U43D-01
Impact of the Inter-annual Variability in CO2 Growth Rate from Atmospheric Transport and Contribution from Latitudinal Partition
A comprehensive analysis was conducted to quantitatively investigate the impact of major CO2 components on the inter-annual variability in the atmospheric CO2, and the contribution of individual latitude bands to the CO2 growth rate as well. A series of numerical experiments were performed with a three-dimensional atmospheric tracer transport model (NIES/FCGCC). Model simulations were driven with NCAR/NCEP reanalysis wind field. Two types of CO2 fluxes were applied to force the model simulations: (1) the first one constitutes the major CO2 reservoirs, including terrestrial biospheric fluxes obtained by Biome BGC model, monthly fossil fuel emission and oceanic fluxes (no inter-annual variation) (2) The second type is global CO2 fluxes deduced using TDI (time-dependent-inverse) analysis from atmospheric measurements (Global View CO2, 2005), which is partitioned into fluxes for five latitude bands. Results indicate that fluxes in the tropical terrestrial biosphere contributes the most to the inter-annual variability in the atmospheric CO2 concentration on global scale (~65%); the atmospheric circulation accounts for partly of the CO2 growth rate in the northern hemisphere and the tropic regions (~30%). The observed low CO2 increase in the early 1990s is suggested to be caused by enhanced CO2 uptake in the northern mid- latitudes and the tropical regions. Additionally, we also found that a fraction of the CO2 growth rate can be ascribed to regional CO2 fluxes, i.e., CO2 fluxes in northern mid and high latitudes account for a large fraction of CO2 fluctuation in northern hemisphere; while fluxes in southern mid-to-high latitudes contribute partly to CO2 variations in the southern hemisphere. We also investigated the relationship between the CO2 anomaly and climate change index, and found that the inter-annual CO2 variability is closely related to climate anomalies like ENSO events,NAO, PNAO and Pacific Decadal Oscillation. The result suggests that accurate and vastly covered observation network are indispensable for improving our quantitative investigation of CO2 fluxes, especially for estimation of changes of regional CO2 sources and sinks.
U43D-02
An Observationally-Based Reconstruction of the 3-Dimensional, Time-Dependent History of Anthropogenic Carbon in the Ocean and its Implications for the Global Carbon Cycle
The release of fossil fuel CO2 to the atmosphere by human activity has been implicated as the predominant cause of global climate change. The ocean plays a crucial role in mitigating the effects of this perturbation to the climate system, sequestering 20% to 35% of anthropogenic CO2 emissions from the atmosphere. While much progress has been made in recent years in understanding and quantifying this sink, considerable uncertainty remains as to the distribution of anthropogenic CO2 in the ocean, and its precise rate of uptake over the industrial era. Here, we present the first observationally-based reconstruction of the 3-dimensional, time-dependent history of anthropogenic carbon in the ocean over the industrial era. Our approach is based on the recognition that the transport of tracers in the ocean is described by a Green's function or "transit-time distribution" which may be estimated from tracer data using Bayesian inversion techniques. Our results show that the Southern Ocean is the primary conduit by which anthropogenic CO enters the ocean (contributing over 40% of the anthropogenic CO2 in the ocean in 2007), although its contribution relative to other surface regions has changed significantly over the industrial period. We also present estimates of the relative size of the various sources and sinks of anthropogenic CO2, and their evolution over the industrial era.
U43D-03
The 20th century carbon budget simulated with the CCCma earth system model CanESM1
The atmosphere-land-ocean CO2 exchange for the 1850-2000 period, as simulated with the Canadian Centre for Climate Modelling and Analysis Earth System Model (CanESM1), is assessed. Land use change (LUC) emissions are estimated interactively on the basis of changes in crop area. In its default configuration, the terrestrial CO2 uptake in the model is higher and atmospheric CO2 concentration lower than observed for the 1850-2000 period. This is likely due to lower simulated LUC emissions in the model because LUC due to changes in pasture area and forest harvesting are not taken into account, although LUC emissions are highly uncertain (± 50% uncertainty). Down-regulation of photosynthesis is observed in many experimental studies that grow plants at ambient and elevated CO2. However, the role of down- regulation of terrestrial photosynthesis in the carbon cycle has not yet been explored. We examine the effect of photosynthesis down-regulation by implementing an empirical down-regulation mechanism based on experimental studies of plant growth under conditions of increased CO2. The rate of increase of terrestrial net primary productivity with CO2 in the model, after down-regulation, is consistent with that inferred from an independent study. When down-regulation is implemented, the 20th century land and ocean carbon uptake and atmospheric CO2 concentration are in good agreement with observation-based estimates. Our results show that down-regulation of terrestrial photosynthesis may play a role in terrestrial carbon uptake similar in magnitude to the uncertainty in LUC emissions. The empirical approach used here also offers a reasonable method of implementing down-regulation for coupled carbon-climate simulations in the absence of a more explicit biogeochemical representation in models.
