Multiscale Observations of Deep Convection in the Northwestern Mediterranean Sea During Winter 2012–2013 Using Multiple Platforms

Abstract

During winter 2012–2013, open‐ocean deep convection which is a major driver for the thermohaline circulation and ventilation of the ocean, occurred in the Gulf of Lions (Northwestern Mediterranean Sea) and has been thoroughly documented thanks in particular to the deployment of several gliders, Argo profiling floats, several dedicated ship cruises, and a mooring array during a period of about a year. Thanks to these intense observational efforts, we show that deep convection reached the bottom in winter early in February 2013 in a area of maximum 28 ± 3 109normalm2. We present new quantitative results with estimates of heat and salt content at the subbasin scale at different time scales (on the seasonal scale to a 10 days basis) through optimal interpolation techniques, and robust estimates of the deep water formation rate of 2.0 ±0.2 Sv. We provide an overview of the spatiotemporal coverage that has been reached throughout the seasons this year and we highlight some results based on data analysis and numerical modeling that are presented in this special issue. They concern key circulation features for the deep convection and the subsequent bloom such as Submesoscale Coherent Vortices (SCVs), the plumes, and symmetric instability at the edge of the deep convection area.

Overturning the Mediterranean Thermohaline Circulation

“…Two key overturning circulations of the Mediterranean Sea are the zonal overturning cell that drives the two‐way exchange at Gibraltar (Somot et al, ) and the western meridional overturning cell associated with the much studied dense water formation of the northwestern Mediterranean Sea (Leaman & Schott, ; MEDOC‐Group, ; Schroeder et al, ; Testor et al, ). We also acknowledge the existence of a deep eastern overturning cell associated with dense water formation in the Adriatic Sea (Roether & Schlitzer, ), although we will focus in the following on the former two cells.…”

“…Indeed, the Mediterranean Sea is characterized by a superposition of intermediate and deep, zonal and meridional overturning cells that drive a so‐called thermohaline circulation (Bergamasco & Malanotte‐Rizzoli, ; Millot & Taupier‐Letage, ; Somot et al, ; Tsimplis et al, ; Wüst, ). This circulation has been studied for more than five decades and is thought to be driven by the convection phenomenon, which connects intermediate and deep layers to the surface at a few specific sites (Leaman & Schott, ; Roether et al, ; Schott et al, ; Schroeder et al, ; Testor et al, ; Wüst, ). Thus, owing to its accessibility for measurements and its overturning circulation, the Mediterranean Sea has been the first (MEDOC‐Group, ) and probably most extensively (Testor et al, ) documented deep convection region.…”

“…This circulation has been studied for more than five decades and is thought to be driven by the convection phenomenon, which connects intermediate and deep layers to the surface at a few specific sites (Leaman & Schott, ; Roether et al, ; Schott et al, ; Schroeder et al, ; Testor et al, ; Wüst, ). Thus, owing to its accessibility for measurements and its overturning circulation, the Mediterranean Sea has been the first (MEDOC‐Group, ) and probably most extensively (Testor et al, ) documented deep convection region.…”

Dense water formation in the north‐western Mediterranean area during HyMeX‐SOP2 in 1/36° ocean simulations: Ocean‐atmosphere coupling impact

“…Over the shelf, the coupled simulation shows a high sensitivity of the mixing to coupling and a larger (but limited) production of dense water ( 29.13 kg m −3 ). Despite the ocean model limitations due to the horizontal resolution of 1/36°, the z coordinate levels and the hydrostatic assumption, CPL produces an overflow of the shelf DWF in the Cap Creus Canyon whose occurrence (referred as “cascading”) is also suggested by some observations [ Estournel et al ., ; Testor et al , ].…”

On the Chaotic Variability of Deep Convection in the Mediterranean Sea

“…Deep convection is localized in a few regions at high latitudes and within semienclosed seas (Marshall & Schott, ). The northwestern Mediterranean Sea (NWMed) is one of them, and its proximity to populated coastal areas makes it a well‐observed DWF area (Estournel et al, ; Leaman & Schott, ; MEDOC‐Group, ; Schott et al, ; Testor et al, ). Deep convection here forms the Western Mediterranean Deep Waters (WMDW), a water mass filling 69% of the Western Mediterranean Sea volume (Waldman, Somot, et al, ) and contributing to form the Mediterranean Outflow Waters which participate in the Global Overturning Circulation (Price et al, ).…”