Light variation in temporal and spatial domains is a key constraint on the photosynthetic perform... more Light variation in temporal and spatial domains is a key constraint on the photosynthetic performance of phytoplankton. The most obvious responses are the modification of cell pigment content either to improve photocapture or to mitigate photo-damage. Very few studies have analyzed whether light variation significantly alters carbon assimilation, especially in a fluctuating light environment as in the mixed layer of the ocean. We addressed the question using a modeling approach, which allows the reproduction of most of the possible scenarios, obtained with great difficulty in laboratory or field experiments. The complete model is based on the dynamic coupling of a photoacclimation and photodamage-repair responses. In this combined model the virtual phytoplankton is exposed to different light regimes (steady, square wave, sinusoidal Light-Dark cycles and fluctuating regimes). The results reconcile controversial results on different photacclimation states achieved during fluctuating light regimes. The model produces a depression of carbon assimilation in any light fluctuating scenario, as compared to steady light regimes, due to the temporal delay between light fluctuations and photoresponses. Those results suggest the possibility of selective pressure during evolution more effective on photoprotective A c c e p t e d m a n u s c r i p t mechanisms than on optimization of light harvesting
Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to ... more Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to the Atlantic basin. Their influence on global ocean circulation is well known, but their role in plankton transport is largely unexplored. We show that, although the coarse taxonomic structure of plankton communities is continuous across the Agulhas choke point, South Atlantic plankton diversity is altered compared with Indian Ocean source populations. Modeling and in situ sampling of a young Agulhas ring indicate that strong vertical mixing drives complex nitrogen cycling, shaping community metabolism and biogeochemical signatures as the ring and associated plankton transit westward. The peculiar local environment inside Agulhas rings may provide a selective mechanism contributing to the limited dispersal of Indian Ocean plankton populations into the Atlantic.
The North Western Mediterranean Sea (NWMed) is currently assumed to contribute to slightly less t... more The North Western Mediterranean Sea (NWMed) is currently assumed to contribute to slightly less than 15% (43.9x1012 g C a-1) of primary production of the whole basin, mostly concentrated in late winter-early spring period. SeaWiFS images show an impressive build-up of phytoplankton biomass in the area, much more significant and atypical (circa 70 days, with secondary winter blooms) than previously
ABSTRACT Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked ... more ABSTRACT Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked to both the production of genotypic diversity and the formation of large-sized initial cells. Only cells below a certain size threshold can be sexualized, but various environmental factors can modulate the success of sexual reproduction. We investigated the role of cell density and physiological conditions of parental strains in affecting the success and timing of sexual reproduction in the marine heterothallic diatom Pseudo-nitzschia multistriata. We also studied the dynamics of the sexual phase in still conditions allowing cell sedimentation and in gently mixed conditions that keep cells in suspension. Our results showed that successful sexual reproduction can only be achieved when crossing parental strains in the exponential growth phase. Evidence was provided for the fact that sexual reproduction is a density-dependent event and requires a threshold cell concentration to start, although this might vary considerably amongst strains. Moreover, the onset of the sexual phase was coupled to a marked reduction of growth of the vegetative parental cells. The crosses carried out in physically mixed conditions produced a significantly reduced number of sexual stages as compared to crosses in still conditions, showing that mixing impairs sexualisation. The results of our experiments suggest that the signalling that triggers the sexual phase is favoured when cells can accumulate, reducing the distance between them and facilitating contacts and/or the perception of chemical cues. Information on the progression of the sexual phase in laboratory conditions help understanding the conditions at which sex occurs in the natural environment.This article is protected by copyright. All rights reserved.
ABSTRACT OGCM's numerical experiments for climatic studies can be performed only after te... more ABSTRACT OGCM's numerical experiments for climatic studies can be performed only after testing their capability to well represent the today ocean circulation. In order to improve the model results we assimilated satellite SST (from NOAA-AVHRR sensors) by means of a nudging method. Daily 1987 - 1992 NASA Pathfinder SST have been interpolated in time and space by means of an objective analysis algorithm to fill gaps in the time series. These data were analyzed to investigate the main variability of the Mediterranean SST field. The 1988 data was selected to be assimilated in the OGCM. To relate more closely the assimilation of the SST data to the physics of the air-sea interaction, here we propose a new parameterization of the surface relaxation time. Actually the use of realistic surface forcing strongly contribute to reproduce the correct hydrological values of the Mediterranean water masses, the right energetic basin budgets and the mesoscale features of the Mediterranean circulation.
