THE CHANGING CARBON CYCLE
Description: The carbon cycle has undergone
changes from 1998-2003 as a result of extensive droughts. The CO2 seasonal amplitude at MLO
halted its increase, and the CO2 growth rate accelerated as a result
of a slowing down of the North American carbon sink. In a series of coupled carbon-climate model
experiments, we show a greater probability of drier soils in the 21st
century, especially in the tropics and in mid-latitude summers as
temperature-driven evapotranspiration exceed precipitation, and a positive
feedback between the carbon cycle and climate. This positive feedback reduces
the land and ocean’s capacity to store fossil fuel CO2 and
accelerates the warming. A fossil fuel emission accelerating rapidly as the
sink capacities decrease leads to further increases in the airborne fraction of
fossil fuel CO2.
Author's Names: I. Fung
Filesize: 58.93 Kb
Added on: 28-Jul-2005 Downloads: 160
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THE EFFECTS OF NITROGEN ADDITION ON THE BELOWGROUND CARBON CYCLE IN TEMPERATE FORESTS AND DESERT
Description: Human activities such as fossil fuel and
fertilizer-use have doubled the amount of biologically active nitrogen entering
ecosystems each year [Vitousek et al.,
1997]. N is the limiting nutrient in many ecosystems
and N availability has been shown to affect plant, root, and soil
respiration. For several temperate
forests, experimental addition of N is associated with a decline in soil CO2
efflux [Bowden et al.,
2004; Burton et al., 2004; Nohrstedt et al., 1989; Swanston et al., 2004]. This decline
could be due to either (1) decreased allocation of C to root metabolism and
growth because N demand of plants can be met with less energy expended
belowground, or (2) decomposition rate due to changes in leaf or root tissue
chemistry, or to changes in the decomposer community. In contrast, the few studies of more water
limited systems do not show decreased soil respiration fluxes [Schaeffer et
al., 2003; Verburg et al., 2004], which could reflect hydrologic control of
belowground C allocation.
Author's Names: N.S. Nowinski, S.E. Trumbore, E.B. Allen, et al
Filesize: 18.62 Kb
Added on: 03-Aug-2005 Downloads: 20
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THE EXPRESSION OF BIOSPHERE RESPONSE TO LIGHT LEVEL CHANGES ON 18O OF ATMOSPHERIC CO2
Description: Observations
suggest the global reflectivity of Earth changed during recent decades. Although there is some ambiguity surrounding
these findings, it is clear that, should there be changes in clouds or
scattering aerosols, a change in the total solar radiation received at the
surface and the fraction of diffuse light could result. Intriguingly, the d18O of CO2
time series measured at Mauna Loa shows variability
during the 1990s that does not match secular trends in CO2
concentration or d13C. While a decrease in total solar radiation
alone would reduce biospheric productivity, an increase in diffuse light can
increase productivity, as has been argued for the period following the eruption
of Pinatubo. Moreover, since the changes in radiation affect the surface latent
energy exchange, the isotopic composition of terrestrial water with which CO2
interacts (specifically leaf and soil water) will be modified and can thus
drive a change in isotopic fluxes.
Author's Names: N. Buenning, D. Noone, C. Still, W. Riley, et al
Filesize: 227.29 Kb
Added on: 27-Jul-2005 Downloads: 144
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THE GLACIAL BURIAL HYPOTHESIS – MISSING LINK IN THE GLACIAL CO2 PROBLEM?
Description:
Organic carbon buried under the great ice sheets of
the Northern Hemisphere is suggested to be the missing link in the atmospheric
CO2 change over the glacial-interglacial cycles. At glaciation, the
advancement of continental ice sheets buries vegetation and soil carbon
accumulated during warmer periods. At deglaciation, this burial carbon is
released back into the atmosphere. In a simulation over two
glacial-interglacial cycles using a synchronously coupled atmosphere-land-ocean
carbon model forced by reconstructed climate change, I found a 547 Gt
terrestrial carbon release from glacial maximum to interglacial, resulting in a
60 Gt (about 30 ppmv) increase in the atmospheric CO2, with the
remainder absorbed by the ocean in a scenario in which ocean acts as a passive
buffer. This is in contrast to previous estimates of a land uptake at deglaciation.
