scholarly journals The Levantine Intermediate Water in the western Mediterranean and its interactions with the Algerian Gyres: insights from 60 years of observation

2021 ◽  
Author(s):  
Katia Mallil ◽  
Pierre Testor ◽  
Anthony Bosse ◽  
Félix Margirier ◽  
Loic Houpert ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Large Scale ◽  
Cross Correlation ◽  
Water Mass ◽  
Potential Temperature ◽  
Western Mediterranean ◽  
Intermediate Water ◽  
Intermediate Depth ◽  
Whole Water

Abstract. The presence of two large scale cyclonic gyres in the Algerian basin influences the general and eddy circulation, but their effect on water mass transfer remain poorly characterized. Our study has confirmed the presence of these gyres using the first direct current measurements of the whole water column collected during the SOMBA-GE2014 cruise, specifically designed to investigate these gyres. Using cruise sections and a climatology from 60 years of in situ measurements, we have also shown the effect of these gyres on the distribution at intermediate depth of Levantine Intermediate Water (LIW) with warmer (~0.15 °C) and saltier (~0.02 g.kg−1) characteristics in the Algerian basin than in the Provençal basin. The Algerian gyres also impact horizontal density gradients with sinking of the isopycnals at the gyres’ centres. Temporal cross-correlation of LIW potential temperature referenced to the signal observed south of Sardinia reveal timescale of transit of 4 months to get to the centre of the Algerian basin. The LIW temperature and salinity trends over various periods are estimated to: +0.0017 ± 0.0014 °C.year−1 and +0.0017 ± 0.0003 year−1 respectively over the 1960–2017 period, and accelerating to +0.059 ± 0.072 °C.year−1 and +0.013 ± 0.006 year−1 over the 2013–2017 period.

scholarly journals Hydrography and Circulation West of Sardinia in June 2014

2017 ◽  
Author(s):  
Michaela Knoll ◽  
Ines Borrione ◽  
Heinz-Volker Fiekas ◽  
Andreas Funk ◽  
Michael P. Hemming ◽  
...  
Keyword(s):  
Eastern Mediterranean ◽  
Potential Temperature ◽  
Atlantic Water ◽  
Western Mediterranean ◽  
Anticyclonic Eddy ◽  
Intermediate Water ◽  
Potential Density ◽  
Sea Trial ◽  
The North

Abstract. In the mainframe of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD instruments, towed devices, and vessel-mounted ADCPs, are presented and compared with previous knowledge. So far, the circulation is not well known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges, as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72 < σΘ [kg m−3] < 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15' E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s−1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transport of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition.

scholarly journals The Mediterranean outflow in the Strait of Gibraltar and its connection with upstream conditions in the Alborán Sea

Ocean Science ◽  
2017 ◽  
Vol 13 (2) ◽  
pp. 195-207 ◽  
Author(s):  
Jesús García-Lafuente ◽  
Cristina Naranjo ◽  
Simone Sammartino ◽  
José C. Sánchez-Garrido ◽  
Javier Delgado
Keyword(s):  
Potential Temperature ◽  
Western Mediterranean ◽  
Altimetry Data ◽  
Alboran Sea ◽  
Strait Of Gibraltar ◽  
Mediterranean Outflow ◽  
Alboran Basin ◽  
In Situ Observations ◽  
Alborán Sea

Abstract. The present study addresses the hypothesis that the Western Alborán Gyre in the Alborán Sea (the westernmost Mediterranean basin adjacent to the Strait of Gibraltar) influences the composition of the outflow through the Strait of Gibraltar. The process invoked is that strong and well-developed gyres help to evacuate the Western Mediterranean Deep Water from the Alborán basin, thus increasing its presence in the outflow, whereas weak gyres facilitate the outflow of Levantine and other intermediate waters. To this aim, in situ observations collected at the Camarinal (the main) and Espartel (the westernmost) sills of the strait have been analysed along with altimetry data, which were employed to obtain a proxy of the strength of the gyre. An encouraging correlation of the expected sign was observed between the time series of potential temperature at the Espartel Sill, which is shown to keep information on the outflow composition, and the proxy of the Western Alborán Gyre, suggesting the correctness of the hypothesis, although the weakness of the involved signals does not allow for drawing definitive conclusions.

scholarly journals The Mediterranean Outflow in the Strait of Gibraltar and its connection with upstream conditions in the Alborán Sea

2016 ◽  
Author(s):  
Jesús García-Lafuente ◽  
Cristina Naranjo ◽  
Simone Sammartino ◽  
José C. Sánchez-Garrido ◽  
Javier Delgado
Keyword(s):  
Potential Temperature ◽  
Western Mediterranean ◽  
Altimetry Data ◽  
Alboran Sea ◽  
Strait Of Gibraltar ◽  
Mediterranean Outflow ◽  
Alboran Basin ◽  
In Situ Observations ◽  
Alborán Sea

