scholarly journals Integrated survey of elemental stoichiometry (C, N, P) from the Western to Eastern Mediterranean Sea

2010 ◽  
Vol 7 (5) ◽  
pp. 7315-7358 ◽  
Author(s):  
M. Pujo-Pay ◽  
P. Conan ◽  
L. Oriol ◽  
V. Cornet-Barthaux ◽  
C. Falco ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Surface Waters ◽  
Eastern Mediterranean ◽  
Vertical Gradient ◽  
Western Basin ◽  
P Limitation ◽  
Severe Deficiency ◽  
Elemental Stoichiometry ◽  
Redfield Ratios

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry in the whole Mediterranean Sea during the summer 2008. During this strong stratified period, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were investigated along a 3000 km transect (BOUM cruise) crossing the Western and Eastern Mediterranean basins. The partitioning of chemical C, N and P species among all these mineral and organic pools has been analysed to produce a detailed spatial and vertical extended examination of the elemental stoichiometry. Surface Mediterranean waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, concomitantly to the gradual deepening of the thermocline and nutriclines. We used threshold in oxygen concentration to discriminate the water column in three layers; surface (Biogenic Layer BL), intermediate (Mineralization Layer ML), and deep layer (DL) and to propose a schematic representation of biogeochemical fluxes between the different compartments and to compare the functioning of the two basins. The stoichiometry revealed a clear longitudinal and vertical gradient in the mineral fraction with a P-depletion evidenced on both dimension. As a consequence of the severe deficiency in phosphorus, the C:N:P ratios in all pools within the BL largely exceed the Redfield ratios. Despite these gradients, the deep estimated fluxes in the mineral compartment tend towards the canonical Redfield values in both basins. A change in particulate matter composition has been evidenced by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. More surprisingly, a decrease in N relative to P with depth was encountered in the whole Mediterranean Sea. We suggest that there was a more rapid recycling of N than P in intermediate waters (below BL) and a complete use of DOP in surface waters. DOC accumulated in surface waters according to the oligotrophic status but this was not the case for nitrogen nor phosphorus. Our data clearly showed a noticeable stability of the DOC:DON ratio (12–13) in the whole Mediterranean Sea, contradicting the fact that N is recycled faster than C in the DOM but in agreement with a P limitation of bacterial activity. Finally, comparisons between these elemental distributions and ratios along the West-East Mediterranean gradient of trophic status provide new insights for identifying and understanding fundamental interactions between marine biogeochemistry and ecosystems, which will help to predict the impacts of environmental climate changes on the Mediterranean marine ecosystems. Indeed, the outflowing through the various Mediterranean straits have been shown to be changing, the functioning of the BL ecosystem could be impacted, not only by changes in nutrients surface sources but also by changes in deep nutrients one.

scholarly journals Integrated survey of elemental stoichiometry (C, N, P) from the western to eastern Mediterranean Sea

2011 ◽  
Vol 8 (4) ◽  
pp. 883-899 ◽  
Author(s):  
M. Pujo-Pay ◽  
P. Conan ◽  
L. Oriol ◽  
V. Cornet-Barthaux ◽  
C. Falco ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Eastern Mediterranean ◽  
Western Basin ◽  
Nutrient Sources ◽  
P Limitation ◽  
Elemental Stoichiometry ◽  
Deep Layers ◽  
Redfield Ratios ◽  
The Mediterranean

