The centre of the Southern Adriatic is an area where vertical mixing (up welling, wintertime convection) has a rather prominent role homogenizing
physical and chemical seawater properties, and controlling the primary production (up welling water is a source of nutrients in the euphotic
zone which stimulates the growth of phytoplankton).
The E2-M3A Station is deployed in the southern Adriatic Sea, at about 1200 m depth, a well known area of dense, deep water formation through open sea convection. These newly formed deep water masses are then exported through the Strait of Otranto to the rest of the Eastern Mediterranean basin.
The dynamics of the area is dominated by the presence of a quasi-permanent cyclonic gyre that intensifies in the winter season creating the conditions for the production of dense and oxygenated waters with the contribution of the saltier intermediate layer dominated by the Levantine Intermediate Water (LIW).
The Adriatic Dense Water (AdDW) formed prevalently by the open-ocean vertical convection, is then exported through the Strait of Otranto to the rest of the Eastern Mediterranean basin and becomes the main component of the Eastern Mediterranean Deep Water (EMDW).
The recorded time-series at the E2-M3A station can be used for studies of long-term changes of Adriatic response to local climatic forcing. The volume of the dense water formed surrounding the station can be correlated to the winter heat losses.
The amount of the dense water formed also determines the water exchange between the Adriatic and Eastern Mediterranean.
Water masses circulation in the Adriatic Sea:
NAdDW = North Adriatic Dense Water;
AdDW = Adriatic Dense Water;
LIW = Levantine intermediate Water
The increasing CO2 concentration in the atmosphere through the exchanges with the surface ocean is determining a
process called Ocean Acidification on a global scale. This process could have a negative impact on many marine
organisms from different trophic levels, with potentially large consequences for the marine ecosystem as well as carbon cycling.
In the global ocean the ocean acidification process has been estimated to be more pronounced in the area where deep
water formation takes places, due to the influence of low seawater temperature which enhances the solubility of
atmospheric CO2 and the physical pump.
The Adriatic is an important player for the circulation in the Mediterranean Sea, which on a smaller scale behaves as an ocean, and represents one of the most important sites of deep water formation. The automatic monitoring of the carbonate system set up on the E2-M3A buoy is measuring two of its main variables i.e. the partial pressure of CO2 (pCO2) and the pH. This allows a better understanding of the processes influencing the carbonate system in the South Adriatic, especially during winter cooling, when dense waters are formed. The aim of the carbonate system automatic monitoring is to understand the role of this physical pump for the transfer process of the CO2 when winter cooled waters sink forming the Adriatic Dense Water which, flowing through Otranto strait, contribute to the Eastern Mediterranean Deep Water. Therefore, following the CO2 transfer would allow to understand the acidification processes in deep waters.
The distribution of pCO2 along the Bari-Dubrovnik section in March 2014 is showed below. It is representative for the winter period.
At 300-500m depth in the
eastern side, the Levantine Intermediated Water (LIW) revealed an elevated pCO2 concentration. High values were
also present close to the bottom, with the presence of Adriatic Dense Water (AdDW).
The pHT measured at in-situ temperature (below) showed an inverse pattern with respect to pCO2 in the same period and along the same transect.
Due to the influence of biological activity and seawater temperature, at the surface the pHT was elevated and
gradually decreased with the depth. Between 300 and 500 m in the eastern side of the section, low pHT values
were present in association with the LIW core. However, in the deepest part of the Southern Adriatic Pit,
the AdDW revealed the most acidified waters.
These findings point out the role of North Adriatic Sea in sequestering and storing a great amount of atmospheric CO2 during deep water formation, which in turns could cause the expansion of the ocean acidification process into the deeper layer of the Adriatic Sea and, consequently, of the whole Mediterranean Sea.
|FixO3 is a FP7 Collaborative Project coordinated by the
National Oceanography Centre, Southampton, UK
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Last update: March 2, 2015 -- Webmaster: R.Iungwirth