Deepwater nutrition is essential in a global food chain

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Eroded seabed rocks provide an essential source of nutrients for moving marine organisms at the bottom of the food chain, according to a new study.

The findings, led by the University of Leeds, show that iron – an essential nutrient for microscopic marine algae, or phytoplankton – is released from sediments on the deep ocean floor.

The research shows that, contrary to the expectation that oxygen in the deep sea will prevent loose iron from escaping from the seabed, there may be a mixture of oxygen and substances. organic stimulates the release of iron from sediments into the ocean.

Published today in the Proceedings of the National Academy of Sciences (PNAS), the research has the potential to influence future approaches to the study of the ocean’s carbon cycle and the management of the marine environment, which will require consideration of the effects of seabed processes on the ecosystem. marine science.

The lead author of the report is Dr Will Homoky, who is a University Academic Fellow at Leeds School of Earth and Environment.

He said: “Our findings show that the shallow surface of the seabed is an important source of iron – a scarce micronutrient – for the ocean.

“We show that the contamination of rock minerals with organic matter and oxygen is the recipe for the production of small pieces of rust, which are small enough to be dispersed and transported in seawater. “These tiny bits of rust and their chemical names explain how iron is found so much that some of the interior of the ocean could come from the deep sediments of the ocean, in a way who once thought it was impossible. “

The nanometer-sized iron grains – known as colloids – could be an important nutrient source for phytoplankton, which is a major food source for a wide range of marine creatures, affecting global food chains.

Phytoplankton are also important in global pollution levels, as they help the ocean remove about a quarter of the carbon dioxide released into the atmosphere each year. .

The research team, funded by the Natural Environment Research Council (NERC), also included scientists from the universities of Southampton, Liverpool, Oxford, South Florida and Southern California – a collaboration that created through the international GEOTRACES program.

The findings will help shape further research into the processes that regulate the occurrence of iron in the world’s oceans and their role in changing marine life and carbon sequestration. atmospheric oxygen.

Dr Homoky said: “Our findings here are important, as they mark a turning point in how we view iron supply from sediments and its potential to reach marine life which is a new way of think of the seabed.

“Our finding of iron colloids is different from other forms of iron taken into the ocean, and will help us design a new generation of marine models to re-evaluate marine life and connections. seabed climate – where there is currently great uncertainty.

“This could help us to better understand how iron in the ocean has contributed to productivity and climate change in the past and inform our approaches to marine conservation and management. . “

The research team analyzed small and detailed differences within the fluid content of sediment samples collected from the South Atlantic Ocean at water depths ranging from 60m down to 5km.

They aimed to understand how the chemical names – or isotopes – of nano-iron names in sediment liquids were formed, and what this tells us about the processes of iron supply to the ocean.

The co-author of the report Dr. Tim Conway is an Associate Professor at the University of South Florida.

He explained: “We can now measure small but significant changes in the chemical production of seawater that were beyond our reach a decade ago.

“Here we have signed an isotope signature belonging to the iron colloids extracted in deep ocean sediments that we can use to trace their voyage in the ocean.

“Our ongoing aim is to learn how far this iron travels and how much of it feeds our seafood networks around the world. ”

Shedding light on iron enrichment in the twilight zone of the ocean

Further information:
William B. Homoky el al., “Iron colloids are abundant in the supply of sediment into the ocean,” PNAS (2021).

Presented by the University of Leeds

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