Anthropogenic CO2 in a dense water formation area of the Mediterranean Sea

作者：Ingrosso Gianmarco; Bensi Manuel; Cardin Vanessa; Giani Michele

来源：Deep Sea Research Part I: Oceanographic Research Papers , 2017, 123: 118-128.

DOI：10.1016/j.dsr.2017.04.004

• Anthropogenic CO2
• Carbonate system
• Ocean acidification
• Adriatic Sea
• Mediterranean Sea

There is growing evidence that the on-going ocean acidification of the Mediterranean Sea could be favoured by its active overturning circulation. The areas of dense water formation are, indeed, preferential sites for atmospheric carbon dioxide absorption and through them the ocean acidification process can quickly propagate into the deep layers.
In this study we estimated the concentration of anthropogenic CO2 (C-ant) in the dense water formation areas of the middle and southern Adriatic Sea. Using the composite tracer TrOCA (Tracer combining Oxygen, inorganic Carbon, and total Alkalinity) and carbonate chemistry data collected throughout March 2013, our results revealed that a massive amount of C-ant) has invaded all the identified water masses. High C-ant) concentration was detected at the bottom layer of the Pomo Pit (middle Adriatic, 96.8 +/- 9.7 pmol kg(-1)) and Southern Adriatic Pit (SAP, 85.2 +/- 9.4 pmol kg(-1)), associated respectively with the presence of North Adriatic Dense Water (NAdDW) and Adriatic Dense Water (AdDW). This anthropogenic contamination was clearly linked to the dense water formation events, which govern strong CO2 flux from the atmosphere to the sea and the sinking of dense, CO2-rich surface waters to the deep sea. However, a very high C-ant level (94.5 +/- 12.5 pmol kg(-1)) was also estimated at the intermediate layer, as a consequence of a recent vertical mixing that determined the physical and biogeochemical modification of the water of Levantine origin (i.e. Modified Levantine Intermediate Water, MLIW) and favoured the atmospheric CO2 intrusion.
The penetration of C-ant in the Adriatic Sea determined a significant pH reduction since the pre-industrial era (-0.139 +/- 0.019 pH units on average). This estimation was very similar to the global Mediterranean Sea acidification, but it was again more pronounced at the bottom of the Porno Pit, within the layer occupied by NAdDW (-0.157 +/- 0.018 pH units), and at the intermediate layer of the recently formed MLIW (-0.143 +/- 0.020 pH units). Our results indicate that the Adriatic Sea could potentially be one of the Mediterranean regions most affected by the ocean acidification and also demonstrate its active role in sequestering and storing C-ant.

• 出版日期2017-5