Projected impacts of 21st century climate change on diapause in Calanus finmarchicus

Diapause plays a key role in the life cycle of high latitude zooplankton. During diapause animals avoid starving in winter by living in deep waters where metabolism is lower and met by lipid reserves. Global warming is therefore expected to shorten the maximum potential diapause duration by increasing metabolic rates and by reducing body size and lipid reserves. This will alter the phenology of zooplankton, impact higher trophic levels and disrupt biological carbon pumps. Here we project the impacts of climate change on the key North Atlantic copepod Calanus finmarchicus under IPCC RCP 8.5. Potential diapause duration is modelled in relation to body size and overwintering temperature. The projections show pronounced geographic variations. Potential diapause duration reduces by more than 30% in the Western Atlantic, whereas in the key overwintering centre of the Norwegian Sea it changes only marginally. Surface temperature rises, which reduce body size and lipid reserves, will have a similar impact to deep water changes on diapause in many regions. Because deep water warming lags that at the surface, animals in the Labrador Sea could offset warming impacts by diapausing in deeper waters. However, the ability to control diapause depth may be limited

Numerical simulation of unconstrained cyclotron resonant maser emission

When a mainly rectilinear electron beam is subject to significant magnetic compression, conservation of magnetic moment results in the formation of a horseshoe shaped velocity distribution. It has been shown that such a distribution is unstable to cyclotron emission and may be responsible for the generation of Auroral Kilometric Radiation (AKR) an intense rf emission sourced at high altitudes in the terrestrial auroral magnetosphere. PiC code simulations have been undertaken to investigate the dynamics of the cyclotron emission process in the absence of cavity boundaries with particular consideration of the spatial growth rate, spectral output and rf conversion efficiency. Computations reveal that a well-defined cyclotron emission process occurs albeit with a low spatial growth rate compared to waveguide bounded simulations. The rf output is near perpendicular to the electron beam with a slight backward-wave character reflected in the spectral output with a well defined peak at 2.68GHz, just below the relativistic electron cyclotron frequency. The corresponding rf conversion efficiency of 1.1% is comparable to waveguide bounded simulations and consistent with the predictions of kinetic theory that suggest efficient, spectrally well defined radiation emission can be obtained from an electron horseshoe distribution in the absence of radiation boundaries.Publisher PD

Numerical simulations of unbounded cyclotron-maser emissions

Numerical simulations have been conducted to study the spatial growth rate and emission topology of the cyclotron-maser instability responsible for stellar/planetary auroral magnetospheric radio emission and intense non-thermal radio emission in other astrophysical contexts. These simulations were carried out in an unconstrained geometry, so that the conditions existing within the source region of some natural electron cyclotron masers could be more closely modelled. The results have significant bearing on the radiation propagation and coupling characteristics within the source region of such non-thermal radio emissions

High-coherence electron and ion bunches from laser-cooled atoms

XXVIII ICPEACCold atom electron and ion sources produce electron bunches and ion beams by photoionisation of laser cooled atoms. They offer high coherence and the potential for high brightness, with applications including ultrafast electron diffractive imaging of dynamic processes at the nanoscale. Here we present our cold atom electron/ion source, with an electron temperature of less than 10 K and a transverse coherence length of 10 nm. We also discuss experiments investigating space-charge effects with ions and the production of ultra-fast electron bunches using a femto-second laser. In the latter experiment we show that it is possible to produce both cold and fast electron bunches with our source.A. J. McCulloch, D. V. Sheludko, C. T. Putkunz, S. D. Saliba, D. J. Thompson, R. W. Speirs, D. Murphy, J. Torrance, B. M. Sparkes, and R. E. Scholte

Microwave emission due to kinetic instabilities in an over-dense mirror-confined plasma

