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Metal and metallothionein (MT) in mixed zooplankton were investigated as means of monitoring metal availability regarding environmental exposure. Spatial and temporal variability of Cd, Cu, Ni, Zn, Fe, Mn and Pb in zooplankton and seawater were studied in Saronikos Gulf (Aegean Sea, Eastern Mediterranean), once every second month during an annual cycle (2011–2012). Particulate organic carbon and chlorophyll α were also measured in seawater samples. Median zooplankton metal concentrations were 0.65, 32.4, 7.1, 864, 1420, 40.2 and 26.8 μg g-1 dw for Cd, Cu, Ni, Zn, Fe, Mn and Pb, respectively, and 109 μg g-1 ww for MTs. Metal levels in zooplankton and MTs were higher at sites influenced by human-derived pressures. Additionally, metal concentrations in pelagic fish flesh from the Greek MED-POL data base were used for bioconcentration and biomagnification factors calculation. Bioconcentration from water to zooplankton was higher than metal transfer from either seston to zooplankton or zooplankton to fish. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.

Normally atmospheric CO2 is the major driver of ocean acidification (OA); however, local discharge/degradation of organic matter (OM) and redox reactions can exacerbate OA in coastal areas. In this work we study the response of nutrient and carbon systems to pH decrease in relation to hydrographically induced intermittent characteristics and examine scenarios for future ocean acidification in a coastal system. Laboratory microcosm experiments were conducted using seawater and surface sediment collected from the deepest part of Elefsis Bay; the pH was constantly being monitored while CO2 gas addition was adjusted automatically. In Elefsis Bay surface pCO2 is already higher than global present atmospheric values, while near the bottom pCO2 reaches 1538 µatm and carbonate saturation states were calculated to be around 1.5. During the experiment, in more acidified conditions, limited alkalinity increase was observed and was correlated with the addition of bicarbonates and OM. Ammonium oxidation was decelerated and a nitrification mechanism was noticed, despite oxygen deficiency, paralleled by reduction of Mn-oxides. Phosphate was found significantly elevated for the first time in lower pH values, without reprecipitating after reoxygenation; this was linked with Fe(II) oxidation and Fe(III) reprecipitation without phosphate adsorption affecting both available dissolved phosphate and (dissolved inorganic nitrogen) DIN:DIP (dissolved inorganic phosphate)ratio. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Naturally occurring microbial decomposition of organic matter (OM) in coastal marine environments cause increased acidity in deeper layers similar or even exceeding the future predictions for global ocean acidification (OA). Experimental studies in coastal areas characterized by increased inputs of OM and nutrients, coping with intermittent hypoxic/anoxic conditions, provide better understanding of the mechanisms affecting nutrients and carbon biogeochemistry under the emerging effects of coastal pH decrease. Laboratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected from the deepest part of Elefsis Bay (Saronikos Gulf, Eastern Mediterranean) focusing to study the co-evolution of processes affected by the decline of dissolved oxygen and pH induced by (a) OM remineralization and (b) the future anthropogenic increase of atmospheric CO2. Under more acidified conditions, a significant increase of total alkalinity was observed partially attributed to the sedimentary carbonate dissolution and the reactive nitrogen species shift towards ammonium. Nitrate and nitrite decline, in parallel with ammonium increase, demonstrated a deceleration of ammonium oxidation processes along with decrease in nitrate production. The decreased DIN:DIP ratio, the prevalence of organic nutrient species against the inorganic ones, the observations of constrained DON degradation and nitrate production decline and the higher DOC concentrations revealed the possible inhibition of OM decomposition under lower pH values. Finally, our results highlight the need for detailed studies of the carbonate system in coastal areas dominated by hypoxic/anoxic conditions, accompanied by other biogeochemical parameters and properly designed experiments to elucidate the processes sequence or alterations due to pH reduction. © 2018 Mediterranean Marine Science.

