29 research outputs found
Neutrino oscillation studies with IceCube-DeepCore
AbstractIceCube, a gigaton-scale neutrino detector located at the South Pole, was primarily designed to search for astrophysical neutrinos with energies of PeV and higher. This goal has been achieved with the detection of the highest energy neutrinos to date. At the other end of the energy spectrum, the DeepCore extension lowers the energy threshold of the detector to approximately 10 GeV and opens the door for oscillation studies using atmospheric neutrinos. An analysis of the disappearance of these neutrinos has been completed, with the results produced being complementary with dedicated oscillation experiments. Following a review of the detector principle and performance, the method used to make these calculations, as well as the results, is detailed. Finally, the future prospects of IceCube-DeepCore and the next generation of neutrino experiments at the South Pole (IceCube-Gen2, specifically the PINGU sub-detector) are briefly discussed
Water-table height and microtopography control biogeochemical cycling in an Arctic coastal tundra ecosystem
Drained thaw lake basins (DTLB's) are the dominant land form of the Arctic
Coastal Plain in northern Alaska. The presence of continuous permafrost
prevents drainage and so water tables generally remain close to the soil
surface, creating saturated, suboxic soil conditions. However, ice wedge
polygons produce microtopographic variation in these landscapes, with raised
areas such as polygon rims creating more oxic microenvironments. The peat
soils in this ecosystem store large amounts of organic carbon which is
vulnerable to loss as arctic regions continue to rapidly warm, and so there
is great motivation to understand the controls over microbial activity in
these complex landscapes. Here we report the effects of experimental
flooding, along with seasonal and spatial variation in soil chemistry and
microbial activity in a DTLB. The flooding treatment generally mirrored the
effects of natural landscape variation in water-table height due to
microtopography. The flooded portion of the basin had lower dissolved
oxygen, lower oxidation-reduction potential (ORP) and higher pH, as did
lower elevation areas throughout the entire basin. Similarly, soil pore
water concentrations of organic carbon and aromatic compounds were higher in
flooded and low elevation areas. Dissolved ferric iron (Fe(III))
concentrations were higher in low elevation areas and responded to the
flooding treatment in low areas, only. The high concentrations of soluble
Fe(III) in soil pore water were explained by the presence of siderophores,
which were much more concentrated in low elevation areas. All the
aforementioned variables were correlated, showing that Fe(III) is
solubilized in response to anoxic conditions. Dissolved carbon dioxide
(CO2) and methane (CH4) concentrations were higher in low
elevation areas, but showed only subtle and/or seasonally dependent effects
of flooding. In anaerobic laboratory incubations, more CH4 was produced
by soils from low and flooded areas, whereas anaerobic CO2 production
only responded to flooding in high elevation areas. Seasonal changes in the
oxidation state of solid phase Fe minerals showed that net Fe reduction
occurred, especially in topographically low areas. The effects of Fe
reduction were also seen in the topographic patterns of pH, as protons were
consumed where this process was prevalent. This suite of results can all be
attributed to the effect of water table on oxygen availability: flooded
conditions promote anoxia, stimulating dissolution and reduction of Fe(III),
and to some extent, methanogenesis. However, two lines of evidence indicated
the inhibition of methanogenesis by alternative e- acceptors such as Fe(III)
and humic substances: (1) ratios of CO2:CH4 evolved from anaerobic
soil incubations and dissolved in soil pore water were high; (2) CH4
concentrations were negatively correlated with the oxidation state of the
soluble Fe pool in both topographically high and low areas. A second set of
results could be explained by increased soil temperature in the flooding
treatment, which presumably arose from the increased thermal conductivity of
the soil surface: higher N mineralization rates and dissolved P
concentrations were observed in flooded areas. Overall, these results could
have implications for C and nutrient cycling in high Arctic areas where
warming and flooding are likely consequences of climate change
Photosynthesis on individual leaves of sugar beet (Beta vulgaris) during the ontogeny at variable water regimes
It is well known that the extent of yield reduction depends not only on the severity of water stress but also on the stage of plant development. Assessing photosynthetic response of individual leaves to water deficit during the ontogeny may, therefore, offer a clue to better understand the whole plant behaviour. This research aimed at investigating the influence of early and late water stress on net photosynthesis (Pn), carbon-isotope discrimination and other related traits on individual leaves during ontogeny. Sugar beet plants were grown in rain-sheltered soil columns of relevant volume (300 L), subdivided into well-watered (WW); early (S1) and late (S2) stress. In general, water stress significantly reduced leaf lifespan and Pn. Relieving the stress at about one-third and two thirds of potential leaf life substantially restored Pn at the levels of WW. Stressing a previously WW leaf brought about a comparatively heavier loss than stressing a leaf since the beginning. As for leaves at different phenological times, the early leaves had higher initial photosynthetic peaks but steeper falls during their lives. An insight into the relationships between Pn and substomatal CO2 concentration (Ci) shows that in mature leaves the photosynthetic
restoration following stress relief did not entail a full recovery of the electron transport rate, the parameter most severely affected by the stress. The partial reversibility of the effects of water deficiency, associated to the anticipated leaf senescence and to the natural slow-down of net assimilation during leaf life, may be seen as a key factor in predicting to what extent the plant can tolerate drought and the damages caused by water stress