The kinetic instabilities of a microwave plasma confined in an open magnetic trap are relevant to understanding various types of radio emission in space plasma, for example, in the magnetospheres of the Earth and the planets, the Sun, and certain types of stars. The high efficiency of the kinetic wave generation mechanism is due to the low group velocity of plasma waves (in comparison with electromagnetic waves), which ensures they enjoy an extended interaction time with nonequilibrium particles resulting in a high integral gain. Emission from the plasma is observed due to various mechanisms for the transformation of plasma waves into electromagnetic waves, for example, as a result of scattering by thermal ions. In view of the universality of the physical mechanisms of radiation generation, essential aspects of natural systems can be reproduced in laboratory magnetic traps under controlled and reproducible conditions. Hitherto the excitation of plasma waves in open magnetic traps has been carried out with the use of electron beams. The technique reported here exploits a plasma generated by irradiating a mirror confined plasma using mm-waves from a gyrotron under electron-cyclotron resonance conditions, a technique also potentially of interest for technological applications. In such a discharge, a two-component plasma is created with a dense cold (background) fraction with an isotropic particle velocity distribution and a less dense high-energy fraction of nonequilibrium electrons with an anisotropic distribution function. In these experiments, bursts of powerful electromagnetic radiation at a frequency close to the upper hybrid resonance and to the second harmonic of the electron gyrofrequency were observed for the first time, accompanied by synchronous precipitation of fast electrons from the trap. The observed bursts were associated with the instability of plasma waves under conditions of a double plasma resonance, with subsequent transformation of the plasma waves into electromagnetic waves. This poster focuses on a theoretical and experimental study of wave generation in a dense magnetoactive plasma at the harmonics of the electron gyrofrequency. In the experiments at the IAP RAS, a detailed study of the fine structure of dynamic spectra using ultra-wideband oscilloscopes with a bandwidth of up to 59 GHz is reported. Theoretical and numerical analysis at relevant plasma parameters is underway at the University of Strathclyde. Comparison of experimental and theoretical data will lead to an understanding of the mechanisms of electromagnetic radiation generation in magnetic traps and the features of the radio emission spectra observed in natural conditions

Experiment and simulations of kinetic instabilities in mirror-confined ECR discharge plasma

Non-Maxwellian electron distribution functions give rise to a rich variety of kinetic instabilities, such as streaming instability, Weibel instability, and electrostatic and electromagnetic cyclotron instabilities. Electron ring-like distributions are ubiquitous in space plasmas and also occur in mirror-confined plasma where the loss-cone cuts a 'hole' in the distribution function. We report recent observations and simulations of instabilities in mirror-confined ECR discharge plasma [1], where excitation on harmonics and half-harmonics of the electron cyclotron frequency have been observed. The relevance to space plasma are also discussed where similar observations by satellites are common [2,3]. Theory and simulations show that electrostatic instabilities take place where two electron Bernstein modes merge [4]. Electromagnetic Vlasov simulations also show the coupling between electrostatic and electromagnetic electron Bernstein modes leading to instabilities near cyclotron harmonics

Ecosystem approach to harvesting in the Arctic : walking the tightrope between exploitation and conservation in the Barents Sea

Funidng: This study was supported by the Changing Arctic Ocean project MiMeMo (NE/R012679/1) jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF/03F0801A). Brierley was also supported by ArcticPRIZE (NE/P005721/1).Projecting the consequences of warming and sea-ice loss for Arctic marine food web and fisheries is challenging due to the intricate relationships between biology and ice. We used StrathE2EPolar, an end-to-end (microbes-to-megafauna) food web model incorporating ice-dependencies to simulate climate-fisheries interactions in the Barents Sea. The model was driven by output from the NEMO-MEDUSA earth system model, assuming RCP 8.5 atmospheric forcing. The Barents Sea was projected to be > 95% ice-free all year-round by the 2040s compared to > 50% in the 2010s, and approximately 2 °C warmer. Fisheries management reference points (FMSY and BMSY) for demersal fish (cod, haddock) were projected to increase by around 6%, indicating higher productivity. However, planktivorous fish (capelin, herring) reference points were projected to decrease by 15%, and upper trophic levels (birds, mammals) were strongly sensitive to planktivorous fish harvesting. The results indicate difficult trade-offs ahead, between harvesting and conservation of ecosystem structure and function.Publisher PDFPeer reviewe

How is climate change affecting marine life in the Arctic?

Rising temperature is melting the ice that covers the Arctic Ocean, allowing sunlight into waters that have been dark for thousands of years. Previously barren ice-covered regions are being transformed into productive seas. Here we explain how computer modelling can be used to predict how this transformation will affect the food web that connects plankton to fish and top-predators like whales and polar bears. Images of starving polar bears have become symbolic of the effects of warming climate. Melting of the sea-ice is expected to reduce the bears’ ability to hunt for seals. However, at the same time, the food web upon which they depend is becoming more productive, so it is not completely clear what the eventual outcome will be for the bears. Computer models help us to understand these systems and inform policy decisions on the management of newly available Arctic resources

Oestrogen receptor beta: how should we measure this?

British Journal of Cancer (2002) 87, 687–687. doi:10.1038/sj.bjc.6600534 www.bjcancer.co