Depth profiles of volatile iodine and bromine-containing halocarbons in coastal Antarctic waters

Measurements of bromoform (CHBr3), diiodomethane (CH2I2), chloroiodomethane (CH2ICl) and bromoiodomethane (CH2IBr)were made in the water column (5100 m depth) of the Southern Ocean within 040 km of the Antarctic sea ice during theANTXX1/2 transect of the German R/V Polarstern, at five locations between 7072°S and 911°W in the Antarctic spring/summer of 20032004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced bysalinity minima and temperature maxima, along with surface maxima in concentrations of CHBr3, CH2I2, CH2ICl and CH2IBr.These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although productionwithin the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurredbetween 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH2I2were decreased whereas CH2ICl concentrations were increased compared to the stations influenced by meltwater, consistent withphotochemical conversion of CH2I2 to CH2ICl, perhaps during upward mixing from a layer at ∼70 m enhanced in iodocarbons.Mean surface (510 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l−1 CHBr3 (range 4478pmol l−1), 4.2 pmol l−1 CH2I2 (range 1.78.2 pmol l−1), 0.8 pmol l−1 CH2IBr (range 0.21.4 pmol l−1), and 0.7 pmol l−1 CH2ICl(range 0.22.4 pmol l−1). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast ofbetween 1 and 100 (mean 32.3, median 10.4) nmol m−2 day−1 and saturation anomalies of 5571082% (mean 783%, median733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH2I2 fluxes ranged from 0.02 to6.1 nmol m− 2 day−1, with mean and median values of 1.9 and 1.1 nmol m− 2 day−1, respectively