Harilaos Kontoyiannis | Hellenic Centre of Marine Research (original) (raw)

Papers by Harilaos Kontoyiannis

Dynamics of atmospheres and oceans, Apr 1, 2024

Deep-sea Research Part Ii-topical Studies in Oceanography, 2020

Abstract The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time ... more Abstract The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time in April 2016 with a combination of direct current measurements comprised by CTD-LADCP (Lowered Acoustic Doppler Current Profiler) grid casts and ship-track ADCP measurements in the upper 500 m, while a mooring was launched at the end of the continental slope and provided yearly current records at 700 m and 30 m off the bottom depth of 4300 m. Horizontal flow structures are mapped in the upper 1000 m via objective analysis of the direct current measurements depicting the Cretan Cyclone at the west, the Rhodes Gyre at the east and anticyclonic circulation in the middle due to Modified Atlantic Water in the upper 80 m and a thick, saline, warm mass extending from ~100 m to ~1500 m, possibly of Cretan origin. The bottom kinetic energy spectra have higher density values than those at 700 m. In the two-month energetic period of end/Jan.-to-end/Mar. 2017, topographic Rossby waves (TRW) with wavelength of ~42 km exist in the window of ~34-19 days with significant coherence between the near-bottom and the 700-m records. At the TRW spectral window, the motions are transverse and the direction of maximum velocity variance veers from nearly along isobaths ~20° (north-northeast) to ~45° (northeast) with decreasing period. The presence of TRWs in the specific time period within 2017 appears to be related to the lateral shifts of the Ierapetra Anticyclone over the sloping bottom of the continental margin.

Journal of Climate, Feb 27, 2013

The influence of the atmospheric circulation on the winter air-sea heat fluxes over the northern ... more The influence of the atmospheric circulation on the winter air-sea heat fluxes over the northern Red Sea is investigated during the period 1985-2011. The analysis based on daily heat flux values reveals that most of the net surface heat exchange variability depends on the behavior of the turbulent components of the surface flux (the sum of the latent and sensible heat). The large-scale composite sea level pressure (SLP) maps corresponding to turbulent flux minima and maxima show distinct atmospheric circulation patterns associated with each case. In general, extreme heat loss (with turbulent flux lower than 2400 W m 22) over the northern Red Sea is observed when anticyclonic conditions prevail over an area extending from the Mediterranean Sea to eastern Asia along with a recession of the equatorial African lows system. Subcenters of high pressure associated with this pattern generate the required steep SLP gradient that enhances the wind magnitude and transfers cold and dry air masses from higher latitudes. Conversely, turbulent flux maxima (heat loss minimization with values from 2100 to 250 W m 22) are associated with prevailing low pressures over the eastern Mediterranean and an extended equatorial African low that reaches the southern part of the Red Sea. In this case, a smooth SLP field over the northern Red Sea results in weak winds over the area that in turn reduce the surface heat loss. At the same time, southerlies blowing along the main axis of the Red Sea transfer warm and humid air northward, favoring heat flux maxima.

The handbook of environmental chemistry, 2020

Journal of ocean engineering and marine energy, Apr 10, 2015

In the Euripus channel, we assess the hydrokinetic tidal resource at the narrowest constriction w... more In the Euripus channel, we assess the hydrokinetic tidal resource at the narrowest constriction which is in the city of Halkida at the Old Bridge. This is accomplished by combining data from (a) several ADCP (Acoustic Doppler Current Profiler) cross-channel snapshot transects at the Old Bridge and (b) a 2-month current meter record obtained at 1.5 m off the bottom at the edge of the cross section at the New Bridge, which is a ∼fourfold wider constriction with lower tidal velocities compared to the Old Bridge. A linear relationship exists between the along-channel velocity at the current meter site and the maximum of the along-channel velocity on the cross section at the Old Bridge. We can, therefore, determine the cross-channel distributions of the along-channel velocity at the Old Bridge during the 2-month period of the current meter record. We examine the use of a 4-m-diameter turbine, suitable to the space limitations at the Old Bridge. This turbine functions for flow velocity values higher than ∼50 cm/s and with a nearly constant efficiency of ∼40-45 % for flow velocity higher than 50 cm/s; a constant 45 % is achieved for all velocity values higher than 150 cm/s. This machine yields an annual energy of ∼28.6 MWh, out of an existing ∼71.5 MWh for its aperture when there is zero efficiency loss. This amount of energy is not enough for wide-scale applications but it covers the needs of an exhibition place for tourists visiting Halkida, which was the first question posed in the beginning of this project.

