Слобожанщина: літературний вимір

To determine diurnal variations in the physical and biological state of Lake Garda in early spring, high-resolution measurements were made of the vertical distribution of temperature and fluorescence in the upper 100 meters during 5–7 March 2014. In this paper, the results of these measurements are presented and a preliminary analysis that focuses on the connection between the vertical mixing coefficient K_T and the chlorophyll-a (chl-a) concentration is given. From these first direct measurements of turbulence-related quantities in Lake Garda, it is found that mixed-layer values of K_Tdecrease, while surface chl-a concentrations increase, over the day. Variations in K_Tcan be connected to the changes in the surface wind stress, while variations in chl-a are negatively correlated with the amplitude of K_T. In addition, satellite observations of the surface chl-a concentration are analysed to test their use for the calibration of the fluorescence measurements and also for their potential utility in remotely determining vertical mixing in the upper layers of the lake

Examining leptogenesis with lepton flavor violation and the dark matter abundance

Within a supersymmetric (SUSY) type-I seesaw framework with flavor-blind universal boundary conditions, we study the consequences of requiring that the observed baryon asymmetry of the Universe be explained by either thermal or non-thermal leptogenesis. In the former case, we find that the parameter space is very constrained. In the bulk and stop-coannihilation regions of mSUGRA parameter space (that are consistent with the measured dark matter abundance), lepton flavor-violating (LFV) processes are accessible at MEG and future experiments. However, the very high reheat temperature of the Universe needed after inflation (of about 10^{12} GeV) leads to a severe gravitino problem, which disfavors either thermal leptogenesis or neutralino dark matter. Non-thermal leptogenesis in the preheating phase from SUSY flat directions relaxes the gravitino problem by lowering the required reheat temperature. The baryon asymmetry can then be explained while preserving neutralino dark matter, and for the bulk or stop-coannihilation regions LFV processes should be observed in current or future experiments.Comment: 20 pages, 5 figures, 1 tabl

Supersymmetric Leptogenesis and the Gravitino Bound

Supersymmetric thermal leptogenesis with a hierarchical right-handed neutrino mass spectrum requires the mass of the lightest right-handed neutrino to be heavier than about 10^9 GeV. This is in conflict with the upper bound on the reheating temperature which is found by imposing that the gravitinos generated during the reheating stage after inflation do not jeopardize successful nucleosynthesis. In this paper we show that a solution to this tension is actually already incorporated in the framework, because of the presence of flat directions in the supersymmetric scalar potential. Massive right-handed neutrinos are efficiently produced non-thermally and the observed baryon asymmetry can be explained even for a reheating temperature respecting the gravitino bound if two conditions are satisfied: the initial value of the flat direction must be close to Planckian values and the phase-dependent terms in the flat direction potential are either vanishing or sufficiently small.Comment: 9 pages. References added, version for Physics Letters

Estimation of Upper Ocean Vertical Mixing from Surface Ocean Colour Observations

The growth of marine phytoplankton is tightly connected to the strength of upper ocean vertical mixing and the depth of the mixed layer. The vertical mixing supplies nutrients from deeper ocean water to the ocean surface. Meanwhile, the mixing also moves phytoplankton cells in and out of the sunlit surface layer. Strong mixing and a deep mixed layer therefore lead to a fast nutrient supply while phytoplankton growth is likely to be light-limited. Weaker mixing and a shallow mixed layer loosen the light- limitation while the nutrient supply is reduced. Thanks to the chlorophyll-a (Chl a) pigments in the phytoplankton cells, changes in the phytoplankton concentration can be remotely tracked with satellite imagery. In this thesis the potentials of using ocean surface Chl a observations to estimate upper ocean vertical mixing are examined for the Northern Atlantic. The central tool in this thesis is a one-dimensional nutrient-phytoplankton (NP) model. To guarantee that the model represents the characteristic growth of the Northern Atlantic, biological model parameters are calibrated to in situ observations of vertical Chl a and nutrient profiles. A sensitivity analysis shows that the surface Chl a concentration is indeed very sensitive not only to the strength of the vertical mixing but also its vertical shape. It is thereby shown that the calibrated NP model is capable to build a bridge between surface Chl a concentrations and vertical mixing. Next, the NP model is coupled to the k − ε turbulence model of the General Ocean Turbulence Model (GOTM) framework. The k − ε model is a common choice to simulate upper ocean turbulent processes. Yet, a comparison of in situ and satellite observations with modelling results shows that the turbulence model overestimates the vertical mixing. As a consequence, modelled surface Chl a concentrations increase too late and too strongly compared to satellite observations. To improve the model results, the turbulence parameters of the k − ε model need to be calibrated. Usually these parameters are calibrated to laboratory and field observations. Since such observations are sparse, the novel approach in this thesis is to use surface Chl a concentrations for the calibration of the turbulence parameters. This novel calibration method is applied in two ways. First, identical twin experiments are set up to examine the robustness of the method. Second, the method is applied to satellite Chl a observations. Applying the calibration method to satellite Chl a observations leads to a model calibration that allows for an earlier and shorter intensification of the modelled surface Chl a. This surface signal very much resembles the early spring blooms common for the subtropical region and is also found in satellite Chl a observations. In comparison to the initial model results, the vertical mixing during winter is reduced by the new parameterisation, which also compares better to observations. It is therefore shown, to our knowledge for the first time, that surface Chl a observations can be used to calibrate parameters in a turbulence model and thereby to estimate upper ocean vertical mixing

Vertical mixing derived from surface chlorophyll-a concentrations of the North Atlantic ocean.

