14 research outputs found
Permafrost-carbon complexities
The thawing and
decomposition of carbon stored in
permafrost generates greenhouse gases that
could further intensify global warming.
Currently, most of the thawed carbon is
assumed to be converted to greenhouse
gases, such as carbon dioxide and methane,
and carbon decomposition is thought to
only occur at the site of the thaw. We argue
that lateral transport of thawed permafrost
carbon from land to ocean will translocate
greenhouse gas release away from the thaw
site, and that storage and burial of thawed
carbon in long- and short-term reservoirs
will attenuate greenhouse gas emissions
Past extreme warming events linked to massive carbon release from thawing permafrost
Between about 55.5 and 52 million years ago, Earth experienced a
series of sudden and extreme global warming events (hyperthermals)
superimposed on a long-term warming trend1. The first and largest
of these events, the Palaeocene–Eocene Thermal Maximum (PETM),
is characterized by a massive input of carbon, ocean acidification2
and an increase in global temperature of about 5 6C within a few
thousand years3. Although various explanations for the PETM have
been proposed4–6, a satisfactory model that accounts for the source,
magnitude and timing of carbon release at the PETM and successive
hyperthermals remains elusive. Here we use a new astronomically
calibrated cyclostratigraphic record from central Italy7 to show that
the Early Eocene hyperthermals occurred during orbits with a com-
bination of high eccentricity and high obliquity. Corresponding
climate–ecosystem–soil simulations accounting for rising concen-
trations of background greenhouse gases8 and orbital forcing show
that the magnitude and timing of the PETM and subsequent
hyperthermals can be explained by the orbitally triggered de-
composition of soil organic carbon in circum-Arctic and
Antarctic terrestrial permafrost. This massive carbon reservoir
had the potential to repeatedly release thousands of petagrams
(1015 grams) of carbon to the atmosphere–ocean system, once a
long-term warming threshold had been reached just before the
PETM. Replenishment of permafrost soil carbon stocks following
peak warming probably contributed to the rapid recovery from each
event9, while providing a sensitive carbon reservoir for the next
hyperthermal10. As background temperatures continued to rise
following the PETM, the areal extent of permafrost steadily
declined, resulting in an incrementally smaller available carbon
pool and smaller hyperthermals at each successive orbital forcing
maximum. A mechanism linking Earth’s orbital properties with
release of soil carbon from permafrost provides a unifying model
accounting for the salient features of the hyperthermals
The effects of litter production and litter depth on soil microclimate in a central european deciduous forest
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Terrestrial biogeochemical feedbacks in the climate system
The terrestrial biosphere is a key regulator of atmospheric chemistry and climate. During past periods of climate change, vegetation cover and interactions between the terrestrial biosphere and atmosphere changed within decades. Modern observations show a similar responsiveness of terrestrial biogeochemistry to anthropogenically forced climate change and air pollution. Although interactions between the carbon cycle and climate have been a central focus, other biogeochemical feedbacks could be as important in modulating future climate change. Total positive radiative forcings resulting from feedbacks between the terrestrial biosphere and the atmosphere are estimated to reach up to 0.9 or 1.5 W m−2 K−1 towards the end of the twenty-first century, depending on the extent to which interactions with the nitrogen cycle stimulate or limit carbon sequestration. This substantially reduces and potentially even eliminates the cooling effect owing to carbon dioxide fertilization of the terrestrial biota. The overall magnitude of the biogeochemical feedbacks could potentially be similar to that of feedbacks in the physical climate system, but there are large uncertainties in the magnitude of individual estimates and in accounting for synergies between these effects
Persistence of soil organic matter as an ecosystem property
Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming