New research involving scientists from the National Oceanography Centre, Southampton (NOCS) highlights the potential utility of iron isotopes for addressing important questions in ocean science. The findings are published in the August edition of the journal Geology.
Large regions of the world's oceans have low primary production despite having plenty of macronutrients such as phosphate, nitrate and silicate. This is due a shortage of the essential micro-nutrient iron, which is needed for the growth of phytoplankton. These tiny, plant-like organisms sit at the base of the marine food chain and collectively draw vast amounts of the greenhouse gas carbon dioxide down from the atmosphere through the process of photosynthesis.
A proportion of the carbon is exported to the deep ocean, making the oceans a major carbon dioxide sink, without which global warming would rapidly accelerate. The natural supply of iron to such 'High Nutrient Low Chlorophyll (HNLC) regions is therefore, albeit indirectly, an important determinant of climate.
The importance of dissolved iron in seawater derived from bottom (benthic) sediments is increasingly recognised as being important. Around the continental margins, in particular, iron is released from the sediments during the decomposition of organic carbon by dissimilatory iron-reducing bacteria - micro-organisms that use elemental iron to obtain energy. This leads to the enrichment of iron in pore fluids and bottom waters. However the ubiquity of sedimentary iron inputs to seawater remains unknown.
Different biological and chemical processes can leave behind characteristic isotopic 'fingerprints'. Of specific interest here, iron isotopes in sediment pore fluids may be a unique tracer of sediment respiration by dissimilatory iron-reducing bacteria.
Dissimilatory iron reduction is thought to be one of the earliest metabolic pathways on Earth , thus sedimentary iron isotopes may also
|Contact: Dr. Rory Howlett|
National Oceanography Centre, Southampton (UK)