Sequence of hydrographic changes in NW Mediterranean deep water due to the exceptional winter of 2005

Abstract

SUMMARY: Time series measurements at a mooring site on the deep slope of the NW Mediterranean from October 2003 to July 2005 revealed the sequence of effects of the anomalously dry, markedly cold, and very windy winter of 2005 in deep water thermohaline properties. At the end of January, a dense water mass that was warmer and saltier than usual reached the deep slope mooring site. Almost simultaneously, the start of deep dense shelf water cascading episodes was observed in the Gulf of Lions' submarine canyons. 30 days later, colder, fresher and even denser waters reached the mooring, with a 5-day delay from an intensification of the Gulf of Lions' cascading. The signature of these waters was detected for 35 days, and by late spring 2005 a new stable water mass situation was reached, with higher thermohaline values than those that characterised the deep layer from October 2003 to January 2005.Keywords: dense water formation, cascading, submarine canyon, deep mooring, northwestern Mediterranean. INVIERNO DE 2005. -Una serie temporal de datos registrados en un anclaje en la parte profunda del talud continental del Mediterráneo noroccidental desde octubre de 2003 a julio de 2005 muestra la secuencia de los efectos del invierno de 2005, anómalamente seco, destacadamente frío y muy ventoso. A finales de enero una masa de agua densa, más caliente y salada de lo habitual, llegó al anclaje del talud profundo. Casi simultáneamente se observó en los cañones del Golfo de León el inicio de episodios de hundimiento profundo de agua densa de plataforma en forma de cascada. Al cabo de 30 días, 5 días después de intensificarse el hundimiento en cascada en el Golfo de León , aguas más frías, menos saladas, y todavía más densas, alcanzaron el anclaje y permanecieron allí durante 35 días. A finales de la primavera de 2005 se alcanzó un nuevo estado estacionario con valores de temperatura y salinidad más elevados que los característicos de la capa profunda desde octubre de 2003 hasta enero de 2005. RESUMEN: SECUENCIA DE CAMBIOS HIDROGRÁFICOS EN EL AGUA PROFUNDA DEL MEDITERRÁNEO NOROCCIDENTAL DURANTE EL EXCEPCIONALPalabras clave: formación de agua densa, hundimiento en cascada, cañón submarino, anclaje profundo, Mediterráneo noroccidental. Schott and Leaman, 1991). Around the MEDOC area, where surface water is typically less salty, and preferably on its N and W sides, a Western Mediterranean Intermediate Water (WIW) is formed under the effect of the same winds (Salat and Font, 1987). The WIW resulting from this second open sea mechanism is fresher and colder than WMDW, because its formation involves more recent Atlantic Water (AW) brought by the Northern Current instead of LIW or TDW, as they are located below the convection limit or offshore. The relatively cold WIW, with a strong interannual variability in its formation, remains below the fresher surface AW and above the LIW layer, and is brought to the southwest along the continental slope by the general circulation.In addition to open sea deep and intermediate offshore convection...

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).…”

“…Abrupt disruption of the long-term warming trend was observed in the Balearic Sea in summer 2005 (Lopez-Jurado et al, 2005;Font et al, 2007). In the Ligurian Sea in 2006, Smith et al (2008) have recorded the more saline, warmer and denser deep water ever recorded in the western Mediterranean deep water.…”

Flux and composition of settling particles across the continental margin of the Gulf of Lion: the role of dense shelf water cascading

“…Probably, most of this material remained in suspension and was transported within the along shore current to distal areas. In fact, cascading waters have been detected offshore as anomalies in water mass properties (Bethoux et al, 2002;Lopez-Jurado et al, 2005;Font et al, 2007). Palanques et al (2009) Lower slope station (SOS1900) recorded higher mass flux values than canyon mouth station (CCC1900).…”

Multiparametric analysis and validation in the western Mediterranean of three global OGCM hindcasts

“…This behaviour is difficult to explain. This could be related to the 2005-2006 deep convection events that caused an increase in salinity at those depths and were studied by Schroeder et al ( , 2008aSchroeder et al ( , 2010, , Font et al (2007) and Smith et al (2008). Another possible explanation is that the peak in EN3 may be due to lack of observations at that depth.…”

“…6), with both years producing strong convection. These results correspond to the deep water formation events described in Schroeder et al ( , 2008aSchroeder et al ( , 2010, Herrmann et al (2010), Font et al (2007) and Smith et al (2008) that were produced by extremely strong forcing during these two winters (heat loss 70% above average according to López-Jurado et al [2005] and low precipitation according to Font et al [2007]). In fact, the ARPERA dataset , which is a dynamical downscaling of the ERA40 dataset (from 150 to 50 km) gives a net winter heat loss for that area of 308 W m -2 for the 2004-2005 winter, whereas other winters show net losses of ~200 W m -2 (Table 1, Schroeder et al 2010).…”