Continental Shelf Research, Dec 1, 2005

The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean... more The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea) are described, for September 2001 and October 2001 and February 2002. The observations were obtained to assess the impact of anthropogenic and natural resuspension processes on the coastal ecosystem. The first two periods represent highly stratified conditions and mild weather conditions; in September trawling is prohibited,

<p>Biotic and abiotic processes that form, alter, t... more <p>Biotic and abiotic processes that form, alter, transport, and remineralize particulate organic carbon, silicon, calcium carbonate, and other minor and trace chemical species in the water column are central to the ocean’s ecological and biogeochemical functioning and of fundamental importance to the ocean carbon cycle. Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the deep sea. During its transit towards the sea floor, most particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO<sub>2</sub>, and hence the rate at which the ocean can absorb CO<sub>2</sub> from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to deciphering the response of the global carbon cycle to natural and human-induced changes.</p><p>Aiming to investigate the significant biogeochemical and ecological features and provide new insights on the sources and cycles of sinking particulate matter, a mooring line of five sediment traps was deployed from 2006 to 2015 (with some gap periods) at 5 successive water column depths (700, 1200, 2000, 3200 and 4300 m) in the SE Ionian Sea, northeastern Mediterranean (‘NESTOR’ site). We have examined the long-term records of downward fluxes for Corg, N<sub>tot</sub>, δ<sup>13</sup>Corg and δ<sup>15</sup>N<sub>tot</sub>, along with the associated ballast minerals (opal, lithogenics and CaCO<sub>3</sub>), lipid biomarkers, Chl-a and PP rates, phytoplankton composition, nutrient dynamics and atmospheric deposition.  </p><p>The satellite-derived seasonal and interannual variability of phytoplankton metrics (biomass and phenology) and atmospheric deposition (meteorology and air masses origin) was examined for the period of the sediment trap experiment. Regarding the atmospheric deposition, synergistic opportunities using Earth Observation satellite lidar and radiometer systems are proposed (e.g. Cloud‐Aerosol Lidar with Orthogonal Polarization - CALIOP, Moderate Resolution Imaging Spectroradiometer - MODIS), aiming towards a four‐dimensional exploitation of atmospheric aerosol loading (e.g. Dust Optical Depth) in the study area.</p><p>Our main goals are to: i) develop a comprehensive knowledge of carbon fluxes and associated mineral ballast fluxes from the epipelagic to the mesopelagic and bathypelagic layers, ii) elucidate the mechanisms governing marine productivity and carbon export and sequestration to depth and iii) shed light on the impact of atmospheric forcing and deposition in respect to regional and large scale circulation patterns and climate variability and the prevailing oceanographic processes (internal variability).</p><p>Acknowledgments</p><p>We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – <strong>CLIMPACT</strong>’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments).</p>

EAEJA, Apr 1, 2003

An array of thirty drifters deployed in the northern Aegean are used to consider the circulation ... more An array of thirty drifters deployed in the northern Aegean are used to consider the circulation in a complex archipelago of islands. The circulation of the Aegean is largely influenced by a combination of buoyancy from freshwaters introduced from the Black Sea via the Dardenelles Straits and from coastal rivers and by wind forcing. The latter is highly structured as

Journal of Physical Oceanography, Apr 1, 2016

The mass and flow fields from June 2006 to May 2009 in the Calypso Deep (bottom depth ;5.2 km) ar... more The mass and flow fields from June 2006 to May 2009 in the Calypso Deep (bottom depth ;5.2 km) are investigated using eddy-resolving surface-to-bottom hydrography (station grid spacing ;0.28) and two tall moorings yielding current-meter records at depths from 700 m to near bottom. A salty warm lens (excess core salinity and temperature are ;0.01 and 0.0258C relative to the surrounding water) of Cretan Deep Water with a core at ;3000 m and a horizontal (vertical) scale of ;50 km (1.5 km) is identified in June 2006 to be locked over the trough. The lens coincides with local maxima in dissolved oxygen. In October 2006 the salinity content of the lens and of all deeper layers is increased; the oxygen maxima are shifted to the bottom layers, indicating an episodic intrusion of higher-density ventilated Adriatic water. The circulation changes from anticyclonic at all depths in June 2006 to cyclonic below ;2.5 km in October 2006, whereas after January 2007 it is cyclonic at all instrumented depths. The measured currents are weak (mean speeds , 5 cm s 21) and persistent in direction, being mostly along the bottom topography at all current-meter depths. After October 2006, the lens erodes due to salt/heat loss caused predominantly by lateral (intrusive) mixing, which works from the outside toward the lens center. The horizontal diffusivity is on the order of ;10 m 2 s 21 , near the center of the lens, and ;10 2 to 10 3 m 2 s 21 , at its periphery, with an average error ;15 times the diffusivity value. In the deepest part of the trough and in periods of predominance of vertical mixing the vertical diffusivity at 4400 m is ;(4 6 3) 3 10 23 m 2 s 21 .

