Distribution, transport, and production of volatile halocarbons in the upper waters of the ice-covered high Arctic Ocean



[1] Volatile halogenated compounds (CHBr3, CH2Br2, CHBr2Cl, and CH2ClI) were measured in the water column and in sea ice brine across the Arctic Ocean, from Barrow, Alaska, to Svalbard, during the Beringia 2005 expedition (August–September) with RV/IB Oden. High concentrations of brominated compounds (up to 42 pmol kg−1 of bromoform) were found under multiyear ice in the surface waters over the Makarov Basin and the Lomonosov Ridge, near the North Pole. Even higher concentrations (bromoform up to 160 pmol kg−1) were found in sea ice brine. We propose that the high load of riverine dissolved organic matter that is transported in the Transpolar Drift is a main factor responsible for the high concentration of brominated volatile compounds found in sea ice brine and upper waters and that cycles of freezing and thawing during the transport enhance the transfer of halocarbons to the seawater. The iodinated compound (CH2ClI) showed a completely different distribution with highest concentrations in water of Pacific origin in the mixed layer and upper halocline of the northern Canada Basin and over the Alpha Ridge. In the southern Canada Basin, low concentrations of halocarbons were found in upper waters. Higher concentrations in water of Pacific origin, especially on the continental shelf, indicate production in the shelf regions, likely in the Chukchi Sea and the East Siberian Sea.