The Samaria and Lithinon canyons at the southern Cretan margin (Eastern Mediterranean) were studied with respect to hydrography, deep currents, particle dynamics and settling fluxes by utilizing: (a) current-meter and sediment trap records from May 2005 to May 2006; and (b) hydrographic and optical measurements along with particulate matter and particulate organic carbon concentrations (PMC and POC, respectively) in two surveys (May and October 2005). The deep currents were very weak with mean velocity ∼3–4 cm s−1 and their direction was controlled by the local bottom topography. The entire area was characterized by very low PMC and POC, depicted both by transmissometry profiles and discrete bottle data. The fluxes of downward settling particles are comparable with the fluxes measured in the broader Eastern Mediterranean and hence point to an oligotrophic environment with low atmospheric and lateral inputs. A series of relatively high total mass fluxes (>1000 mg m−2 d−1) were recorded near the head of the Samaria canyon, at the trap closest to Crete, and was attributed to: (a) high temporal lithogenic inputs (mineral calcite) transferred to the sea by a small, intermittent stream flowing through the Samaria gorge, which was activated by short rainfall events and spring snowmelt; and (b) inputs of numerous coccoliths of E. huxleyi and calcite by shallow sediment resuspension generated by wind-induced waves. Apart from this local-scale event, there was very little evidence of matter transfer through the canyons, thus, during the one-year of observations, the canyons were dormant. Because of this lack of down-canyon transport during the study period, open slopes and canyons exhibited roughly similar characteristics in terms both of particle dynamics and fluxes. However, the presence of coarse-grained sediments along the canyon axes point to episodic canyon activity, occurring at unknown time scales and periodicity. © 2017 Elsevier Ltd

A natural pH gradient caused by marine CO2 seeps off the Methana peninsula (Saronikos Gulf, eastern Peloponnese peninsula) was used as a natural laboratory to assess potential effects of ocean acidification on coccolithophores. Coccolithophore communities were therefore investigated in plankton samples collected during September 2011, September 2016 and March 2017. The recorded cell concentrations were up to ~50 x103 cells/l, with a high Shannon index of up to 2.8, along a pH gradient from 7.61 to 8.18, with values being occasionally

In order to identify how ocean acidification will influence biological interactions and fluxes among planktonic organisms and across trophic levels, a large-scale mesocosm experiment was performed in the oligotrophic Northwestern Mediterranean Sea in the framework of the European MedSeA project. Nine mesocosms were deployed in the Bay of Calvi (Corsica, France) in summer 2012. Six mesocosms were subjected to different levels of CO2 partial pressures (pCO2; 550, 650, 750, 850, 1000 and 1250 μatm) covering the range of atmospheric pCO2 anticipated for the end of this century depending on future emission scenarios, and the last three mesocosms were unaltered (ambient pCO2 of ∼450 μatm). During this 21-day experiment, we monitored copepod egg and naupliar stocks, estimated copepod (Acartia clausi and Centropages typicus) feeding rates and determined the abundance and taxonomic composition of the mesozooplankton community at the start and at the completion of the experiment. This community was clearly dominated by copepods and its final composition slightly varied between mesocosms most likely due to natural and experimental variability that cannot be related to CO2 conditions. The abundances of eggs and nauplii as well as feeding rates of A. clausi and C. typicus on diatoms, dinoflagellates and ciliates showed no significant differences among CO2 levels. The above findings suggest that the experimental set-up especially for the specific trophic conditions and the short duration of the experiment did not provide the information on the effect of acidification that was expected. The acidification might have an effect on planktonic communities and even worsen the problems imposed by food limitation, therefore on this short time scale experiment and under the extreme ologotrophic conditions the signal that dominates was the food limitation. © 2016 Elsevier Ltd

International audience; A compilation of several cruises data from 1998 to 2013 was used to derive polynomial fits that estimate total alkalinity (AT) and total inorganic carbon (CT) from measurements of salinity and temperature in the Mediterranean Sea surface waters. The optimal equations were chosen based on the 10-fold cross validation results and revealed that a second and third order polynomials fit the AT and CT data respectively. The AT surface fit showed an improved root mean square error (RMSE) of ±10.6 μmol kg−1. Furthermore we present the first annual mean CT parameterization for the Mediterranean Sea surface waters with a RMSE of ±14.3 μmol kg−1. Excluding the marginal seas of the Adriatic and the Aegean, these equations can be used to estimate AT and CT in case of the lack of measurements. The seven years averages (2005–2012) mapped using the quarter degree climatologies of the World Ocean Atlas 2013 showed that in surface waters AT and CT have similar patterns with an increasing eastward gradient. The surface variability is influenced by the inflow of cold Atlantic waters through the Strait of Gibraltar and by the oligotrophic and thermohaline gradient that characterize the Mediterranean Sea. The summer-winter seasonality was also mapped and showed different patterns for AT and CT. During the winter, the AT and CT concentrations were higher in the western than in the eastern basin, primarily due to the deepening of the mixed layer and upwelling of dense waters. The opposite was observed in the summer where the eastern basin was marked by higher AT and CT concentrations than in winter. The strong evaporation that takes place in this season along with the ultra-oligotrophy of the eastern basin determines the increase of both AT and CT concentrations.