In early spring of 1986, 1992 and 1995, newly formed deep water masses were observed in the cyclo... more In early spring of 1986, 1992 and 1995, newly formed deep water masses were observed in the cyclonic Rhodes Gyre of the Eastern Mediterranean at depths reaching ∼1000 m in 1995 and exceeding 1000 m in 1986 and 2000 m in 1992. Levantine Intermediate Water (LIW) formation was observed at localized source areas south of the East Cretan Straits at the periphery or near the center of the Ierapetra Anticyclone. Adittional massive LIW formation was observed in 1992 in anticyclonic circulation structures north of Cyprus. The lateral scales of the newly formed water masses in cyclonic structures appear roughly proportional to the penetration depth of the convection, so that a large lateral scale indicating a massive production would be associated with a deep rather than an intermediate formation.

Springer eBooks, 1999

... D'Alcala, A. Theocharis, S. Brenner, G. Boudillon, E. Ozsoy (1998). The eastern Mediterr... more ... D'Alcala, A. Theocharis, S. Brenner, G. Boudillon, E. Ozsoy (1998). The eastern Mediterranean in the'80s and in the'90s: The transition in the intermediate and deep circulation, in preparation.. 5. Laskaratos A. and S. Tsandilas (1998). Seasonal cycle of a coherent eddy in the ...

Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2019

Two successive cruises in the Cretan Sea and Cretan Passage (West Levantine basin) during April a... more Two successive cruises in the Cretan Sea and Cretan Passage (West Levantine basin) during April and June 2016 surveyed the physical characteristics of the water masses in these large Eastern Mediterranean basins. Data confirm that the hydrographical status is far different from that of the Eastern Mediterranean Transient (EMT) period; however, the basins have not yet returned to the pre-EMT status. In the Cretan Sea, intermediate water masses of both Cretan and Levantine origins are detected. The stagnating bottom waters of this basin still hold high salinity, density, and dissolved oxygen values, remnant of the EMT deep water formation episodes. Characterised by low salinity and oxygen values, transitional waters of Mediterranean origin are present between intermediate and bottom layers throughout the Cretan Sea. Intermittent weak outflow of warm and saline masses of Cretan origin towards the Eastern Mediterranean is observed at the bottom of both east and west Cretan Straits. In the Cretan Passage, there is no sign of the Ierapetra anticyclonic gyre, possibly related to the seasonality of the gyre or linked to larger scale Eastern Mediterranean circulation variability. The observed surface circulation in this area is comprised of a series of smaller gyres between the Cretan Cyclone and the Rhodes Gyre. The bottom waters of the Cretan Passage present a west-to-east gradient of increasing salinity and decreasing oxygen related to the propagation of new Adriatic Deep Water from the Ionian Sea towards the Levantine basin.

International Journal of Climatology, 2009

Satellite and reanalysis data for the period 1982-2004 were used to study the long-term variabili... more Satellite and reanalysis data for the period 1982-2004 were used to study the long-term variability of the winter-mean sea surface temperature (SST) in the Black and Aegean Seas and its connection with the major atmospheric forcing: surface air temperature (SAT), surface wind and North Atlantic Oscillation (NAO) and East Atlantic-West Russia (EAWR) teleconnection patterns. In spite of some differences, the general tendencies of SST variability in both basins are similar. The major climatic event (i.e. SST decreases below the climatic mean followed by the sharp increase of SST, occurred during the period 1986-1999) and its connection with the atmospheric forcing are evident both in the Black and Aegean Seas. During the investigated period, the southwestern wind regime occurred over the Black Sea and the northeastern wind regime over the Aegean. It is shown that the variability of the meridional component of the surface wind (which provides the most of the atmospheric heat transport into the basins) is well correlated with the large-scale atmospheric patterns (NAO and EAWR). The major difference is that in the Black Sea the NAO intensification/weakening results in the weakening/strengthening of the southern wind, whereas in the Aegean Sea EAWR/NAO intensification/weakening produce strengthening/weakening of the northern wind. The long-term variability of the SST is well correlated with the variability of the SAT, which in turn is highly correlated with the meridional component of the surface wind. However, a remarkable feature is that in the Black Sea an increase/decrease of the SAT is associated with the strengthening/weakening of the southern wind. On the contrary, in the Aegean Sea, an increase/decrease of the SAT is associated with the weakening/strengthening of the northern wind. The simple basic scheme of influence of the large-scale atmospheric forcing on the long-term SST variability during the positive NAO and EAWR phase is proposed.

