Holocene Labrador Sea planktonic foraminiferal oxygen isotopes and trace element data, and ice rafted debris percentage

Formation of Labrador Sea Water proper commenced about 7000 years ago during the Holocene interglacial. To test whether fresher surface water conditions may have inhibited Labrador Sea Water convection during the early Holocene we measured planktonic foraminiferal (Globigerina bulloides) oxygen isotopes (d18O) and Mg/Ca ratios at Orphan Knoll (cores HU91-045-093 and MD95-2024, 3488 m) in the Labrador Sea to reconstruct shallow subsurface summer conditions (temperature and seawater d18O). Lighter foraminiferal d18O values are recorded during the early Holocene between 11000 and 7000 years ago. Part of these lighter foraminiferal d18O values can be explained by increased calcification temperatures. Reconstructed seawater d18O values were, however, still on average 0.5 per mil lighter compared with those of recent times, confirming that fresher surface waters in the Labrador Sea were probably a limiting factor in Labrador Sea Water formation during the early Holocene.

Characteristics and aldehyde concentrations of diamond dust events near Barrow, Alaska

Diamond dust (DD) refers to tiny ice crystals that form frequently in the Polar troposphere under clear sky conditions. They provide surfaces for chemical reactions and scatter light. We have measured the specific surface area (SSA) of DD at Barrow in March-April 2009. We have also measured its chemical composition in mineral and organic ions, dissolved organic carbon (DOC), aldehydes, H2O2, and the absorption spectra of water-soluble chromophores. Mercury concentrations were also measured in spring 2006, when conditions were similar. The SSA of DD ranges from 79.9 to 223 m**2/kg . The calculated ice surface area in the atmosphere reaches 11000 (±70%) µm**2/cm**3, much higher than the aerosol surface area. However, the impact of DD on the downwelling and upwelling light fluxes in the UV and visible is negligible. The composition of DD is markedly different from that of snow on the surface. Its concentrations in mineral ions are much lower, and its overall composition is acidic. Its concentrations in aldehydes, DOC, H2O2 and mercury are much higher than in surface snows. Our interpretation is that DOC from the oceanic surface microlayer, coming from open leads in the ice off of Barrow, is taken up by DD. Active chemistry in the atmosphere takes place on DD crystal surfaces, explaining its high concentrations in aldehydes and mercury. After deposition, active photochemistry modifies DD composition, as seen from the modifications in its absorption spectra and aldehyde and H2O2 content. This probably leads to the emissions of reactive species to the atmosphere.

Meiobenthos at the Arctic Håkon Mosby Mud Volcano

Håkon Mosby Mud Volcano (HMMV, SW Barents Sea slope, 1280 m) is one of the numerous cold methane-venting seeps existing along the continental margins. Analyses of video-guided core samples revealed extreme differences in the diversity and density of the metazoan meiobenthic communities associated with the different sub-habitats (centre, microbial mats, Pogonophora field, outer rim) of this mud volcano. Diversity was lowest in the sulphidic, microbial mat sediments that supported the highest standing stock, with unusually high densities (11000 ind./10 cm**2) of 1 nematode species related to Geomonhystera disjuncta. Stable carbon isotope analyses revealed that this nematode species was thriving on chemosynthetically derived food sources in these sediments. Ovoviviparous reproduction has been identified as an important adaptation of parents securing the survival and development of their brood in this toxic environment. The proliferation of this single species in exclusive association with free-living, sulphide-oxidising bacteria (Beggiatoa) indicates that its dominance is strongly related to trophic specialisation, evidently uncommon among the meiofauna. This chemoautotrophic association was replaced by copepods in the bare, sulphide-free sediments of the volcano's centre, dominated by aerobic methane oxidation as the chemosynthetic process. Copepods and nauplii reached maximum densities and dominance in the volcano's centre (500 ind./10 cm**2). Their strongly depleted carbon isotope signatures indicated a trophic link with methane-derived carbon. This proliferation of only selected meiobenthic species supported by chemosynthetically derived carbon suggests that, in addition to the sediment geochemistry, the associated reduced meiobenthic diversity may equally be related to the trophic resource specificity in HMMV sub-habitats.