Sediment cores were taken from the continental shelf of the Gulf of Cadiz (North East Atlantic) in the framework of the EMIGAS Spanish project ('Zonas de emisión de gases efecto invernadero en los sistemas litorales: influencia de las entradas costeras y del metabolismo bentónico'). Sampling stations were selected in two areas of the Gulf of Cádiz: a) the Bay of Cádiz and its outer region (n = 5), and b) the Guadalquivir prodelta (n=4). The data reported in this work were collected during 3 cruises on board RV 'Mytilus,' covering 3 seasonal periods: June 2006, November 2006, and February 2007. We obtained porewater profiles of total alkalinity (TA) and pH using a refined protocol based on the original method designed by Gomez-Parra and Forja (1994). pH was measured in 2 mL of pore water using a glass-combined electrode calibrated in the total pH scale using a TRIS buffer solution. TA was computed from the titration curve with 0.1 M HCl by means of the equivalent volume (Methrom, 794). Near-bottom water pH varied in the ranges of 7.90 – 8.10 in the Bay of Cadiz, and 8.02 – 8.12 in the Gualdaquivir prodelta, whereas TA ranged from ~2200 – 2300 μmol kg−1 in both areas. Porewater profiles of TA increased with depth and with decline in pH, with the highest maximum values of 12406 μmol kg−1 and 19761 μmol kg−1 recorded below 10 cm depth in Summer and Autumn in Guadalquivir prodelta area.