Preliminary investigation of olimpi field, Mediterranean Sea, using in-situ and laboratory radio-tracing methods

Abstract In-situ and laboratory data of radioisotopes were acquired and interpreted for the Olimpi field, Mediterranean Sea. Standard oceanographic parameters and in-situ radon progeny profiles were analysed for four different sites, utilizing a state-of-the-art gamma-ray spectrometer optimized for deep sea research. In addition, a sediment core recovered from the Gelendzhik mud diapir plateau was analysed by means of high resolution laboratory gamma-ray methods providing vertical distribution of excess lead 210Pb, potassium 40K, and caesium 137Cs. Water column profiles of radon progenies revealed higher concentrations above mud volcano areas/structures in comparison to the selected reference site. This increase is likely attributed to higher emanation rates of radon gas in areas which are affected by the local diapirism. In all cases the concentration of radon progeny almost linearly decreased toward the surface due to radioactive decay and dilution processes, however differences in the concentration slopes between sites indicates a continuous release of fluids in the Moscow and Milano sites. The profile of the excess 210Pb in the Gelendzhik sediment core revealed two different accumulation rates. Using two local maxima of 137Cs, two dating points were used to suggest that an intense mud flow event took place during 1963–1986. Also, as the activity concentration of 40K increased by almost 30% during this period, and the chemical constituent of the accumulated material differed from the underneath layers, a material of different origin is presumed. Moreover, in the period 1986–2016 the accumulation rate was much lower indicating the absence of other, more recent, intense mud flow events in the neighbouring area of the core sampling.