Using SVD Analysis of Combined Altimetry and Ocean Color Satellite Data for Assessing Basin Scale Physical-Biological Coupling in the Mediterranean Sea

We present a method for the remote retrieval of the sea surface currents in the Mediterranean Sea. Combining the altimeter-derived currents with sea-surface temperature information, we created daily, gap-free high resolution maps of sea surface currents for the period 2012–2016. The quality of the new multi-sensor currents has been assessed through comparisons to other surface-currents estimates, as the ones obtained from drifting buoys trajectories (at the basin scale), or HF-Radar platforms and ocean numerical model outputs in the Malta–Sicily Channel. The study yielded that our synergetic approach can improve the present-day derivation of the surface currents in the Mediterranean area up to 30% locally, with better performances for the the meridional component of the motion and in the western section of the basin. The proposed reconstruction method also showed satisfying performances in the retrieval of the ageostrophic circulation in the Sicily Channel. In this area, assuming the High Frequency Radar-derived currents as reference, the merged multi-sensor currents exhibited improvements with respect to the altimeter estimates and numerical model outputs, mainly due to their enhanced spatial and temporal resolution.

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A high-resolution free-surface model of the Mediterranean Sea

Ocean Science ◽

10.5194/os-4-1-2008 ◽

2008 ◽

Vol 4 (1) ◽

pp. 1-14 ◽

Cited By ~ 144

Author(s):

M. Tonani ◽

N. Pinardi ◽

S. Dobricic ◽

I. Pujol ◽

C. Fratianni

Keyword(s):

Free Surface ◽

Mediterranean Sea ◽

General Circulation ◽

Forecast Model ◽

Surface Model ◽

Argo Data ◽

Basic Model ◽

Basin Scale ◽

Before And After ◽

The Mediterranean

Abstract. This study describes a new model implementation for the Mediterranean Sea with what is currently the highest vertical resolution over the Mediterranean basin. The resolution is of 1/16°×1/16° in the horizontal and has 72 unevenly spaced vertical levels. This model has been developed in the frame of the EU-MFSTEP project and is the operational forecast model currently used at the basin scale. The model considers an implicit free surface and this characteristic enhances the model's capability to simulate the sea surface height variability and the net transport at the Strait of Gibraltar. In this study we show the calibration/validation experiments performed before and after the model was used for forecasting. The first experiment consists of a six-year simulation forced by a perpetual year forcing, and the other experiment is a simulation from January 1997 to December 2004, forcing the model with 6-h atmospheric forcing fields from ECMWF. The model Sea Level Anomaly has been compared for the first time with satellite SLA and with ARGO data to provide evidence of the quality of the simulation. The results show that this model is capable of reproducing most of the variability of the general circulation in the Mediterranean Sea. However, some basic model inadequacies stand out and should be corrected in the near future.

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New toolbox in ArcGIS for the reconstruction of missing satellite data using DINEOF algorithm: a case study of reconstruction of Chlorophyll-a gaps over the Mediterranean Sea

10.1117/12.2069691 ◽

2014 ◽

Author(s):

Andreas Nikolaidis ◽

Stavros Stylianou ◽

Georgios Georgiou ◽

Diofantos Hadjimitsis ◽

Evangelos Akylas

Keyword(s):

Mediterranean Sea ◽

Chlorophyll A ◽

Satellite Data ◽

The Mediterranean

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Interannual variability of the Mediterranean trophic regimes from ocean color satellites

Biogeosciences Discussions ◽

10.5194/bgd-12-14941-2015 ◽

2015 ◽

Vol 12 (17) ◽

pp. 14941-14980 ◽

Cited By ~ 4

Author(s):

N. Mayot ◽

F. D'Ortenzio ◽

M. Ribera d'Alcalà ◽

H. Lavigne ◽

H. Claustre

Keyword(s):

