86 research outputs found
Numerical modelling of physical processes governing larval transport in the southern North Sea
A three-dimensional hydrodynamic model (GETM) was coupled with a particle
tracking routine (GITM) to study the inter-annual variability in transport
paths of particles in the North Sea and English Channel. For validation, a
comparison with observed drifter trajectories is also presented here. This
research investigated to what extent variability in the hydrodynamic
conditions alone (reflecting passive particle transport) contributed to
inter-annual variability in the transport of eggs and larvae. In this
idealised study, no a priori selection of specific spawning grounds or
periods was made and no active behaviour (vertical migration) or mortality
was included. In this study, egg and larval development towards coastal
nursery areas was based solely on sea water temperature, while settlement
areas were defined by a threshold water depth. Results showed strong
inter-annual variability in drift direction and distance, caused by a
combination of wind speed and direction. Strong inter-annual variability was
observed both in absolute amount of settlement in several coastal areas, and
in the relative importance of the different areas. The effects of wind and
temperature variability are minor for settlement along the western shores of
the North Sea and in the English Channel, but have a very significant impact
on settlement along the eastern shores of the North Sea. Years with strong
south-westerly winds across the Dover Straight resulted in higher settlement
figures along its eastern shores of the North Sea (standard deviation
37% of the mean annual settlement value). Settlement in the western
Dutch Wadden Sea did not only show inter-annual variability, but patterns
were also variable within each year and revealed seasonal changes in the
origin of particles: during winter, stronger currents along with colder
temperatures generally result in particles originating from further away
Behavioral Traits are Affected by Selective Breeding for Increased Wheel-Running Behavior in Mice
Voluntary physical activity may be related to personality traits. Here, we investigated these relations in two mouse lines selectively bred for high voluntary wheel-running behavior and in one non-selected control line. Selection lines were more explorative and âinformation gatheringâ in the open-field test, either with increased upright positions or horizontal locomotion toward the middle ring. Furthermore, one of the selection lines had an increased risk-taking behavior relative to the control line in approaching a novel object placed in the center of the open field. However, anxiety behavior was increased in selection lines during the plus-maze test. Maze learning was not statistically different among lines, but routine behavior was increased in both selection lines when the maze exit after 2 days of testing was displaced. Specifically, in the displaced maze, selected mice traveled more frequently to the old, habituated exit, bypassing the new exit attached to their home cage. Although the generality of the results would need to be confirmed in future studies including all eight lines in the selection experiment, the increased routine and exploratory behavior (at least in the lines used in the present study) may be adaptive to sustain high activity levels
Modification of turbulent dissipation rates by a deep Southern Ocean eddy
The impact of a mesoscale eddy on the magnitude and spatial distribution of diapycnal ocean mixing is investigated using a set of hydrographic and microstructure measurements collected in the Southern Ocean. These data sampled a baroclinic, mid-depth eddy formed during the disintegration of a deep boundary current. Turbulent dissipation is suppressed within the eddy, but is elevated by up to an order of magnitude along the upper and lower eddy boundaries. A ray-tracing approximation is employed asa heuristic device to elucidate how the internal wave field evolves in the ambient velocity and stratification conditions accompanying the eddy. These calculations are consistent with the observations, suggesting reflection of internal wave energy from the eddy center and enhanced breaking through critical layer processes along the eddy boundaries. These results have important implications for understanding where and how internal wave energy is dissipated in the presence of energetic deep geostrophic flows
Quantitative permeability imaging of plant tissues
A method for mapping tissue permeability based on time-dependent diffusion measurements is presented. A pulsed field gradient sequence to measure the diffusion encoding time dependence of the diffusion coefficients based on the detection of stimulated spin echoes to enable long diffusion times is combined with a turbo spin echo sequence for fast NMR imaging (MRI). A fitting function is suggested to describe the time dependence of the apparent diffusion constant in porous (bio-)materials, even if the time range of the apparent diffusion coefficient is limited due to relaxation of the magnetization. The method is demonstrated by characterizing anisotropic cell dimensions and permeability on a subpixel level of different tissues of a carrot (Daucus carota) taproot in the radial and axial directions
Sea-level change in the Dutch Wadden Sea
Rising sea levels due to climate change can have severe consequences for coastal populations and ecosystems all around the world. Understanding and projecting sea-level rise is especially important for low-lying countries such as the Netherlands. It is of specific interest for vulnerable ecological and morphodynamic regions, such as the Wadden Sea UNESCO World Heritage region.
