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

2011 ◽  
Vol 8 (1) ◽  
pp. 323-354
Author(s):  
D. Lamy ◽  
C. Jeanthon ◽  
J. Ras ◽  
F. Van Wambeke ◽  
O. Dahan ◽  
...  
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 basins 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 ultra-oligotrophic 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.

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

2011 ◽  
Vol 8 (4) ◽  
pp. 973-985 ◽  
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.

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

2015 ◽  
Vol 12 (23) ◽  
pp. 7025-7046 ◽  
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.

scholarly journals Thermodynamic Forecasts of the Mediterranean Sea Acidification

2016 ◽  
Vol 17 (2) ◽  
pp. 508 ◽  
Author(s):  
C. GOYET ◽  
A. HASSOUN ◽  
E. GEMAYEL ◽  
F. TOURATIER ◽  
M. ABBOUD-ABI SAAB ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Initial Conditions ◽  
Mixed Layer Depth ◽  
Total Alkalinity ◽  
Western Basin ◽  
Eastern Basin ◽  
Emissions Scenarios ◽  
The Mediterranean ◽  
Ph Decrease ◽  
Thermodynamic Equations

Anthropogenic CO2 is a major driver of the present ocean acidification. This latter is threatening the marine ecosystems and has been identified as a major environmental and economic menace. This study aims to forecast from the thermodynamic equations, the acidification variation (ΔpH) of the Mediterranean waters over the next few decades and beyond this century. In order to do so, we calculated and fitted the theoretical values based upon the initial conditions from data of the 2013 MedSeA cruise. These estimates have been performed both for the Western and for the Eastern basins based upon their respective physical (temperature and salinity) and chemical (total alkalinity and total inorganic carbon) properties. The results allow us to point out four tipping points, including one when the Mediterranean Sea waters would become acid (pH<7). In order to provide an associated time scale to the theoretical results, we used two of the IPCC (2007) atmospheric CO2 scenarios. Under the most optimistic scenario of the “Special Report: Emissions Scenarios” (SRES) of the IPCC (2007), the results indicate that in 2100, pH may decrease down to 0.245 in the Western basin and down to 0.242 in the Eastern basin (compared to the pre-industrial pH). Whereas for the most pessimistic SRES scenario of the IPCC (2007), the results for the year 2100, forecast a pH decrease down to 0.462 and 0.457, for the Western and for the Eastern basins, respectively. Acidification, which increased unprecedentedly in recent years, will rise almost similarly in both Mediterranean basins only well after the end of this century. These results further confirm that both basins may become undersaturated (< 1) with respect to calcite and aragonite (at the base of the mixed layer depth), only in the far future (in a few centuries).

scholarly journals Springtime contribution of dinitrogen fixation to primary production across the Mediterranean Sea

Ocean Science ◽  
2013 ◽  
Vol 9 (3) ◽  
pp. 489-498 ◽  
Author(s):  
E. Rahav ◽  
B. Herut ◽  
A. Levi ◽  
M. R. Mulholland ◽  
I. Berman-Frank
Keyword(s):  
Primary Production ◽  
Mediterranean Sea ◽  
N2 Fixation ◽  
Eastern Mediterranean ◽  
Dominant Role ◽  
Early Spring ◽  
Western Basin ◽  
Eastern Basin ◽  
The Mediterranean ◽  
Planktonic Communities

Abstract. Dinitrogen (N2) fixation rates were measured during early spring across the different provinces of Mediterranean Sea surface waters. N2 fixation rates, measured using 15N2 enriched seawater, were lowest in the eastern basin and increased westward with a maximum at the Strait of Gibraltar (0.10 to 2.35 nmol N L−1 d−1, respectively). These rates were 3–7 fold higher than N2 fixation rates measured previously in the Mediterranean Sea during summertime and we estimated that methodological differences alone did not account for the seasonal changes we observed. Higher contribution of N2 fixation to primary production (4–8%) was measured in the western basin compared to the eastern basin (∼2%). Our data indicates that these differences between basins may be attributed to changes in N2-fixing planktonic communities and that heterotrophic diazotrophy may play a significant role in the eastern Mediterranean while autotrophic diazotrophy has a more dominant role in the western basin.

