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 Mauro Mecozzi ⁎, Marco Pietroletti, Gianluca Trifirò, Laura Nisini Laboratory of Chemometrics and Environmental Applications, ISPRA, Via di Castel Romano 100, 00128 Rome, Italy abstract article info Article history: Received 4 September 2013 Received in revised form 17 December 2013 Accepted 21 December 2013 Available online 30 December 2013 Keywords: Marine Antarctic cores Gaschromatographic analysis Biogenic hydrocarbons Anthropogenic hydrocarbons Petrogenic hydrocarbon Two-dimensional correlation analysis Multivariate time series analysis In this paper we describe the use of innovative methods for the study of the hydrocarbon distribution in environ- mental 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, anthro- pogenic 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 minor- ity 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 anal- ysis (2DCORR) 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 2DCORR and MTSA techniques allows us to retrieve information which, on the opposite, can be hardly retrieved by means of the con- ventional examination of GC results based on comparisons of the hydrocarbon contents and markers. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The estimation of the hydrocarbon sources in the marine environ- ment is a complex study because it depends on the contemporary pres- ence of several hydrocarbons arising from petroleum spills and naval transport (Wang et al., 1999a, 1999b; Wang and Fingas, 1995), the life cycle of aquatic organisms (Bieger et al., 1997) and weathering process- es (Ibbotson and Ibhadon, 2010). The estimation of hydrocarbon sources in Antarctica is even more complex than in other areas because due to the low presence of human activities Antarctica shows reduced levels of pollutants. For this reason Antarctica is generally considered as a background area for the study of environmental pollution in many ecosystems (Cripps and Priddle, 1991; Cripps, 1992a, 1992b). In any case, the presence of hydrocarbons from petroleum sources in Antarctica has been confirmed. In fact, detailed studies describe the effects of anthropogenic hydrocarbons on living organisms depending on little oil and fuel spills from naval transport and other human activ- ities (Cripps, 1992b; Kennicutt and Sweet, 1992; Eppley, 1992). More recent studies describe the temporal and spatial variation of oil contam- ination and the related toxicity on living organisms in specific sites such as the King George Island (Caruso Bicego et al., 2003), MCMURDO sta- tion (Crockett and White, 2003; Negri et al., 2006), the Macquarie island (Rayner et al., 2007) and the Gerlache Inlet sea (Stortini et al., 2009). At last, the review by Fuoco et al. (2009) describes the contamination from organic pollutants in Antarctica with many details. Due to the presence of petroleum products, the MARPOL regulation has prohibited recently the use of crude oils with a density higher than 900 kg m -3 at 15 °C in naval and cargo transports to control the oil dispersion in Antarctica (News report, 2011). The correct assessment of anthropogenic hydrocarbon sources in Antarctica is affected by their general low contents, by the simultaneous presence of biogenic sources arising from the life cycle of aquatic organ- ism (Cripps, 1992a, 1992b) and by petrogenic sources depending on the eroded material from old sediments (Harada et al., 1995). Marine Chemistry 159 (2014) 9–18 ⁎ Corresponding author. Tel.: +39 06 50073287. E-mail addresses: mauro.mecozzi@isprambiente.it, mauromecozzi2004@libero.it (M. Mecozzi). 0304-4203/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.marchem.2013.12.003 Contents lists available at ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem