The Mitch Laboratory   

 RESEARCH     

 Oceanography and Global Warming 

Oceanic dissolved organic matter is an important global carbon component, and has important impacts on the net flux of CO₂ between the ocean and atmosphere.  First, absorption of solar irradiation by chromophores within DOM partly controls algal productivity by limiting the depth of the photic zone. Second, oceanic DOM serves as an important source of nutrition for heterotrophic phytoplankton.

We seek to understand some of the important abiotic chemical reaction pathways responsible for carbon turnover. In particular, we looked at the role of halogen radicals formed by the reaction of hydroxyl radical (OH*) with seawater bromide:

OH* + Br- ↔ Br*
Br* + Br- ↔ Br2*-

Hydroxyl radicals form during sunlight illumination of oceanic dissolved organic matter.  Although they are highly reactive oxidants, oceanographers agree that they react predominantly with bromide, rather than organic matter.  We are examining the importance of the halogen radicals formed in this process for oxidizing and controlling the turnover of oceanic dissolved organic matter.  We found that photobleaching behavior was consistent with chromophore oxidation by halogen radicals, but hydroxyl radical production was insufficient to account for the necessary halogen radical production.  We are currently examining alternative avenues for halogen radical production.

Grebel, J.E.; Pignatello, J.J.; Song, W.; Cooper, W.J.; Mitch, W.A. Impact of halides on the photobleaching of dissolved organic matter. Marine Chem., 2009, 115, 134-144. (Full Text)

BACK