Search results for "Deep chlorophyll maximum"
showing 10 items of 20 documents
Ten Years of Paleoceanographic Studies at ODP Site 963 (Central Mediterranean Sea)
2014
The geographical location, the shape and the circulation pattern makes the Mediterranean Sea an ideal laboratory to study the interplay between different climatic systems, abrupt climate changes and the response of marine ecosystems. The Ocean Drilling Program Site 963 was drilled in the Northwestern part of the Sicily Channel, the sill that divides the western from the eastern Mediterranean Sea. Numerous papers have been published on Site 963 sediments in the last decade, investigating Mediterranean paleoceanographic themes. Here we offer a synthetic framework of these investigations carried out by sub-centennial resolution. We present the whole sequence of suborbital climatic oscillations…
Spatio-temporal behaviour of five picophytoplankton populations in Tyrrhe- nian Sea: Model and data
2014
Recent works presented detailed analyses of spatio-temporal dynamics in marine ecosystems, reproducing real vertical distributions of phytoplankton biomass. These study however do not take into account the changes in environmental variables. On the contrary, seasonal variations can influence considerably the primary production, i.e. phytoplankton biomass, in marine ecosystems, determining significative consequences in the whole food chain, in particular fish species, whose growth is mainly explained by seasonal changes in the chlorophyll concentration, a marker of phytoplankton species. Here we present a one-dimensional reaction-diffusion-taxis model to describe the spatio-temporal dynamics…
Reaction-diffusion-taxis model for spatio-temporal dynamics of five picophytoplankton populations
2014
Recently new models were devised to study spatio-temporal dynamics of phytoplankton populations in view of obtaining more precise predictions of the vertical biomass distributions in marine ecosystems. These studies can be crucial from the point of view of shery. Indeed the abundance of fi sh species is strictly connected with primary production, i.e. phytoplankton biomass, responsible for chlorophyll concentration. In this work a one-dimensional deterministic reaction-di ffusion-taxis model is used to reproduce the spatio-temporal dynamics, along a water column, of five picophytoplankton populations sampled in a real ecosystem. In our analysis, to better reproduce the spatio-temporal behav…
Metagenomics uncovers a new group of low GC and ultra-small marine Actinobacteria
2013
We describe a deep-branching lineage of marine Actinobacteria with very low GC content (33%) and the smallest free living cells described yet (cell volume ca. 0.013 μm(3)), even smaller than the cosmopolitan marine photoheterotroph, 'Candidatus Pelagibacter ubique'. These microbes are highly related to 16S rRNA sequences retrieved by PCR from the Pacific and Atlantic oceans 20 years ago. Metagenomic fosmids allowed a virtual genome reconstruction that also indicated very small genomes below 1 Mb. A new kind of rhodopsin was detected indicating a photoheterotrophic lifestyle. They are estimated to be ~4% of the total numbers of cells found at the site studied (the Mediterranean deep chloroph…
STOCHASTIC DYNAMICS OF TWO PICOPHYTOPLANKTON POPULATIONS IN A REAL MARINE ECOSYSTEM
2013
A stochastic reaction-diffusion-taxis model is analyzed to get the stationary distribution along water column of two species of picophytoplankton, that is picoeukaryotes and Prochlorococcus. The model is valid for weakly mixed waters, typical of the Mediterranean Sea. External random fluctuations are considered by adding a multiplicative Gaussian noise to the dynamical equation of the nutrient concentration. The statistical tests show that shape and magnitude of the theoretical concentration profile exhibit a good agreement with the experimental findings. Finally, we study the effects of seasonal variations on picophytoplankton groups, including an oscillating term in the auxiliary equation…
Stochastic models for phytoplankton dynamics in marine ecosystems
2014
In this thesis, the stochastic advection-reaction-diffusion models are analyzed to obtain the vertical stationary spatial distributions of the main groups of picophytoplankton, which account about for 80% of total chlorophyll on average in Mediterranean Sea. In Chapter 1 we give a short presentation of the experimental and phytoplanktonic data collected during different oceanographic surveys in Mediterranean Sea. In Chapter 2 we introduce the deterministic and stochastic approaches (one-population model) adopted to describe the picoeukaryotes dynamics in Sicily Channel. Moreover, numerical results for the biomass concentration are compared with experimental data by using chi-squared goodnes…
Conflicting coccolithophore and geochemical evidence for productivity levels in the Eastern Mediterranean sapropel S1
2011
Abstract The cyclic development of anoxic conditions in the eastern Mediterranean deep sea waters is one of the most fascinating research topics in paleoceanographic studies. In combination with bottom water stagnation, enhanced primary production is a common explanation for the deposition of organic-rich layers (sapropels). This is supported by extensive evidence from both geochemical and micropaleontological studies. The correspondence of recent sapropel layers with peaks of the lower photic zone coccolithophore species Florisphaera profunda has been interpreted as a proxy for the development of a deep chlorophyll maximum (DCM), due to the pycnocline/nutricline shallowing into the lower p…
Spatio-temporal behaviour of the deep chlorophyll maximum in Mediterranean Sea: Development of a stochastic model for picophytoplankton dynamics
2013
In this paper, by using a stochastic reaction-diffusion-taxis model, we analyze the picophytoplankton dynamics in the basin of the Mediterranean Sea, characterized by poorly mixed waters. The model includes intraspecific competition of picophytoplankton for light and nutrients. The multiplicative noise sources present in the model account for random fluctuations of environmental variables. Phytoplankton distributions obtained from the model show a good agreement with experimental data sampled in two different sites of the Sicily Channel. The results could be extended to analyze data collected in different sites of the Mediterranean Sea and to devise predictive models for phytoplankton dynam…
A stochastic reaction-diffusion-taxis model for picophytoplankton dynamics
2011
The dynamics of picophytoplankton communities in marine environment is studied by astochastic reaction-dìffusìon-taxis model, analyzing the time evolution of the biomass concentration along a water column. The model is based on two stochastic differentìal equations, where the random fluctuations of the environmental variables are considered by inserting two multiplicative noise terms. Specifically, the model describes the dynamics of diffusion of picophytoplankton biomass and nutrient concentrations. In the proposed model the marine environment is characterized by poorly mixed waters and picophytoplankton is subject to intraspecific competition for light and nutrients. By numerically solvin…
A stochastic reaction-diffusion-taxis model for two picophytoplankton populations
2012
In this work, the stationary distributions of two populations of picophytoplankton, i.e. picoeukaryotes and Prochlorococcus, are studied. This two groups account on average for 60% of the total chlorophyll a (chl a) and divinil chlorophyll a (divinil chl a) concentration in Mediterranean Sea. The interaction of these populations with the environment occurs through two factors that limit the growth of the aquatic microorganisms: light intensity and nutrient, i.e. phosphorus. The dynamics of the two picophytoplanktonic groups, distributed at different depth along a water column (one-dimensional spatial domain), is analyzed starting from a deterministic reaction-diffusion-taxis model. This con…