Distribution and cycling of total organic carbon across the Almeria-Oran Front in the Mediterranean Sea: Implications for carbon cycling in the western basin

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

Biogeosciences Discussions ◽

10.5194/bgd-12-6147-2015 ◽

2015 ◽

Vol 12 (8) ◽

pp. 6147-6213

Author(s):

A. Guyennon ◽

M. Baklouti ◽

F. Diaz ◽

J. Palmieri ◽

J. Beuvier ◽

...

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Mediterranean Sea ◽

Coupled Model ◽

Nutrient Concentrations ◽

Biogeochemical Model ◽

Carbon Export ◽

Western 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. This has direct implications on the stock of dissolved organic carbon (DOC), whose high variability has already been well-documented even if measurements are still sparse and are associated with important uncertainties. We here propose a Mediterranean Basin-scale view of the export of organic carbon, under its dissolved and particulate forms. For this purpose, we have used a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). This is the first Basin-scale application of the biogeochemical model Eco3M-MED and is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are consistent with each other. As for surface chlorophyll, nutrient concentrations, and productivity, strong differences between the Western and Eastern Basins are evidenced by the model for organic carbon export, with only 39% of organic carbon (particulate and dissolved) export taking place in the Western Basin. The major result is that except for the Alboran Sea, dissolved organic carbon (DOC) contribution to organic carbon export is higher than that of particulate (POC) in the whole Basin, 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.

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Modeling Carbon Budgets and Acidification in the Mediterranean Sea Ecosystem Under Contemporary and Future Climate

Frontiers in Marine Science ◽

10.3389/fmars.2021.781522 ◽

2022 ◽

Vol 8 ◽

Author(s):

Cosimo Solidoro ◽

Gianpiero Cossarini ◽

Paolo Lazzari ◽

Giovanni Galli ◽

Giorgio Bolzon ◽

...

Keyword(s):

Surface Water ◽

Organic Carbon ◽

Ocean Acidification ◽

Mediterranean Sea ◽

Carbon Cycling ◽

Emission Scenario ◽

Large Increment ◽

The Mediterranean ◽

Carbon Component ◽

Epipelagic Layer

We simulate and analyze the effects of a high CO2 emission scenario on the Mediterranean Sea biogeochemical state at the end of the XXI century, with a focus on carbon cycling, budgets and fluxes, within and between the Mediterranean sub-basins, and on ocean acidification. As a result of the overall warming of surface water and exchanges at the boundaries, the model results project an increment in both the plankton primary production and the system total respiration. However, productivity increases less than respiration, so these changes yield to a decreament in the concentrations of total living carbon, chlorophyll, particulate organic carbon and oxygen in the epipelagic layer, and to an increment in the DIC pool all over the basin. In terms of mass budgets, the large increment in the dissolution of atmospheric CO2 results in an increment of most carbon fluxes, including the horizontal exchanges between eastern and western sub-basins, in a reduction of the organic carbon component, and in an increament of the inorganic one. The eastern sub-basin accumulates more than 85% of the absorbed atmospheric CO2. A clear ocean acidification signal is observed all over the basin, quantitatively similar to those projected in most oceans, and well detectable also down to the mesopelagic and bathypelagic layers.

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Ecology of aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea

Biogeosciences ◽

10.5194/bg-8-973-2011 ◽

2011 ◽

Vol 8 (4) ◽

pp. 973-985 ◽

Cited By ~ 28

Author(s):

D. Lamy ◽

C. Jeanthon ◽

M. T. Cottrell ◽

D. L. Kirchman ◽

F. Van Wambeke ◽

...

Keyword(s):

Mediterranean Sea ◽

Bacterial Growth ◽

Growth Response ◽

Anoxygenic Phototrophic Bacteria ◽

Carbon Limitation ◽

Organic Substrates ◽

Western Basin ◽

Eastern Basin ◽

Nutrient Additions ◽

The Mediterranean

Abstract. Aerobic anoxygenic phototrophic (AAP) bacteria are photoheterotrophic prokaryotes able to use both light and organic substrates for energy production. They are widely distributed in coastal and oceanic environments and may contribute significantly to the carbon cycle in the upper ocean. To better understand questions regarding links between the ecology of these photoheterotrophic bacteria and the trophic status of water masses, we examined their horizontal and vertical distribution and the effects of nutrient additions on their growth along an oligotrophic gradient in the Mediterranean Sea. Concentrations of bacteriochlorophyll-a (BChl-a) and AAP bacterial abundance decreased from the western to the eastern basin of the Mediterranean Sea and were linked with concentrations of chlorophyll-a, nutrient and dissolved organic carbon. Inorganic nutrient and glucose additions to surface seawater samples along the oligotrophic gradient revealed that AAP bacteria were nitrogen- and carbon-limited in the ultraoligotrophic eastern basin. The intensity of the AAP bacterial growth response generally differed from that of the total bacterial growth response. BChl-a quota of AAP bacterial communities was significantly higher in the eastern basin than in the western basin, suggesting that reliance on phototrophy varied along the oligotrophic gradient and that nutrient and/or carbon limitation favors BChl-a synthesis.