Spatial Distribution ◽

Mediterranean Sea ◽

Interannual Variability ◽

Deep Convection ◽

Regional Scale ◽

Ocean Color ◽

Run Off ◽

The Mediterranean ◽

The One ◽

The Impact

Abstract. D'Ortenzio and Ribera d'Alcalà (2009, DR09 hereafter) divided the Mediterranean Sea into "bioregions" based on the climatological seasonality (phenology) of phytoplankton. Here we investigate the interannual variability of this bioregionalization. Using 16 years of available ocean color observations (i.e. SeaWiFS and MODIS), we analyzed the spatial distribution of the DR09 trophic regimes on an annual basis. Additionally, we identified new trophic regimes, with seasonal cycles of phytoplankton biomass different from the DR09 climatological description and named "Anomalous". Overall, the classification of the Mediterranean phytoplankton phenology proposed by DR09 (i.e. "No Bloom", "Intermittently", "Bloom" and "Coastal"), is confirmed to be representative of most of the Mediterranean phytoplankton phenologies. The mean spatial distribution of these trophic regimes (i.e. bioregions) over the 16 years studied is also similar to the one proposed by DR09. But at regional scale some annual differences, in their spatial distribution and in the emergence of "Anomalous" trophic regimes, were observed compared to the DR09 description. These dissimilarities with the DR09 study were related to interannual variability in the sub-basin forcing: winter deep convection events, frontal instabilities, inflow of Atlantic or Black Sea Waters and river run-off. The large assortment of phytoplankton phenologies identified in the Mediterranean Sea is thus verified at interannual level, confirming the "sentinel" role of this basin to detect the impact of climate changes on the pelagic environment.

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Characterisation of extreme events waves in marine ecosystems: the case of Mediterranean Sea

10.5194/bg-2020-34 ◽

2020 ◽

Author(s):

Valeria Di Biagio ◽

Gianpiero Cossarini ◽

Stefano Salon ◽

Cosimo Solidoro

Keyword(s):

Cluster Analysis ◽

Mediterranean Sea ◽

Extreme Events ◽

Marine Ecosystems ◽

Horizontal Resolution ◽

Ecosystem Functions ◽

Biogeochemical Model ◽

Open Sea ◽

Basin Scale ◽

The Mediterranean

Abstract. We propose a new method to identify and characterise the occurrence of prolonged extreme events in marine ecosystems on the basin scale. There is a growing interest about events that can affect ecosystem functions and services in a changing climate. Our method identifies extreme events as peak occurrences over 99th percentile thresholds computed from local time series and defines an Extreme Events Wave (EEW) as a connected region including these events. The EEWs are characterised by a set of novel indexes, referred to initiation, extent, duration and strength. The indexes, associated to the areas covered by each EEW, are then statistically analysed to highlight the main features of the EEWs on the considered domain. We applied the method to the winter-spring daily chlorophyll field of a validated multidecadal hindcast provided by a coupled hydrodynamic-biogeochemical model of the Mediterranean open-sea ecosystem, with 1/12° horizontal resolution. This allowed to identify the maxima of chlorophyll as exceptionally high and prolonged blooms and to characterise their phenomenology in the period 1994–2012. A fuzzy k-means cluster analysis on the EEWs indexes provided a bio-regionalisation of the Mediterranean Sea associated to the occurrence of chlorophyll EEWs with different regimes.

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Subsurface iron accumulation and rapid aluminum removal in the Mediterranean following African dust deposition

Biogeosciences ◽

10.5194/bg-18-6435-2021 ◽

2021 ◽

Vol 18 (24) ◽

pp. 6435-6453

Author(s):

Matthieu Bressac ◽

Thibaut Wagener ◽

Nathalie Leblond ◽

Antonio Tovar-Sánchez ◽

Céline Ridame ◽

...

Keyword(s):

Mediterranean Sea ◽

Comprehensive Evaluation ◽

Vertical Mixing ◽

Western Mediterranean ◽

Surface Mixed Layer ◽

Dust Deposition ◽

Near Surface ◽

Surface Ocean ◽

Basin Scale ◽

The Mediterranean

Abstract. Mineral dust deposition is an important supply mechanism for trace elements in the low-latitude ocean. Our understanding of the controls of such inputs has been mostly built on laboratory and surface ocean studies. The lack of direct observations and the tendency to focus on near-surface waters prevent a comprehensive evaluation of the role of dust in oceanic biogeochemical cycles. In the frame of the PEACETIME project (ProcEss studies at the Air-sEa Interface after dust deposition in the MEditerranean sea), the responses of the aluminum (Al) and iron (Fe) cycles to two dust wet deposition events over the central and western Mediterranean Sea were investigated at a timescale of hours to days using a comprehensive dataset gathering dissolved and suspended particulate concentrations, along with sinking fluxes. Dissolved Al (dAl) removal was dominant over dAl released from dust. The Fe / Al ratio of suspended and sinking particles revealed that biogenic particles, and in particular diatoms, were key in accumulating and exporting Al relative to Fe. By combining these observations with published Al / Si ratios of diatoms, we show that adsorption onto biogenic particles, rather than active uptake, represents the main sink for dAl in Mediterranean waters. In contrast, systematic dissolved Fe (dFe) accumulation occurred in subsurface waters (∼ 100–1000 m), while dFe input from dust was only transient in the surface mixed layer. The rapid transfer of dust to depth, the Fe-binding ligand pool in excess to dFe in subsurface (while nearly saturated in surface), and low scavenging rates in this particle-poor depth horizon are all important drivers of this subsurface dFe enrichment. At the annual scale, this previously overlooked mechanism may represent an additional pathway of dFe supply for the surface ocean through diapycnal diffusion and vertical mixing. However, low subsurface dFe concentrations observed at the basin scale (

