Effects of iron stress on chromatic adaptation by natural phytoplankton communities in the Southern Ocean

Effects of iron stress on chromatic adaptation were studied in natural phytoplankton communities collected in the Pacific region of the Southern Ocean. Iron enrichment experiments (48 to 72 h) were performed, incubating plankton communities under white, green and blue light respectively, with and without addition of 2 nM Fe. Pigment ratios were affected by iron addition only to a minor extent. The pigment composition as dictated by the light conditions was similar for both the iron-enriched and the unamended bottles. Upon iron addition, phytoplankton auto-fluorescence, as estimated by flow cytometry, decreased markedly, indicating iron stress of the endemic phytoplankton community. It was concluded that iron did not control chromatic adaptation via the pigment composition, but exerted a clear effect on the efficiency of electron transfer

Signatures for short-range correlations in {16}O, observed in the reaction {16}O(e,e'pp){14}C.

The reaction O-16(e,e'pp)C-14 has been studied at a transferred four-momentum (omega,\q\) = (210 MeV, 300 MeV/c). The differential cross sections for the transitions to the ground state and the lowest excited states in C-14 were determined as a function of the momentum of the recoiling C-14 nucleus and the angle between the momentum of the proton emitted in the forward direction and the momentum transfer q. A comparison of the data to the results of calculations, performed with a microscopic model, shows clear signatures for short-range correlations in the O-16 ground state

Methods for biogeochemical studies of sea ice: the state of the art, caveats, and recommendations

Over the past two decades, with recognition that the ocean’s sea-ice cover is neither insensitive to climate change nor a barrier to light and matter, research in sea-ice biogeochemistry has accelerated significantly, bringing together a multi-disciplinary community from a variety of fields. This disciplinary diversity has contributed a wide range of methodological techniques and approaches to sea-ice studies, complicating comparisons of the results and the development of conceptual and numerical models to describe the important biogeochemical processes occurring in sea ice. Almost all chemical elements, compounds, and biogeochemical processes relevant to Earth system science are measured in sea ice, with published methods available for determining biomass, pigments, net community production, primary production, bacterial activity, macronutrients, numerous natural and anthropogenic organic compounds, trace elements, reactive and inert gases, sulfur species, the carbon dioxide system parameters, stable isotopes, and water-ice-atmosphere fluxes of gases, liquids, and solids. For most of these measurements, multiple sampling and processing techniques are available, but to date there has been little intercomparison or intercalibration between methods. In addition, researchers collect different types of ancillary data and document their samples differently, further confounding comparisons between studies. These problems are compounded by the heterogeneity of sea ice, in which even adjacent cores can have dramatically different biogeochemical compositions. We recommend that, in future investigations, researchers design their programs based on nested sampling patterns, collect a core suite of ancillary measurements, and employ a standard approach for sample identification and documentation. In addition, intercalibration exercises are most critically needed for measurements of biomass, primary production, nutrients, dissolved and particulate organic matter (including exopolymers), the CO2 system, air-ice gas fluxes, and aerosol production. We also encourage the development of in situ probes robust enough for long-term deployment in sea ice, particularly for biological parameters, the CO2 system, and other gases

Possible pathways between depression, emotional and external eating. A structural equation model

Contains fulltext : 76772.pdf (publisher's version ) (Closed access)Emotional and external eating appear to co-occur and both have been shown to correlate to neuroticism, especially depression. However, there is evidence suggesting that emotional and external eating are independent constructs. In this study we revisited the relation between depression, emotional, and external eating. Using structural equation modelling, we examined whether depression, emotional and external eating are directly related and also indirectly related through the intervening concepts alexithymia and impulsivity. Participants were 549 females concerned about their weight. They filled out instruments on emotional and external eating, depression, alexithymia, and impulse regulation. The relational structure between the model variables was explored for one half of the participants and this solution was checked using the other half. Our data showed a moderate relationship between emotional and external eating. Depression was positively and directly associated with emotional eating, but not with external eating. In addition, depression was indirectly related to emotional eating through both alexithymia and impulsivity. A significant relation was found between impulsivity and external eating. Results suggest potential mediating pathways between depression and emotional eating, while no relation appeared to exist between depression and external eating. Emotional and external eating would appear to be different constructs

Variation of particulate carbohydrate pools over time and depth in a diatom-dominated plankton community at the Antarctic Polar Front

Carbohydrate dynamics were studied in an algal community dominated by the diatom Fragilariopsis kerguelensis at the Antarctic Polar Front during austral autumn 1999. Water-extractable mono- and polysaccharide concentrations from the particulate fraction were measured at six depths in the upper 100 in at seven stations along a N-S transect (20degreesE, 48-50degreesS) during 2 consecutive days. In addition, field populations were incubated on deck for 18 h at four different light intensities. Polysaccharide concentrations varied between 2.7 and 13.6 mug/l, monosaccharide concentrations between 2.5 and 8.9 mug/l. Near the surface (0-60 in), a diet pattern was observed in the polysaccharide concentration when normalised to the chlorophyll a or the monosaccharide concentration. The deck incubations supported the hypothesis that this pattern resulted from the diurnal accumulation and nocturnal consumption of reserve glucan. More polysaccharides accumulated at high light intensities than at low light intensities, in accordance with the observed decrease in normalised polysaccharide concentration with depth. In addition, the lower concentrations at depth might be explained by consumption: polysaccharides that were accumulated during time spent near the surface were subsequently respired when cells were transported to deeper and dimmer water layers. The variation in carbohydrate pools over-time and depth described here must be considered of ecological relevance to phytoplankton in the Southern Ocean subjected to extended periods of darkness (hours to days) due to vertical mixing and advection