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. This is especially crucial for polar regions experiencing rapid warming where climate-induced changes in diatom communities have already been seen. In this study I will carry out 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. This will allow me to 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.

The following summary lists potential users of the proposed research and how each will benefit from it:

- Research scientists studying halogen biogeochemistry
This work will create new knowledge on volatile halogen production in seawater which will contribute to the development of modelling tools that can be used to accurately predict the impact of climate change on sea-to-air halogen flux and associated atmospheric processes such as ozone depletion and new particle formation. This will help marine and atmospheric investigators to gauge where to position halogen biogeochemistry in the ranking of priority topics for future research.

- The wider scientific community and delivering bodies
The wider scientific areas that will benefit from the new knowledge gained through this work include microbial physiology, biogeochemical modelling, atmospheric chemistry and climate system feedbacks. An improved understanding of the physiological and ecological functions of volatile halogen production will allow researchers in these areas to determine how this process fits within their own work.

Additionally, an understanding of how volatile halogen production by diatoms will change with future climate-induced stresses to ocean systems will help scientists and delivering bodies, such as the UK Met Office, to resolve the importance of including halogen biogeochemistry in climate models.

- Intermediary organisations
By contributing to new scientific knowledge and providing parameterisations that can be used in 3-D climate models, the results of this study may feed in to assessments and reports produced by intermediary organisations [e.g. Intergovernmental Panel on Climate Change, World Meteorological Organisation] which are at the interface between basic research and policy.

- School children
The concept behind this work is that microbes can play an important role in processes occurring at the global scale. I will present this exciting and intriguing topic to school children at University of York Science Awareness events to 'engage young people with contemporary research to enhance their experience of science, encouraging more to pursue science studies.....' which is a key aim of the RCUK Science and Society Strategy.