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 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: 27
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TEMPORAL VARIATIONS OF CO2 AND ITS CARBON AND OXYGEN ISOTOPIC RATIOS IN A COOL-TEMPERATE ...
Description:
Using discrete air
sampling, atmospheric CO2 and its stable carbon (d13C) and oxygen (d18O) isotopic ratios have been measured since 1994 in a
cool-temperate deciduous forest in central Japan influenced strongly by the
Asian monsoon. In this paper, the results are shown and the temporal variations
on different time scales are discussed.
Author's Names: S. Murayama, N. Saigusa, S. Yamamoto, C. Takamura, et al
Filesize: 94.30 Kb
Added on: 03-Aug-2005 Downloads: 25
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ON THE SENSITIVITY OF OCEAN BIOGEOCHEMISTRY AND AIR-SEA CO2 FLUX TO CLIMATE DRIVEN VARIATIONS ...
Description:
A
coupled Biogeochemistry-Ecosystem-Circulation (BEC)
ocean model is used to examine the sensitivity of ocean biogeochemical cycling
and air-sea CO2 exchange to variations in mineral dust deposition
from the atmosphere. Mineral dust
deposition estimates from four different climate regimes are used to force the
ocean model. Our estimated climate-induced
changes in dust deposition to the oceans significantly modify phytoplankton
community composition, and global-scale rates of nitrogen fixation, export
production, and air-sea CO2 flux. Dust driven variations in air-sea CO2
exchange exceeding 1 PgC/yr are of similar magnitude to present net oceanic
anthropogenic uptake. Dust deposition
directly modifies rates of export production and CO2 flux over large
regions where iron is the primary growth-limiting nutrient. Dust deposition also indirectly influences
these rates by modifying the rates of nitrogen fixation in the tropics and
subtropics where nitrogen is the primary limiting nutrient. Initially the direct pathway dominates the
ocean biogeochemical response to dust variations, but over multi-decadal
timescales the indirect response may be equally important. Our predicted decrease in mineral dust
deposition over the next century would significantly slow oceanic uptake of CO2
and act as a positive feedback mechanism for the ongoing global warming.
Author's Names: J. K. Moore, S. C. Doney, K. Lindsay, and N. Mahowald
Filesize: 22.54 Kb
Added on: 02-Aug-2005 Downloads: 17
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EMISSIONS TARGETS FOR CO2 STABILIZATION AS MODIFIED BY CARBON CYCLE FEEDBACKS
Description:
This study examines
the potential for feedbacks between the carbon cycle, atmospheric carbon
dioxide (CO2) increases and climate change to affect the
anthropogenic emissions that are required to stabilize future levels of CO2
in the atmosphere. Using a coupled climate-carbon cycle model, I found that
positive carbon cycle-climate feedbacks reduced allowable emissions by an
amount that varied with the model’s climate sensitivity. Emissions were further reduced if CO2
fertilization was assumed to be inactive in the model, as this removed an
otherwise important negative feedback on atmospheric CO2.
Author's Names: H. Damon Matthews
Filesize: 62.30 Kb
Added on: 02-Aug-2005 Downloads: 23
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IMPACT OF THE SOUTHERN ANNULAR MODE ON THE SOUTHERN OCEAN CARBON CYCLE
Description:
The
Southern Annular Mode (SAM) is the
leading mode of intraseasonal to interannual variability over the entire
Southern Hemisphere, yet the impact of the SAM
on the Southern Ocean carbon cycle is largely unknown. We investigate the
impact of the SAM on surface wind,
sea surface temperature (SST), chlorophyll concentration, and sea ice
concentration on the basis of 8-day averaged satellite observations. We find that Southern Ocean circulation and
biogeochemistry react quite sensitively to this mode of variability,
potentially resulting in air-sea CO2 flux anomalies. Since variations
in atmospheric CO2 congruent with the SAM
are small, we hypothesize that the SAM
produces anomalous air-sea fluxes of both natural and anthropogenic CO2,
which act to compensate each other.
