Biogenic bromine production in the arctic

Abstract

Bottom ice microalgae and a common kelp, Agarum cribosum, have been shown to contain and release organohalides during spring in the high Canadian Arctic. Although a variety of brominated, chlorinated or mixed-halogen compounds are present in algal tissues, bromoform (CHBr3) dominates tissue content and emission. Tissue loads for ice algae (n = 24) averaged 679 ± 355 ng CHBr3 (g dry weight)-1 and kelp (n = 3) tissues had 1806 ± 1037 ng CHBr3 (g dry weight)-1. Ice algal release averaged 998 ± 1119 ng CHBr3 (g dry weight)-1 h-1 for 31 experiments but values ranged from 124 to 5434 ng CHBr3 (g dry weight)-1 h-1. In three experiments kelp released from 41 to 58 ng CHBr3 (g dry weight)-1 h-1 with an average of 52 ± 8 ng CHBr3 (g dry weight)-1 h-1. On a carbon-specific basis the rates of emission are similar for both algal groups. However, the fragments of kelp blades that we used may have had a 'wound' response with artificially high release. Emission of CHBr3 by ice algae in the light is about twice that in the dark while seawater 'controls' change little, if at all. Dark release of bromoform by kelp averaged 87% of light values. A positive relationship was found between CHBr3 emission by ice algae and carbon fixation which explains over half of the variance. Bromoform release was also reduced to varying degrees by additions of metabolic inhibitors. Time series of release by ice algae show that CHBr3 production in the light was largely linear over the span of our routine experiments. Biogenic release of CHBr3, particularly by ice algae, constitutes a globally significant source of organobromine.