Journal Of Geophysical Research: Oceans, Nov 1, 2015

A variety of data based on hydrographic measurements, satellite observations, reanalysis database... more A variety of data based on hydrographic measurements, satellite observations, reanalysis databases, and meteorological observations are used to explore the interannual variability and factors governing the deep water formation in the northern Red Sea. Historical and recent hydrographic data consistently indicate that the ventilation of the near-bottom layer in the Red Sea is a robust feature of the thermohaline circulation. Dense water capable to reach the bottom layers of the Red Sea can be regularly produced mostly inside the Gulfs of Aqaba and Suez. Occasionally, during colder than usual winters, deep water formation may also take place over coastal areas in the northernmost end of the open Red Sea just outside the Gulfs of Aqaba and Suez. However, the origin as well as the amount of deep waters exhibit considerable interannual variability depending not only on atmospheric forcing but also on the water circulation over the northern Red Sea. Analysis of several recent winters shows that the strength of the cyclonic gyre prevailing in the northernmost part of the basin can effectively influence the sea surface temperature (SST) and intensify or moderate the winter surface cooling. Upwelling associated with periods of persistent gyre circulation lowers the SST over the northernmost part of the Red Sea and can produce colder than normal winter SST even without extreme heat loss by the sea surface. In addition, the occasional persistence of the cyclonic gyre feeds the surface layers of the northern Red Sea with nutrients, considerably increasing the phytoplankton biomass.

Springer eBooks, Nov 19, 2013

This chapter provides a long-term case study illustrating responses of a coastal Gulf in the Medi... more This chapter provides a long-term case study illustrating responses of a coastal Gulf in the Mediterranean Sea to reduced loading of sewage. Saronikos Gulf receives effluents from the Athens metropolitan area (population over 5 million). Until 1994, sewage discharged untreated into the surface waters of Keratsini and Elefis Bays. Sewage treatment first started in the Psitallia sewage treatment plant where the wastes discharged into inner Saronikos Gulf at 63 m depth. By the end of 2004, the secondary stage of the Psittalia sewage plant was operational.

Journal of Geophysical Research, 1990

During 1984, velocity, bottom pressure and thermocline depth data were obtained from deployments ... more During 1984, velocity, bottom pressure and thermocline depth data were obtained from deployments of tall current meter moorings, bottom pressure gauges and inverted echo sounders at five sites on the anticyclonic side of the Gulf Stream at 73'W. An additional number of inverted echo sounders, deployed in several nearby sites, allowed us to construct daily regional maps of the thermocline topography. Using this data base we examined the momentum balance and the pressure work in the eddy kinetic energy balance at 500 m above the seafloor and at a depth of 400 m. At 500 m off the bottom, the correlations between fluctuating geostrophic currents, inferred from pressure differences between sites, and suitably averaged observed currents provide observational confirmation of the geostrophic balance in the deep Gulf Stream, within our ability to measure it. At 400 m depth, the ageostrophic current was computed using velocity measurements, curvature estimates from the thermocline maps, and the momentum equation in natural coordinates. Comparison of observed and ageostrophic velocities showed occasional departures from geostrophy of 0(30% to 60%) with duration from 2 to 5 days. These ageostrophic events were caused by tangential and centripetal accelerations, mostly during the coalescence of two cold-core rings with the stream. The mean departure from geostrophy at 400 m during the deployment period was 7%. The mean effect of the pressure work, on the anticyclonic side of the stream at 400 m, was to decrease the eddy kinetic energy at a rate of-3 x 10-a ergs cm-s s-l; a value with magnitude as large as that of the barotropic instability term. The pressure work record is very episodic with peaks, during the ageostrophic events, close to 30 times larger than the mean estimate and with both positive and negative values. At 500 m off the bottom, the pressure work was found to be insignificantly different from zero. 1.

Nuclear Instruments and Methods in Physics Research, 2011

The long optical base transmissometer (LAMS-Long Arm Marine Spectrophotometer) constructed in 200... more The long optical base transmissometer (LAMS-Long Arm Marine Spectrophotometer) constructed in 2008 by NESTOR group is described. The data of the recent water transparency measurements in the NESTOR site and in the Capo Passero site in the wavelength range 378-522 nm are presented

The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly i... more The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly impacted by the greater metropolitan area of Greece’s capital, Athens, is examined through a series of state-of-the-art numerical models that address the hydrodynamics (Delft3D-FLOW), the wave regime (SWAN), the biogeochemistry, and pollution related to species of heavy metals and polyaromatic hydrocarbons (Delft3D-WAQ).The study so far has focused on calibrating model components and on reproducing the seasonal thermohaline conditions, known circulation patterns and the variability of biogeochemical constituents (chlorophyll-a, nutrients, dissolved and particulate matter) and pollutant concentrations, focusing on the vicinity of inner Saronikos.The annual cycle ‘Nov 2009 - Oct 2010’ is simulated, forced with atmospheric data from the ERA5 database. Three sets of open boundary conditions data are tested (Mediterranean Sea Physics Reanalysis dataset by Copernicus and two implementations of ...

