-centennial time scales. These fluctuations can be linked to short-term changes in river runoff driven by northern hemisphere climatic variability.

Benthic megafaunal composition at the Arctic deep-sea observatory HAUSGARTEN

The Long-Term Ecological Research (LTER) observatory HAUSGARTEN, in the eastern Fram Strait, provides us the valuable ability to study the composition of benthic megafaunal communities through the analysis of seafloor photographs. This, in combination with extensive sampling campaigns, which have yielded a unique data set on faunal, bacterial, biogeochemical and geological properties, as well as on hydrography and sedimentation patterns, allows us to address the question of why variations in megafaunal community structure and species distribution exist within regional (60-110 km) and local (<4 km) scales. Here, we present first results from the latitudinal HAUSGARTEN gradient, consisting of three different stations (N3, HG-IV, S3) between 78°30'N and 79°45'N (2351 - 2788 m depth), obtained via the analysis of images acquired by a towed camera (OFOS - Ocean Floor Observation System) in 2011. We assess variability in megafaunal densities, species composition and diversity as well as biotic and biogenic habitat features, which may cause the patterns observed. While there were significant regional-scale differences in megafaunal composition and densities between the stations (N3 = 26.74 ± 0.63; HG-IV = 11.21 ± 0.25; S3 = 18.34 ± 0.39 individuals/m**2), significant local differences were only found at HG-IV. Regional-scale variations may be due to the significant differences in ice coverage at each station as well as the different quantities of protein available, whereas local-scale differences at HG-IV may be a result of variation in bottom topography or factors not yet identified.