Two-dimensional correlation analysis and multivariate time series analysis as innovative tools for the study and the comparison of the hydrocarbon distributions in marine antarctic cores

摘要

In this paper we describe the use of innovative methods for the study of the hydrocarbon distribution in environmental samples such as marine sedimentary Antarctic cores. In the first and conventional step of this study, we determined by GC analysis the hydrocarbon markers which allow us to estimate the presence of biogenic, anthropogenic and petrogenic sources. These markers were the Carbon Preference Index (CPI), the Low Molecular Weight to High Molecular Weight (LMW/HMW), the pristane to phytane (Pry/Phy), the C_(17) to pristine (C_(17)/Pri) and the C_(18) to phytane (C_(18)/Phy) ratios, the presence of the so called unresolved complex mixtures (UCM), and the sum of two and three rings to the sum of higher ring (PAH(2.3)/PAH(4.6)) ratio. This part of the study showed the prevalent biogenic origin of hydrocarbons present in each sedimentary core with a minority presence of anthropogenic and pyrogenic sources of hydrocarbons. In the second and innovative step of this study we examined the GC chromatographic data sets of the cores by means of two-dimensional correlation analysis (2DC0RR) techniques such as two-dimensional mapping (2DMAP) and two-dimensional disrelation (2DDIS) analysis. The results of 2DMAP showed a more homogeneous distribution of hydrocarbons present in the inshore core whereas the offshore core showed to be highly heterogeneous. 2DDIS results confirmed these findings describing these differences as related to the presence of a wide content of hydrocarbons within the C_(20)-C_(40) range in the offshore core, depending reasonably on its specific stratigraphic and hydrologic conditions. At last, we applied Multivariate Time Series Analysis (MTSA) to study the effect of time on the spatial distribution of hydrocarbons along the sections of the cores. MTSA confirmed the different hydrological conditions present in the two sites. The innovative approach for the examination of hydrocarbon distribution by 2DC0RR and MTSA techniques allows us to retrieve information which, on the opposite, can be hardly retrieved by means of the conventional examination of GC results based on comparisons of the hydrocarbon contents and markers.