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

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 σ_θ=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 σ_θ 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.