Chemical characterisation of a volcanic event (about AD 1500) at Styx Glacier plateau, northern Victoria Land, Antarctica

A dark layer (similar to 1 cm thick, 93.41 m deep) was identified in an ice core (116 m deep, covering the period similar to 1350-1995) drilled at Styx Glacier plateau, northern Victoria Land, Antarctica. The ice-core section was dated around AD 1500 +/- 20 by a firn-densification model. A chemical characterisation was performed on ten subsamples (resolution 3 cm) located around the dark layer by ion chromatography. The concentration/depth profiles of anions (Cl(-), Br(-), NO(3)(-), H(2)PO(4)(-), SO(4)(2-)), cations (Na(+), NH(4)(+), K(+), Mg(2+), Ca(2+)) and some organic anions (acetate, formate, propionate and methanesulphonate (MSA)) indicate very high concentration peaks for all the components. However, non-sea-salt sulphate (nssSO(4)(2-)) and F(-) show the greatest increase with respect to background values (370 and 860 times, respectively). A crustal contribution is attributed to Ca(2+) and MSA. The profiles of gas-phase emitted substances (HF, HBr, HNO(3) and carboxylic acid) suggest gas emission just before the volcanic eruption. Chloride depletion is evident in the dark layer with respect to Na(+)/Cl(-) sea-water ratio. At present, it is not possible to attribute an unambiguous source to the volcanic event, but several pieces of evidence lead us to believe that this may be a time-limited local event.