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The effect of cyclones crossing the Mediterranean region on sea level anomalies at the Mediterranean Sea coast

10.5194/nhess-2019-6 ◽

2019 ◽

Author(s):

Piero Lionello ◽

Dario Conte ◽

Marco Reale

Keyword(s):

Mediterranean Sea ◽

Sea Level ◽

Eastern Mediterranean ◽

Storm Track ◽

Western Mediterranean ◽

Residual Water ◽

Positive Anomaly ◽

Western Basin ◽

Sea Level Anomalies ◽

The Mediterranean

Abstract. Large positive and negative sea level anomalies at the coast of the Mediterranean Sea are linked to intensity and position of cyclones moving along the Mediterranean storm track, with dynamics involving different factors. This analysis is based on a model hindcast and considers nine coastal stations, which are representative of sea level anomalies with different magnitude and characteristics. When a shallow water fetch is present, the wind around the cyclone center is the main cause of sea level positive and negative anomalies, depending on its onshore or offshore direction. The inverse barometer effect produces a positive anomaly at the coast near the cyclone pressure minimum and a negative anomaly at the opposite side of the Mediterranean Sea, because a cross-basin mean sea level pressure gradient is associated to the presence of a cyclone. Further, at some stations, negative sea level anomalies are reinforced by a residual water mass redistribution within the basin, which is associated with a transient response to the atmospheric pressure forcing. Though the link between presence of a cyclone in the Mediterranean has comparable importance for positive and negative anomalies, the relation between cyclone position and intensity is stronger for the magnitude of positive events. Area of cyclogenesis, track of the central minimum and position at the time of the event differ depending on the location where the sea level anomaly occurs and on its sign. The western Mediterranean is the main cyclogenesis area for both positive and negative anomalies, overall. Atlantic cyclones mainly produce positive sea level anomalies in the western basin. At the easternmost stations, positive anomalies are caused by Cyclogenesis in the Eastern Mediterranean. North Africa cyclogeneses are a major source of positive anomalies at the central African coast and negative anomalies at the eastern Mediterranean and North Aegean coast.

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New Evidence of Mediterranean Climate Change and Variability from Sea Surface Temperature Observations

Remote Sensing ◽

10.3390/rs12010132 ◽

2020 ◽

Vol 12 (1) ◽

pp. 132 ◽

Cited By ~ 9

Author(s):

Andrea Pisano ◽

Salvatore Marullo ◽

Vincenzo Artale ◽

Federico Falcini ◽

Chunxue Yang ◽

...

Keyword(s):

Climate Change ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Mediterranean Sea ◽

Sea Surface ◽

Western Basin ◽

Mean Values ◽

The Mediterranean ◽

The Impact ◽

Northeastern Atlantic

Estimating long-term modifications of the sea surface temperature (SST) is crucial for evaluating the current state of the oceans and to correctly assess the impact of climate change at regional scales. In this work, we analyze SST variations within the Mediterranean Sea and the adjacent Northeastern Atlantic box (west of the Strait of Gibraltar) over the last 37 years, by using a satellite-based dataset from the Copernicus Marine Environment Monitoring Service (CMEMS). We found a mean warming trend of 0.041 ± 0.006 ∘ C/year over the whole Mediterranean Sea from 1982 to 2018. The trend has an uneven spatial pattern, with values increasing from 0.036 ± 0.006 ∘ C/year in the western basin to 0.048 ± 0.006 ∘ C/year in the Levantine–Aegean basin. The Northeastern Atlantic box and the Mediterranean show a similar trend until the late 1990s. Afterwards, the Mediterranean SST continues to increase, whereas the Northeastern Atlantic box shows no significant trend, until ~2015. The observed change in the Mediterranean Sea affects not only the mean trend but also the amplitude of the Mediterranean seasonal signal, with consistent relative increase and decrease of summer and winter mean values, respectively, over the period considered. The analysis of SST changes occurred during the “satellite era” is further complemented by reconstructions also based on direct in situ SST measurements, i.e., the Extended Reconstructed SST (ERSST) and the Hadley Centre Sea Ice and Sea Surface Temperature dataset (HadISST), which go back to the 19th century. The analysis of these longer time series, covering the last 165 years, indicates that the increasing Mediterranean trend, observed during the CMEMS operational period, is consistent with the Atlantic Multidecadal Oscillation (AMO), as it closely follows the last increasing period of AMO. This coincidence occurs at least until 2007, when the apparent onset of the decreasing phase of AMO is not seen in the Mediterranean SST evolution.