Dynamics of atmospheres and oceans, Apr 1, 2024

Deep-sea Research Part Ii-topical Studies in Oceanography, 2020

Abstract The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time ... more Abstract The 1.5° lat. x 3.5° lon. Levantine area south of Crete was surveyed for the first time in April 2016 with a combination of direct current measurements comprised by CTD-LADCP (Lowered Acoustic Doppler Current Profiler) grid casts and ship-track ADCP measurements in the upper 500 m, while a mooring was launched at the end of the continental slope and provided yearly current records at 700 m and 30 m off the bottom depth of 4300 m. Horizontal flow structures are mapped in the upper 1000 m via objective analysis of the direct current measurements depicting the Cretan Cyclone at the west, the Rhodes Gyre at the east and anticyclonic circulation in the middle due to Modified Atlantic Water in the upper 80 m and a thick, saline, warm mass extending from ~100 m to ~1500 m, possibly of Cretan origin. The bottom kinetic energy spectra have higher density values than those at 700 m. In the two-month energetic period of end/Jan.-to-end/Mar. 2017, topographic Rossby waves (TRW) with wavelength of ~42 km exist in the window of ~34-19 days with significant coherence between the near-bottom and the 700-m records. At the TRW spectral window, the motions are transverse and the direction of maximum velocity variance veers from nearly along isobaths ~20° (north-northeast) to ~45° (northeast) with decreasing period. The presence of TRWs in the specific time period within 2017 appears to be related to the lateral shifts of the Ierapetra Anticyclone over the sloping bottom of the continental margin.

Journal of Climate, Feb 27, 2013

The influence of the atmospheric circulation on the winter air-sea heat fluxes over the northern ... more The influence of the atmospheric circulation on the winter air-sea heat fluxes over the northern Red Sea is investigated during the period 1985-2011. The analysis based on daily heat flux values reveals that most of the net surface heat exchange variability depends on the behavior of the turbulent components of the surface flux (the sum of the latent and sensible heat). The large-scale composite sea level pressure (SLP) maps corresponding to turbulent flux minima and maxima show distinct atmospheric circulation patterns associated with each case. In general, extreme heat loss (with turbulent flux lower than 2400 W m 22) over the northern Red Sea is observed when anticyclonic conditions prevail over an area extending from the Mediterranean Sea to eastern Asia along with a recession of the equatorial African lows system. Subcenters of high pressure associated with this pattern generate the required steep SLP gradient that enhances the wind magnitude and transfers cold and dry air masses from higher latitudes. Conversely, turbulent flux maxima (heat loss minimization with values from 2100 to 250 W m 22) are associated with prevailing low pressures over the eastern Mediterranean and an extended equatorial African low that reaches the southern part of the Red Sea. In this case, a smooth SLP field over the northern Red Sea results in weak winds over the area that in turn reduce the surface heat loss. At the same time, southerlies blowing along the main axis of the Red Sea transfer warm and humid air northward, favoring heat flux maxima.

The handbook of environmental chemistry, 2020

Journal of ocean engineering and marine energy, Apr 10, 2015

In the Euripus channel, we assess the hydrokinetic tidal resource at the narrowest constriction w... more In the Euripus channel, we assess the hydrokinetic tidal resource at the narrowest constriction which is in the city of Halkida at the Old Bridge. This is accomplished by combining data from (a) several ADCP (Acoustic Doppler Current Profiler) cross-channel snapshot transects at the Old Bridge and (b) a 2-month current meter record obtained at 1.5 m off the bottom at the edge of the cross section at the New Bridge, which is a ∼fourfold wider constriction with lower tidal velocities compared to the Old Bridge. A linear relationship exists between the along-channel velocity at the current meter site and the maximum of the along-channel velocity on the cross section at the Old Bridge. We can, therefore, determine the cross-channel distributions of the along-channel velocity at the Old Bridge during the 2-month period of the current meter record. We examine the use of a 4-m-diameter turbine, suitable to the space limitations at the Old Bridge. This turbine functions for flow velocity values higher than ∼50 cm/s and with a nearly constant efficiency of ∼40-45 % for flow velocity higher than 50 cm/s; a constant 45 % is achieved for all velocity values higher than 150 cm/s. This machine yields an annual energy of ∼28.6 MWh, out of an existing ∼71.5 MWh for its aperture when there is zero efficiency loss. This amount of energy is not enough for wide-scale applications but it covers the needs of an exhibition place for tourists visiting Halkida, which was the first question posed in the beginning of this project.

