Deep seawater inherent optical properties in the Southern Ionian Sea

The NEMO (NEutrino Mediterranean Observatory) Collaboration has been carrying out since 1998 an evaluation programme of deep sea sites suitable for the construction of the future Mediterranean km3 Čerenkov neutrino telescope. We investigated the seawater optical and oceanographic properties of several deep sea marine areas close to the Italian Coast. Inherent optical properties (light absorption and attenuation coefficients) have been measured as a function of depth using an experimental apparatus equipped with standard oceanographic probes and the commercial transmissometer AC9 manufactured by WETLabs. This paper reports on the visible light absorption and attenuation coefficients measured in deep seawater of a marine region located in the Southern Ionian Sea, 60–100 km SE of Capo Passero (Sicily). Data show that blue light absorption coefficient is about 0.015 m−1 (corresponding to an absorption length of 67 m) close to the one of optically pure water and it does not show seasonal variation.