Stuart Larsen

Project Title

Dimethylsulphoniopropionate (DMSP) production of sub-tropical coccolithophores in response to environmental forcing

Abstract

My research, Larsen (2005), indicates the climate system is potentially very sensitive to changes in the flux of ultraviolet (UV) light, via its affect on the marine production of the biogenic trace gas dimethyl sulphide (DMS).

DMS is derived from its precursor dimethylsulphoniopropionate (DMSP) which is produced by marine phytoplankton, notably the coccolithophores (Class: Prymnesiophyceae).

DMS is emitted from the oceans into the atmosphere where it is oxidised to sulphates, forming the principal source of cloud condensation nuclei (CCN) over the subtropical oceans. These CCN are of major climatic importance as they determine the number of cloud droplets and so radiative properties of maritime clouds. Much effort has focussed on different aspects of this process, however, a unified understanding of the way in which different environmental conditions affect the intracelluar and overall net production of dimethylsulphoniopropionate (DMSP), the precursor to DMS, and the very first step in the process, has still not been obtained.

From a climatic perspective, the oceans between the sub-tropics, 30S-30N absorb more than 60% of the incoming solar energy. Within these oceans, the dominant DMSP producers are expected to be the coccolithophores of which the three most important are Emiliania huxleyi, Gephyrocapsa oceanica and Umbellosphaera irregularis , Hagino and Okada (2004).

Work to date has focussed on E. huxleyi, to which my study will contribute. No literature exists on the DMSP content, let alone the environmental factors which affect it, for either G. oceanica or U. irregularis . As both species dominate the sub-tropical flora over a larger area than E. huxleyi , and may well be more competitive in a globally warming world, it is vital to understand the role they play.

The aim of this study is to culture these three species under a range of conditions simulating the environment from the peak of the last Glaciation (18000 years BP) to the Enhanced Greenhouse Climate (AD 2200). Cell volume, intracellular DMSP content and growth rate will be measured under varying temperature, salinity, ultraviolet/visible light regimes in order to determine the effect of these on net DMSP production.

I have proposed that greenhouse warming will increase the sensitivity of the DMS-climate system to natural UV (Larsen, 2008). At the same time, surface UVB levels may also rise in the tropics from changes in the stratospheric circulation (Jiang et al. 2007). In either case, my hypothesis predicts reduced DMS/DMSP production and so a positive feedback to greenhouse warming. The data obtained from this project will thus provide an important test of my hypotheses.

Supervisors

• Prof. John Beardall

See also

Publications