Extreme winter 2012 in the Adriatic: an example of climatic effect on the BiOS rhythm

[摘要] Adriatic and Ionian seas are Mediterranean sub-basins linked through theBimodal Oscillating System mechanism responsible for decadal reversals of theIonian basin-wide circulation. Altimetric maps showed that the last cyclonicmode started in 2011 but unexpectedly in 2012 reversed to anticyclonic. Werelated this "premature" inversion to the extremely strong winter in 2012,which caused the formation of very dense Adriatic waters, flooding Ionianflanks in May and inverting the bottom pressure gradient. Using Lagrangianfloat measurements, the linear regression between the sea surface height andthree isopycnal depths suggests that the southward deep-layer flow coincidedwith the surface northward geostrophic current and the anticycloniccirculation regime. Density variations at depth in the northwestern Ionianrevealed the arrival of Adriatic dense waters in May and maximum density inSeptember. Comparison between the sea level height in the northwesternIonian and in the basin centre showed that in coincidence with the arrival ofthe newly formed Adriatic dense waters the sea level was lowered in thenorthwestern flank, inverting the surface pressure gradient. Toward the endof 2012, the density gradient between the basin flanks and its centre went tozero, coinciding with the weakening of the anticyclonic circulation andeventually with its return to the cyclonic pattern. Thus, the premature andtransient reversal of Ionian surface circulation originated from theextremely harsh winter in the Adriatic, resulting in the formation andspreading of highly dense bottom waters. The present study highlights theremarkable sensitiveness of the Adriatic–Ionian BiOS to climatic forcing.

[学科分类] 海洋学与技术