GLOBAL NEWS
GLOBAL:
HOW BOTTOM NODULES STAY
ON TOP
Rare metallic elements found in clumps on the deep-ocean
floor mysteriously remain uncovered despite the shifting
sands and sediment many leagues under the sea. Scientists
now think they know why, and it could have important
implications for mining these metals while preserving the
strange fauna at the bottom of the ocean.
The growth of these deep-sea nodules—metallic lumps of
manganese, iron, and other metals found in all the major
ocean basins—is one of the slowest known geological
processes. These ringed concretions, which are potential
sources of rare-earth and other critical elements, grow on
average just 10 to 20 millimetres every million years. Yet
in one of earth science’s most enduring mysteries, they
somehow manage to avoid being buried by sediment
despite their locations in areas where clay accumulates at
least 100 times faster than the nodules grow.
Understanding how these agglomerations of metals remain
on the open sea floor could help geoscientists provide advice
on accessing them for industrial use. A new study published
in Geology will help scientists understand this process better.
“It is important that any mining of these resources is done
in a way that preserves the fragile deep-sea environments
in which they are found,” says lead author Dr Adriana
Dutkiewicz, an ARC Future Fellow in the School of
Geosciences at The University of Sydney.
Rare-earth and other critical elements are essential for
the development of technologies needed for low-carbon
economies. They will play an increasingly important role
for next-generation solar cells, efficient wind turbines, and
rechargeable batteries that will power the renewables
revolution.
From scouring bottom currents to burrowing animals,
researchers have proposed a number of mechanisms to
account for this enigma. But solving it depends on a better
understanding of where the nodules are situated and
the environmental conditions that prevail there. Now a
global study published in Geology uses predictive machine
learning to investigate which factors control the location of
polymetallic nodules. The results offer new insights to inform
deep-sea mineral exploration as well as its regulation.
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African Mining Publication
“The International Seabed Authority is currently preparing
new environmental regulations to govern deep-sea mining,”
says Dutkiewicz. “Our analysis represents a global, data-
driven synthesis to impartially inform these policies and
deep-ocean environmental management.”
Dutkiewicz and co-authors Dr Alexander Judge and
Professor Dietmar Müller combined open-access data for
thousands of polymetallic nodules with global datasets of
key environmental parameters to create a machine-learning
model that ranks the factors controlling nodule location. The
resulting map predicts where polymetallic nodules are most
likely to occur.
The authors were surprised to find that globally the nodules
occur in regions where the bottom current speeds are far too
slow to remove sediment. Instead, the nodules are associated
with seafloor fauna.
“Organisms such as star fish, octopods and molluscs seem
to keep the nodules at the seafloor surface by foraging,
burrowing and ingesting sediment on and around them,”
says Dutkiewicz.
“Although these organisms occur in relatively low
concentrations on the abyssal seafloor, they are still
abundant enough to locally affect sediment accumulation.”
This insight is supported by direct seafloor observations
of nodule fields by independent studies. “Our conclusion
is that deep-sea ecosystems and nodules are inextricably
connected,” Dutkiewicz adds.
The study results also suggest that the regions where
nodules are most likely to occur are more extensive than
what has previously been assumed and include vast areas
that are yet to be explored findings with important industrial
as well as conservation implications.
“Our map highlights regions that may be important
economically,” Dutkiewicz explains, “but at the same time
draws attention to areas of the seafloor that may be hotspots
for diverse deep-sea organisms that we know little about.”
Because the techniques used by the researchers can
be modified to investigate other seafloor features, this
approach—as well as the conclusion that there is an apparent
“symbiosis” between deep-sea fauna and the nodules—could
also have implications for future biodiversity research.
“Vast regions of the deep sea are unexplored,” says
Dutkiewicz “so the consequences of nodule mining for deep-
sea ecosystems need to be carefully evaluated.”
African Mining
African Mining February 2020
15