scholarly journals Springtime contribution of dinitrogen fixation to primary production across the Mediterranean Sea

2013 ◽  
Vol 10 (1) ◽  
pp. 1-26 ◽  
Author(s):  
E. Rahav ◽  
B. Herut ◽  
A. Levi ◽  
M. R. Mulholland ◽  
I. Berman-Frank
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
N2 Fixation ◽  
Eastern Mediterranean ◽  
Dominant Role ◽  
Early Spring ◽  
Strait Of Gibraltar ◽  
Western Basin ◽  
Eastern Basin ◽  
The Mediterranean

Abstract. Dinitrogen (N2) fixation rates were measured during early spring across the different provinces of Mediterranean Sea surface waters. N2 fixation rates, measured using 15N2 enriched seawater, were lowest in the eastern basin and increased westward with a maximum at the Strait of Gibraltar (0.10 to 2.35 nmol N L−1 d−1, respectively). These rates were 3–7 fold higher than N2 fixation rates measured previously in the Mediterranean Sea during summertime. Moreover, comparisons between N2 fixation rates measured during dark versus natural light incubations (48 h) show higher rates during dark incubations at the eastern Mediterranean stations but lower rates at the western stations. This suggests that heterotrophic diazotrophy has a significant role in the Eastern Mediterranean while autotrophic diazotrophy has a more dominant role in the Western basin.

scholarly journals Modelling of the anthropogenic tritium transient and its decay product helium-3 in the Mediterranean Sea using a high-resolution regional model

2014 ◽  
Vol 11 (6) ◽  
pp. 2691-2732
Author(s):  
M. Ayache ◽  
J.-C. Dutay ◽  
P. Jean-Baptiste ◽  
K. Beranger ◽  
T. Arsouze ◽  
...  
Keyword(s):  
High Resolution ◽  
Mediterranean Sea ◽  
Deep Water ◽  
Eastern Mediterranean ◽  
Decay Product ◽  
Regional Model ◽  
Western Basin ◽  
Eastern Basin ◽  
Helium 3 ◽  
The Mediterranean

Abstract. This numerical study provides the first simulation of the anthropogenic tritium invasion and its decay product helium-3 (3He) in the Mediterranean Sea. The simulation covers the entire tritium (3H) transient generated by the atmospheric nuclear-weapon tests performed in the 1950s and early 1960s and run till 2011. Tritium, helium-3 and their derived age estimates are particularly suitable for studying intermediate and deep-water ventilation and spreading of water masses at intermediate/deep levels. The simulation is made using a high resolution regional model NEMO-MED12 forced at the surface with prescribed tritium evolution derived from observations. The simulation is compared to measurements of tritium and helium-3 performed along large-scale transects in the Mediterranean Sea during the last few decades on cruises of Meteor M5/6, M31/1, M44/4, M51/2, M84/3, and Poseidon 234. The results show that the input function used for the tritium, generates a realistic distribution of the main hydrographic features of the Mediterranean Sea circulation. In the eastern basin, the results highlight the weak formation of Adriatic Deep Water in the model, which explains its weak contribution to the Eastern Mediterranean Deep Water in the Ionian sub-basin. It produces a realistic representation of the Eastern Mediterranean Transient signal, simulating a deep-water formation in the Aegean sub-basin at the beginning of the 1993, with a realistic timing of deep-water renewal in the eastern basin. In the western basin, the unusual intense deep convection event of winter 2005 in the Gulf of Lions during the Western Mediterranean Transition is simulated. However the spreading of the recently ventilated deep water toward the South is too weak. The ventilation and spreading of the Levantine Intermediate Water from the eastern basin toward the western basin is simulated with realistic tracer-age distribution compared to observation-based estimates.

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

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.

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

2020 ◽  
Vol 12 (1) ◽  
pp. 132 ◽  
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.

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

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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