Author's Names: N.S. Lovenduski, N. Gruber, A. Hawes, and D.W.J. Thompson
Filesize: 115.90 Kb
Added on: 01-Aug-2005 Downloads: 22
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POTENTIAL VARIATIONS IN THE O-17 TO O-18 RELATION OF WATER AND ICE SAMPLES
Description: It is generally assumed
that the variations of O-17 and O18 contents of water samples are closely
related. In literature there are different relations described, for instance
the Craig relation that assumes O-17 to vary half compared to O-18. O-17 of
water can be determined from the measured ...
Author's Names: M. C. Leuenberger
Filesize: 53.59 Kb
Added on: 01-Aug-2005 Downloads: 18
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HIGH RESOLUTION 13C MEASUREMENTS FROM THE EPICA DOME C ICE CORE
Description: Measurements of the isotopic
composition of carbon dioxide were performed on EPICA Dome C ice on 76
different depth levels covering the last 40’000 years. The time resolution is
in the order of 500 years for the last 18’000 years. For each depth level at
least two determinations were obtained. The d13C signals show different
trends during the last 18000 years that are anti-parallel to the CO2
concentration evolution as measured on the same ice core. However millennial
scale deviations from these trends are observed for at least three time
periods. The robustness and significance of these deviations are investigated
by Monte Carlo simulations performed with
different subsets of the measurements. The decreases of carbon isotopes could
be connected with observed step-like increases of the CO2 concentration.
Furthermore, a similar evolution as for stable carbon isotopes is visible for
detrended radiocarbon. We will discuss potential mechanisms responsible for the
trends as well as for the millennial scale deviations in carbon-13, including
changes in the thermohaline circulation as well as potential influences of a
changing 17O-18O relationship.
Author's Names: M. C. Leuenberger, M. Eyer, Serge Bogni, et al
Filesize: 105.00 Kb
Added on: 01-Aug-2005 Downloads: 21
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HOW RESILIENT MAY THE AMAZON RAIN FOREST CARBON BALANCE BE TO CLIMATE CHANGE?
Description:
The Amazon region represents a large
stock of biomass as well as a potentially important sink for additional
atmospheric CO2. Climate change, land-use changes and their
interaction present a risk to this role in the global carbon cycle. Both
positive and negative feedbacks exist in the system that can lead to resilience
but also to accelerated break-down of the carbon stocks and sinks. A set of
linked projects will investigate elements of these processes in the coming
years.
Author's Names: Bart Kruijt, Flavio Luizao, Antonio Nobre, et al
Filesize: 24.45 Kb
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PROPOSING A MECHANISTIC UNDERSTANDING OF ATMOSPHERIC CO2 DURING THE LATE PLEISTOCENE...
Description: Paleo-climate records in ice cores revealed high
variability in temperature, atmospheric dust content and carbon dioxide. The
longest CO2 record from the Antarctic ice core of the Vostok station
went back in time as far as about 410 kyr BP showing a switch of glacials and
interglacials in all those parameters approximately every 100 kyr during the
last four glacial cycles with CO2 varying between 180-300 ppmv [Petit et al., 1999]. New measurements of dust and the
isotopic temperature proxy deuterium of the EPICA Dome C (EDC) ice core covered
the last 740 kyr, however, revealed glacial cycles of reduced temperature
amplitude [EPICA community members, 2004]. These
new archives offer the possibility to propose atmospheric CO2 for
the pre-Vostok time span as called for in the EPICA challenge [Wolff et al., 2004]. Here, we contribute to this challenge
using a box model of the isotopic carbon cycle [Köhler et
al., 2005] based on process understanding previously derived for
Termination I. Our results show that major features of the Vostok period are
reproduced while prior to Vostok our model predicts significantly smaller
amplitudes in CO2 variations.
Author's Names: P. Köhler, and H. Fischer
Filesize: 48.63 Kb
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