Continental Shelf Research, Dec 1, 2005

The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean... more The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea) are described, for September 2001 and October 2001 and February 2002. The observations were obtained to assess the impact of anthropogenic and natural resuspension processes on the coastal ecosystem. The first two periods represent highly stratified conditions and mild weather conditions; in September trawling is prohibited,

<p>Biotic and abiotic processes that form, alter, t... more <p>Biotic and abiotic processes that form, alter, transport, and remineralize particulate organic carbon, silicon, calcium carbonate, and other minor and trace chemical species in the water column are central to the ocean’s ecological and biogeochemical functioning and of fundamental importance to the ocean carbon cycle. Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the deep sea. During its transit towards the sea floor, most particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO<sub>2</sub>, and hence the rate at which the ocean can absorb CO<sub>2</sub> from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to deciphering the response of the global carbon cycle to natural and human-induced changes.</p><p>Aiming to investigate the significant biogeochemical and ecological features and provide new insights on the sources and cycles of sinking particulate matter, a mooring line of five sediment traps was deployed from 2006 to 2015 (with some gap periods) at 5 successive water column depths (700, 1200, 2000, 3200 and 4300 m) in the SE Ionian Sea, northeastern Mediterranean (‘NESTOR’ site). We have examined the long-term records of downward fluxes for Corg, N<sub>tot</sub>, δ<sup>13</sup>Corg and δ<sup>15</sup>N<sub>tot</sub>, along with the associated ballast minerals (opal, lithogenics and CaCO<sub>3</sub>), lipid biomarkers, Chl-a and PP rates, phytoplankton composition, nutrient dynamics and atmospheric deposition.  </p><p>The satellite-derived seasonal and interannual variability of phytoplankton metrics (biomass and phenology) and atmospheric deposition (meteorology and air masses origin) was examined for the period of the sediment trap experiment. Regarding the atmospheric deposition, synergistic opportunities using Earth Observation satellite lidar and radiometer systems are proposed (e.g. Cloud‐Aerosol Lidar with Orthogonal Polarization - CALIOP, Moderate Resolution Imaging Spectroradiometer - MODIS), aiming towards a four‐dimensional exploitation of atmospheric aerosol loading (e.g. Dust Optical Depth) in the study area.</p><p>Our main goals are to: i) develop a comprehensive knowledge of carbon fluxes and associated mineral ballast fluxes from the epipelagic to the mesopelagic and bathypelagic layers, ii) elucidate the mechanisms governing marine productivity and carbon export and sequestration to depth and iii) shed light on the impact of atmospheric forcing and deposition in respect to regional and large scale circulation patterns and climate variability and the prevailing oceanographic processes (internal variability).</p><p>Acknowledgments</p><p>We acknowledge support of this work by the Action ‘National Network on Climate Change and its Impacts – <strong>CLIMPACT</strong>’, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments).</p>

EAEJA, Apr 1, 2003

An array of thirty drifters deployed in the northern Aegean are used to consider the circulation ... more An array of thirty drifters deployed in the northern Aegean are used to consider the circulation in a complex archipelago of islands. The circulation of the Aegean is largely influenced by a combination of buoyancy from freshwaters introduced from the Black Sea via the Dardenelles Straits and from coastal rivers and by wind forcing. The latter is highly structured as

Journal of Physical Oceanography, Apr 1, 2016

The mass and flow fields from June 2006 to May 2009 in the Calypso Deep (bottom depth ;5.2 km) ar... more The mass and flow fields from June 2006 to May 2009 in the Calypso Deep (bottom depth ;5.2 km) are investigated using eddy-resolving surface-to-bottom hydrography (station grid spacing ;0.28) and two tall moorings yielding current-meter records at depths from 700 m to near bottom. A salty warm lens (excess core salinity and temperature are ;0.01 and 0.0258C relative to the surrounding water) of Cretan Deep Water with a core at ;3000 m and a horizontal (vertical) scale of ;50 km (1.5 km) is identified in June 2006 to be locked over the trough. The lens coincides with local maxima in dissolved oxygen. In October 2006 the salinity content of the lens and of all deeper layers is increased; the oxygen maxima are shifted to the bottom layers, indicating an episodic intrusion of higher-density ventilated Adriatic water. The circulation changes from anticyclonic at all depths in June 2006 to cyclonic below ;2.5 km in October 2006, whereas after January 2007 it is cyclonic at all instrumented depths. The measured currents are weak (mean speeds , 5 cm s 21) and persistent in direction, being mostly along the bottom topography at all current-meter depths. After October 2006, the lens erodes due to salt/heat loss caused predominantly by lateral (intrusive) mixing, which works from the outside toward the lens center. The horizontal diffusivity is on the order of ;10 m 2 s 21 , near the center of the lens, and ;10 2 to 10 3 m 2 s 21 , at its periphery, with an average error ;15 times the diffusivity value. In the deepest part of the trough and in periods of predominance of vertical mixing the vertical diffusivity at 4400 m is ;(4 6 3) 3 10 23 m 2 s 21 .

