## 3 Materials and Methods  
### Research Activity in the Augusta Bay Performed by ISMAR-CNR Bologna  
A seismic survey in the Augusta Bay was carried out in October 2003 using a CHIRP II (Datasonic) sub-bottom profiler with the following operational characteristics: frequency sweep between 2 and 7 kHz; sampling interval of 125 ms; high resolution of a few centimeters; SeisPhro processing software [27; 44]. Internal structures of the sediment layers were recognized and permitted to discriminate between undisturbed, laminated sediment layers, and chaotic sequences (Figure 2a). Bottom reflectivities were calculated in order to obtain a first approximation of grain size structures [44]. The sampling strategy for the definition of Hg contamination in sediment cores was designed according to seismic data, bottom reflectivities, and historical informationvi retrieved from local public (Port Authority, Municipality of Siracusa) and private (industries) archives relative to the dredging and dumping areas. As a result, much attention was paid during sampling to avoid the dredged and dumping areas or zones close to piers and/or influenced by docking and manoeuvring of ships. Core G (Figure 1a) was sampled on purpose in an area of supposed illegal dumping of dredged material from the harbor, in order to check the existence and effects of this practice. Sediment cores were collected with the gravity corer SW-104, patented by CNR and especially designed to preserve undisturbed sediment-water interfaces. Newly arisen legal questions relative to the Hg sources in surficial sediments asked for a second sampling in 2005. Surficial sediments were sampled in the southern sector of the Augusta Harbor (Figure 1a) in order to be analysed for Hg and hexachlorobenzene (HCB) [27]. After collection, sediment cores were kept vertical (in order to avoid intra-layer mixing and interstitial water migration) while scanning for magnetic susceptibility (using a Bartington meter, on each centimeter every 10 s) and X-radiographies (with a radiogenic industrial tube Gilardoni CPX-91 160 equipped with a Be window and industrial camera films). These two parameters are useful for a first-rate approximation of internal structures  
Figure 2: (**a**) Map of the seismic survey realized in the Augusta Bay and Harbor, together with CHIRP profiles and seismic surface reflectivities relative to L, A, H, and G core locations; (**b**) \({}^{210}\)Pb and \({}^{137}\)Cs activity\(-\)depth distributions for cores L, A, D, H, G, and F. Profiles are presented also vs. years of deposition, calculated from the S values. When detected, the \({}^{137}\)Cs 1963 peak is indicated. Modified from [27]. and as a support for chronologies. Indeed, if highly magnetic tephra layers are observed, then a correlation with historical eruptions can be made. Cores were then extruded and carefully sectioned in 1-3 cm intervals with higher resolution at the top. Sediments were analysed for bulk dry density (assuming a particle density of 2.5 g cm\({}^{-3}\)), organic matter content (% of C and N, \(\delta^{13}\)C and \(\delta^{15}\) N on a [PERSON] CHNS Elemental Analyser), mineral composition (from 2\({}^{\circ}\) to 60\({}^{\circ}\) on a Philips PW 1710 CuK X-ray diffractometer, operating at 30 mA and 40 kV), grain size (through wet sieving and analyses with an X-ray Micromeritic SediGraph set on a 4-12 \(\phi\) size range) and chronology. This latter was obtained through: (1) acid extraction and alpha spectrometry of \({}^{210}\)Po for \({}^{210}\)Pb determinations (assuming secular equilibrium), and (2) non-destructive gamma spectrometry of dry samples for \({}^{137}\)Cs. For \({}^{210}\)Pb, accuracy was estimated by repeated measurements of the standard reference material (SRM) IAEA 300 (Baltic Sea sediment) and the results were within uncertainties. Precision, calculated from independent analyses of the same sample, was 4.6%. For \({}^{137}\)Cs, accuracy was checked by counting the international SRM S7 IAEA Baltic Sea sediment, and the results were within uncertainties.