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry along an East-West transect of 3000 km across the Mediterranean Sea during summer 2008 (BOUM cruise). During this period of strong stratification, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were examined to produce a detailed spatial and vertically extended description of the elemental stoichiometry of the Mediterranean Sea. Surface waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, with the phosphacline deepening to a greater extent than that for corresponding nitracline and thermocline depths. We used the minimum oxygen concentration through the water column in combination with 2 fixed concentrations of dissolved oxygen to distinguish an intermediate layer (Mineralization Layer; ML) from surface (Biogenic Layer; BL), and deep layers (DL). Whilst each layer was represented by different water masses, this approach allowed us to propose a schematic box-plot representation of the biogeochemical functioning of the two Mediterranean basins. Despite the increasing oligotrophic nature and the degree of P-depletion along the West to East gradient strong similarities were encountered between eastern and western ecosystems. Within the BL, the C:N:P ratios in all pools largely exceeded the Redfield ratios, but surprisingly, the nitrate vs. phosphate ratios in the ML and DL tended towards the canonical Redfield values in both basins. A change in particulate matter composition has been identified by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. Our data showed a noticeable stability of the DOC:DON ratio (12–13) throughout the Mediterranean Sea. This is in good agreement with a P-limitation of microbial activities but in contradiction of the accepted concept that N is recycled faster than C. The western and eastern basins had similar or close biological functioning. Differences come from variability in the allochtonous nutrient sources in terms of quantity and quality, and to the specific hydrodynamic features of the Mediterranean basins.

scholarly journals Lack of P-limitation of phytoplankton and heterotrophic prokaryotes in surface waters of three anticyclonic eddies in the stratified Mediterranean Sea

2011 ◽  
Vol 8 (2) ◽  
pp. 525-538 ◽  
Author(s):  
T. Tanaka ◽  
T. F. Thingstad ◽  
U. Christaki ◽  
J. Colombet ◽  
V. Cornet-Barthaux ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Surface Waters ◽  
Ammonium Phosphate ◽  
Turnover Time ◽  
General Notion ◽  
Western Basin ◽  
P Limitation ◽  
Levantine Basin ◽  
Heterotrophic Prokaryotes ◽  
Anticyclonic Eddies

Abstract. We investigated the identity of the limiting nutrient of the pelagic microbial food web in the Mediterranean Sea using nutrient manipulated microcosms during summer 2008. Experiments were carried out with surface waters at the center of anticyclonic eddies in the Western Basin, the Ionian Basin, and the Levantine Basin. In situ, the ratio of N to P was always higher in both dissolved and particulate organic fractions compared to the Redfield ratio, suggesting a relative P-starvation. In each experiment, four different treatments in triplicates (addition of ammonium, phosphate, a combination of both, and the unamended control) were employed and chemical and biological parameters monitored throughout a 3–4 day incubation. Temporal changes of turnover time of phosphate and ATP, and alkaline phosphatase activity during the incubation suggested that the phytoplankton and heterotrophic prokaryotes (Hprok) communities were not P-limited at the sites. Furthermore, statistical comparison among treatments at the end of the incubation did not support a hypothesis of P-limitation at the three study sites. In contrast, primary production was consistently limited by N, and Hprok growth was not limited by N nor P in the Western Basin, but N-limited in the Ionian Basin, and N and P co-limited in the Levantine Basin. Our results demonstrated the gap between biogeochemical features (an apparent P-starved status) and biological responses (no apparent P-limitation). We question the general notion that Mediterranean surface waters are limited by P alone during the stratified period.

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 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 The Mediterranean Sea Overturning Circulation

2019 ◽  
Vol 49 (7) ◽  
pp. 1699-1721 ◽  
Author(s):  
Nadia Pinardi ◽  
Paola Cessi ◽  
Federica Borile ◽  
Christopher L. P. Wolfe
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Eastern Mediterranean ◽  
Deep Ocean ◽  
Western Mediterranean ◽  
The Other ◽  
Strait Of Gibraltar ◽  
Water Formation ◽  
Dense Water Formation ◽  
Meridional Overturning

