by three legs designed to identify and characterize areas of high primary productivity, which will serve as indicators of the ecosystem health. This paper reports the hydrographic data collected during the second leg of the Coriolis II cruise. This leg 10 was aimed to study the frontal dynamics associated to a region of high tidal dissipation rate south of the Gulf, and to study the vertical displacements of the pycnocline at a fixed site in the center of the Gulf mouth. To this end, high-resolution data was collected in the southern tidal front, including quasi-continuous CTD vertical profiles, underway surface temperature and salinity, Scanfish II CTD and shipboard ADCP data. The data sets are available in the National Oceanographic Data Center slightly over than 100 m in the central region (Fig. 1). Its broad mouth extends 230 km from Bahía San Gregorio to Cabo Tres Puntas along the meridian 65°45' W, connecting the Gulf with the Argentine Continental Shelf through a sill that increases in the S-N direction, reaching a maximum depth of ∼ 60 m near 46°48' S (Fig. 1). This geomorphological feature in interaction 20 with tidal mixing produces changes of well-stratified conditions to well-mixed conditions within a few kilometers during the warm seasons.The SJG circulation is driven by intense westerly winds and high amplitude tides (Palma et al., 2004; Tonini et al., 2006; Moreira et al., 2011). Estimates of tidal energy dissipation by bottom friction derived from numerical models results (Glorioso and Flather, 1995and Flather, , 1997 Palma et al., 2004; Moreira et al., 2011) suggest that most of the dissipation occurs at the mouth of the SJG, mainly in the southeast region. The dissipation rate is high enough to break up the seasonal thermocline and give rise to the formation of an intense tidal front. Due to its configuration and variability, the tidal front enhances the biological productivity nearby (Glembocki et al., 2015), plays a key role in the development of ecological processes and is closely related to fishery resources (Acha et al., 2015; Alemany et al., 2014). Studying the frontal variability, both spatial and temporal, is essential to 5 understand the mechanism responsible for that enhancement and to define main frontal properties related to biological effects.Thus, the use of a high-resolution sampler system was key to evidence the high-frequency frontal variability (Carbajal et al., in review).The main objective of MARES leg 2 was to evaluate the high-frequency variations of the Southern Tidal Front (STF) of the SJG. In order to achieve this purpose, a high-resolution sampling was carried out for a complete tidal cycle during three 10 tidal states (see Sect. 2.1). Knowledge of mesoscale variability is not only crucial to interpreting the biological influence of the fronts (Landeira et al., 2014), but it will also contribute to the establishment of new conservation strategies and the management of marine resources. In this article, we will describe the cruise design and the procedures used f...