Q&A: How Desert Dust Storms Supply Vital Nutrients to the Oceans

A dust story in El Fasher, North Darfur. This is a natural weather phenomenon in Darfur which occurs regularly between March and July every year. It affects all aspects of daily life in the region, including airline flights. Scientists say these storms have a range of affects that are not clearly understood. Courtesy: CC By 2.0/ Mohamad Almahady, UNAMID.

A dust story in El Fasher, North Darfur. This is a natural
weather phenomenon in Darfur which occurs regularly between March
and July every year. It affects all aspects of daily life in the
region, including airline flights. Scientists say these storms have
a range of affects that are not clearly understood. Courtesy: CC By
2.0/ Mohamad Almahady, UNAMID.

By Samira Sadeque
UNITED NATIONS, Nov 9 2020 (IPS)

When sand and dust storms (SDS) rage in the Sahara Desert, more
than 10,000 km away in the Caribbean Sea the very same storms have
a range of effects on the 1,360 species of shorefish that populate
the waters there.

According to a
report
released last week by the United Nations Environment
Programme (UNEP), each year about half a billion tonnes of
nutrients, minerals, and organic inorganic matter is transferred to
the oceans through SDS.

But as Dr. Nick Middleton, a fellow in physical geography at St
Anne’s College at the University of Oxford and author of the UNEP
report titled “Impacts
of Sand and Dust Storms on Oceans
”, told IPS, “our
understanding of how dust affects marine waters is far from
complete”.�

Though he added that the upcoming U.N. Decade of Ocean Science
for Sustainable Development will be an exciting opportunity to help
scientists gain a better understanding of issues such as how much
dust from SDS reaches the oceans. In his interview, Middleton said
that this decade is an important time to consider the ways in which
SDS affect issues such as biodiversity, the climate, and food
systems.

“The U.N. Decade offers exciting opportunities to improve our
understanding of some of these basic issues. Nobody lives
permanently in the open oceans, so historically we have had to rely
on scientists on ships to take measurements when and where they are
able.

“Hence, the data we have on dust in the atmosphere and
deposited over the oceans is patchy and sporadic at best. The use
of geostationary satellites is improving our capacity to monitor
dust, but there is no substitute for taking real samples at sea,â€
Middleton told IPS.

And as Jian Lu, Director of the Science Division at UNEP, said
in the report: “Desert dust is a principal driver of oceanic
primary productivity, which forms the base of the marine food web
and fuels the global carbon cycle.†

“One of the clear messages from this report is the simple fact
that many aspects of the impacts of SDS on the oceans are only
partially understood,†Lu said. “Despite the limited knowledge,
the impacts of SDS on oceans—their ecosystem functions, goods and
services—are potentially numerous and wide-ranging, thus
warranting continued careful monitoring and research.â€

“Many scientists predict that as our climate warms dust storms
will become more frequent in certain parts of the world where the
climate becomes drier and soils will be protected by less
vegetation,†Middleton added. “More dust in these places will
inevitably have complex feedback effects on climate and what
happens in the oceans.â€

Excerpts of the interview below.

Inter Press Service (IPS): Jian Liu said in the
report the impacts of sand and dust storms on the oceans are only
partially understood. What are some under-reported issues about the
impact of sand and dust storms on oceans?

Dr Nick Middleton (NM): One aspect that needs more accurate
assessment is the amount of desert dust transported to the
world’s oceans each year. When they occur, we can see great
plumes of dust above the oceans on satellite imagery, but we only
have a rough idea of how much dust is involved. We estimate that
anything between one billion and five billion tonnes of desert dust
are emitted into the atmosphere by SDS every year on average. Two
billion tonnes is the current best estimate, and 25 percent of that
reaches the oceans, with all sorts of effects on marine ecosystems.
However, most of these estimates come from computer models which
are imperfect at simulating all the numerous processes involved in
lifting, transporting and depositing dust to the sea.

We know that desert dust delivers some vital nutrients to the
oceans, but our understanding of how dust affects marine waters is
far from complete. For instance, dust probably has an impact on the
energy balance in several oceans, affecting the circulation of heat
and salt. These circulation regimes have implications for marine
life, but our understanding of the details is hazy at best.