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Modelling Present and Future Climate in the Mediterranean Sea: A Focus on Sea-Level Change

10.21203/rs.3.rs-653703/v1 ◽

2021 ◽

Author(s):

Gianmaria Sannino ◽

Adriana Carillo ◽

Roberto Iacono ◽

Ernesto Napolitano ◽

Massimiliano Palma ◽

...

Keyword(s):

Mediterranean Sea ◽

Sea Level ◽

Ocean Dynamics ◽

Scenario Simulation ◽

Surface Salinity ◽

Western Basin ◽

Regional Patterns ◽

Adequate Treatment ◽

Level Information ◽

The Mediterranean

Abstract We present results of three simulations of the Mediterranean Sea climate: a hindcast, a historical run, and a RCP8.5 scenario simulation reaching the year 2100. The simulations are performed with MED16, a new, tide-including implementation of the MITgcm model, which covers the Mediterranean - Black Sea system with a resolution of 1/16°, further increased at the Gibraltar and Turkish Straits. Validation of the hindcast simulation against observations and numerical reanalyses has given excellent results, proving that the model is also capable of reproducing near-shore sea level variations. Moreover, the spatial structure of the elevation field compares well with altimetric observations, especially in the Western basin, due to the use of improved sea level information at the Atlantic lateral boundary and to the adequate treatment of the complex, hydraulically driven dynamics across the Gibraltar Strait.Under the RCP8.5 future scenario, the temperature is projected to generally increase while the surface salinity decreases in the portion of the Mediterranean affected by the penetration of the Atlantic stream, and increases elsewhere. The warming of sea waters results in the partial inhibition of deep-water formation.The scenario simulation allows for a detailed characterization of the regional patterns of future sea level, arising from ocean dynamics, and indicates a relative sinking of the Mediterranean with respect to the Atlantic more pronounced than the current one. Explicit tidal forcing and an accurate resolution of the Gibraltar Strait are proved to be key features in the designing of numerical simulations for the Mediterranean Sea.

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The dissolved yellow substance and the shades of blue in the Mediterranean Sea

Biogeosciences ◽

10.5194/bg-6-2625-2009 ◽

2009 ◽

Vol 6 (11) ◽

pp. 2625-2636 ◽

Cited By ~ 44

Author(s):

A. Morel ◽

B. Gentili

Keyword(s):

Mediterranean Sea ◽

Vertical Mixing ◽

Wide Field ◽

Western Basin ◽

Abrupt Decrease ◽

Spectral Bands ◽

Yellow Substance ◽

The Mediterranean ◽

A New Technique ◽

High Level

Abstract. When the nominal algorithms commonly in use in Space Agencies are applied to satellite Ocean Color data, the retrieved chlorophyll concentrations in the Mediterranean Sea are recurrently notable overestimates of the field values. Accordingly, several regionally tuned algorithms have been proposed in the past to correct for this deviation. Actually, the blueness of the Mediterranean waters is not as deep as expected from the actual (low) chlorophyll content, and the modified algorithms account for this peculiarity. Among the possible causes for such a deviation, an excessive amount of yellow substance (or of chromophoric dissolved organic matter, CDOM) has been frequently cited. This conjecture is presently tested, by using a new technique simply based on the simultaneous consideration of marine reflectance determined at four spectral bands, namely at 412, 443, 490, and 555 nm, available on the NASA-SeaWiFS sensor (Sea–viewing Wide Field-of-view Sensor). It results from this test that the concentration in yellow colored material (quantified as ay, the absorption coefficient of this material at 443 nm) is about twice that one observed in the nearby Atlantic Ocean at the same latitude. There is a strong seasonal signal, with maximal ay values in late fall and winter, an abrupt decrease beginning in spring, and then a flat minimum during the summer months, which plausibly results from the intense photo-bleaching process favored by the high level of sunshine in these areas. Systematically, the ay values, reproducible from year to year, are higher in the western basin compared with those in the eastern basin (by about 50%). The relative importance of the river discharges into this semi-enclosed sea, as well as the winter deep vertical mixing occurring in the northern parts of the basins may explain the high yellow substance background. The regionally tuned [Chl] algorithms, actually reflect the presence of an excess of CDOM with respect to its standard (Chl-related) values. When corrected for the presence of the actual CDOM content, the [Chl] values as derived via the nominal algorithms are restored to more realistic values, i.e., approximately divided by about two; the strong autumnal increase is smoothed whereas the spring bloom remains as an isolated feature.