The aim of this work is to assess trace metal pollution status (Cd, Cu, Ni, Pb, Zn) in the waters of Saronikos Gulf, Greece, in line with the WFD and MSFD European Directives, based on data collected over a decade (2000-2010). Dissolved metal background levels are estimated for the first time for Greek marine waters and the upper limits are: Cd: 0.574nmolL-1; Cu: 8.26nmolL-1; Ni: 7.94nmolL-1; Pb: 2.60nmolL-1; Zn: 115nmolL-1. The variability of dissolved and particulate metals reflected the presence of several point sources and revealed the importance of natural mechanisms acting as non-point sources. The status of Saronikos Gulf is classified as 'High' for most metals studied. An exception to this is the enclosed Elefsis Bay where Cu, Ni and Zn concentrations are found above background. Our work will assist the implementation of WFD and MSFD directives in Greece. © 2014 Elsevier Ltd.

The dynamics of dissolved organic matter (DOM) in the Marmara Sea-Dardanelles Straits-North Aegean Sea were investigated using measurements of dissolved organic carbon and nitrogen (DOC, DON), PARAFAC modeling of 3-D excitation-emission fluorescence spectra and bacterial production (BP) and respiration (BR) rates. In the surface brackish waters, chemical parameters showed an increase from the Aegean to the Marmara (DOC: 65-217μmolL-1; DON: 3.08-9.34μmolL-1; Dissolved Inorganic Nitrogen (DIN): 0.044-1.38), followed by an increase in BP rates (7.2-195nmolL-1d-1). In the subsurface waters, DIN also showed an increase in the Marmara basin (0.085-9.79μmolL-1) followed by an increase in BP rates (3.3-17.4nmolL-1d-1). PARAFAC modeling revealed three fluorescent components: λex/λem

A seasonal morphological variability is observed in Emiliania huxleyi var. huxleyi specimens, collected from discrete water samples in the Aegean Sea. Biometric analyses reveal a consistent pattern of increase in the size of coccoliths and coccospheres, including the thickness of the inner tube elements (INT), in winter/spring time low sea surface temperature and moderate productivity samples when compared with summer time high temperature-low productivity samples. The small range of salinity change in the Aegean Sea and the absence of seasonal pattern in nutrient content do not support any association with the observed increase in E. huxleyi coccolith size. A relatively increased [HCO3-] content is observed during spring-time interval related with the increase in the coccolith size, however it remains unclear which parameter of the carbonate system causes the observed effects. © 2009 Elsevier Masson SAS. All rights reserved.

Distribution, production and grazing of the copepod community were investigated in the northern Aegean Sea, which is characterized by a permanent thermohaline front. Cruises were conducted along a transect crossing the frontal area during spring and late summer. Biomass and production of autotrophs were measured by size fractionation and heterotrophic nanoflagellates and ciliates were also studied. Copepod biomass, production and grazing impact on the phytoplankton and ciliate populations were estimated. The copepod community was sampled with a 45 μm net to include the smallest species and their developmental stages. The size, structure and distribution of the phytoplankton imply that most carbon was fixed by picoplankton during both seasons and throughout the study area. The partitioning of carbon among the different plankton compartments was not a broad-based pyramid and the biomass of heterotrophs was higher than that of autotrophs, except in the non-frontal region during spring. Copepod biomass was substantially higher in the frontal area. Our results showed that the small-sized copepods (calanoids and cyclopoids) dominated in terms of biomass and production, but also had a greater influence on the efficiency of the trophic coupling between the primary producers and the protozooplankton than the larger species, stressing their importance in the northern Aegean Sea and the Eastern Mediterranean in general. © The Author 2007. Published by Oxford University Press. All rights reserved.