AbstractThe time-mean zonal and meridional overturning circulations of the entire Mediterranean Sea are studied in both the Eulerian and residual frameworks. The overturning is characterized by cells in the vertical and either zonal or meridional planes with clockwise circulations in the upper water column and counterclockwise circulations in the deep and abyssal regions. The zonal overturning is composed of an upper clockwise cell in the top 600 m of the water column related to the classical Wüst cell and two additional deep clockwise cells, one corresponding to the outflow of the dense Aegean water during the Eastern Mediterranean Transient (EMT) and the other associated with dense water formation in the Rhodes Gyre. The variability of the zonal overturning before, during, and after the EMT is discussed. The meridional basinwide overturning is composed of clockwise, multicentered cells connected with the four northern deep ocean formation areas, located in the Eastern and Western Mediterranean basins. The connection between the Wüst cell and the meridional overturning is visualized through the horizontal velocities vertically integrated across two layers above 600 m. The component of the horizontal velocity associated with the overturning is isolated by computing the divergent components of the vertically integrated velocities forced by the inflow/outflow at the Strait of Gibraltar.

scholarly journals Microbial community genomics in eastern Mediterranean Sea surface waters

2009 ◽  
Vol 4 (1) ◽  
pp. 78-87 ◽  
Author(s):  
Roi Feingersch ◽  
Marcelino T Suzuki ◽  
Michael Shmoish ◽  
Itai Sharon ◽  
Gazalah Sabehi ◽  
...  
Keyword(s):  
Microbial Community ◽  
Mediterranean Sea ◽  
Surface Waters ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Eastern Mediterranean Sea

scholarly journals On the Circulation and Thermohaline Properties of the Eastern Mediterranean Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Milena Menna ◽  
Riccardo Gerin ◽  
Giulio Notarstefano ◽  
Elena Mauri ◽  
Antonio Bussani ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Mixed Layer ◽  
Eastern Mediterranean ◽  
Mixed Layer Depth ◽  
Eastern Mediterranean Sea ◽  
Salt Fingers ◽  
Main Circulation ◽  
Satellite Altimetry Data

The circulation of the Eastern Mediterranean Sea is characterized by numerous recurrent or permanent anticyclonic structures, which modulate the pathway of the main currents and the exchange of the water masses in the basin. This work aims to describe the main circulation structures and thermohaline properties of the Eastern Mediterranean with particular focus on two anticyclones, the Pelops and the Cyprus gyres, using in-situ (drifters and Argo floats) and satellite (altimetry) data. The Pelops gyre is involved in the circulation and exchange of Levantine origin surface and intermediate waters and in their flow toward the Ionian and the Adriatic Sea. The Cyprus Gyre presents a marked interannual variability related to the presence/absence of waters of Atlantic origin in its interior. These anticyclones are characterized by double diffusive instability and winter mixing phenomena driven by salty surface waters of Levantine origin. Conditions for the salt finger regime occur steadily and dominantly within the Eastern Mediterranean anticyclones. The winter mixing is usually observed in December–January, characterized by instability conditions in the water column, a gradual deepening of the mixed layer depth and the consequent downward doming of the isohalines. The mixing generally involves the first 200 m of the water column (but occasionally can affect also the intermediate layer) forming a water mass with well-defined thermohaline characteristics. Conditions for salt fingers also occur during mixing events in the layer below the mixed layer.

Climate and carbon cycle changes drive the hydrographic configuration of the eastern Mediterranean through the Tortonian-Messinian Transition

2021 ◽  
Author(s):  
Evangelia Besiou ◽  
George Kontakiotis ◽  
Assimina Antonarakou ◽  
Andreas Mulch ◽  
Iuliana Vasiliev
Keyword(s):  
Carbon Cycle ◽  
Water Column ◽  
Surface Waters ◽  
Late Miocene ◽  
Eastern Mediterranean ◽  
Sea Surface ◽  
Time Interval ◽  
Climate Modelling ◽  
Paleoenvironmental Reconstruction ◽  
Crete Island

