Fossil trees on Peru's Central Andean Plateau tell a tale of dramatic environmental change

Date:
August 28, 2020
Source:
Smithsonian Tropical Research Institute
Summary:
The anatomy of plant fossils including an enormous tree that
grew 10 million years ago in the now arid, high-elevation Central
Andean Plateau calls current paleoclimate models into question,
suggesting that the area was more humid than models predict.



FULL STORY ==========================================================================
As the Earth's surface transforms, entire ecosystems come and go. The
anatomy of fossil plants growing in the Andean Altiplano region 10
million years ago calls current paleoclimate models into question,
suggesting that the area was more humid than models predict.


==========================================================================
On an expedition to the Central Andean Plateau, researchers from the Smithsonian Tropical Research Institute (STRI) and colleagues were
astounded to find a huge fossil-tree buried in the cold, grassy plain. The plant fossil record from this high-altitude site in southern Peru contains dramatic reminders that the environment in the Andes mountains changed drastically during the past 10 million years, but not in the ways that
climate models of the past suggest. Findings from the expedition are
presented in the journal Science Advances.

"This tree and the hundreds of fossil wood, leaf and pollen samples
we collected on the expedition, reveal that when these plants were
alive the ecosystem was more humid -- even more humid than climate
models of the past predicted," said Camila Martinez, a fellow at STRI,
who recently finished her doctorate at Cornell University. "There is
probably no comparable modern ecosystem, because temperatures were higher
when these fossils were deposited 10 million years ago." The anatomy
of the petrified (permineralized) wood the researchers found is very
much like wood anatomy in low-elevation tropical forests today. Indeed,
the altitude then was probably only 2,000 meters above sea level.

But that ecosystem did not last for long. Today, the arid, intermountain plateau lies at 4,000 meters above sea level.

Five million year-old fossils from the same sites confirmed that the
Puna ecosystem that now dominates the Andes' high mountain plateaus had
been born: the younger pollen samples were mostly from grasses and herbs, rather than from trees. Leaf material was from ferns, herbs and shrubs, indicating that the plateau had already risen to its current altitude.

"The fossil record in the region tells us two things: both the altitude
and the vegetation changed dramatically over a relatively short period
of time, supporting a hypothesis that suggests the tectonic uplift of
this region occurred in rapid pulses," said Carlos Jaramillo, STRI staff scientist and project leader.

"Andean uplift played an important role in shaping the climate of
South America, but the relationship between the rise of the Andes, local climates and vegetation is still not well understood," Martinez said. "By
the end of this century, changes in temperature and atmospheric carbon
dioxide concentrations will again approximate the conditions 10 million
years ago. Understanding the discrepancies between climate models and
data based on the fossil record help us to elucidate the driving forces controlling the current climate of the Altiplano, and, ultimately,
the climate across the South American continent.

Author affiliations include: STRI; Cornell University; CNRS, EPHE,
IRD, Montpellier; Universidad Nacional Auto'noma de Me'xico; Museo de
Historia Natural, Lima, Peru; University of Rochester, Rochester, New
York; and the Florida Institute of Technology.


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


========================================================================== Journal Reference:
1. C. Marti'nez, C. Jaramillo, A. Correa-Metri'o, W. Crepet,
J. E. Moreno,
A. Aliaga, F. Moreno, M. Iban~ez-Mejia, M. B. Bush. Neogene
precipitation, vegetation, and elevation history of the Central
Andean Plateau. Science Advances, 2020; 6 (35): eaaz4724 DOI:
10.1126/ sciadv.aaz4724 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200828140308.htm

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