Warm summers and ion concentrations in snow: comparison of present day with Medieval Warm Epoch from snow pits and an ice core from Lomonosovfonna, Svalbard - Virkkunen, Kristiina; Moore, John; Isaksson, Elisabeth; Pohjola, Veijo; Perämäki, Paavo; Grinsted, Aslak; Kekonen, Teija (International Glaciological Society, 2007)