Spring 2009 water mass distribution, mixing and transport in the southern Adriatic after a low production of winter dense waters

Abstract

Enhanced mixing of North Adriatic Dense Water (NAdDW) occurs in a strong frontal region as this cold and fresh intermediate water enters the southern Adriatic basin and meets warm and salty Modified Levantine Intermediate Water (MLIW) coming from the Ionian Sea. This study examines how NAdDW was mixed and transformed as it traveled southward from the Gargano to the Bari region and investigates the pathway and intrusion patterns of MLIW in late winter/spring 2009. Hydrographic data are analyzed to compute source water fractions via a least-squares analysis method and combined with ADCP data to compute source water volume fluxes. Results show that despite an anomalous low year for NAdDW production in the Adriatic, a warmer, fresher and lighter version of traditional NAdDW (i.e. 2009 NAdDW) endured its journey from Gargano to Bari. In the Gargano region, 2009 NAdDW (with fractions up to 80–90%) traveled southward in a non-continuous thin, dense vein between 35m and 100m isobaths, with diluted cores (>50%) extending to 140m depth, and with fluxes of −0.05Sv, to the southeast, south of Palagruz˘a Sill. Near the sill, 2009 NAdDW was further mixed and diluted with MLIW and surface water. By the time it reached the Bari region, the 2009 NAdDW fraction in the water column was reduced to about 20%. MLIW intrusions observed over the Sill and in northern sections of the study area suggest a splitting of MLIW pathways (stemming from the main South Adriatic rim pathway) towards the central Adriatic. Source water fraction results combined with velocity and seismic oceanography data show that eddies in the study area are one mechanism for the generation of MLIW intrusions towards the northwest.