12 | New Scientist | 9 November 2019
Field notes Amazon Tall Tower ObservatoryDiscovering rainforest secrets high above the trees
I took almost an hour to ascend the 1500 steps
of the tallest tower in Latin America, says Fred PearceIT WAS a long climb – 325 metres
above the floor of the pristine
Amazon rainforest, a metre higher
than the Eiffel Tower in Paris.
Rising out of the steamy jungle,
temperatures peaked just under
the canopy and then started
to drop. Above 150 metres, a
stiff, cool breeze blew. From the
top, the trees looked like a mass
of tiny broccoli heads stretching
unbroken to the horizon.
I was met at the top by Meinrat
Andreae, director of the Max
Planck Institute for Chemistry in
Mainz, Germany. In 2007, he first
proposed erecting the structure
to sniff the Amazon forest’s breath
and examine its interactions with
the atmosphere. In this remote
spot, 150 kilometres north
of Brazil’s jungle city of Manaus,
he hoped it could provide
“a window on our planet’s
atmospheric chemistry before
industrialisation”.
Andreae got his wish – during
the November to May wet
season at least, when clean air
from the Atlantic blows across
800 kilometres of largely intact
forest. But our climb was in late
September, the end of the dry
season, when the winds from the
south cross the deforested areasof the Amazon. With forest fires in
recent weeks burning faster than
they have in the past decade, the
air below us was thick with haze.
Since the Amazon Tall Tower
Observatory was inaugurated
in late 2015, its instruments have
sampled the air above the forest
hour by hour, looking at levels
of carbon dioxide, sulphur
compounds, pollen and other
substances. In makeshift labs at the
tower’s base, researchers derive
other vital data, such as rates
of photosynthesis in the trees.
Some of the chemistry is
unexpected. “We know there are
reactions going on in the air thatNews
PAULO BRANDO/IPAM/WHRCHuman geneticsImportant gene
variants in African
people being missedMORE than a quarter of the genetic
variation found among people in
25 Ugandan villages has never
previously been recorded, because
most human genetics studies focus
on people of European descent. This
oversight could have a significant
impact on global human health,
because the variants included genesassociated with cardiovascular
and metabolic diseases.
Human genetics studies have
suffered from a lack of diversity
and more research on people from
different parts of the world is
needed, says Deepti Gurdasani at
Queen Mary University of London,
who led the work in Uganda.
“European ancestry populations
make up 16 per cent of the global
population, but approximately
80 per cent of participants in
genetic studies,” says Alicia Martinat the Broad Institute in Cambridge,
Massachusetts, meaning other
groups are under-represented.
Gurdasani and her colleagues
analysed DNA from 6000 people
in south-west Uganda. About 29 per
cent of the gene variants they found
weren’t present in one of the world’s
largest human genome sequence
databases (Cell, doi.org/ddmk).
Although some data sets do
include people of African descent,
such as African-Americans,
Gurdasani says this isn’t enough.The ancestors of modern African-
Americans came from specific parts
of Africa and so this doesn’t capture
the genetic diversity that exists
within the African continent.
Because all humans originated
in Africa, those who migrated away
took only a fraction of the genetic
diversity with them. “Two individuals
within an African population will be
much more different than two
individuals within a European
population,” says Gurdasani. ❚
Layal LiverpoolThe Amazon
Ta l l To w e r
Observatory
is 325 metres
highJOST LAVRIC/MPI-BGCabout 500 litres a day into the
atmosphere. More intriguing are
the physics and chemistry that
turn that water into rain clouds.
The key seems to be volatile
organic compounds, such as the
isoprenes and terpenes emitted
by most trees. In the air around
the tower’s summit, these
compounds oxidise into the tiny
molecular seeds around which
raindrops form – but not enough
to provide the volume of rain we
see. Andreae’s hunch is that other
compounds – fast-reacting
sesquiterpenes – could be the
missing link, but they are hard to
spot as they disappear quickly.
While straining to understand
pristine climatic processes,
Andreae’s team is increasingly
worried about the polluted air
coming from the south. Back at
the research camp, his colleague
Matthias Sorgel told me about
ozone generated by the fires. He
is measuring up to 70 parts per
billion (ppb), a level normally
found in urban smogs. “We
don’t know the sensitivity of
rainforest trees to ozone,” he said.
“But as a rule of thumb, levels
above 40 ppb are toxic to plants.
As the burning gets closer, it is
poisoning pristine forest.” ❚we haven’t accounted for yet,” said
Andreae. “That means there are
probably tree emissions we are
ignorant about.” Uncovering
them may unlock the mystery
of how the trees maintain rainfall
so far from the ocean. We know
rainforests recycle rainfall on a
heroic scale: each tree releases