Santiago, Rocío; Aparicio, Alberto; Álvarez, Marta; Castaño, Mónica; Caínzos, Verónica; Pelayo, Víctor; Fajar, Noelia (2018): Biogeochemical characterization of water masses over oceanic seamounts off two CTD dives measured during MEDWAVES cruise in 2016 [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.890197

The main objective of the work conducted by the biogeochemical oceanography team was to determine the biogeochemichal role of the Mediterranean Water, over and around the Formigas, Ormonde and Seco de los Olivos seamounts, as well as the Gazul Mud volcano (ATLAS Task 1.3 and task 3.1, potential contribution also to tasks 2.1 and 2.2).Greater emphasis has been done on fine scale biogeochemical characterization 500 meters above the bottom with emphasis on CO2 variables to determine extant characteristics and any future threats / sensibility for benthic communities (ATLAS Tasks 1.3, 2.4 and 3.1 and potential contribution to task 2.2). The biogeochemical parameters measured have been dissolved oxygen (DO), pH, Total Alkalinity (TA), carbonate ion concentration (CO32-), Dissolved Inorganic Carbon (DIC) and inorganic nutrients (nitrate, nitrite, silicate and phosphate). pH in seawater was measured following the methodology by Clayton & Byrne (1993) using a double-wavelength spectrophotometric procedure (Byrne 1987). It has been reported at 25 °C and on the Total scale (pH25T). Total Alkalinity (TA) was analyzed following a double end point potentiometric technique by Pérez & Fraga (1987) further improved in Pérez et al. (2000). The carbonate ion concentration (CO32-) was determined spectrophotometrically following the recent method first proposed by Patsavas et al. (2015), after the works by Byrne and Yao (2008) and Easley et al. (2013). Dissolved Inorganic Carbon (DIC) samples were analysed using a VINDTA 3D system (www.MARIANDA.com). The fundament is extracting the CO2 from the seawater sample by adding phosphoric acid, followed by coulometric detection (Johnson et al., 1993). Inorganic nutrients were determined using colorimetric methods using a SEAL Analytical QuAAtro analyzer. Nitrate was measured with Cu-Cd reduction Naphthylenediamine photometric method. Nitrite was measured with Naphthylenediamine photometric method. Both methods are from Grasshoff et al (1983). Silicate and phosphate were measured with Molybdenum blue method from Murphy & Riley (1962). Some data have been subjected to quality control based on the WOCE/Go-Ship flags (Flag_O2; Flag_pH25T; Flag_TA; Flag_CO3; Flag_DIC). A Flag=2 means an acceptable data; flag=3 means a questionable data; flag=9 not sample measured. More information about the quality controls in Olsen et al. (2016; doi:10.5194/essd-8-297-2016).