Abstract. The present study addresses the hypothesis that the Western Alborán Gyre in the Alborán Sea (the westernmost Mediterranean basin adjacent to the Strait of Gibraltar) influences the composition of the outflow through the Strait of Gibraltar. The process invoked is that strong and well-developed gyres help to evacuate the Western Mediterranean Deep Water from the Alborán basin, thus increasing its presence in the outflow, whereas weak gyres facilitates the outflow of Levantine and other Intermediate waters. To this aim, in situ observations collected at Camarinal (the main) and Espartel (the westernmost) sills of the Strait have been analysed along with altimetry data, which were employed to obtain a proxy of the strength of the gyre. An encouraging correlation of the expected sign was observed between the time series of potential temperature at Espartel sill, which is shown to keep information on the outflow composition, and the proxy of the Western Alborán Gyre, suggesting the correctness of the hypothesis, although the weakness of the involved signals does not allow for drawing definitive conclusions.

scholarly journals Joint use of satellite and in-situ data for coastal monitoring

2011 ◽  
Vol 8 (3) ◽  
pp. 955-998 ◽  
Author(s):  
F. Gohin
Keyword(s):  
Continental Shelf ◽  
Mediterranean Sea ◽  
North Sea ◽  
Annual Cycle ◽  
Large Scale ◽  
Chlorophyll Concentration ◽  
Western Mediterranean ◽  
Statistical Characteristics ◽  
Monitoring Networks

Abstract. Sea surface Temperature, Chlorophyll and turbidity are three variables of the coastal environment commonly measured by monitoring networks. The observation networks are often based on coastal stations which do not provide a sufficient coverage to val-idate the model outputs or to be used in assimilation over the continental shelf. Conversely, the products derived from satellite reflectance show generally a decreasing quality shoreward and an accurate assessment of these data is required. In this text, we show that the satellite-derived chlorophyll products, obtained through a dedicated coastal algorithm, fulfil the first requirement of a monitoring system: the ability to represent correctly the mean annual cycle. The annual cycle, mean and percentile 90 of the chlorophyll concentration, derived from MERIS/ESA and MODIS/NASA, have been compared to in-situ observations at twenty six selected stations from the Mediterranean Sea to the North-Sea. Keeping in mind the validation, the forcing or the assimilation in hydrological, sediment-transport or ecological models, the non-algal Suspended Particulate Matter (SPM) is also a parameter which is expected from the satellite imagery. However, the monitoring networks measure essentially the turbidity and a consistency between chlorophyll, representative of the phytoplankton biomass, non-algal SPM, and turbidity is required. In this study, we derive the satellite turbidity from chlorophyll and non-algal SPM with a common formula applied to in-situ or satellite observations. The distribution of the satellite-derived turbidity shows the same main statistical characteristics that measured in-situ; which satisfies our first condition to monitor the long-term changes or the large-scale spatial variation over the continental shelf and along the shore. For the first time, maps of turbidity, so useful for the surveillance of the benthic habitats, are proposed operationally from space on areas as different as the Southern North-Sea or the Western Mediterranean Sea, with validation at coastal stations.

scholarly journals On the structure of the extra-tropical transition layer from in-situ observations

2012 ◽  
Vol 12 (10) ◽  
pp. 28033-28068
Author(s):  
I. Pisso ◽  
K. S. Law ◽  
F. Fierli ◽  
P. H. Haynes ◽  
P. Hoor ◽  
...  
Keyword(s):  
Transition Layer ◽  
Large Scale ◽  
Trace Gases ◽  
Potential Temperature ◽  
Local Maximum ◽  
Upper Limit ◽  
Relative Coordinates ◽  
In Situ Observations ◽  
Definition Of

Abstract. In-situ observations of atmospheric tracers from multiple measurement campaigns over the period 1994–2007 were combined to investigate the Extra-tropical Transition Layer (ExTL) region and the properties of large scale meridional transport. We used potential temperature, equivalent latitude and distance relative to the local dynamical tropopause as vertical coordinates to highlight the behaviour of trace gases in the tropopause region. Vertical coordinates based on constant PV surfaces allowed us to relate the dynamical definition of the tropopause with trace gases distributions and vertical gradients and hence analyse its latitudinal dependence and seasonal variability. Analysis of the available data provides a working definition of the upper limit of the ExTL based on the upper limit of the region of high vertical CO gradient in PV relative coordinates. A secondary local maximum in vertical O3 gradient can be used a proxy for the lower limit, although it is less clearly defined than that of CO. The sloping isopleths of CO and O3 mixing ratios and the CO mixing ratio gradient are consistent with isopleths in purely dynamical diagnostics such as χ30 d, the proportion of air masses in contact with the PBL within one month and underline the differences between the PV based and chemical tropopauses. The use of tropopause relative coordinates allows different seasons to be analysed together to produce climatological means. The weak dependence of dynamical diagnostics of transport on the absolute values of tracer concentrations makes them a suitable process-oriented tool to evaluate global chemical models and make Lagrangian comparisons.

