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Influence of physical and biological factors on seasonal variability of North Adriatic's carbonate system

The considerable amount of anthropogenic carbon dioxide absorbed by oceans since the Industrial Revolution, brought to acidification of the sea on a global scale and it represents one of the worst danger of this century for marine ecosystems. The negative impact of this phenomenon could be greater especially in coastal ecosystems, characterized by a higher variability, like the North Adriatic Sea. The main physical and biological factors characterizing temporal and spatial variability of the carbonate system have been studied, on a seasonal scale, focusing on a representative area of the North Adriatic, composed by a transect from Po delta to Istria. Samplings have been performed on a monthly basis in 6 sampling stations arranged along the transect, at 4 depths. Alkalinity, pH and the major physico-chemical descriptors, like salinity, temperature and dissolved oxygen, have been considered. The preliminary data show a strong influence of riverine waters on the majority of the parameters, indeed, smaller variations of temperature, pHT (25°C), total alkalinity (AT), dissolved inorganic carbonate (DIC) and oxygen concentration have been observed in the oriental sector of the basin (oligotrophic) rather than in the occidental sector (mesotrophic). During spring, with the beginning of stratification, superficial waters were characterized by negative values of apparent oxygen utilization (AOU) and by high values of pH in situ ; index of the prevailing of primary production processes. In the months in which a greater contribution of riverine waters have been found, both alkalinity and DIC were increasing in correspondence with higher nutrients concentration (NO3, PO4 e SiO4). Alkalinity showed a significant negative correlation with salinity (p<0.0001) for depths between 0 and 10m. Beyond the thermal effect on the balances which govern pH, an inverse linear regression between AOU and pHT(25°C) was indicating a crucial influence of primary production and respiration processes in determining pH.

Acidification; Carbonate system; northern Adriatic Sea

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