U43D-04
Enhanced Terrestrial Carbon Uptake in the Northern High Latitudes in the 21st Century from the C4MIP Model Projections
The ongoing and projected rapid warming in the Arctic region under climate change may lead to dramatic changes in the ecosystems and carbon cycle in the Northern High Latitudes (NHL; poleward of 60˚N). On the one hand, warming and higher CO2 stimulate vegetation growth wherein tundra transitions to boreal forests, taking up CO2 from the atmosphere. On the other hand, warming accelerates decomposition of dead organic matter, losing soil carbon to the atmosphere. The resulting net land-atmosphere CO2 flux is important for future carbon-cycle climate feedback and climate change. Here, the NHL carbon storage is investigated using the simulations from the Coupled Carbon Cycle Climate Model Intercomparison Project (C4MIP). Our analysis suggests that the NHL is highly likely to be a carbon sink with a 11-model mean of 0.4 PgC yr-1 by 2100, and a cumulative increase of 40 PgC from 1860, of which 18 PgC comes from vegetation (a 47% increase) and 22 PgC, surprisingly, comes from soil carbon (an 8% increase). The future carbon sink in the NHL is mainly attributable to CO2 fertilization and warming, both effects enhancing vegetation growth, with warming more important according to the C4MIP models. Warming also tends to increase soil decomposition and drain soil carbon, but this is compensated by increased vegetation turnover, a rarely highlighted factor. This biomass turnover is caused by higher vegetation productivity. This leads to the soil being a carbon sink in the 21st century. However, after 2060, the NHL soil carbon growth rate begins to decrease because soil decomposition accelerates at high temperature and catches up with the input from biomass turnover. Such competing mechanisms may lead to a switch of NHL soil pool from a net carbon sink to source only after 2100. All these effects are enhanced as a result of positive carbon cycle-climate feedbacks.
U43D-05
Reconciling Modeled Ocean Carbon Fluxes With Atmospheric 13C Observations
As atmospheric greenhouse gas concentrations have continued to rise, researchers have sought to identify how this change affects Earth's natural CO2 sinks. In order to close the atmospheric CO2 budget, several major factors must be accounted for: fossil fuel flux, ocean flux, and land flux. The rare stable isotope of carbon, 13C, can be used as a tool to help distinguish between these fluxes. One drawback to this method is that photosynthesis and respiration are not contemporaneous, and because the 13C of atmospheric CO2 is being continuously depleted through the burning of 12C-rich fossil fuels, there is an isotopic 'disequilibrium flux' between CO2 moving into and out of the ocean and land reservoirs. In this study, we use a combination of atmospheric CO2 and 13CO2 data, fossil fuel emission estimates, and recent ocean model results for the ocean CO2 flux, within a box-inverse model. We calculate time series of land flux, disequilibrium flux and photosynthetic fractionation from 1991 through 2007. Our findings reveal that if ocean variability is as small as is suggested by the ocean model, and the isotopic variability is forced into the disequilibrium flux, then the resulting disequilibrium flux has very large interannual variability (up to ~40 PgC‰/yr), as well as an increasing trend. Conversely, if the disequilibrium flux is held constant or allowed to increase linearly without variability, then high interannual variability for the ocean and land fluxes results. An intriguing possibility is that both the ocean model predictions and the atmospheric measurements can be satisfied by driving the variability into the photosynthetic fractionation term, εab. Under this scenario, relatively small interannual variations in net carbon exchange of C3 and C4 vegetation would be sufficient to explain the otherwise seemingly incongruent nature of the ocean model results and atmospheric observations. Our findings also suggest an independent trend through time of either uptake by the biosphere or disequilibrium flux. Best estimates will be presented for land, ocean, and disequilibrium fluxes, as well as photosynthetic fractionation and C4 net terrestrial exchange.
U43D-06
Constraining the Terrestrial Carbon Cycle With Atmospheric Measurements of Carbonyl Sulfide.
