Saturation levels of methyl bromide in the coastal waters off Tasmania

Abstract

Methyl bromide (CH3Br) was highly supersaturated for over 2 years in the surface coastal seawater off Tasmania. Persistent supersaturations were observed near to shore throughout the year with no evidence of a seasonal cycle. At the same time, a site farther offshore (still under coastal influence) was also predominantly supersaturated but to a lesser extent. Notably, the annual pattern varied over the consecutive years covered in this systematic study. The observed supersaturations are in broad agreement with that which would be predicted by the relationships with the sea surface temperature (SST) derived by Groszko and Moore [1998] and King et al. [2000] for SSTs in the range of 12° to 20°C, although not the seasonal variation predicted by King et al. [2002]. There is much variability, as expected, which is not explained by the SST relationships. The presence of the prymnesiophyte Phaeocystis is found to be related to the seawater concentrations of CH3Br in this work. Our results tentatively indicate that the release of CH3Br into the seawater may be a response to nitrate limiting conditions.