The physiological and ecological functions of volatile halogen production by marine diatoms

The oceans are a major reservoir of halogens including chlorine, bromine and iodine in the form of halide ions. Various biological and chemical reactions convert the halides to volatile halogen species which can move across the sea surface and into the atmosphere. The volatile halogens produced in the marine environment include organic compounds like CH2I2 and CH2BrI and reactive inorganic species like I2 and Br2. Once in the atmosphere the halogens are involved in ozone cycling and can influence the formation of clouds. A major source of organic and inorganic volatile halogens in the oceans is a phytoplankton group known as diatoms which live in open waters and in sea-ice. While experiments have shown that diatoms produce volatile halogens we do not understand why they do this or how it might impact other organisms around them. One idea is that diatoms produce volatile halogens to protect themselves against damage from reactive oxygen species and another is that they do this to defend themselves against other microbes or grazing invertebrates. It is important that we understand the reasons why diatoms produce the volatile halogens so we known when and where halogen emissions from the oceans to the atmosphere will take place and are able to predict how climate change will influence this. In this study I will do laboratory experiments to explore if volatile halogen production helps to protect the diatoms from oxidative stress and if this has any impact on the abundance or composition of bacteria in the seawater around them. I will produce mathematical relationships that describe volatile halogen production by diatoms in the presence of bacteria. These relationships will allow computer models of volatile halogen production in seawater to be developed which will tell us how halogen emissions will change in the future and how this will impact atmospheric chemistry.