IPS: The U.N.  Decade of Ocean Science for
Sustainable Development (2021–2030) is scheduled to start in
2021. What are some issues that you believe should be addressed
during this time?

NM: The U.N. Decade could initiate a great leap forward in our
understanding if it presided over the establishment of a network of
study sites across different oceans to take long-term measurements
of dust in the atmosphere and as it is deposited on the ocean
surface. Buoys can be used as platforms for autonomous sampling of
dust and other weather variables, and their data transmitted to
researchers.

Long-term datasets are vitally important, but they cannot
replace experiments conducted from ships at sea. The U.N. Decade
can also promote coordinated experiments involving both atmospheric
and marine measurements to address some of the processes in which
desert dust is important. One such role is how iron and phosphorus
carried with desert dust helps to fertilise large areas of ocean
surface, and may also impact local climate.

IPS: The report establishes a link between desert
dust and coral reef systems; it also suggests a potential link
between disease arising from microorganisms and a decline in coral
reefs worldwide. What kind of impact do sand and dust storms have
on biological diversity overall, and on human life?

NM: Dust raised in SDS and transported to the oceans helps to
sustain the biodiversity of large marine areas. One of the most
direct effects is the incorporation of tiny dust particles into
coral skeletons as they grow. Nutrients carried on desert dust
particles also fuel the growth of marine microorganisms such as
phytoplankton, which form the base of the marine food web.

Human society relies on fish and other products from the sea,
but the fertilising effect of desert dust is also thought to have
an impact on algal blooms, some of which are detrimental to
economic activity and human health. Certain harmful algal blooms
contain species that produce strong toxins which become
concentrated up the food chain, becoming harmful to people who eat
contaminated seafood.

IPS: Dust has significant impacts on weather and
climate in several ways. In what ways are sand and dust storms
linked to issues such as climate change? 

NM: Dust in the atmosphere affects the energy balance of the
Earth system because these fine particles scatter, absorb and
re-emit radiation in the atmosphere. Dust particles also serve as
nuclei on which water vapour condenses, helping to form clouds, and
the chemical composition of dust affects the acidity of rainfall.
Dust from the Sahara is regularly transported through the
atmosphere over the tropical North Atlantic Ocean where it can have
a cooling effect on sea surface temperatures. In turn, the cooler
sea surface changes wind fields and the development of hurricanes.
A year with more Saharan dust usually translates into fewer
hurricanes over the North Atlantic.

Future trends in desert dust emissions are uncertain. They will
depend on changes in atmospheric circulation and precipitation –
how much falls, when and where.

IPS: Are there ways in which sand and dust storms
have an impact (direct or indirect) on the coronavirus
pandemic? 

NM: Links between sand and dust storms and the coronavirus
pandemic are quite possible, but inevitably work on such potential
links at an early stage. We know that SDS are a risk factor for a
range of respiratory and cardiovascular diseases, so someone
exposed to both COVID-19 and air pollution from dust storms may
experience particularly harmful effects. For instance, one recent
study in Northern Italy established an association between higher
mortality rates due to COVID-19 and peaks of atmospheric
concentrations of small particulate matter. Saharan dust frequently
contributes to poor air quality in Italy, but a direct causal link
between desert dust and suffering from COVID-19 has not been
established to date. There are numerous other factors to take into
account.

We also know that many SDS source areas contribute many types of
microorganisms (such as fungi, bacteria and viruses) to desert
dust, and that these microorganisms are very resilient. SDS can
also transport viruses over great distances (greater than 1,000
km), sometimes between continents. Long-range transport of desert
dust has been linked to some historical dispersal/outbreak events
of several diseases, including Avian influenza outbreaks in areas
downwind of Asian dust storms.

The post
Q&A: How Desert Dust Storms Supply Vital Nutrients to the
Oceans
appeared first on Inter Press Service.

Source: FS – All – Ecology – News
Q&A: How Desert Dust Storms Supply Vital Nutrients
to the Oceans