Dr. Darci Rush

Geochemist Darci Rush searches the sea and ocean floors for traces of bacteria from the distant past. ‘Microorganisms, such as bacteria and unicellular algae formed the foundations of life on earth and are still vital for all life, both above and below the surface. For example, they play a crucial role in the carbon and nitrogen cycles and, consequently, the regulation of the climate.’

Bacteria consume methane

‘One of the specific substances I examine is the strong greenhouse gas methane. Methane (CH4) is produced by microorganisms under anoxic conditions in the seafloor. When it is released from the floor, it could escape into the atmosphere via the water column. In the atmosphere, each methane molecule retains twenty times as much heat as a CO2 molecule. On its way to the surface, part of that methane is consumed by bacteria, which use it as a source of carbon. I try to understand exactly where the equilibria lie: under which conditions was more or less methane released from the ocean floor in the past, and subsequently, how much was reabsorbed into the food chains of the ocean?’

Anoxic seas

‘Another molecule I’m interested in is nitrogen. In areas with little to no oxygen, deep in the ocean, I examine how nitrogen is removed from the food chain by bacteria both now and in the past. By removing nitrogen, the bacteria ensure that it is no longer available for the growth of algae higher in the water. Consequently, those algae can no longer contribute to the capture of CO2 from the atmosphere. As such deep, anoxic areas, like in the Gulf of Mexico, are increasing in size, there will be a growing number of locations where nitrogen will be removed from the nutrient cycle.’

Practical starting points

‘My interest in the chemistry of the oceans is mainly academic: I want to understand how things work. Yet at the same time, this work clearly has a practical side too. The pollution of the Gulf of Mexico with waste from American agriculture has a large influence on the development of anoxic zones and consequently on the climate too. My work therefore provides starting points for tackling ocean pollutions and the disruption of the climate system.’