Here we test the hypothesis that winds have an important role in determining the rate of exchange... more Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO 2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way 5 in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry.
This paper presents a detailed analysis of the formation and subsequent evolution of filament-18 ... more This paper presents a detailed analysis of the formation and subsequent evolution of filament-18 like structures observed in a relatively small area of the mid-Tyrrhenian Sea (Mediterranean Sea).
Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace eleme... more Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace elements) record from the sediments of Ocean Drilling Program Site 963 (central Mediterranean basin), which shows centennial/millennial-scale resemblance to the high-northern latitude rapid temperature fluctuations documented in the Greenland ice cores between 20 and 70 kyr BP.
ABSTRACT Extreme atmospheric events, such as storms, can temporarily increase the vertical diffus... more ABSTRACT Extreme atmospheric events, such as storms, can temporarily increase the vertical diffusivity in the upper ocean by several orders of magnitude, causing variability in the deep chlorophyll maximum (DCM). In this study, we investigate the impact of intermittent vertical mixing on the deep chlorophyll maximum. For this purpose, we analyze a one-dimensional phytoplankton-nutrient model exposed to short-term fluctuations in vertical diffusivity generated by internal waves. As a first step, we use singular perturbations to analyze the impact of a single burst of turbulence on the DCM characteristics. The simulations show that the DCM exhibits a long transient response, even after a single short perturbation. In particular, a single burst of turbulence (i) spreads out the DCM, thereby reducing the local phytoplankton maximum, and (ii) gives rise to a diffusion-driven enhancement of nutrient availability, producing a temporary increase in the phytoplankton growth rates at and above the DCM. Subsequently, we introduce a realistic annual sequence of fluctuations in vertical diffusivity in our model, and we also incorporate the seasonal cycle of light conditions. Fluctuations in vertical diffusivity were derived from high-resolution measurements from the POMME experiment in the north-east Atlantic Ocean, where the contribution of internal waves to the variation in vertical mixing has been characterized for more than one year. The annual light cycle, in combination with intermittent vertical mixing, leads to the superposition of a series of complex dynamical responses. At seasonal and shorter time scales, the vertically integrated productivity is temporally augmented by periods of medium/high diffusivity. Seasonal variation in light availability modifies the DCM response to mixing variability.
Light variation in temporal and spatial domains is a key constraint on the photosynthetic perform... more Light variation in temporal and spatial domains is a key constraint on the photosynthetic performance of phytoplankton. The most obvious responses are the modification of cell pigment content either to improve photocapture or to mitigate photo-damage. Very few studies have analyzed whether light variation significantly alters carbon assimilation, especially in a fluctuating light environment as in the mixed layer of the ocean. We addressed the question using a modeling approach, which allows the reproduction of most of the possible scenarios, obtained with great difficulty in laboratory or field experiments. The complete model is based on the dynamic coupling of a photoacclimation and photodamage-repair responses. In this combined model the virtual phytoplankton is exposed to different light regimes (steady, square wave, sinusoidal Light-Dark cycles and fluctuating regimes). The results reconcile controversial results on different photacclimation states achieved during fluctuating light regimes. The model produces a depression of carbon assimilation in any light fluctuating scenario, as compared to steady light regimes, due to the temporal delay between light fluctuations and photoresponses. Those results suggest the possibility of selective pressure during evolution more effective on photoprotective A c c e p t e d m a n u s c r i p t mechanisms than on optimization of light harvesting
Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to ... more Agulhas rings provide the principal route for ocean waters to circulate from the Indo-Pacific to the Atlantic basin. Their influence on global ocean circulation is well known, but their role in plankton transport is largely unexplored. We show that, although the coarse taxonomic structure of plankton communities is continuous across the Agulhas choke point, South Atlantic plankton diversity is altered compared with Indian Ocean source populations. Modeling and in situ sampling of a young Agulhas ring indicate that strong vertical mixing drives complex nitrogen cycling, shaping community metabolism and biogeochemical signatures as the ring and associated plankton transit westward. The peculiar local environment inside Agulhas rings may provide a selective mechanism contributing to the limited dispersal of Indian Ocean plankton populations into the Atlantic.