Vertical mixing is thought to play an essential role in phytoplankton blooms, yet measurements of mixing properties are very sparse. This paper presents a methodology to estimate profiles of the upper-ocean vertical mixing from satellite color observations, using a coupled turbulence-phytoplankton model and data assimilation-based calibration techniques. The method is tested at a location in the eastern North Atlantic for which an integrated set of observations (vertical mixing, phytoplankton, nutrients) is available. Results of identical twin experiments show that the method is very robust and achieves accurate turbulence model parameter calibrations even with noisy or sparsely sampled observations. The application of surface chlorophyll-a (Chl a) concentration to MODIS Aqua satellite observations leads two independent cases (data for the years 2009 and 2011) to a calibration of the model parameterization that produces weaker winter mixing compared to the standard configuration. As a consequence of the weaker mixing, the timing and intensity of increased surface Chl a satellite observations in spring and summer was reproduced by the model. Moreover, the weaker mixing resembles the in situ observations of vertical mixing better than the stronger mixing based on the standard configuration. This shows that the new calibration indeed improves the performance of the turbulence model

Sensitivity of phytoplankton distributions to vertical mixing along a North Atlantic transect

Using in situ data of upper ocean vertical mixing along a transect in the North Atlantic and a one-dimensional phytoplankton growth model, we study the sensitivity of the surface phytoplankton concentration to vertical mixing distributions. The study is divided into two parts. In the first part, the model is calibrated to the observations. The optical model parameters are determined from measurements of the light attenuation. The biological parameters are calibrated to three different reference stations with observed vertical profiles of the chlorophyll a (Chl a) concentration and the nutrient concentration. In the second part, the sensitivity of the three model calibrations to the vertical mixing is studied. Therefore measured vertical mixing profiles are applied to the model. These mixing profiles are based on the measurements along the transect and are treated as a set of possible mixing situations of the North Atlantic. Results show that shifts in vertical mixing are able to induce a transition from an upper chlorophyll maximum to a deep one and vice versa. Furthermore, a clear correlation between the surface phytoplankton concentration and the mixing induced nutrient flux is found for nutrient-limited cases. This may open up the possibility to extract characteristics of vertical mixing from satellite ocean colour data using data-assimilation methods

Документальнi публiкацiї з iсторiї Пiвнiчного Лiвобережжя на сторiнках «Черниговских губернских ведомостей» (дореформений перiод)

Antarctic coastal sea ice often grows in water that has been supercooled by interaction with an ice shelf. In these situations, ice crystals can form at depth, rise and deposit under the sea-ice cover to form a porous layer that eventually consolidates near the base of the existing sea ice. The least consolidated portion is called the sub-ice platelet layer. Congelation growth eventually causes the sub- ice platelet layer to become frozen into the sea-ice cover as incorporated platelet ice. In this study, we simulate these processes in three dimensions using Voronoi dynamics to govern crystal growth kinetics. Platelet deposition, in situ growth and incorporation into the sea-ice cover are integrated into the model. Heat and mass transfer are controlled by diffusion. We extract and compare spatial–temporal distributions of porosity, salinity, temperature and crystallographic c-axes with observations from McMurdo Sound, Antarctica. The model captures the crystallographic structure of incorporated platelet ice as well as the topology of the sub-ice platelet layer. The solid fraction, which has previously been poorly constrained, is simulated to be ~0.22, in good agreement with an earlier estimate of 0.25 ± 0.06. This property of the sub-ice platelet layer is important for biological processes, and for the freeboard–thickness relationship around Antarctica

Diurnal variation of turbulence-related quantities in Lake Garda

To determine diurnal variations in the physical and biological state of Lake Garda in early spring, high-resolution measurements were made of the vertical distribution of temperature and fluorescence in the upper 100 meters during 5–7 March 2014. In this paper, the results of these measurements are presented and a preliminary analysis that focuses on the connection between the vertical mixing coefficient KT and the chlorophyll-a (chl-a) concentration is given. From these first direct measurements of turbulence-related quantities in Lake Garda, it is found that mixed-layer values of KT decrease, while surface chl-a concentrations increase, over the day. Variations in KT can be connected to the changes in the surface wind stress, while variations in chl-a are negatively correlated with the amplitude of KT. In addition, satellite observations of the surface chl-a concentration are analysed to test their use for the calibration of the fluorescence measurements and also for their potential utility in remotely determining vertical mixing in the upper layers of the lak

Phytoplankton community structure in relation to vertical stratification along a north-south gradient in the Northeast Atlantic Ocean

Climate change is affecting the hydrodynamics of the world’s oceans. How these changes will influence the productivity, distribution and abundance of phytoplankton communities is an urgent research question. Here we provide a unique high-resolution mesoscale description of the phytoplankton community composi- tion in relation to vertical mixing conditions and other key physicochemical parameters along a meridional section of the Northeast Atlantic Ocean. Phytoplankton, assessed by a combination of flow cytometry and pigment fingerprinting (HPLC-CHEMTAX), and physicochemical data were collected from the top 250 m water column during the spring of 2011 and summer of 2009. Multivariate analysis identified water column stratification (based on 100 m depth-integrated Brunt–Va€isa€l€a frequency N2) as one of the key drivers for the distribution and separation of different phytoplankton taxa and size classes. Our results demonstrate that increased stratification (1) broadened the geographic range of Prochlorococcus as oligotrophic areas expanded northward, (2) increased the contribution of picoeukaryotic phytoplankton to total autotrophic organic car- bon (< 20 lm), and (3) decreased the abundances of diatoms and cryptophytes. We discuss the implications of our findings for the classification of phytoplankton functional types in biogeochemical and ecological ocean models. As phytoplankton taxonomic composition and size affects productivity, biogeochemical cycling, ocean carbon storage and marine food web dynamics, the results provide essential information for models aimed at predicting future states of the ocean