Physical oceanography from the northwestern Weddell Sea

We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of the three austral winters 1989, 1997, and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data from the shallow shelf off the tip of the Antarctic Peninsula, spanning a period of 17 yr, shows a salinity decrease of 0.09 for the whole water column, which has a residence time of <1 yr. We interpret this freshening as being caused by a combination of reduced salt input due to a southward sea ice retreat and higher precipitation during the late 20th century on the western Weddell Sea continental shelf. However, less salinification might also result from a delicate interplay between enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves and increased Larsen C ice loss.

Relative abundance of prokaryotes in sediments of the Håkon Mosby mud volcano (Z1-Z3, all habitats)

CARD-FISH was performed as previously described in Ruff et al., (2013; doi:10.1371/journal.pone.0072627) with the following modifications. 4-6 µl of 25-fold diluted sediment were used for filtration. Archaeal cell walls were permeabilized with 0.1M HCl for 2 min to detect ANME-3 cells, or Proteinase K solution (15 µg ml-1 (Merck, Darmstadt, Germany) in 0.05 M EDTA (pH 8), 0.1 M Tris-HCl (pH 8), 0.5 M NaCl) for 2-4 min at room temperature for all other archaea. Bacterial cell walls were permeabilized with lysozyme solution (1000kU/ml) for 60 min at 37°. Cells were stained with DAPI (1µg/ml), embedded in mounting medium and counted in 40-60 independent microscopic fields using an Axiophot II epifluorescence microscope (Carl Zeiss, Jena, Germany).

CFC, and noble gas measurements during POLARSTERN cruise ANT-XXIX/3

During the austral summer expedition PS81, ANT-XXIX/3 with the German research ice breaker Polarstern in 2013, research was carried out to investigate the role of environmental factors on the distribution of benthic communities and marine mammal and krill densities around the northern tip of the Antarctic Peninsula. For these studies collated in this special issue and studies in this area, we present a collection of environmental parameters with probable influence on the marine ecosystems around the Antarctic Peninsula.

(Table 1) Upper Carboniferous spores abundances from ODP Holes 172-1062B, 172-1063A and 172-1063B

Color variations were interpreted in paleoceanographic terms for the late Pliocene-Pleistocene sediments recovered by ODP Leg 172 on deep-sea drifts at Blake-Bahama Outer Ridge and northeastern Bermuda Rise. The color-derived parameters used in interpretation included predicted carbonate content, terrigenous fluxes, and hematite content. Abundance of Upper Carboniferous spores indicates that the hematite is probably derived from the Permo-Carboniferous red beds of the Canadian Maritimes. In the last 800 kyr sedimentation pattern changes on the Blake-Bahama Outer Ridge were determined by the sediment delivery to the deep basin as well as circulation changes. Sediment delivery increased during glacials (especially during the last 500 kyr and particularly since Stage 6). A fundamental change in the thermohaline circulation occurred at about 500 ka corresponding to the end of the Mid-Pleistocene Transition period at the onset of the predominant 100-kyr climate cyclicity. Sedimentation related to WBUC had intensified at that time and had become more focused at depths below 3000 m. Changes in hematite content and sedimentation rate show a pulse of sediment via the St. Lawrence outlet at the Pliocene-Pleistocene boundary suggesting that a likely change in the hydrography/physiography of the Laurentide Ice Sheet could have been involved in the climatic and ocean circulation changes at that time.

(Table 1) Color, Fe-C-S chemistry and carbonate content from ODP Sites 172-1062 and 172-1063

Reflectance spectra collected during ODP Leg 172 were used in concert with solid phase iron chemistry, carbonate content, and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments. Factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color. On the western North Atlantic drifts, sediment color is the result of primary mineralogy as well as diagenetic changes. Sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and Fe2+/Fe3+ changes in clay minerals. Hematite, most likely derived from the Permo-Carboniferous red beds of the Canadian Maritimes, is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components. Various intensities for diagenesis result from changes in organic carbon content, sedimentation rates, and H2S production via anaerobic methane oxidation. Iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and/or increased reactive iron flux in glacials.