Project Alma Mater

Absorption of Light, Macro algae and Atmosphere

 

Marie Curie Intra European Fellowship (IEF)

 

Project No: 3012109

 

Persons in Charge: Dr. Ranjini Raghunandan, Dr. Andy Ruth

 

 

 

Background Methodology Outreach Project Output

 

 

 

Background of Research Problem

The transport and transformation of substances within the Earth system (within the atmosphere, hydrosphere, biosphere and lithosphere) are known as biogeochemical cycles. Elements involved in natural biogeochemical cycling include H, C, N, O, P, S and I. For the marine environment, which is present in large parts of Ireland, the cycles involving sea-to-air exchange processes are particularly relevant. A large variety of different gases enter the atmosphere from seawater and many affect our climate. Many aspects of the sea-to-air or air-to-sea exchange mechanisms are not understood in detail yet. Knowing the total gas fluxes and composition of gases evolving from the sea is a precondition for the development of global models describing biogeochemical cycles.

 

For the marine environment the iodine cycle is of particular importance. Atomic iodine is known to be one of the most important catalytic species for the removal of ozone in the marine troposphere. It also plays a crucial role in nucleation processes leading to the growth of marine aerosol. One major channel for atomic iodine formation is the photolysis of molecular iodine (I₂) and other iodocarbons, whose dominant source in the marine troposphere is still under intense investigation. Present knowledge concerning the transfer of iodine (and in general of halogen compounds such as Br and Cl) from the sea into the atmosphere is limited due to the lack of quantitative information on total net fluxes and their partitioning into fluxes of individual compounds. Models largely rely on data from calculations that are based on balance considerations rather than quantitative in situ measurements. Direct elusion of I₂ from the open ocean surface by reaction with tropospheric ozone or through sunlight driven oxidation of iodide ions in seawater have been proposed as production pathways of molecular iodine in the past. More recently biogenic emission (so-called iodovolatilization) of I₂ by phytoplankton in open waters and especially via macrophytic algae in coastal areas is believed to be the driving force of the marine iodine cycle. It is known that iodide (and bromide) ion concentrations within macro-algae are up to 3x10⁴ times higher than in seawater. When algae are put under stress at low tide (e.g. through exposure to sun light, micro-organisms or oxidants such as ozone) the ions are presumably involved in plant defence mechanisms, which lead to the release of I₂ and a number of volatile iodocarbons such as CH₃I, C₂H₅I, 1-C₃H₇I, 2-C₃H₇I, CH₂ICl, CH₂IBr, or CH₂I₂. Studies of air composition in the marine boundary layer suggest that the iodocarbon concentrations are influenced by seaweed populations and distribution, as well as tide height. However, the different potential mechanisms leading to the generation of I₂ and iodo- or halocarbons in the marine boundary layer (MBL) are still being debated (Fig. 1).