Deep and intermediate water in the western Mediterranean under the influence of the Eastern Mediterranean Transient

Abstract

The well known changes in the deep thermohaline circulation of the eastern Mediterranean Sea, the so‐called Eastern Mediterranean Transient (EMT), which modified the outflow characteristics through the Sicily Strait, led to significant changes in the western Mediterranean Sea since the early 90's. In spring 2005 an oceanographic survey, carried out in the central part of the western basin, showed the presence of a recently formed layer of western Mediterranean deep water, spreading at the bottom of the whole Algero‐Provençal Basin. It was characterized by unusual θ‐S shapes, as its temperature, salinity and density were higher with respect both to the resident deep waters and to the climatological values. The possible influence of the EMT on the deep water formation processes occurred in the Gulf of Lions in the previous winter is here evidenced, even taking into account other data sets previously collected in the western Mediterranean.

Hydrological changes in the Ligurian Sea (NW Mediterranean, DYFAMED site) during 1995–2007 and biogeochemical consequences

“…Increases in the salinity of LIW in the eastern basin have been reported linked to rivers damming and/or decreasing precipitations (Rohling and Bryden, 1992;Krahman and Schott, 1998;Bethoux and Gentili, 1999). The increase of salinity and temperature observed in the western basin in LIW in [2002][2003][2004] has been attributed to a signal of propagation of EMT in the Western Mediterranean Sea (Lopez-Jurado et al, 2005;Schröder et al, 2006;Font et al, 2007).…”

“…Strong changes during winter 2004/2005 have been evidenced elsewhere in the western Mediterranean (0.2 • C and 0.04 psu decreases of temperature and salinity in water down to 1500 m, complex thermohaline structure in deeper levels) (Lopez-Jurado et al, 2005;Schröder et al, 2006;Smith et al, 2008). Schröder et al (2006) (Fig.…”

Observations of new western Mediterranean deep water formation using Argo floats 2004–2006

“…Such studies suggest deep convection within the western basin is reasonably understood, with the processes involved classified under three progressive phases (MEDOC Group, 1970;Marshall and Schott, 1999 This cyclonic surface circulation is an important factor in pre-conditioning as it localises the convective region by limiting exchange of the waters exposed to persistent surface forcing with more stably stratified waters outside the gyre (Marshall and Schott, 1999;Send et al, 1999). The cyclonic circulation also draws the LIW toward the surface, to be more easily exposed to mixed layer (ML) entrainment (Schott et al, 1993) with the subsequent density increase of surface waters ultimately allowing for deeper convection of the water column (Skliris and Lascaratos, 2004).…”

“…The typical water column structure of the western basin consists of three major water masses along with Mediterranean Bottom Water (at depths >3000 m), which is not of relevance to this study. The AtCorrespondence to: H. L. Bryden (hlb@noc.soton.ac.uk) lantic Water (AW -S in the range 36.5 to 37.5, θ highly variable) originates from surface inflows in the Strait of Gibraltar and is recognised as a fresh, buoyant surface layer (0-200 m) which is steadily modified as it flows eastward through mixing and air-sea interactions (Bryden and Stommel, 1984;Send et al, 1999). The Levantine Intermediate Water (LIW -S in the range 38.45 to 38.75, θ >13.2 • C) lies below this layer (400-600 m), it is formed in the Levantine Basin of the eastern basin and is recognised by a distinct subsurface salinity maximum in vertical profiles (Rohling and Bryden, 1992).…”

Importance of the variability of hydrographic preconditioning for deep convection in the Gulf of Lion, NW Mediterranean

“…At the eastern entrance, a modification of convective regime in the eastern Mediterranean called the Eastern Mediterranean Transient (EMT) led to an export of salt towards the western Mediterranean through the strait of Sicily. Schroeder et al (2006) emphasised the possible effect of the EMT on deep water formation in the Gulf of Lion, arguing that a progressive heat and salt accumulation in the intermediate layer, due to the EMT propagation, may have led to the formation of a saltier, warmer (and denser) WMDW. The cascading of cold and dense water formed on the Gulf of Lion's shelf, as observed by Font et al (2007) and Canals et al (2006) in canyons of the continental slope at the end of winter [2004][2005], is another phenomenon that potentially affects the variability and characteristics of WMDW formation (Béthoux et al, 2002).…”