The Jabuka Pit, a continental shelf depression in the middle Adriatic Sea, acts as a collection basin for the dense water formed during winter in the northern Adriatic. Its deep waters are usually renewed at least every second year. The deep waters of Jabuka Pit remained practically isolated after the strong flushing occurred in early spring 1993. Our data from May 1993 to November 1994, permitted to follow, step by step, the oxygen consumption and the nutrient and carbon regeneration in the deep layer of Jabuka Pit during this period of isolation. Extremely high oxygen consumption and nutrients and carbon regeneration rates were estimated; the oxygen reduction rate is about 66.5 μmol/kg/yr, while the accompanying increasing rate of nitrate is 2.64 μmol/kg/yr, of silicate 4.2 μmol/kg/yr, of phosphate 0.24 μmol/kg/yr and of ΣCO 2 81.0 μmol/kg/yr. The temporal evolution of the regeneration ratios of nitrogen and carbon, as well as of the N inorg/PO 4 ratio, imply that possibly other processes, besides aerobic respiration, like denitrification, take place and modulate the values of the ratios. Furthermore, the changes of the concentrations of oxygen, nitrate, phosphate and ΣCO 2 in the deep layers of Jabuka Pit were exploited in order to estimate the elemental composition of the organic matter that is remineralised. Our results suggest that the most probable empirical formula that corresponds to the composition of the organic matter in the study system is (C 4H 6ON) 8; (C 6H 10O 5) 3; (CH 2) 108 being 11.4% carbohydrates, 20.3% proteins and 68.3% lipids. Furthermore, the investigation of our results show that there is evidence that the observed changes of the concentrations of the chemical parameters are better interpreted if additionally to the remineralisation of organic matter, small-scale CaCO 3 dissolution with simultaneous denitrification processes are considered. © 2004 Elsevier Ltd. All rights reserved.

A series of seasonal cruises and Eulerian current measurements in the Otranto Strait were carried out to study the biogeochemical characteristics of the strait and to estimate the exchange of water, dissolved and particulate matter between the Adriatic and the Ionian Sea. From the biogeochemical distributions obtained, the role for the Adriatic Sea in supporting the N:P ratio anomaly of the Mediterranean is hypothesized. Examining the bottom oxygen distribution, the deep ventilation of the Eastern Mediterranean seems to follow a more complex pathway than previously hypothesized Fluxes computation shows a net outflow through the strait for nitrate, phosphate and silicate, while a slight net inflow was obtained for POC and PN.

A series of chemical parameters were studied in the water, particulate matter and sediments of Aetoliko lagoon, a wetland in western Greece, after an ecological impact at the end of November 1990, which resulted in massive death of fish. The permanent anoxic conditions in the deeper water layer of the lagoon, with the simultaneous formation of hydrogen sulfide, are the main characteristics of the system. The dramatic reduction of the dissolved oxygen in the surface water which was substituted by the hydrogen sulfide of the near bottom water layer caused the sudden death of organisms. This phenomenon also affected the nutrients. Ammonia was the main nitrogen form; phosphates and silicates were concentrated in near bottom waters, and the concentrations of nitrates and nitrites were much lower in December than 3 months later in the surface waters. The behaviour of trace metals also indicated that in the extraordinary conditions studied, the main mechanisms of transport of metals among the main phases of the system (dissolved-particulate-sediments) were severely disturbed. © 1994.

Caesium-137 activity concentrations (137Cs) were measured between 2003 and 2014 in the water column of Lemnos and Cretan deep basins of the Aegean Sea. The purpose was to assess water-mass dynamics and mixing processes by combining typical oceanographic data with the activity concentrations of 137Cs. The radiological data, combined with dissolved oxygen profiles, provided substantially more information than solely temperature and salinity regarding processes such as water-mass identification, formation and mixing. In each basin it was possible to determine stagnant periods, where turbulent mixing was dominant, as well as periods where replenishment of the deep basins had been taken place. At Lemnos basin, the data profile in 2013 proved evidence of water column ventilation down to 800 m and replenishment of the deep basin by less saline water mass. The 137Cs information provided evidence for contribution of water from the Black Sea to the intermediate and deep layers of the South Aegean (Cretan) basin. The profiles of 2013 and 2014 were characterized by the return of 137Cs inventories to pre-Chernobyl levels.