NW Adriatic Sea variability in relation to chlorophyll-<I>a</I> dynamics in the last 20 years (1986?2005)

International audienceThis paper presents a long-term time series (1986?2005) of hydrological and biogeochemical data, both published and unpublished. Data were collected in the north-western area of the Adriatic Sea, at two stations that are considered hydrodynamically and trophically different. The time series have been statistically and graphically investigated on a monthly scale in order to find not only possible chlorophyll-a trends over time, but also links between the concentrations of chlorophyll-a and the variability in the environment, as well as trophic differences between the two areas. Basically, in both cases the statistical test results show no significant trends in either the average chlorophyll-a values or in dispersion of the data, in contrast with significant trends in temperature and salinity. The two areas have similar hydrological features, yet they present significant differences in the amount of nutrient inputs: these are in fact higher at the coastal site, which is characterized by a prevalence of surface blooms, while they are lower at the offshore station, which is mainly affected by intermediate blooms. Nonetheless, throughout the whole water column, chlorophyll-a concentrations are only slightly different. Both areas are affected by riverine discharge, though in the first case considered chlorophyll-a concentrations are also driven strongly by the seasonal cycle. Finally, the results show that the two stations are not trophically different, although some controlling factors, such as zooplankton grazing in one case and light attenuation in the other, may regulate the growth of phytoplankton

NW Adriatic Sea biogeochemical variability in the last 20 years (1986–2005)

International audience; This paper presents a long-term time series (1986?2005) of hydrological and biogeochemical data, both published and unpublished. Data were collected in the north-western area of the Adriatic Sea, at two stations that are considered hydrodynamically and trophically different. The time series have been statistically and graphically analysed on a monthly scale in order to study the annual climatologies, links between the concentrations of chlorophyll-a and the variability in the environment, trophic differences between the two areas and chlorophyll-a trends over time. Basically, the two areas have similar hydrological features, yet they present significant differences in the amount of nutrient inputs: these are in fact higher at the coastal site, which is characterized by a prevalence of surface blooms, while they are lower at the offshore station, which is mainly affected by blooms at intermediate depths. Nonetheless, throughout the whole water column, chlorophyll-a concentrations are only slightly different. Both areas are affected by riverine discharge, though chlorophyll-a concentrations are also driven strongly by the seasonal cycle at the station closer to the coast. Results show that the two stations are not trophically different, although some controlling factors, such as zooplankton grazing in one case and light attenuation in the other, may further regulate the growth of phytoplankton. In both cases no significant trends are detected in either the average chlorophyll-a values or in dispersion of the data, in contrast with significant trends in temperature and salinity

NW Adriatic Sea biogeochemical variability in the last 20 years (1986–2005)

This paper presents a long-term time series (1986–2005) of hydrological and biogeochemical data, both published and unpublished. Data were collected in the north-western area of the Adriatic Sea, at two stations that are considered hydrodynamically and trophically different. The time series have been statistically and graphically analysed on a monthly scale in order to study the annual climatologies, links between the concentrations of chlorophyll-a and the variability in the environment, trophic differences between the two areas and chlorophyll-a trends over time. Basically, the two areas have similar hydrological features, yet they present significant differences in the amount of nutrient inputs: these are in fact higher at the coastal site, which is characterized by a prevalence of surface blooms, while they are lower at the offshore station, which is mainly affected by blooms at intermediate depths. Nonetheless, throughout the whole water column, chlorophyll-a concentrations are only slightly different. Both areas are affected by riverine discharge, though chlorophyll-a concentrations are also driven strongly by the seasonal cycle at the station closer to the coast. Results show that the two stations are not trophically different, although some controlling factors, such as zooplankton grazing in one case and light attenuation in the other, may further regulate the growth of phytoplankton. In both cases no significant trends are detected in either the average chlorophyll-a values or in dispersion of the data, in contrast with significant trends in temperature and salinity

Spin Excitations in a Fermi Gas of Atoms

We have experimentally investigated a spin excitation in a quantum degenerate Fermi gas of atoms. In the hydrodynamic regime the damping time of the collective excitation is used to probe the quantum behavior of the gas. At temperatures below the Fermi temperature we measure up to a factor of 2 reduction in the excitation damping time. In addition we observe a strong excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure

