A repeat seasonal hydrographic survey of the Balearic Sea, monitoring the Ibiza and Mallorca Channels. 31 CTD stations were carried out over 3.5 days; the first day involves 10 CTD stations across the Mallorca Channel (MC). the second and third days 18 CTD stations forming two transects across the Ibiza Channel (IC); An additional stop was made for maintenance of the Ibiza Channel buoy, where surface samples were taken for comparison with the buoy’s sensors. The fourth day three GARICAST profiles were taken in the Mallorca channel.