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Optical Properties and Biochemical Indices of Marine Particles in the Open Mediterranean Sea: The R/V Maria S. Merian Cruise, March 2018

Frontiers in Earth Science ◽

10.3389/feart.2021.614703 ◽

2021 ◽

Vol 9 ◽

Author(s):

Spyros Chaikalis ◽

Constantine Parinos ◽

Jürgen Möbius ◽

Alexandra Gogou ◽

Dimitris Velaoras ◽

...

Keyword(s):

Optical Properties ◽

Particulate Matter ◽

Organic Carbon ◽

Mediterranean Sea ◽

Particulate Organic Carbon ◽

Beam Attenuation ◽

Median Diameter ◽

The Mediterranean ◽

Biochemical Indices ◽

Beam Attenuation Coefficient

A rich data set on particulate matter optical properties and parameters (beam attenuation coefficient, volume concentration, particle size and PSD slope), accompanied by measurements of biochemical indices (particulate organic carbon, particulate nitrogen and their stable isotopic composition) was obtained from the surface to deep waters across the Mediterranean Sea, in March-April 2018. A decrease of beam attenuation coefficients, total particle volume concentrations, particulate organic carbon and nitrogen concentrations was noted towards the eastern Mediterranean Sea (EMed) in comparison to the western Mediterranean Sea (WMed). LISST-derived optical properties were significantly correlated with water mass characteristics. Overall, the most turbid water mass identified in the Mediterranean Sea was the Surface Atlantic water (AW), and the most transparent was the Transitional Mediterranean Water (TMW) in the Cretan Sea, whereas a general decrease in particulate matter concentration is observed from the WMed towards the EMed. Relatively depleted δ13C-POC values in the particle pool of the open Mediterranean Sea can be attributed to contribution from terrestrial inputs, mainly via atmospheric deposition. Throughout the entire water column, a significant positive correlation between particle beam attenuation coefficient and particulate organic carbon concentration is observed in the open Mediterranean Sea. Such relationship suggests the predominance of organic particles with biogenic origin. POC concentration and particle median diameter D50 are significantly and negatively correlated both in the WMed and the EMed Sea, confirming that small particles are POC-rich. At depth, a prominent decrease of most measured parameters was observed, with the exception of particle median diameter that increased substantially in the EMed towards the deep sea, suggesting potentially enhanced aggregation processes. The low particle size distribution slope ξ observed in the EMed, corresponding to larger particle populations, supports the above notion. Basin-wide Rayleigh-type isotopic fractionation in vertical profiles of δ15N-PN across the Mediterranean Sea, underlines the differences in the trophic characters of the two sub-basins and highlights the role of circulation changes on biogeochemical parameters and the redistribution of particulate matter as a source of nutrients in the water column.

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Eukaryotic community composition in the sea surface microlayer across an east-west transect in the Mediterranean Sea

10.5194/bg-2020-249 ◽

2020 ◽

Author(s):

Birthe Zäncker ◽

Michael Cunliffe ◽

Anja Engel

Keyword(s):

Mediterranean Sea ◽

Community Composition ◽

Significant Proportion ◽

Sea Surface ◽

Surface Microlayer ◽

Tyrrhenian Sea ◽

Ionian Sea ◽

Western Basin ◽

Sea Surface Microlayer ◽

The Mediterranean

Abstract. The sea surface microlayer (SML) represents the boundary layer at the air-sea interface. Microbial eukaryotes in the SML potentially influence air-sea gas exchange directly by taking up and producing gases, and indirectly by excreting and degrading organic matter, which may modify the viscoelastic properties of the SML. However, little is known about the controlling factors that influence microbial eukaryote community composition in the SML. We studied the composition of the microbial community, transparent exopolymer particles and polysaccharides in the SML during the PEACETIME cruise along a west-east transect in the Mediterranean Sea, covering the western basin, Tyrrhenian Sea and Ionian Sea. At the stations located in the Ionian Sea, fungi were found in high relative abundances determined by 18S sequencing efforts, making up a significant proportion of the sequences recovered. At the same time, bacterial and phytoplankton counts were decreasing from west to east, while transparent exopolymer particle (TEP) abundance and total carbohydrate (TCHO) concentrations remained the same between Mediterranean basins. Thus, the presence of substrates for fungi, such as Cladosporium known to take up phytoplankton-derived polysaccharides, in combination with decreased substrate competition by bacteria suggests that fungi could be thriving in the neuston of the Ionian Sea.

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