In early spring of 1986, 1992 and 1995, newly formed deep water masses were observed in the cyclo... more In early spring of 1986, 1992 and 1995, newly formed deep water masses were observed in the cyclonic Rhodes Gyre of the Eastern Mediterranean at depths reaching ∼1000 m in 1995 and exceeding 1000 m in 1986 and 2000 m in 1992. Levantine Intermediate Water (LIW) formation was observed at localized source areas south of the East Cretan Straits at the periphery or near the center of the Ierapetra Anticyclone. Adittional massive LIW formation was observed in 1992 in anticyclonic circulation structures north of Cyprus. The lateral scales of the newly formed water masses in cyclonic structures appear roughly proportional to the penetration depth of the convection, so that a large lateral scale indicating a massive production would be associated with a deep rather than an intermediate formation.

Springer eBooks, 1999

... D'Alcala, A. Theocharis, S. Brenner, G. Boudillon, E. Ozsoy (1998). The eastern Mediterr... more ... D'Alcala, A. Theocharis, S. Brenner, G. Boudillon, E. Ozsoy (1998). The eastern Mediterranean in the'80s and in the'90s: The transition in the intermediate and deep circulation, in preparation.. 5. Laskaratos A. and S. Tsandilas (1998). Seasonal cycle of a coherent eddy in the ...

Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2019

Two successive cruises in the Cretan Sea and Cretan Passage (West Levantine basin) during April a... more Two successive cruises in the Cretan Sea and Cretan Passage (West Levantine basin) during April and June 2016 surveyed the physical characteristics of the water masses in these large Eastern Mediterranean basins. Data confirm that the hydrographical status is far different from that of the Eastern Mediterranean Transient (EMT) period; however, the basins have not yet returned to the pre-EMT status. In the Cretan Sea, intermediate water masses of both Cretan and Levantine origins are detected. The stagnating bottom waters of this basin still hold high salinity, density, and dissolved oxygen values, remnant of the EMT deep water formation episodes. Characterised by low salinity and oxygen values, transitional waters of Mediterranean origin are present between intermediate and bottom layers throughout the Cretan Sea. Intermittent weak outflow of warm and saline masses of Cretan origin towards the Eastern Mediterranean is observed at the bottom of both east and west Cretan Straits. In the Cretan Passage, there is no sign of the Ierapetra anticyclonic gyre, possibly related to the seasonality of the gyre or linked to larger scale Eastern Mediterranean circulation variability. The observed surface circulation in this area is comprised of a series of smaller gyres between the Cretan Cyclone and the Rhodes Gyre. The bottom waters of the Cretan Passage present a west-to-east gradient of increasing salinity and decreasing oxygen related to the propagation of new Adriatic Deep Water from the Ionian Sea towards the Levantine basin.

International Journal of Climatology, 2009

Satellite and reanalysis data for the period 1982-2004 were used to study the long-term variabili... more Satellite and reanalysis data for the period 1982-2004 were used to study the long-term variability of the winter-mean sea surface temperature (SST) in the Black and Aegean Seas and its connection with the major atmospheric forcing: surface air temperature (SAT), surface wind and North Atlantic Oscillation (NAO) and East Atlantic-West Russia (EAWR) teleconnection patterns. In spite of some differences, the general tendencies of SST variability in both basins are similar. The major climatic event (i.e. SST decreases below the climatic mean followed by the sharp increase of SST, occurred during the period 1986-1999) and its connection with the atmospheric forcing are evident both in the Black and Aegean Seas. During the investigated period, the southwestern wind regime occurred over the Black Sea and the northeastern wind regime over the Aegean. It is shown that the variability of the meridional component of the surface wind (which provides the most of the atmospheric heat transport into the basins) is well correlated with the large-scale atmospheric patterns (NAO and EAWR). The major difference is that in the Black Sea the NAO intensification/weakening results in the weakening/strengthening of the southern wind, whereas in the Aegean Sea EAWR/NAO intensification/weakening produce strengthening/weakening of the northern wind. The long-term variability of the SST is well correlated with the variability of the SAT, which in turn is highly correlated with the meridional component of the surface wind. However, a remarkable feature is that in the Black Sea an increase/decrease of the SAT is associated with the strengthening/weakening of the southern wind. On the contrary, in the Aegean Sea, an increase/decrease of the SAT is associated with the weakening/strengthening of the northern wind. The simple basic scheme of influence of the large-scale atmospheric forcing on the long-term SST variability during the positive NAO and EAWR phase is proposed.