This carbon source originates from glacial burial, continental shelf and other
land areas in response to changes in ice cover, sea level, and climate. The
input of light isotope enriched terrestrial carbon causes atmospheric Δ13C to drop by about 0.3permil at deglaciation,
followed by rapid rise towards a high interglacial value in response to oceanic
warming and regrowth on land. Together with other ocean based mechanisms such
as change in ocean temperature, the glacial burial hypothesis may offer a full
explanation of the observed 80-100 ppmv atmospheric CO2 change.
Author's Names: N. Zeng
Filesize: 58.69 Kb
Added on: 09-Aug-2005 Downloads: 23
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THE INFLUENCE OF THE NAO ON THE CONTINENTAL SHELF PUMP ON THE NORTHWEST-EUROPEAN SHELF
Description:
Using a coupled 3D
hydrodynamic-biogeochemical model system for the Northwest-European shelf we
simulated the years 1993-96, which exhibit an extremely strong transition from
a NAOI-high to a NAOI-low regime. The induced temperature-shift had two
consequences for the carbon budget of the North Sea:
Firstly it increased the CO2 solubility and secondly it destabilized
the water column in spring 1996. The latter effect was the precondition for
mixing events which brought new nitrogen for primary production into the upper
layer. Consequently the air-sea flux was 540 Gmol C a-1 in 1996, the
NAOI-low year, and it was 203 Gmol C a-1 in 1995, the year with the
highest NAOI.
Author's Names: J. Paetsch, W. Kuehn, A.V. Borges, Y. Bozec, et al
Filesize: 16.39 Kb
Added on: 03-Aug-2005 Downloads: 20
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THE INTERPLAY BETWEEN SOURCES OF METHANE AND BIOGENIC VOCS IN GLACIAL-INTERGLACIAL FLUCTUATIONS ...
Description: Recent analyses of ice core methane
concentrations have suggested that methane emissions from wetlands were the
primary driver for prehistoric changes in atmospheric methane. However, these
data conflict as to the location of wetlands, magnitude of emissions, and the
environmental controls on methane oxidation. The flux of other reactive trace
gases to the atmosphere also controls apparent atmospheric methane
concentrations because these compounds compete for the hydroxyl radical (OH),
which is the primary atmospheric sink for methane. In a series of coupled
biosphere-atmosphere chemistry-climate modelling experiments, we simulate the
methane and biogenic volatile organic compound emissions from the terrestrial
biosphere from the Last Glacial Maximum (LGM) to present. Using an atmospheric
chemistry-climate model, we simulate the atmospheric concentrations of methane,
the hydroxyl radical, and numerous other reactive trace gas species. Over the
past 21,000 years methane emissions from wetlands increased slightly to the end
of the Pleistocene, but then decreased again, reaching levels at the
preindustrial Holocene that were similar to the LGM.
Author's Names: Jed O. Kaplan, Gerd Folberth, and Didier A. Hauglustaine
Filesize: 106.89 Kb
Added on: 29-Jul-2005 Downloads: 24
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THE MID-LATITUDE WESTERLIES, ATMOSPHERIC CO2 AND CLIMATE CHANGE DURING THE ICE AGES
Description:
An idealized general circulation model is constructed
of the ocean’s deep circulation and CO2 system that reproduces the
main features of glacial-interglacial CO2 cycles, including the
tight correlation between atmospheric CO2 and Antarctic
temperatures, the lead of Antarctic temperatures over CO2 at
terminations, and the shift of the ocean’s 13C minimum from the
North Pacific to the Atlantic sector of the Southern Ocean. The model is based
on a new idea about the nature of the glacial-interglacial cycles in which the
driving force is independent of the orbital forcing and is not in the ocean.
The key to glacial-interglacial transitions, we claim, is a relationship
between the mid-latitude westerly winds, atmospheric CO2, and the
mean state of the atmosphere. Cold glacial climates seem to have
equatorward-shifted westerlies, which allow more respired CO2 to
accumulate in the deep ocean. Warm climates like the present have
poleward-shifted westerlies that flush respired CO2 out of the deep
ocean.