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New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling

Biogeosciences ◽

10.5194/bg-12-7025-2015 ◽

2015 ◽

Vol 12 (23) ◽

pp. 7025-7046 ◽

Cited By ~ 21

Author(s):

A. Guyennon ◽

M. Baklouti ◽

F. Diaz ◽

J. Palmieri ◽

J. Beuvier ◽

...

Keyword(s):

Organic Carbon ◽

Mediterranean Sea ◽

Coupled Model ◽

Phosphate Limitation ◽

Biogeochemical Model ◽

Carbon Export ◽

Western Basin ◽

Eastern Basin ◽

Basin Scale ◽

The Mediterranean

Abstract. The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities, resulting in a potential major role of dissolved organic carbon (DOC) export in the biological pump. Strong DOC accumulation in surface waters is already well documented, though measurements of DOC stocks and export flux are still sparse and associated with major uncertainties. This study provides the first basin-scale overview and analysis of organic carbon stocks and export fluxes in the Mediterranean Sea through a modeling approach based on a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). The model is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are also of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are mutually consistent. Strong differences between the western and eastern basins are evidenced by the model for organic carbon export. Though less oligotrophic than the eastern basin, the western basin only supports 39 % of organic carbon (particulate and dissolved) export. Another major result is that except for the Alboran Sea, the DOC contribution to organic carbon export is higher than that of particulate organic carbon (POC) throughout the Mediterranean Sea, especially in the eastern basin. This paper also investigates the seasonality of DOC and POC exports as well as the differences in the processes involved in DOC and POC exports in light of intracellular quotas. Finally, according to the model, strong phosphate limitation of both bacteria and phytoplankton growth is one of the main drivers of DOC accumulation and therefore of export.

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Spatiotemporal variability of alkalinity in the Mediterranean Sea

Biogeosciences ◽

10.5194/bg-12-1647-2015 ◽

2015 ◽

Vol 12 (6) ◽

pp. 1647-1658 ◽

Cited By ~ 35

Author(s):

G. Cossarini ◽

P. Lazzari ◽

C. Solidoro

Keyword(s):

Mediterranean Sea ◽

Seasonal Cycle ◽

Sea Water ◽

Eastern Mediterranean ◽

Surface Flux ◽

Spatiotemporal Variability ◽

The Black Sea ◽

Biogeochemical Model ◽

Basin Scale ◽

The Mediterranean

Abstract. The paper provides a basin-scale assessment of the spatiotemporal distribution of alkalinity in the Mediterranean Sea. The assessment is made by integrating the available observations into a 3-D transport–biogeochemical model. The results indicate the presence of complex spatial patterns: a marked west-to-east surface gradient of alkalinity is coupled to secondary negative gradients: (1) from marginal seas (Adriatic and Aegean Sea) to the eastern Mediterranean Sea and (2) from north to south in the western region. The west–east gradient is related to the mixing of Atlantic water entering from the Strait of Gibraltar with the high-alkaline water of the eastern sub-basins, which is correlated to the positive surface flux of evaporation minus precipitation. The north-to-south gradients are related to the terrestrial input and to the input of the Black Sea water through the Dardanelles. In the surface layers, alkalinity has a relevant seasonal cycle (up to 40 μmol kg−1) that is driven by physical processes (seasonal cycle of evaporation and vertical mixing) and, to a minor extent, by biological processes. A comparison of alkalinity vs. salinity indicates that different regions present different relationships: in regions of freshwater influence, the two quantities are negatively correlated due to riverine alkalinity input, whereas they are positively correlated in open sea areas of the Mediterranean Sea.

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