Carbonly sulfide (OCS), an analog of carbon dioxide, is emerging as a useful atmospheric tracer of the terrestrial carbon cycle. Previous studies have shown that OCS is taken up by leaves and soils, and its principle source to the atmosphere is oxidation of sulfur compounds produced in the oceans. Industrial activity and biomass burning are additional sources and oxidation in the stratosphere is an additional sink. In leaves, the rate of its uptake is closely linked to the rate of CO2 uptake in gross primary production (GPP). In soils, OCS uptake is controlled by diffusion and enzyme activity which is assumed to scale with heterotrophic respiration. Thus, ecosystem uptake of OCS can be related to the sum of photosynthesis and respiration while that of CO2 reflects the difference between these two processes. Flask samples and IR absorption spectroscopy are used to measure OCS concentration in the global atmosphere. A global modeling framework is needed to make use of these measurements for carbon cycle studies. We have incorporated the biochemical and biophysical mechanisms controlling OCS exchange into a land surface/terrestrial carbon cycle model (SIB), and we have used this model to simulate global OCS and CO2 fluxes and transported these together with other known sources and sinks in a chemical transport model (PCTM). The ocean source was adjusted to optimize the fit to the seasonal cycle of OCS concentration measurements at 13 background atmospheric stations sampled by NOAA. This modeling framework exhibits good skill in simulating vertical profiles of CO2 and OCS measured routinely by NOAA and by several atmospheric sampling campaigns.
U43D-07
Interannual to Interdecadal CO2 Flux Variability in the Earth System Model
Spatio-temporal variability of surface CO2 fluxes in an Earth System Model (ESM) is analyzed. The climate variability modifies both the ocean-atmosphere CO2 flux and the land-atmosphere CO2 flux. The earlier studies, by using observed/assimilated data set, show that tropical oceanic climate variability has strong impacts on the land skin temperature and soil moisture, and there is a negative correlation between the oceanic and terrestrial CO2 fluxes. However, those data set only covers less than recent 20 years and is insufficient for identifying the decadal and longer periodic variabilities. To investigate the possible impact of interannual to interdecadal climate variability upon the CO2 flux exchange, the last 48 years of the ESM output is examined. The global-sum of the terrestrial CO2 anomaly has a variance much greater in amplitude and longer in periodic timescale, compared to that of the oceanic one. In some years terrestrial CO2 anomaly negatively correlates with oceanic one but in other years positively, as the periodic timescale is different between the two. Standard deviation analysis by latitudinal bands shows that anomalous CO2 flux comes 47 percent from tropical continents, 36 percent from northern continents in mid-high latitudes, and 7 percent from tropical oceans, indicating the importance of direct and indirect impact of tropical climate variabilities. To determine the spatial pattern of the variability, a series of composite analyses are performed. As a result, the oceanic CO2 variability peaks when the eastern tropical Pacific has great sea surface temperature anomaly (SSTA). The terrestrial CO2 variability, in contrast, peaks when the SSTA appears in the central tropical Pacific. The former variability quite resembles to the ENSO-mode and the latter to the ENSO-modoki, although the simulated ENSO is much weaker than the real ENSO and the vice versa for the ENSO-modoki, according to the EOF analysis. Our result implies that the oceanic and terrestrial CO2 flux anomalies may correlate either positively or negatively depending on the relative phase of the two oceanic modes in the tropical Pacific.
U43D-08
Airborne remote-sensing of atmospheric CH4 and CO2 with MAMap: first results of measurements over wetlands in Germany and a N-S transect from Canada to Chile
The Methane Airborne Mapper (MAMap) was designed for CO2 and CH4 remote sensing of the atmospheric column between an aircraft and the Earth's surface. The instrument is specified to detect mixing ratio variations below the aircraft of <3% of the atmospheric background as well as a ground pixel size of 20m x 20m (700m flight height, 200 km/h flight speed). It allows the detection of CO2 and CH4 gradients on a local, regional and global scale, and provides a link between ground-based and satellite- based measurements. The goal of the MAMap measurements is to improve the knowledge of CH4 and CO2 sources and sinks. In 2007 and 2008, several flight campaigns over bogs and wetlands have been conducted in Germany and correlated to ground-based measurements. A first version of the data retrieval has been developed using a modified version of the WFM-DOAS algorithm. WFM-DOAS is also used for the retrieval of CH4 and CO2 column concentrations from nadir measurements by SCIAMACHY onboard ENVISAT. In November 2008, a transect from Oshawa, Canada to Punta Arenas, Chile will be flown onboard the AWI POLAR 5 aircraft. Along the flight path CH4 and CO2 measurements will be conducted by MAMap. Besides the N-S track (Canada-USA-Bahamas-Panama-Ecuador-Peru-Chile), an additional W-E track from Guayaquil (Ecuador) to Iquitos (Peru) and back is planned, covering large areas of Peruvian rainforest. One focus of this project is the evaluation of tropical rain forest and savannah as sources/sinks of CH4 and CO2. Discrepancies between the models and satellite data regarding atmospheric CH4 concentrations over the tropics have been reported in the past. A first assessment of MAMap measurements performed in 2008 over wetlands in Germany and the AWI-POLAR 5 campaign will be presented.