Here we provide an overview of sea-level projections for the 21st century for the Wadden Sea region and a condensed review of the scientific data, understanding and uncertainties underpinning the projections. The sea-level projections are formulated in the framework of the geological history of the Wadden Sea region and are based on the regional sea-level projections published in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5). These IPCC AR5 projections are compared against updates derived from more recent literature and evaluated for the Wadden Sea region. The projections are further put into perspective by including interannual variability based on long-term tide-gauge records from observing stations at Den Helder and Delfzijl.
We consider three climate scenarios, following the Representative Concentration Pathways (RCPs), as defined in IPCC AR5: the RCP2.6 scenario assumes that greenhouse gas (GHG) emissions decline after 2020; the RCP4.5 scenario assumes that GHG emissions peak at 2040 and decline thereafter; and the RCP8.5 scenario represents a continued rise of GHG emissions throughout the 21st century. For RCP8.5, we also evaluate several scenarios from recent literature where the mass loss in Antarctica accelerates at rates exceeding those presented in IPCC AR5.
For the Dutch Wadden Sea, the IPCC AR5-based projected sea-level rise is 0.07±0.06m for the RCP4.5 scenario for the period 2018â30 (uncertainties representing 5â95%), with the RCP2.6 and RCP8.5 scenarios projecting 0.01m less and more, respectively. The projected rates of sea-level change in 2030 range between 2.6mmaâ1 for the 5th percentile of the RCP2.6 scenario to 9.1mmaâ1 for the 95th percentile of the RCP8.5 scenario. For the period 2018â50, the differences between the scenarios increase, with projected changes of 0.16±0.12m for RCP2.6, 0.19±0.11m for RCP4.5 and 0.23±0.12m for RCP8.5. The accompanying rates of change range between 2.3 and 12.4mmaâ1 in 2050. The differences between the scenarios amplify for the 2018â2100 period, with projected total changes of 0.41±0.25m for RCP2.6, 0.52±0.27m for RCP4.5 and 0.76±0.36m for RCP8.5. The projections for the RCP8.5 scenario are larger than the high-end projections presented in the 2008 Delta Commission Report (0.74m for 1990â2100) when the differences in time period are considered. The sea-level change rates range from 2.2 to 18.3mmaâ1 for the year 2100.
We also assess the effect of accelerated ice mass loss on the sea-level projections under the RCP8.5 scenario, as recent literature suggests that there may be a larger contribution from Antarctica than presented in IPCC AR5 (potentially exceeding 1m in 2100). Changes in episodic extreme events, such as storm surges, and periodic (tidal) contributions on (sub-)daily timescales, have not been included in these sea-level projections. However, the potential impacts of these processes on sea-level change rates have been assessed in the report
Modelling mammalian energetics: the heterothermy problem
Global climate change is expected to have strong effects on the worldâs flora and fauna. As a result, there has been a recent increase in the number of meta-analyses and mechanistic models that attempt to predict potential responses of mammals to changing climates. Many models that seek to explain the effects of environmental temperatures on mammalian energetics and survival assume a constant body temperature. However, despite generally being regarded as strict homeotherms, mammals demonstrate a large degree of daily variability in body temperature, as well as the ability to reduce metabolic costs either by entering torpor, or by increasing body temperatures at high ambient temperatures. Often, changes in body temperature variability are unpredictable, and happen in response to immediate changes in resource abundance or temperature. In this review we provide an overview of variability and unpredictability found in body temperatures of extant mammals, identify potential blind spots in the current literature, and discuss options for incorporating variability into predictive mechanistic models
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