The oceans play an important role in the biogeochemical cycles of atmospheric gases including the greenhouse gases carbon dioxide and methane that contribute to global warming. Our recent experiments revealed that the ultraviolet component of sunlight drives photochemical reactions that can produce methane and carbon dioxide from organic matter in seawater.
Carbon monoxide is also formed which indirectly contributes to global warming by reacting with compounds that would otherwise destroy methane. It is important that we understand the sources of methane that enter the atmosphere because it contributes to global warming with a potential 25 times that of carbon dioxide.
This project will expose samples of sea water, sampled by boat along the sea inlet Loch Etive, to controlled levels of ultraviolet radiation in order to observe the effect of organic matter from the surrounding land and rivers and the interactions with ocean salinity.
We will also look for photochemical emissions of nitrous oxide which has a global warming potential 310 times that of carbon dioxide. Phytoplankton is a potential source of some of the observed photochemical emissions and we will examine individual species in experiments that simulate sunlight to identify which types of organisms are involved. We will also expose sea water inside gas-tight bags floated at the sea surface in order to quantify these effects in natural sunlight.
The results from the project will improve our understanding of atmospheric gas budgets and inform us of the importance of photochemical formation of greenhouse gases in marine coastal waters.