Eroded seabed rocks are providing an essential source of nutrition for drifting marine organisms at the base of the food chain, according to new research.
From: The University of Leeds
March 22, 2021 -- The findings, led by
the University of Leeds, show that iron -- an essential nutrient for
microscopic marine algae, or phytoplankton -- is being released from sediments
on the deep ocean floor.
The research shows that contrary to the
expectation that oxygen in the deep-sea prevents actually encourage the release
of iron from sediments into the ocean.
Published today (22 March) in the Proceedings
of the National Academy of Sciences (PNAS), the research could
influence future approaches to studying the ocean carbon cycle and managing the
marine environment, which must consider effects of seafloor processes on marine
ecology.
Report lead author is Dr Will Homoky, a
University Academic Fellow at Leeds' School of Earth and Environment.
He said: "Our findings reveal that
the shallow surface of the deep seafloor provides an important source of iron
-- a scarce micronutrient -- for the ocean.
"We show that the degradation of
rock minerals with organic matter and oxygen is a recipe to produce tiny rust
particles, which are small enough to be dissolved and carried in seawater.
"These tiny rust particles and their chemical signatures explain how iron
found in large parts of the ocean interior could have come from deep ocean
sediments, in a manner which was once thought to be practically impossible."
The nanometre sized iron particles --
known as colloids -- could provide an important source of nutrition for
phytoplankton, which provide the primary food source for a wide range of sea
creatures, affecting global food chains.
The phytoplankton are also important
amid rising worldwide pollution levels, as they help the ocean remove about one
quarter of carbon dioxide emitted annually to the atmosphere.
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 formed through the international GEOTRACES
programme.
The findings will help shape further
study of the processes that regulate the occurrence of iron in the world's
oceans and the role they play in moderating marine life and atmospheric carbon
dioxide.
Dr Homoky said: "Our findings here
are significant, because they mark a turning point in the way we view iron
supply from sediments and its potential to reach marine life that paves a new
way of thinking about the seafloor.
"Our discovered production of iron
colloids is different to other forms of iron supplied to the ocean, and will
help us design a new generation of ocean models to re-evaluate marine life and
climate connections to the seafloor -- where large uncertainty currently
exists.
"This could help us to better
understand how iron in the ocean has contributed to past productivity and
climatic variations and inform our approaches to marine conservation and
management."
The research team analysed tiny and
precise variations 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 -- or isotope -- signatures of nano-sized iron in the sediment fluids
had been formed, and what this tells us about iron supply processes to the
ocean.
Report co-author Dr Tim Conway is
Assistant Professor at University of South Florida.
He explained: "We can now measure
tiny but important variations in the chemical make-up of seawater that were
beyond our reach a decade ago.
"Here we have characterised an
isotope signature belonging to the iron colloids produced in deep ocean
sediments that we can use to trace their journey in the ocean.
"Our continuing goal is to learn
how far this iron travels and how much of it nourishes our marine food webs
around the globe."
https://www.sciencedaily.com/releases/2021/03/210322175033.htm
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