scholarly journals Contribution of Thermohaline Staircases to Deep Water Mass Modifications in the Western Mediterranean Sea From Microstructure Observations

2021 ◽  
Vol 8 ◽  
Author(s):  
Bruno Ferron ◽  
Pascale Bouruet-Aubertot ◽  
Katrin Schroeder ◽  
Harry L. Bryden ◽  
Yannis Cuypers ◽  
...  

Recent observations from profiles of temperature and salinity in the Algerian Sea showed that salt finger mixing can significantly warm and salinify the deep waters within a period of 2 years, thereby contributing to the erosion of deep water properties formed during winter convection episodes. In this study, heat, salt, and buoyancy fluxes associated with thermohaline staircases are estimated using microstructure observations from four locations of the Western Mediterranean Sea: The Tyrrhenian Sea, the Algerian Sea, the Sardino-Balearic Sea, and the Ligurian Sea. Those fluxes are compared to the rare estimates found in the Mediterranean Sea. Microstructure data show that the temperature variance dissipation rate is one to three orders of magnitude larger in the strong steps that separate weakly stratified layers than in the layers, while the turbulent kinetic energy dissipation rate remains usually weak both in steps and layers. In the steps, the turbulent eddy diffusivity of salt is on average twice as large as that of temperature. The buoyancy flux ratio decreases with the density ratio. It is found that staircases induce a downward heat transfer rate of 46 to 103 × 109 W over the whole western basin, and a downward salt transfer rate of 4.5 to 10.3 × 103 kg s–1 between 1000 and 2000 m. This heat convergence is 2–5 times as large as the western Mediterranean geothermal heat flux in this depth range. Over the whole western basin, heat and salt convergences from salt-fingering staircases are 50% to 100% of those generated by mechanical mixing. Finally, it is found that heat and salt convergences from geothermal heating, salt-fingering and mechanical mixing can balance a deep water upwelling of 0.4 × 106 m3 s–1.

Ocean Science ◽  
2008 ◽  
Vol 4 (2) ◽  
pp. 133-149 ◽  
Author(s):  
R. O. Smith ◽  
H. L. Bryden ◽  
K. Stansfield

Abstract. The deep convection that occurs in the western basin of the Mediterranean Sea was investigated using Argo float data over two consecutive winters in 2004–2005 and 2005–2006. The results showed deep mixed layers reaching 2000 m in surprising locations, namely the eastern Catalan subbasin (39.785° N, 4.845° E) and the western Ligurian subbasin (43.392° N, 7.765° E). Subsequently, new deep water was formed in March of 2005 and 2006 with θ=12.89–12.92°C, S=38.48–38.49 and σθ=29.113 kg m−3. The deep water produced in the Ligurian subbasin during 2006 was more saline, warmer and denser than any historical observations of western Mediterranean deep water. The results show S, θ and σθ in the western Mediterranean deep water are higher than 1990s values, with a salinity increase of 1.5×10−3 yr−1, a temperature increase of 3.6×10−3 °C yr−1 and a density increase of 4.0×10−4 kg m−3 yr−1 apparent from a dataset of western Mediterranean deep water properties spanning 1955–2006.


2021 ◽  
Author(s):  
Iván Manuel Parras Berrocal ◽  
Ruben Vazquez ◽  
William David CabosNarvaez ◽  
Dimitry Sein ◽  
Oscar Alvarez Esteban ◽  
...  

2007 ◽  
Vol 4 (5) ◽  
pp. 733-783 ◽  
Author(s):  
R. O. Smith ◽  
H. L. Bryden

Abstract. The deep convection that occurs in the western basin of the Mediterranean Sea was investigated using ARGO float data over two consecutive winters in 2004–2005 and 2005–2006. The results showed deep mixed layers reaching 2000 m in surprising locations, namely the eastern Catalan subbasin (39.785° N, 4.845° E) and the western Ligurian subbasin (43.392° N, 7.765° E). Subsequently, new deep water was formed in March of 2005 and 2006 with θ=12.89–12.92°C, S=38.48–38.49 and σθ=29.113 kg m−3. The deep water produced in the Ligurian subbasin during 2006 was more saline, warmer and denser than any historical observations of Western Mediterranean Deep Water. The results show S, θ and σθ in the Western Mediterranean Deep Water are higher than 1990s values, with a salinity increase of 1.5×10−3 yr−1, a temperature increase of 3.6×10−3°C yr−1 and a density increase of 4.0×10−4 kg m−3 yr−1 apparent from a dataset of WMDW properties spanning 1955–2006.


2020 ◽  
Author(s):  
Stéphanie H. M. Jacquet ◽  
Christian Tamburini ◽  
Marc Garel ◽  
Aurélie Dufour ◽  
France Van-Vambeke ◽  
...  

Abstract. We report on the sub-basins variability of particulate organic carbon (POC) remineralization in the central and western Mediterranean Sea during a late spring period (PEACETIME cruise). POC remineralization rates (MR) were estimated using the excess non-lithogenic particulate barium (Baxs) inventories in mesopelagic waters (100–1000 m) and compared with prokaryotic heterotrophic production (PHP). MR range from 25 ± 2 to 306 ± 70 mg C m−2 d−1. Results reveal larger MR processes in the Algerian (ALG) basin compared to the Tyrrhenian (TYR) and Ionian (ION) basins. Baxs inventories and PHP also indicates that significant remineralization occurs over the whole mesopelagic layers in the ALG basin in contrast to the ION and TYR basins where remineralization is mainly located in the upper 500 m horizon. We propose that this may be due to particle injection pumps likely driven by strong winter convection in the Western basin of the Mediterranean Sea. This implies significant differences in the remineralization length scale of POC in the central Mediterranean Sea relative to the western region.


2014 ◽  
Vol 11 (15) ◽  
pp. 4211-4223 ◽  
Author(s):  
M. D. Krom ◽  
N. Kress ◽  
K. Fanning

Abstract. Although silica is a key plant nutrient, there have been few studies aimed at understanding the Si cycle in the eastern Mediterranean Sea (EMS). Here we use a combination of new measurements and literature values to explain the silicic acid distribution across the basin and to calculate a silica budget to identify the key controlling processes. The surface water concentration of ∼1 μM, which is unchanging seasonally across the basin, was due to the inflow of western Mediterranean Sea (WMS) water at the Straits of Sicily. It does not change seasonally because there is only a sparse population of diatoms due to the low nutrient (N and P) supply to the photic zone in the EMS. The concentration of silicic acid in the deep water of the western Ionian Sea (6.3 μM) close to the S Adriatic are an of formation was due to the preformed silicic acid (3 μM) plus biogenic silica (BSi) from the dissolution of diatoms from the winter phytoplankton bloom (3.2 μM). The increase of 4.4 μM across the deep water of the EMS was due to silicic acid formed from in situ diagenetic weathering of aluminosilicate minerals fluxing out of the sediment. The major inputs to the EMS are silicic acid and BSi inflowing from the western Mediterranean (121 × 109 mol Si yr−1 silicic acid and 16 × 109 mol Si yr−1 BSi), silicic acid fluxing from the sediment (54 × 109 mol Si yr−1) and riverine (27 × 109 mol Si yr−1) and subterranean groundwater (9.7 × 109 mol Si yr−1) inputs, with only a minor direct input from dissolution of dust in the water column (1 × 109 mol Si yr−1). This budget shows the importance of rapidly dissolving BSi and in situ weathering of aluminosilicate minerals as sources of silica to balance the net export of silicic acid at the Straits of Sicily. Future measurements to improve the accuracy of this preliminary budget have been identified.


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