Quality evaluation of olive oil by statistical analysis of multicomponent stable isotope dilution assay data of aroma active compounds

An instrumental method for the evaluation of olive oil quality was developed. Twenty-one relevant aroma active compounds were quantified in 95 olive oil samples of different quality by headspace solid phase microextraction (HS-SPME) and dynamic headspace coupled to GC-MS. On the basis of these stable isotope dilution assay results, statistical evaluation by partial least-squares discriminant analysis (PLS-DA) was performed. Important variables were the odor activity values of ethyl isobutanoate, ethyl 2-methylbutanoate, 3-methylbutanol, butyric acid, E,E-2,4-decadienal, hexanoic acid, guaiacol, 2-phenylethanol, and the sum of the odor activity values of Z-3-hexenal, E-2-hexenal, Z-3-hexenyl acetate, and Z-3-hexenol. Classification performed with these variables predicted 88% of the olive oils? quality correctly. Additionally, the aroma compounds, which are characteristic for some off-flavors, were dissolved in refined plant oil. Sensory evaluation of these models demonstrated that the off-flavors rancid, fusty, and vinegary could be successfully simulated by a limited number of odorants

Random-phase approximation study of collective excitations in the Bose-Fermi mixed condensate of alkali-metal gases

We perform Random Phase Approximation (RPA) study of collective excitations in the bose-fermi mixed degenerate gas of Alkali-metal atoms at T=0. The calculation is done by diagonalization in a model space composed of particle-hole type excitations from the ground state, the latter being obtained from the coupled Gross-Pitaevskii and Thomas-Fermi equations. We investigate strength distributions for different combinations of bose and fermi multipole ($L$) operators with $L=0,1,2,3$. Transition densities and dynamical structure factors are calculated for collective excitations. Comparison with the sum rule prediction for the collective frequency is given. Time dependent behavior of the system after an external impulse is studied.Comment: 28 pages, 13 figures, submitted to Phys. Rev.

Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica

Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175° E–74° S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990–2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces the observed magnitude of the biogenic fluxes, especially those found in the bottom sediment trap, but the peaks are markedly delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that the timing of the observed fluxes depends first and foremost on the timing of surface production and on a combination of size-distribution and quality of the autochtonous biogenic material. It is hypothesized that the bottom sediment trap collects material originated from the rapid sinking of freshly-produced particles and also from the previous year's production period

Fermi-Bose quantum degenerate ^40 K - ^87 Rb mixture with attractive interaction

We report on the achievement of simultaneous quantum degeneracy in a mixed gas of fermionic ^40 K and bosonic ^87 Rb. Potassium is cooled to 0.3 times the Fermi temperature by means of an efficient thermalization with evaporatively cooled rubidium. Direct measurement of the collisional cross-section confirms a large interspecies attraction. This interaction is shown to affect the expansion of the Bose-Einstein condensate released form the magnetic trap, where it is immersed in the Fermi sea.Comment: 5 pages, 4 figures, replaced one figure plus some change

Laser probing of Cooper-paired trapped atoms

We consider a gas of trapped Cooper-paired fermionic atoms which are manipulated by laser light. The laser induces a transition from an internal state with large negative scattering length (superfluid) to one with weaker interactions (normal gas). We show that the process can be used to detect the presence of the superconducting order parameter. Also, we propose a direct way of measuring the size of the gap in the trap. The efficiency and feasibility of this probing method is investigated in detail in different physical situations.Comment: 9 pages, 8 figure

Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica

Abstract Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175^{o}E - 74^{o}S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990-2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces quite well the magnitude of the biogenic fluxes, expecially those observed in the bottom sediment trap, but the peaks are delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that observed fluxes could be explained by the size-distribution and quality of the locally-produced biogenic material. It is hypothesized that the bottom sediment trap collects material originated from rapid sinking of particles and also from previous years production periods, likely modulated by advective and aggregation mechanisms which are still not resolved by the model