New Scientist - USA (2019-11-09)

12 | New Scientist | 9 November 2019

Field notes Amazon Tall Tower Observatory

Discovering 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 Pearce

IT 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 areas

of 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 that

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Human genetics

Important gene

variants in African

people being missed

MORE 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 genes

associated 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 Martin

at 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 Liverpool

The Amazon

Ta l l To w e r

Observatory

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about 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