Journal Of Geophysical Research: Oceans, Nov 1, 2015

A variety of data based on hydrographic measurements, satellite observations, reanalysis database... more A variety of data based on hydrographic measurements, satellite observations, reanalysis databases, and meteorological observations are used to explore the interannual variability and factors governing the deep water formation in the northern Red Sea. Historical and recent hydrographic data consistently indicate that the ventilation of the near-bottom layer in the Red Sea is a robust feature of the thermohaline circulation. Dense water capable to reach the bottom layers of the Red Sea can be regularly produced mostly inside the Gulfs of Aqaba and Suez. Occasionally, during colder than usual winters, deep water formation may also take place over coastal areas in the northernmost end of the open Red Sea just outside the Gulfs of Aqaba and Suez. However, the origin as well as the amount of deep waters exhibit considerable interannual variability depending not only on atmospheric forcing but also on the water circulation over the northern Red Sea. Analysis of several recent winters shows that the strength of the cyclonic gyre prevailing in the northernmost part of the basin can effectively influence the sea surface temperature (SST) and intensify or moderate the winter surface cooling. Upwelling associated with periods of persistent gyre circulation lowers the SST over the northernmost part of the Red Sea and can produce colder than normal winter SST even without extreme heat loss by the sea surface. In addition, the occasional persistence of the cyclonic gyre feeds the surface layers of the northern Red Sea with nutrients, considerably increasing the phytoplankton biomass.

Springer eBooks, Nov 19, 2013

This chapter provides a long-term case study illustrating responses of a coastal Gulf in the Medi... more This chapter provides a long-term case study illustrating responses of a coastal Gulf in the Mediterranean Sea to reduced loading of sewage. Saronikos Gulf receives effluents from the Athens metropolitan area (population over 5 million). Until 1994, sewage discharged untreated into the surface waters of Keratsini and Elefis Bays. Sewage treatment first started in the Psitallia sewage treatment plant where the wastes discharged into inner Saronikos Gulf at 63 m depth. By the end of 2004, the secondary stage of the Psittalia sewage plant was operational.

Journal of Geophysical Research, 1990

During 1984, velocity, bottom pressure and thermocline depth data were obtained from deployments ... more During 1984, velocity, bottom pressure and thermocline depth data were obtained from deployments of tall current meter moorings, bottom pressure gauges and inverted echo sounders at five sites on the anticyclonic side of the Gulf Stream at 73'W. An additional number of inverted echo sounders, deployed in several nearby sites, allowed us to construct daily regional maps of the thermocline topography. Using this data base we examined the momentum balance and the pressure work in the eddy kinetic energy balance at 500 m above the seafloor and at a depth of 400 m. At 500 m off the bottom, the correlations between fluctuating geostrophic currents, inferred from pressure differences between sites, and suitably averaged observed currents provide observational confirmation of the geostrophic balance in the deep Gulf Stream, within our ability to measure it. At 400 m depth, the ageostrophic current was computed using velocity measurements, curvature estimates from the thermocline maps, and the momentum equation in natural coordinates. Comparison of observed and ageostrophic velocities showed occasional departures from geostrophy of 0(30% to 60%) with duration from 2 to 5 days. These ageostrophic events were caused by tangential and centripetal accelerations, mostly during the coalescence of two cold-core rings with the stream. The mean departure from geostrophy at 400 m during the deployment period was 7%. The mean effect of the pressure work, on the anticyclonic side of the stream at 400 m, was to decrease the eddy kinetic energy at a rate of-3 x 10-a ergs cm-s s-l; a value with magnitude as large as that of the barotropic instability term. The pressure work record is very episodic with peaks, during the ageostrophic events, close to 30 times larger than the mean estimate and with both positive and negative values. At 500 m off the bottom, the pressure work was found to be insignificantly different from zero. 1.

Nuclear Instruments and Methods in Physics Research, 2011

The long optical base transmissometer (LAMS-Long Arm Marine Spectrophotometer) constructed in 200... more The long optical base transmissometer (LAMS-Long Arm Marine Spectrophotometer) constructed in 2008 by NESTOR group is described. The data of the recent water transparency measurements in the NESTOR site and in the Capo Passero site in the wavelength range 378-522 nm are presented

The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly i... more The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly impacted by the greater metropolitan area of Greece’s capital, Athens, is examined through a series of state-of-the-art numerical models that address the hydrodynamics (Delft3D-FLOW), the wave regime (SWAN), the biogeochemistry, and pollution related to species of heavy metals and polyaromatic hydrocarbons (Delft3D-WAQ).The study so far has focused on calibrating model components and on reproducing the seasonal thermohaline conditions, known circulation patterns and the variability of biogeochemical constituents (chlorophyll-a, nutrients, dissolved and particulate matter) and pollutant concentrations, focusing on the vicinity of inner Saronikos.The annual cycle ‘Nov 2009 - Oct 2010’ is simulated, forced with atmospheric data from the ERA5 database. Three sets of open boundary conditions data are tested (Mediterranean Sea Physics Reanalysis dataset by Copernicus and two implementations of ...