Measuring how the Arctic responds to climate change

Date:
August 24, 2021
Source:
University of East Anglia
Summary:
The Arctic has been warming more than twice as fast as the rest of
the planet. Meanwhile CO2 measurements show substantial increases
in the amount of carbon absorbed into and emitted by Arctic plants
and soil.

Scientists assumed this was playing a large role in changes to
the Arctic carbon cycle. But they were not able to measure carbon
uptake and release independently. This study provides insights
into this important process based on the modelling of atmospheric
measurements of carbonyl sulfide.



FULL STORY ========================================================================== Researchers at the University of East Anglia have helped develop a new
way to measure how Arctic plants respond to climate change.


==========================================================================
Over the past few decades, the Arctic has been warming more than twice as
fast as the rest of the planet. At the same time, long-term atmospheric
carbon dioxide measurements have shown substantial increases in the
amount of carbon absorbed into and emitted by plants and soil -- the terrestrial ecosystem -- in the Arctic every year.

Scientists had assumed this terrestrial ecosystem was playing a large
role in the changes they're seeing in the Arctic carbon cycle.

But they lacked a technique to measure carbon uptake and release
independently.

And this is key for understanding how the biosphere is responding to
climate change driven by fossil fuel emissions.

Now a new study, published in the journal Proceedings of the National
Academy of Sciences, provides new insights into this important process
over the Arctic and boreal region, based on the modelling of atmospheric measurements of a related chemical -- carbonyl sulfide.

Led by researchers at the National Oceanic and Atmospheric Administration (NOAA), the international team of scientists developed a new way of
analysing atmospheric measurements of the trace-gas carbonyl-sulfide,
together with atmospheric CO2 measurements, to provide information on the
total amount of carbon taken up by land-vegetation during photosynthesis.



==========================================================================
Dr Parvadha Suntharalingam, from UEA's School of Environmental
Sciences,and a co-author on the study, said: "This work gives us new
and valuable information about the processes controlling CO2 uptake by land-based vegetation in the boreal area of the Arctic.

"Carbonyl sulfide is taken by plants during photosynthesis, but unlike
CO2, it is not released back into the atmosphere by the ecosystem
respiration processes. It therefore gives us a way of separating the
two key processes - - photosynthesis and respiration -- that control
how CO2 is exchanged between the land-vegetation and the atmosphere.

"This research provides new estimates of the uptake of carbon by
terrestrial ecosystems in North American high-latitude regions.

"It reduces the uncertainties in comparison to previous assessments,
and also investigates the influence of other environmental factors --
such as temperature and solar radiation -- on the processes controlling
carbon uptake by these high-latitude ecosystems.

"Our analysis shows the potential of using measurements of
carbonyl-sulfide as an independent means of obtaining additional
information on key carbon cycle processes," she added.



==========================================================================
Lead researcher Lei Hu, a Cooperative Institute for Research in
Environmental Sciences (CIRES) scientist working at NOAA in Colorado,
said: "We now can study how Arctic terrestrial ecosystems react to climate change at process levels, because we are able to separate photosynthetic
uptake and ecosystem respiration on regional scales." What is carbonyl sulfide? Scientists have long known plants absorb carbon dioxide, or CO2,
to fuel photosynthesis during the growing season, and then emit it back
to the atmosphere during fall and winter when plant tissue decays. This give-and-take, set against rapidly rising atmospheric CO2 levels, makes
it impossible for scientists to directly estimate how CO2 uptake by photosynthesis is changing over time based on measurements of CO2 alone.

However, plants need other nutrients, including sulfur -- which is not
released at the end of the growing season. Carbonyl sulfide, or COS,
is a simple molecule that is very similar to CO2.

While CO2 is made up of one carbon atom and two oxygen atoms, COS consists
of one carbon atom, one oxygen atom and a sulfur atom. Continually
produced by oceanic processes, it can also be found in volcanic gases,
crude oil combustion, sulfurous marshes and soils, as well as diesel
exhaust, natural gas, and refinery emissions.

It is present in the atmosphere in tiny amounts (parts per
trillion). Uptake by plants is the dominant process that removes COS
from the atmosphere.

How are Arctic ecosystems changing? In the new study, Hu and a team
of researchers from NOAA, the University of Colorado, Colorado State University, University of California -- Santa Cruz, NASA/Universities
Space Research Association, Rutgers University, and UEA analysed
atmospheric measurements of carbonyl sulfide collected from NOAA's Global Greenhouse Gas Reference Network from 2009 to 2013 to investigate carbon cycling in the North American Arctic and boreal regions.

The UEA contribution provided data and information on the oceanic sources
of carbonyl-sulfide to the atmosphere. Oceanic emissions provide the
largest global source of COS to the atmosphere -- so accurate knowledge of these fluxes is needed when using atmospheric measurements to identify and quantify the uptake of COS and CO2 by vegetation during photosynthesis.

The team estimated plants over this region took up 3.6 billion metric
tons of carbon from the atmosphere during photosynthesis each year. They
also found that warming temperatures were causing increases in both net
uptake in spring and net off-gassing in fall, but not equally, due to regulation by both temperature and light.

From 1979-1988 to 2010-2019, the annual spring soil temperature in the
region increased by an average of 0.9 ?, while the autumn temperature
increased by 1.8 ?. The researchers found that in spring, the soil
temperature increase helps to ramp up photosynthetic uptake of carbon as sunlight floods the region. In the autumn, the amount of carbon taken
up by plants is reduced by the dwindling amount of sunlight, despite
soil temperatures remaining elevated until late autumn.

In contrast, when it came to giving off CO2, the scientists found the
rate was mainly controlled by temperature.

The results were also consistent with satellite remote-sensing-based
gross primary production estimates in both space and time, boosting
confidence in the findings.

Implications for the future One of the big unknowns about the future
Arctic is whether plant communities around the Northern Hemisphere will continue to increase their carbon uptake as atmospheric CO2 rises. One
way to obtain a clearer picture, Hu said, would be to make more COS measurements from the region.

If Arctic surface temperature continues to increase, especially in the
fall and winter, the Arctic may start emitting more CO2 than it takes up, exacerbating climate change.

Expanding the atmospheric COS observing system could improve scientists' ability to monitor how much carbon land plants are removing from the
atmosphere as CO2 levels increase and climate changes, which would
improve understanding of the climate-carbon cycle feedbacks and climate projections in the Arctic and Boreal regions.

This study was funded in part by NASA, with ongoing support from NOAA's
Global Monitoring Laboratory.

'COS-derived GPP relationships with temperature and light help explain
high- latitude atmospheric CO2 seasonal cycle amplification' is published
in the Proceedings of the National Academy of Sciences.

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


========================================================================== Journal Reference:
1. Lei Hu, Stephen A. Montzka, Aleya Kaushik, Arlyn E. Andrews, Colm
Sweeney, John Miller, Ian T. Baker, Scott Denning, Elliott Campbell,
Yoichi P. Shiga, Pieter Tans, M. Carolina Siso, Molly Crotwell,
Kathryn McKain, Kirk Thoning, Bradley Hall, Isaac Vimont, James
W. Elkins, Mary E. Whelan, Parvadha Suntharalingam. COS-derived GPP
relationships with temperature and light help explain high-latitude
atmospheric CO2 seasonal cycle amplification. Proceedings of the
National Academy of Sciences, 2021; 118 (33): e2103423118 DOI:
10.1073/pnas.2103423118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210824135336.htm

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