No glacial fertilization effect in the Antarctic Ocean

Date:
April 19, 2022
Source:
University of Bonn
Summary:
Can iron-rich dust fertilize the ocean, stimulate algae growth
there, and thereby capture carbon dioxide from the atmosphere? An
international research team used deep-sea sediment cores from the
Scotia Sea to investigate whether this hypothetical greenhouse gas
sink had an effect during ice ages. Although dust input was high
during ice ages, no evidence of a fertilization effect could be
found in the Antarctic Ocean.

Rather, the production of algae, for example, and thus carbon
dioxide sequestration, was high only during warm periods when dust
input was low.



FULL STORY ========================================================================== Changes in the concentration of atmospheric carbon dioxide (CO2) are
considered to be the main cause of past and future climate change. A long-standing debate centers on whether the roughly 30 percent lower CO2 content of the ice-age atmosphere was caused by iron fertilization. It is argued that iron-rich dust is carried into the ocean by wind and water,
where it stimulates the growth of algae that absorb more CO2. As the
algae die and then sink permanently into the depths of the ocean, the
CO2 also remains there like in a trap. Although there is clear evidence
that dust input increased during the ice ages, the fertilization effect
is controversial, at least for the Antarctic Ocean.


==========================================================================
In a recent study, an international team of 38 researchers from 13
countries led by Dr. Michael Weber from the Institute for Geosciences
at the University of Bonn investigated this question. As part of the
Integrated Ocean Discovery Program (IODP), the team traveled to the
Scotia Sea on the drillship "JOIDES Resolution" and spent two months
in 2019 bringing up cores from the seafloor at depths of 3,000 to
4,000 meters. Weber: "We collected the highest-resolution and longest
climate archive ever obtained near Antarctica and its main dust source, Patagonia." 1.5 million years of climate history In the 200-meter-long deep-sea core U1537, the climate history of the last 1.5 million years was recorded in detail. This allows the reconstruction of the dust input to
be nearly doubled, since Antarctic ice cores only cover the last 800,000
years. Current records from the deep ocean show that dust deposition
during the ice ages was actually five to 15 times higher. This is also reflected in the ice cores.

However, the researchers found no evidence of a fertilization effect from
dust in the Antarctic Ocean during the ice ages. Rather, the production
of algae, for example, and thus carbon CO2 sequestration, was high only
during warm periods when dust input into the Scotia Sea was low. This
means that during cold periods, other processes prevented the CO2
captured in the ocean from escaping into the atmosphere and triggering
warming. The main factors here are much more extensive sea ice cover,
more intense stratification in the ocean, and reduced dynamics of the
current systems, which contributed to a reduction in the CO2 content of
the atmosphere during cold periods.

The opposing trends in dust deposition and oceanic productivity during
the ice ages and interglacial periods of the Pleistocene are accompanied
by long-term, gradual changes in the climate system in the southern
polar region.

Bioproductivity was particularly high during the interglacial periods of
the last 400,000 years, but during the mid-Pleistocene transition 1.2
million to 700,000 years ago, it differed little from that during cold
periods. As the transition progressed, the dust input covered larger
and larger areas in the Southern Hemisphere. Abrupt changes continued
to occur 900,000 years ago, indicating greater glaciation of Antarctica.

"There is indeed evidence of a fertilization effect during the ice
ages in cores outside the Antarctic zone," Weber concludes. "However,
our study shows that atmospheric CO2 fluctuations do not depend solely
on iron fertilization from dust deposition. In the Antarctic Ocean, it
is rather a complex interplay of a westerly wind system, productivity,
and feedback with sea ice. This relationship has been consistent over
the last 1.5 million years."

========================================================================== Story Source: Materials provided by University_of_Bonn. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Michael E. Weber, Ian Bailey, Sidney R. Hemming, Yasmina M. Martos,
Brendan T. Reilly, Thomas A. Ronge, Stefanie Brachfeld, Trevor
Williams, Maureen Raymo, Simon T. Belt, Lukas Smik, Hendrik Vogel,
Victoria L.

Peck, Linda Armbrecht, Alix Cage, Fabricio G. Cardillo, Zhiheng
Du, Gerson Fauth, Christopher J. Fogwill, Marga Garcia, Marlo
Garnsworthy, Anna Glu"der, Michelle Guitard, Marcus Gutjahr, Iva'n
Herna'ndez-Almeida, Frida S. Hoem, Ji-Hwan Hwang, Mutsumi Iizuka,
Yuji Kato, Bridget Kenlee, Suzanne OConnell, Lara F. Pe'rez, Osamu
Seki, Lee Stevens, Lisa Tauxe, Shubham Tripathi, Jonathan Warnock,
Xufeng Zheng. Antiphased dust deposition and productivity in the
Antarctic Zone over 1.5 million years.

Nature Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-29642-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220419092327.htm

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