scholarly journals Modeling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

Ocean Science ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 77-89 ◽  
Author(s):  
M. A. Ahumada ◽  
A. Cruzado
Keyword(s):  
Mediterranean Sea ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Western Mediterranean ◽  
Ocean Model ◽  
Intermediate Water ◽  
Princeton Ocean Model ◽  
The Mediterranean ◽  
Northwestern Mediterranean

Abstract. The Princeton Ocean Model – POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea – OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers, the model results have confirmed that Levantine Intermediate Water (LIW) and Western Mediterranean Deep Water (WMDW) follow essentially a cyclonic path during all year.

scholarly journals Large- to submesoscale surface circulation and its implications on biogeochemical/biological horizontal distributions during the OUTPACE cruise (southwest Pacific)

2018 ◽  
Vol 15 (8) ◽  
pp. 2411-2431 ◽  
Author(s):  
Louise Rousselet ◽  
Alain de Verneil ◽  
Andrea M. Doglioli ◽  
Anne A. Petrenko ◽  
Solange Duhamel ◽  
...  
Keyword(s):  
Large Scale ◽  
Water Mass ◽  
Finite Size ◽  
Small Scale ◽  
General Direction ◽  
The North ◽  
Mesoscale Structures ◽  
Surface Circulation ◽  
Biogeochemical Parameters

Abstract. The patterns of the large-scale, meso- and submesoscale surface circulation on biogeochemical and biological distributions are examined in the western tropical South Pacific (WTSP) in the context of the OUTPACE cruise (February–April 2015). Multi-disciplinary original in situ observations were achieved along a zonal transect through the WTSP and their analysis was coupled with satellite data. The use of Lagrangian diagnostics allows for the identification of water mass pathways, mesoscale structures, and submesoscale features such as fronts. In particular, we confirmed the existence of a global wind-driven southward circulation of surface waters in the entire WTSP, using a new high-resolution altimetry-derived product, validated by in situ drifters, that includes cyclogeostrophy and Ekman components with geostrophy. The mesoscale activity is shown to be responsible for counter-intuitive water mass trajectories in two subregions: (i) the Coral Sea, with surface exchanges between the North Vanuatu Jet and the North Caledonian Jet, and (ii) around 170∘ W, with an eastward pathway, whereas a westward general direction dominates. Fronts and small-scale features, detected with finite-size Lyapunov exponents (FSLEs), are correlated with 25 % of surface tracer gradients, which reveals the significance of such structures in the generation of submesoscale surface gradients. Additionally, two high-frequency sampling transects of biogeochemical parameters and microorganism abundances demonstrate the influence of fronts in controlling the spatial distribution of bacteria and phytoplankton, and as a consequence the microbial community structure. All circulation scales play an important role that has to be taken into account not only when analysing the data from OUTPACE but also, more generally, for understanding the global distribution of biogeochemical components.

scholarly journals Large to submesoscale surface circulation and its implications on biogeochemical/biological horizontal distributions during the OUTPACE cruise (SouthWest Pacific)

2017 ◽  
Author(s):  
Louise Rousselet ◽  
Alain de Verneil ◽  
Andrea M. Doglioli ◽  
Anne A. Petrenko ◽  
Solange Duhamel ◽  
...  
Keyword(s):  
Large Scale ◽  
Water Mass ◽  
Finite Size ◽  
Small Scale ◽  
General Direction ◽  
The North ◽  
Mesoscale Structures ◽  
Surface Circulation ◽  
Biogeochemical Parameters

Abstract. The patterns of the large-scale, meso- and submesoscale surface circulation on biogeochemical and biological distributions are examined in the Western Tropical South Pacific (WTSP) in the context of the OUTPACE cruise (Feb–April 2015). Multi-disciplinary original in situ observations were achieved along a zonal transect through the WTSP and their analysis was coupled with satellite data. The use of Lagrangian diagnostics allows for the identification of water mass pathways, mesoscale structures, and submesoscale features such as fronts. In particular, we confirmed the existence of a global wind-driven southward circulation of surface waters in the entire WTSP, using a new high-resolution altimetry-derived product, validated by in situ drifters, that includes cyclogeostrophy and Ekman components with geostrophy. Two subregions show counter-intuitive water mass trajectories due to mesoscale circulation: i) the Coral Sea with surface exchanges between the North Vanuatu Jet and the North Caledonian Jet; and ii) the zonal band between 180° W and 170° W with an eastward propagation whereas a westward general direction dominates. Fronts and small-scale features, detected with Finite-Size Lyapunov Exponents (FSLE), are correlated with 25 % of surface tracer gradients which reveals the significance of such structures in the generation of submesoscale surface gradients. Additionally, two high-frequency sampling transects of biogeochemical parameters and micro-organism abundances demonstrate the influence of fronts in controlling the spatial distribution of bacteria and phytoplankton, and as a consequence the microbial community structure. All circulation scales play an important role that has to be taken into account when analysing the data from OUTPACE but also, more generally, to understand the global distribution of biogeochemical components.