The North Western Mediterranean Sea (NWMed) is currently assumed to contribute to slightly less t... more The North Western Mediterranean Sea (NWMed) is currently assumed to contribute to slightly less than 15% (43.9x1012 g C a-1) of primary production of the whole basin, mostly concentrated in late winter-early spring period. SeaWiFS images show an impressive build-up of phytoplankton biomass in the area, much more significant and atypical (circa 70 days, with secondary winter blooms) than previously
ABSTRACT Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked ... more ABSTRACT Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked to both the production of genotypic diversity and the formation of large-sized initial cells. Only cells below a certain size threshold can be sexualized, but various environmental factors can modulate the success of sexual reproduction. We investigated the role of cell density and physiological conditions of parental strains in affecting the success and timing of sexual reproduction in the marine heterothallic diatom Pseudo-nitzschia multistriata. We also studied the dynamics of the sexual phase in still conditions allowing cell sedimentation and in gently mixed conditions that keep cells in suspension. Our results showed that successful sexual reproduction can only be achieved when crossing parental strains in the exponential growth phase. Evidence was provided for the fact that sexual reproduction is a density-dependent event and requires a threshold cell concentration to start, although this might vary considerably amongst strains. Moreover, the onset of the sexual phase was coupled to a marked reduction of growth of the vegetative parental cells. The crosses carried out in physically mixed conditions produced a significantly reduced number of sexual stages as compared to crosses in still conditions, showing that mixing impairs sexualisation. The results of our experiments suggest that the signalling that triggers the sexual phase is favoured when cells can accumulate, reducing the distance between them and facilitating contacts and/or the perception of chemical cues. Information on the progression of the sexual phase in laboratory conditions help understanding the conditions at which sex occurs in the natural environment.This article is protected by copyright. All rights reserved.
ABSTRACT OGCM's numerical experiments for climatic studies can be performed only after te... more ABSTRACT OGCM's numerical experiments for climatic studies can be performed only after testing their capability to well represent the today ocean circulation. In order to improve the model results we assimilated satellite SST (from NOAA-AVHRR sensors) by means of a nudging method. Daily 1987 - 1992 NASA Pathfinder SST have been interpolated in time and space by means of an objective analysis algorithm to fill gaps in the time series. These data were analyzed to investigate the main variability of the Mediterranean SST field. The 1988 data was selected to be assimilated in the OGCM. To relate more closely the assimilation of the SST data to the physics of the air-sea interaction, here we propose a new parameterization of the surface relaxation time. Actually the use of realistic surface forcing strongly contribute to reproduce the correct hydrological values of the Mediterranean water masses, the right energetic basin budgets and the mesoscale features of the Mediterranean circulation.
Here we test the hypothesis that winds have an important role in determining the rate of exchange... more Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO 2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way 5 in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry.
This paper presents a detailed analysis of the formation and subsequent evolution of filament-18 ... more This paper presents a detailed analysis of the formation and subsequent evolution of filament-18 like structures observed in a relatively small area of the mid-Tyrrhenian Sea (Mediterranean Sea).
Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace eleme... more Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace elements) record from the sediments of Ocean Drilling Program Site 963 (central Mediterranean basin), which shows centennial/millennial-scale resemblance to the high-northern latitude rapid temperature fluctuations documented in the Greenland ice cores between 20 and 70 kyr BP.
ABSTRACT Extreme atmospheric events, such as storms, can temporarily increase the vertical diffus... more ABSTRACT Extreme atmospheric events, such as storms, can temporarily increase the vertical diffusivity in the upper ocean by several orders of magnitude, causing variability in the deep chlorophyll maximum (DCM). In this study, we investigate the impact of intermittent vertical mixing on the deep chlorophyll maximum. For this purpose, we analyze a one-dimensional phytoplankton-nutrient model exposed to short-term fluctuations in vertical diffusivity generated by internal waves. As a first step, we use singular perturbations to analyze the impact of a single burst of turbulence on the DCM characteristics. The simulations show that the DCM exhibits a long transient response, even after a single short perturbation. In particular, a single burst of turbulence (i) spreads out the DCM, thereby reducing the local phytoplankton maximum, and (ii) gives rise to a diffusion-driven enhancement of nutrient availability, producing a temporary increase in the phytoplankton growth rates at and above the DCM. Subsequently, we introduce a realistic annual sequence of fluctuations in vertical diffusivity in our model, and we also incorporate the seasonal cycle of light conditions. Fluctuations in vertical diffusivity were derived from high-resolution measurements from the POMME experiment in the north-east Atlantic Ocean, where the contribution of internal waves to the variation in vertical mixing has been characterized for more than one year. The annual light cycle, in combination with intermittent vertical mixing, leads to the superposition of a series of complex dynamical responses. At seasonal and shorter time scales, the vertically integrated productivity is temporally augmented by periods of medium/high diffusivity. Seasonal variation in light availability modifies the DCM response to mixing variability.
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Papers by D. Iudicone