Author's Names: J.R. Toggweiler, J.L. Russell, S.R. Carson
Filesize: 12.05 Kb
Added on: 04-Aug-2005 Downloads: 19
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THE POTENTIAL FOR WIDESPREAD, THRESHOLD DIEBACK OF FORESTS IN NORTH AMERICA UNDER RAPID GLOBAL ...
Description:
The
MC1 Dynamic General Vegetation Model (DGVM) was used to assess the impacts of
global warming on North American ecosystems, north of Mexico, under 6 future climate
scenarios (3 General Circulation Models X 2 emission scenarios). The simulations were begun in 1900 using
observed climate and CO2 until 2000, then transferring to the future
scenarios to 2100. Carbon sequestration
over the continent occurred in the late 20th century and for a short
period into the 21st century, being fostered largely by increased
precipitation, enhanced water-use efficiency and mild temperature
increases. However, these ‘greening’
processes were overtaken by the exponential effects of increasing temperature
on evaporative demand and respiration, producing a subsequent decline. Simulation
experiments suggested that fire suppression could significantly mitigate the
carbon losses, yet many ecosystems were still forced to a lower carrying
capacity.
Author's Names: R.P. Neilson, J.M. Lenihan, D. Bachelet, et al
Filesize: 39.41 Kb
Added on: 03-Aug-2005 Downloads: 26
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THE SOIL CARBON CO2 FERTILIZATION FACTOR: THE MEASURE OF AN ECOSYSTEM’S CAPACITY TO INCREASE ...
Description:
This research introduces the concept of a “CO2
fertilization factor for soil carbon” (SigmaCF). The SigmaCF is a measure of an
ecosystem’s capacity to increase soil carbon storage in response to elevated
carbon dioxide levels. This research describes the mathematical derivation of
SigmaCF and illustrates how SigmaCF can be determined experimentally, using
data from three different CO2 enrichment experiments. I have
developed this concept to compare the results of carbon dioxide enrichment
experiments having different soil carbon turnover times, different levels of CO2
enrichment, and different lengths of exposure to elevated carbon dioxide
levels. The SigmaCF can also be used to estimate increases in soil carbon
uptake due to observed contemporary increases in atmospheric carbon dioxide
levels. This approach approximates the extent to which elevated carbon dioxide
levels increase soil carbon storage. I calculated SigmaCF for three
experimental settings—a mixed forest, and stands of loblolly pine and white oak
trees—by measuring changes in carbon inventories and radiocarbon ratios. The
forest had a SigmaCF of 1.8, which would imply a global sequestration of 5.5
billion tons C/year during the 1990's (in the highly-unlikely event that all
terrestrial vegetation shows this same response to elevated carbon dioxide
levels). The loblolly pine stand had a SigmaCF of 0.9 (2.8 billion tons C/year)
and the white oak stand had a SigmaCF of 1.18 (3.5 billion tons C/year). These
results show that elevated carbon dioxide levels in the atmosphere are
increasing the flux of carbon from the atmosphere to soil.
Author's Names: K.G. Harrison
Filesize: 11.91 Kb
Added on: 29-Jul-2005 Downloads: 22
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THE WINTER ARCTIC OSCILLATION, THE TIMING OF SPRING, AND CARBON FLUXES IN THE NORTHERN HEMISPHERE
Description:
Increased winter temperatures associated with the
observed positive trend in the winter Arctic Oscillation can partially explain
trends towards earlier spring leafout in the northern hemisphere. Increased spring drawdown associated with
earlier leafout, coupled with increased winter respiration due to warmer
temperatures, indicate the trend in the winter Arctic Oscillation can help
explain observed increases in the seasonal amplitude of atmospheric CO2 concentration.
Author's Names: K.M. Schaefer, A.S. Denning, and O. Leonard
Filesize: 68.55 Kb
Added on: 04-Aug-2005 Downloads: 27
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