<p>The Late Miocene has been considered one of the most climatically stable periods of the Cenozoic, time span characterized by minor long-term cooling and ice growth. Especially, the Tortonian-Messinian Transition is recognized as a priority for paleoenvironmental reconstruction and climate modelling due to the significant paleoenvironmental changes preceding the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Here, we present stable oxygen (δ<sup>18</sup>O) and carbon (δ<sup>13</sup>C) isotopes measured on benthic and planktonic foraminifera from Potamida section (Crete Island, eastern Mediterranean). The δ<sup>18</sup>O results indicate a decoupling between the surface and the bottom water column starting before the Tortonian-Messinian boundary. The difference between planktonic and benthic oxygen isotope signals (Δδ<sup>18</sup>O) further provides an estimate of the degree of water column stratification during that time. The δ<sup>13</sup>C data indicate a generally trend towards lighter values as an excellent illustration of the Late Miocene Carbon Isotope Shift (LMCIS; 7.6-6.6 Ma) due to progressive restriction of the Mediterranean basin, with the exception of the 7.38-7.26 Ma time interval where significantly heavier δ<sup>13</sup>C values are documented in both records. Such changes in carbon cycle seem to be most pronounced in the planktonic foraminiferal record (surface waters) through a 6-cycle development indicative of a cyclic productivity pattern during the latest Tortonian. The entire record is substantiated by sea surface temperature (SST) estimates based on TEX<sub>86</sub> biomarker based proxy. The reconstructed SST record shows that a warm phase characterized the late Tortonian sea surface (~27⁰C), time followed by a strong, steady cooling starting with earliest Messinian, when the SSTs dropped to values as low as 20⁰C. The outcome of the combined stable isotope and biomarker based SST data hint to increased salinity in the surface waters already before the Messinian, while at the Tortonian-Messinian Transition, the conditions in the surface waters changed towards cooler (~24⁰C) and normal salinity conditions.</p>

scholarly journals Thalassospira sp. Isolated from the Oligotrophic Eastern Mediterranean Sea Exhibits Chemotaxis toward Inorganic Phosphate during Starvation

2011 ◽  
Vol 77 (13) ◽  
pp. 4412-4421 ◽  
Author(s):  
Annemarie Hütz ◽  
Karin Schubert ◽  
Jörg Overmann
Keyword(s):  
Mediterranean Sea ◽  
Water Column ◽  
Inorganic Phosphate ◽  
Phosphate Uptake ◽  
Eastern Mediterranean ◽  
Phosphate Limitation ◽  
Soluble Phosphate ◽  
Free Living ◽  
Eastern Mediterranean Sea ◽  
Content Type

ABSTRACTThe eastern Mediterranean Sea represents an ultraoligotrophic environment where soluble phosphate limits the growth of bacterioplankton. Correspondingly, genes coding for high-affinity phosphate uptake systems and for organophosphonate utilization are highly prevalent in the plankton metagenome. Chemotaxis toward inorganic phosphate constitutes an alternative strategy to cope with phosphate limitation, but so far has only been demonstrated for two bacterial pathogens and an archaeon, and not in any free-living planktonic bacterium. In the present study, bacteria affiliated with the genusThalassospirawere found to constitute a regular, low-abundance member of the bacterioplankton that can be detected throughout the water column of the eastern Mediterranean Sea. A representative (strain EM) was isolated in pure culture and exhibited a strong positive chemotaxis toward inorganic phosphate that was induced exclusively in phosphate-starved cultures. Phosphate-depleted cells were 2-fold larger than in exponentially growing cultures, and 43% of the cells retained their motility even during prolonged starvation over 10 days. In addition,Thalassospirasp. strain EM was chemotactically attracted by complex substrates (yeast extract and peptone), amino acids, and 2-aminoethylphosphonate but not by sugar monomers. Similarly to the isolate from the eastern Mediterranean, chemotaxis toward phosphate was observed in starved cultures of the other two available isolates of the genus,T. lucentensisDSM 14000TandT. profundimarisWP0211T. AlthoughThalassospirasp. represents only up to 1.2% of the total bacterioplankton community in the water column of the eastern Mediterranean Sea, its chemotactic behavior potentially leads to an acceleration of nutrient cycling and may also explain the persistence of marine copiotrophs in this extremely nutrient-limited environment.

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