Description: A new profiling bottom lander (Profiluren) mounted with microelectrodes can measure oxygen profiles through the undisturbed sediment-water interface with 25-50 µm spatial resolution. The high spatial resolution of the in situ profiles reveal the thickness of the diffusive boundary layer (DBL) and allow calculations of: 1) the diffusive oxygen flux through the DBL, 2) the limitation of mass transfer between sediment and water due to the DBL and, 3) the oxygen consumption in discrete layers of the mm thick aerobic zone of marine sediments. The lander is thus an excellent tool for in situ analysis of oxygen dynamics at the sediment-water interface. Here we demonstrate two in situ oxygen profiles from a Danish coastal sediment at 15 m water depth, and discuss the impact of high resolution oxygen measurements.

Description: The aims of the Aegean Hydrothermal Fluxes and Biological Production project were to estimate the fluxes of fluids, chemicals, heat and bacteria from hydrothermal vents, establish the controls on venting dynamics, measure the productivity in the region of the vents and establish the effect of the vents on biodiversity of both prokaryotes and eukaryotes. This paper presents an initial synthesis of the project results. Research was done both by land-based SCUBA diving and from several vessels at a number of active sites in the near-shore coastal regions of Milos and Kos, with some additional studies at Methana, Lesbos and Santorini. Vent water composition showed very large variations. This was due to the mixing, of hydrothermal reservoir fluids, vapour condensate and seawater altered by interactions of fluid-sediment-bacteria in different proportions, in the gasohydrothermal vents. The composition ranged from nearly sea water with only slightly reduced pH, to higher or lower salinity fluids with a pH as low as 3 and with large enrichments in heavy and trace metals. Phase separation was a common feature at these shallow vents. The dry gas phase was mainly C02, but with significant amounts of H2S, CH4 and H2. These fluids commonly passed through soft sediments before venting from the seafloor and induced a convection cell of pore-water entrainment from deeper sediment layers into the water column with a consequent ‘re-charge’ down-flow of seawater into the sediment around the vent outlets. Such complex conditions may well explain the high biodiversity of Bacteria, Archaea and epifaunal species surrounding the vents. As many as 44 % of the archaeal lineages detected were found to represent novel phyla. Epifaunal diversity was particularly high with over 200 species recorded at the shallower Milos vents. These vents may form a ‘steppingstone’ for warmer water species to colonise the surrounding areas when water temperatures permit.

Description: We review and evaluate the design and operation of twenty-seven known autonomous benthic chamber and profiling lander instruments. We have made a detailed comparison of the different existing lander designs and discuss the relative strengths and weaknesses of each. Every aspect of a lander deployment, from preparation and launch to recovery and sample treatment is presented and compared. It is our intention that this publication will make it easier for future lander builders to choose a design suitable for their needs and to avoid unnecessary mistakes.

Description: A cryogenic achromatic half-wave plate (HWP) for submillimetre astronomical polarimetry has been designed, manufactured, tested and deployed in the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). The design is based on the five-slab Pancharatnam recipe and it works in the wavelength range 200–600 μm, making it the broadest-band HWP built to date at (sub)millimetre wavelengths. The frequency behaviour of the HWP has been fully characterized at room and cryogenic temperatures with incoherent radiation from a polarizing Fourier transform spectrometer. We develop a novel empirical model, complementary to the physical and analytical ones available in the literature, that allows us to recover the HWP Mueller matrix and phase shift as a function of frequency and extrapolated to 4 K. We show that most of the HWP non-idealities can be modelled by quantifying one wavelength-dependent parameter, the position of the HWP equivalent axes, which is then readily implemented in a map-making algorithm. We derive this parameter for a range of spectral signatures of input astronomical sources relevant to BLASTPol, and provide a benchmark example of how our method can yield improved accuracy on measurements of the polarization angle on the sky at submillimetre wavelengths.