Deep convection in the Lofoten Basin: ARGO vs MITgcm

2020 ◽  
Author(s):  
Aleksandr Fedorov ◽  
Belonenko Tatyana
Keyword(s):  
Mixed Layer ◽  
Water Mass ◽  
Deep Convection ◽  
Mixed Layer Depth ◽  
Intermediate Water ◽  
Model Data ◽  
Layer Depth ◽  
Russian Science ◽  
Intermediate Water Mass

&lt;p&gt;The Lofoten basin (the LB) contains relatively warm and salty waters regarding border basins such as Greenland and Barents Seas. Variability of the processes inside occurring in the basin reflects on the climate as on the mesoscales as on the interannual scales. We use a term mixed layer depth (MLD) as a border of the pycnocline in the water column, this parameter lets us evaluate the intensity of the convection in the region. Several methods of MLD calculations are tested in the current study: Kara, Montegut, and Dukhovskoy. The convection in the basin destructs stratification and forms massive intermediate water mass. The MITgcm data for 1993-2012 and over 5000 in-situ Argo T, S profiles for 2001-2017 were used in the calculations of the MLD.&lt;/p&gt;&lt;p&gt;We consider the maximum MLD (mMLD) in the region and its spatial distribution. The mMLD is higher in the central part of the LB and corresponds to the location of the Lofoten basin eddy (the LBE). Here the mMLD reaches 1000 meters, the medium maximum is 400 meters based both on the in-situ and model data. The maximum mixed layer depth &amp;#8203;&amp;#8203;varies in the range of 400-1000 meters according to both datasets were used. The MLD over 400 meters is observed from January to May every year.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Acknowledgments: &lt;/strong&gt;The authors acknowledge the support of the Russian Science Foundation (project No. 18-17-00027). The results of the MITgcm were provided by D.L. Volkov, Cooperative Institute for Marine and Atmospheric Studies, University of Miami, USA.&lt;/p&gt;

scholarly journals Water Mass Analysis of Effect of Climate Change on Air–Sea CO2 Fluxes: The Southern Ocean

2012 ◽  
Vol 25 (11) ◽  
pp. 3894-3908 ◽  
Author(s):  
Roland Séférian ◽  
Daniele Iudicone ◽  
Laurent Bopp ◽  
Tilla Roy ◽  
Gurvan Madec
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Large Scale ◽  
Climate Model ◽  
Water Mass ◽  
Water Masses ◽  
Biogeochemical Model ◽  
Carbon Uptake ◽  
Intermediate Water

Impacts of climate change on air–sea CO2 exchange are strongly region dependent, particularly in the Southern Ocean. Yet, in the Southern Ocean the role of water masses in the uptake of anthropogenic carbon is still debated. Here, a methodology is applied that tracks the carbon flux of each Southern Ocean water mass in response to climate change. A global marine biogeochemical model was coupled to a climate model, making 140-yr Coupled Model Intercomparison Project phase 5 (CMIP5)-type simulations, where atmospheric CO2 increased by 1% yr−1 to 4 times the preindustrial concentration (4 × CO2). Impacts of atmospheric CO2 (carbon-induced sensitivity) and climate change (climate-induced sensitivity) on the water mass carbon fluxes have been isolated performing two sensitivity simulations. In the first simulation, the atmospheric CO2 influences solely the marine carbon cycle, while in the second simulation, it influences both the marine carbon cycle and earth’s climate. At 4 × CO2, the cumulative carbon uptake by the Southern Ocean reaches 278 PgC, 53% of which is taken up by modal and intermediate water masses. The carbon-induced and climate-induced sensitivities vary significantly between the water masses. The carbon-induced sensitivities enhance the carbon uptake of the water masses, particularly for the denser classes. But, enhancement strongly depends on the water mass structure. The climate-induced sensitivities either strengthen or weaken the carbon uptake and are influenced by local processes through changes in CO2 solubility and stratification, and by large-scale changes in outcrop surface (OS) areas. Changes in OS areas account for 45% of the climate-induced reduction in the Southern Ocean carbon uptake and are a key factor in understanding the future carbon uptake of the Southern Ocean.

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