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

Data of AT (total alkalinity) and CT (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 CO2 system in the North Aegean Sea and estimate the anthropogenic CO2 (CANT) concentrations.

Extremely high concentrations of AT and CT were recorded in the upper layer of the North Aegean reflecting the high loads of AT and CT by the brackish BSW (Black Sea Water) outflowing through the Dardanelles strait and by the local rivers runoff. Both AT and CTexhibit strong negative linear correlation with salinity in the upper layer (0–20 m). Investigation of the AT-S relationship along with the salinity adjustment of AT revealed excess alkalinity throughout the water column in relation to surface waters implying the possible occurrence of non-carbonate alkalinity inputs and of other processes taking place probably over the extended shelves that contribute to the alkalinity surplus.

The intermediate layer occupied by the Modified Levantine Intermediate Water (MLIW) mass exhibits the lowest CT and AT concentrations, while rather elevated AT and CTconcentrations 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 CO2 content was detected at intermediate and deep layers of the North Aegean reflecting the effective transportation of the absorbed atmospheric CO2 at the surface to the deeper waters via the dense water formation episodes. The MLIW layer is more affected by the penetration of CANT than the NAgDW that fills the deep part of the basin. The observed variability of CANT 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 CANT 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 CO2.

Krasakopoulou E., Souvermezoglou E., Giannoudi L. & Goyet C., in press. Carbonate system parameters and anthropogenic CO2 in the North Aegean Sea in October 2013. Continental Shelf Research. Article (subscription required).

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