Primary characterization of pCO2 in the three bays of Algiers coast

The carbonate system in Mediterranean coastal zones remains inadequately quantified, exhibiting substantial discrepancies in research on CO₂ partial pressure (pCO₂), particularly in the insufficiently studied Algero-Provencal sub-basin. This study addresses a critical knowledge gap by providing the first characterization of carbonate chemistry parameters along the Algerian coast, a region previously lacking published data. The findings contribute to enhancing the accuracy of regional and global ocean biogeochemical models, particularly for the southern Mediterranean.The Algiers coastline comprises three bays: Bou-Ismail Bay (BB) to the west, Algiers Bay (BA) at the center, and Zemmouri Bay (BZ) to the east. A detailed dataset was assembled from direct and indirect measurements of carbonate system parameters in the surface waters of the three bays collected during spring and summer campaigns from 2011 to 2017. The carbonate system exhibited significant heterogeneity.During the June 2014 campaign, pCO₂levels exhibited considerable variation among the three bays. BA exhibited the lowest pCO₂ at 284.6 µatm, whereas BB and BZ recorded markedly elevated values of approximately 516 µatm. The extensive spatial range of approximately 250 µatm was predominantly influenced by biological processes, with BA exhibiting greater photosynthetic activity and dissolved oxygen (DO) levels compared to BB and BZ. Sampling campaigns were conducted in BA and BB from 2011 to 2017. pCO₂ and DO levels in BA and BB demonstrated considerable temporal variability. In BA, pCO₂ fluctuated between a minimum of 227 µatm during a phytoplankton bloom in July 2013 (with DO supersaturation at 180 %) and a maximum of 466 µatm in April 2011, attributed to rainfall and respiratory processes(with DO undersaturation at 76 %). In BB, spring campaigns (March 2015 and 2017) exhibited DO saturation levels (102–112 %) and lower pCO₂ values (392 µatm), while summer campaigns demonstrated pCO₂ supersaturation (up to 541 µatm) and DO undersaturation (70 %) attributable to thermal and respiratory processes.