Recent studies have provided a better understanding of carbonate system parameters and their spatial and temporal variability in several areas of the Mediterranean Sea. This study uses a new dataset that covered the entire Algerian Basin during the summer of 2014 (SOMBA cruise) to describe the distribution of carbonate system parameters. The findings show that almost the entire basin was a source of CO2 to the atmosphere during the studied period. Besides the well-known TrOCA (Tracer combining Oxygen, Carbon and total Alkalinity) approach, the study proposes new parametrization for the standard back calculation method to assess the anthropogenic carbon concentration. The results of both approaches yield similar distributions and concentration ranges (81 ± 4.3 and 69 ± 5.2 μmol/kg, respectively). This study assesses the errors for both approaches and emphasizes the importance of mesoscale and submesoscale structures on anthropogenic carbon sequestration and the distribution of carbonate parameters in the Algerian Basin. It shows that these features enhance basin ventilation and acidification. The first inventory of the anthropogenic carbon trapped by the Algerian Basin is estimated at 0.44-0.53 ± 0.06 Pg C, based on the new dataset. Highlights► The first high resolution spatial coverage of the Algerian Basin allowed a detailed study of the carbonate parameters. ► A refitted back-calculation method is applied to estimate anthropogenic carbon concentrations. ► Highlighting the role of the submesoscale processes in the increase of anthropogenic carbon sequestration. ► The estimated acidification of the Algerian Basin, from the preindustrial era to 2014, range between −0.19 and −0.1 pH unit. ► The first estimate of the anthropogenic carbon inventory trapped by the Algerian Basin is at 0.44-0.53 ± 0.06 Pg C.

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<p>Algerian Basin Circulation Unmanned Survey – ABACUS - has been carried on since 2014 across the Algerian Basin to investigate high resolution variability of the first 1000 m of the ocean and to fill the gap in data collection in this area of the Western Mediterranean Sea.</p><p>Five deep SLOCUM G2 glider missions were carried out in the AB between 2014 and 2022 by Università degli Studi di Napoli Parthenope, in collaboration with Balearic Islands Coastal Observing and Forecasting System (SOCIB) and the Mediterranean Institute for Advanced Studies (IMEDEA CSIC-UIB), with the participation of scientists from Algeria, France and Canada. A sixth mission (ABACUS 2023) is indeed in progress. ABACUS projects were supported since 2014 through the Trans National Access (TNA) calls of JERICO, JERICO-NEXT and JERICO S3 programmes and through the SOCIB glider facility open access programme.</p><p>Recently, ABACUS line was also added to the Boundary Ocean Observing Network (BOON) of the OceanGliders programme that proposes the long term and sustained observation of oceanographic features using the unique capabilities of the gliders.</p><p>To date, a total of 22 deep glider ABACUS transects were realized between the island of Mallorca and the Algerian coast. Each mission had an average duration of about 40 days and was mainly carried out during fall and/or early winter (2014–2018, 2021-2022) or spring (2018, 2022). All the glider surveys were conducted along neighboring SARAL/AltiKa (2014-2016) and Sentinel-3A (2018, 2021-2022) satellite groundtracks. The timing of the glider missions were accurately planned to optimize the synopticity between in situ and remote sensed observations.</p><p>All the ABACUS gliders were equipped with a glider-customized CTD measuring temperature, conductivity/salinity and pressure/depth; a two-channel combo fluorometer sensor by WetLabs (for Chl-a concentration and turbidity measurement); and an oxygen optode by AADI to measure absolute oxygen concentration and saturation. During the last two missions, the glider was also equipped with a passive acoustic probe to study wind and rain events during the mission, as well as the presence of marine mammals in the monitored area.</p><p>ABACUS data are freely available through a dedicated webpage and cooperation with new scientists is strongly encouraged. This presentation aims at making the scientific community aware of the importance and possibilities offered by ABACUS and similar glider monitoring lines, as well as at enlarging the ABACUS science team to fully exploit the collected ocean observations.</p>