Search

Gradient- and curl-type or E- and B-type polarizations have been routinely analyzed to study the physics contributing to the cosmic microwave background polarization and galactic foregrounds. They characterize the parity-even and parity-odd properties of the underlying physical mechanisms, such as, for example, hydromagnetic turbulence in the case of dust polarization. Here, we study spectral correlation functions characterizing the parity-even and parity-odd parts of linear polarization for homogeneous and inhomogeneous turbulence to show that only the inhomogeneous helical case can give rise to a parity-odd polarization signal. We also study nonhelical turbulence and suggest that a strong non-vanishing (here negative) skewness of the E polarization is responsible for an enhanced ratio of the EE to the BB (quadratic) correlation in both the helical and nonhelical cases. This could explain the enhanced EE/BB ratio observed recently for dust polarization. We close with a preliminary assessment of using the linear polarization of the Sun to characterize its helical turbulence without being subjected to the pi ambiguity that magnetic inversion techniques have to address., QC 20190206

We develop a two-scale formalism to determine global magnetic helicity spectra in systems where the local magnetic helicity has opposite signs on both sides of the equator, giving rise to cancellation with conventional methods. We verify this approach using first a synthetic one-dimensional magnetic field and then two-dimensional slices from a three dimensional a effect-type dynamo-generated magnetic field, with forced turbulence of opposite helicity above and below the midplane of the domain. We then apply this formalism to global solar synoptic vector magnetograms. To improve the statistics, data from three consecutive Carrington rotations (2161-2163) are combined into a single map. We find that the spectral magnetic helicity representative of the northern hemisphere is negative at all wavenumbers and peaks at approximate to 0.06 Mm(-1) (scales around 100 Mm). There is no evidence of bihelical magnetic fields that are found in three-dimensional turbulence simulations of helicity-driven a effect-type dynamos.

This review examines interregional linkages and gives an overview perspective on marine ecosystem functioning in the north-eastern Atlantic. It is based on three of the 'systems' considered by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OCEANS was established in 2004 under the European Framework VI funding programme to promote integration of marine ecological research within Europe), the Arctic and Nordic Seas, North Atlantic shelf seas and North Atlantic. The three systems share common open boundaries and the transport of water, heat, nutrients and particulates across these boundaries modifies local processes. Consistent with the EUR-OCEANS concept of 'end-to-end' analyses of marine food webs, the review takes an integrated approach linking ocean physics, lower trophic levels and working up the food web to top predators such as marine mammals. We begin with an overview of the regions focusing on the major physical patterns and their implications for the microbial community, phytoplankton, zooplankton, fish and top predators. Human-induced links between the regional systems are then considered and finally possible changes in the regional linkages over the next century are discussed. Because of the scale of potential impacts of climate change, this issue is considered in a separate section. The review demonstrates that the functioning of the ecosystems in each of the regions cannot be considered in isolation and the role of the atmosphere and ocean currents in linking the North Atlantic Ocean, North Atlantic shelf seas and the Arctic and Nordic Seas must be taken into account. Studying the North Atlantic and associated shelf seas as an integrated 'basin-scale' system will be a key challenge for the early twenty-first century. This requires a multinational approach that should lead to improved ecosystem-based approaches to conservation of natural resources, the maintenance of biodiversity, and a better understanding of the key role of the nor

ver the last 40 years, underwater stereo-image measurement systems have employed stereo-cameras and paired single cameras in a variety of configurations. Both still and movie cameras have been used, based on film, video tube and digital sensors. Whilst measurement configurations of all varieties have been used, the transect has been, and still is, the predominant sampling technique. These basic approaches to photogrammetric geometry and sampling techniques are still in use today; however, the image quality has advanced considerably and the use of fully digital video systems and digital still cameras is now commonplace. The wider use of precalibrated, self-contained stereo-image systems, plus the substantial improvements in image resolution and image fidelity, is enabling new possibilities for accurate and reliable measurement of 3-dimensional lengths, surfaces and volumes. These advances are leading to significant improvements in the effectiveness of the management of marine ecosystems for conservation and the estimation of biomass for aquaculture. This work reviews the status of underwater stereo-image measurement and illustrates applications of stereo-image measurement in marine biology and ecology.

Octopuses of the family Octopodidae adopt two major life-history strategies. The first is the production of relatively few, large eggs resulting in well-developed hatchlings that resemble the adults and rapidly adopt the benthic habit of their parents. The second strategy is production of numerous small eggs that hatch into planktonic, free-swimming hatchlings with few suckers, simple chromatophores and transparent musculature. These distinctive planktonic stages are termed paralarvae and differ from conspecific adults in their morphology, physiology, ecology and behaviour. This study aims to review available knowledge on this subject. In benthic octopuses with planktonic stages, spawning characteristics and duration of planktonic life seem to play an important role in their dispersal capacities. Duration of the hatching period of a single egg mass can range from 2 days to 11 wk, while duration of the planktonic stage can range from 3 wk to half a year, depending on the species and temperature. Thus these paralarvae possess considerable potential for dispersal. In some species, individuals reach relatively large sizes while living as part of the micronekton of oceanic, epipelagic waters. Such forms appear to delay settlement for an unknown period that is suspected to be longer than for paralarvae in more coastal, neritic waters. During the planktonic period, paralarval octopuses feed on crustaceans as their primary prey. In addition to the protein, critical to the protein-based metabolism of octopuses (and all cephalopods), the lipid and copper contents of the prey also appear important in maintaining normal growth. Littoral and oceanic fishes are their main predators and defence behaviours may involve fast swimming speeds, use of ink decoys, dive responses and camouflage. Sensory systems of planktonic stages include photo-, mechano- and chemoreceptors controlled by a highly evolved nervous system that follows the general pattern described for adult cephalopods. On

Mid-ocean ridges are vast features of all oceans but their fauna and ecological significance remain poorly understood. Ridge studies in recent decades were understandably biased in favour of the newly discovered chemosynthetic ecosystems. Investigations of photosynthesis-based systems and communities associated with ridges were scattered and few despite their much larger scale and significance for ocean productivity patterns and biogeography and for the management of human activities on the high seas. This knowledge gap was recognised by the Census of Marine Life (CoML) programme and led to the initiation of a dedicated field project on non-chemosynthetic systems and communities of a mid-ocean ridge. The present collection of articles highlights results from the project ‘Patterns and Processes of the Ecosystems of the northern Mid-Atlantic’ (MAR-ECO), the CoML field project that aims to explore the diversity and distribution patterns of photosynthesis-based communities of mid-ocean ridges by a range of classical and new technologies and methods. In 2003–2005, comprehensive investigations were conducted on pelagic and epibenthic macro- and megafauna of the Mid-Atlantic Ridge between Iceland and the Azores. Several research vessels participated in the first field phase of the project, but the majority of the results were from a 2-month international expedition on the Norwegian vessels R.V. G.O. Sars and the chartered fishing vessel M.S. Loran in 2004. This introduction explains the background and goals of MAR-ECO, summarizes the strategies and sampling efforts, and briefly introduces future plans as the project enters a second field phase in 2007–2009.