Carbonate system parameters and anthropogenic CO2 in the North Aegean Sea during October 2013

Abstract Data of A T (total alkalinity) and C T (total inorganic carbon) collected during October 2013, on a N-S transect crossing the North of Lemnos basin allowed to identify the peculiarities of the CO 2 system in the North Aegean Sea and estimate the anthropogenic CO 2 (C ANT ) concentrations. Extremely high concentrations of A T and C T were recorded in the upper layer of the North Aegean reflecting the high loads of A T and C T by the brackish BSW (Black Sea Water) outflowing through the Dardanelles strait and by the rivers runoff. Both A T and C T exhibit strong negative linear correlation with salinity in the upper layer (0–20 m). Investigation of the A T -S relationship along with the salinity adjustment of A T revealed excess alkalinity throughout the water column in relation to the surface waters implying a possible occurrence of non-carbonate alkalinity inputs as well as of other processes that take place probably over the extended shelves and contribute to the alkalinity surplus. The intermediate layer occupied by the Modified Levantine Intermediate Water (MLIW) mass exhibits the lowest C T and A T concentrations, while rather elevated A T and C T concentrations characterize the North Aegean Deep Water (NAgDW) mass filling the deep layer of the North of Lemnos basin linked to previous dense water formation episodes. High anthropogenic CO 2 content was detected at intermediate and deep layers of the North Aegean reflecting the effective transportation of the absorbed atmospheric CO 2 from the surface to the deeper waters via the dense water formation episodes. The MLIW layer is more affected by the penetration of C ANT than the NAgDW that fills the deep part of the basin. The observed variability of C ANT distribution reflects the influence of the intensity of dense water formation events, of the different θ/S properties of the newly formed dense waters as well as of the diverse submarine pathways followed by the cascading dense waters. The invasion of C ANT has lead to more acidic conditions and to lower saturation degree of calcium carbonate in relation to the preindustrial era. The findings of this study provide baseline information about the carbonate system properties of the North Aegean and highlight its active role in sequestering and storing anthropogenic CO 2 .