Changes In Atmospheric CO2 Concentration Research Articles

Stomatal-based inference models for reconstruction of atmospheric CO2 concentration: a method assessment using a calibration and validation approach

We investigated changes in atmospheric CO2 concentration (hereafter [CO2]) over the period AD 1700—2002 as reconstructed using the inverse relationship between stomatal frequencies (SF) of Betula nana leaves from northern Europe and [CO2]. The predictive ability of SF-inference models was assessed using a method of independent validation that involves two steps: (1) a training set of leaves grown between AD 1843 and 2002 was used to generate inference models; (2) the models were then applied to a fossil SF record of leaves grown between AD 1700 and 2002 that was split into two parts, a validation period (after AD 1850) and a reconstruction period (AD 1700—1850). Although our inference models had uncertainties comparable with other SF-inference models (root mean square error (RMSE) = c. 18—19 ppmv), uncertainties arising from the independent validation were larger (RMSE = c. 31—34 ppmv). Smoothed SF-inferred [CO 2] values after AD 1850 corresponded better to the industrial [CO 2] increase observed from instrumental records and from high-resolution ice cores, corroborating the accuracy of the reconstruction method in capturing a long-term (decadal- to centennial-scale) signal. This also indicates that in our record higher-frequency signals (eg, [CO2] maxima around AD 1750) are potentially less reliable. In an attempt to estimate the maximum reconstruction uncertainty (± 67 ppmv), we considered (i) the RMSE of the validation (validation error) and (ii) the maximum difference between reconstructions obtained with different inference models during the validation period (method error). We suggest that reconstruction uncertainties may be reduced by reducing the uncertainty of our inference models, with a subfossil record characterized by lower variability in the SF time series over the validation period, and by smoothing the reconstruction. This study shows that independent validation is an important step to assess the precision and accuracy of quantitative proxy-based reconstructions.

A revised estimate of the processes contributing to global warming due to climate‐carbon feedback

Coupled climate‐carbon cycle models have shown that anthropogenic climate change has a negative effect on natural carbon sinks i.e., climate change induces a reduction in both land and ocean carbon uptake leading to an additional amount of CO2 in the atmosphere. Friedlingstein et al. (2006) concluded that such supplementary CO2 in the atmosphere would lead to an additional climate warming in 2100. However, as given by Friedlingstein et al. (2006), the role of non‐CO2 greenhouse gases (GHGs) and aerosols was neglected both for their direct impact on climate and their indirect impact on the carbon cycle. Besides, the climate models used for IPCC AR4 accounted for the radiative forcing of all GHGs and anthropogenic aerosols but neglected the climate‐carbon cycle feedback. In IPCC AR4, Meehl et al. (2007) attempted to reconcile these two methods in order to derive the global warming that would arise from both all anthropogenic forcings and climate‐carbon cycle feedback. Here we show that the approach they used is wrong for several reasons. First, as previously done by Friedlingstein et al. (2006), they considered that the warming is proportional to the change in atmospheric CO2 concentration. This assumption leads to consider that the gain in temperature is equal to the gain in CO2. However, because of the non‐linearity of the climate response to increased CO2 concentrations, the gain in temperature is lower than the gain in CO2. Second, they assumed that the temperature gains of the climate‐carbon cycle feedback generated by CO2, non‐CO2 GHGs and aerosols are all equal. We show here that, because of the specific spatial and temporal distribution of the radiative forcing exerted by those external perturbations, the temperature gains are all different. Based on our revised method, we found that, for the SRES A2 scenario, the projected global warming in 2100, due to increases in atmospheric CO2, non‐CO2 GHGs and anthropogenic sulphate aerosols, is 2.3–5.6°C. This is accidentally nearly equal to the original one of Meehl et al. (2007) (2.4–5.6°C).

Leaf isoprene emission rate as a function of atmospheric CO2 concentration

AbstractThere is considerable interest in modeling isoprene emissions from terrestrial vegetation, because these emissions exert a principal control over the oxidative capacity of the troposphere. We used a unique field experiment that employs a continuous gradient in CO2 concentration from 240 to 520 ppmv to demonstrate that isoprene emissions in Eucalyptus globulus were enhanced at the lowest CO2 concentration, which was similar to the estimated CO2 concentrations during the last Glacial Maximum, compared with 380 ppmv, the current CO2 concentration. Leaves of Liquidambar styraciflua did not show an increase in isoprene emission at the lowest CO2 concentration. However, isoprene emission rates from both species were lower for trees grown at 520 ppmv CO2 compared with trees grown at 380 ppmv CO2. When grown in environmentally controlled chambers, trees of Populus deltoides and Populus tremuloides exhibited a 30–40% reduction in isoprene emission rate when grown at 800 ppmv CO2, compared with 400 ppmv CO2. P. tremuloides exhibited a 33% reduction when grown at 1200 ppmv CO2, compared with 600 ppmv CO2. We used current models of leaf isoprene emission to demonstrate that significant errors occur if the CO2 inhibition of isoprene is not taken into account. In order to alleviate these errors, we present a new model of isoprene emission that describes its response to changes in atmospheric CO2 concentration. The model logic is based on assumed competition between cytosolic and chloroplastic processes for pyruvate, one of the principal substrates of isoprene biosynthesis.

Links between iron supply, marine productivity, sea surface temperature, and CO2 over the last 1.1 Ma

Paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric CO2 concentrations. However, the mechanisms behind glacial/interglacial (G/IG) variations in atmospheric CO2 concentrations observed in the Antarctic ice cores are still not fully understood. Here we present a new multiproxy data set of sea surface temperatures (SST), dust and iron supply, and marine export productivity, from the marine sediment core PS2489‐2/ODP Site 1090 located in the subantarctic Atlantic, that allow us to evaluate various hypotheses on the role of the Southern Ocean (SO) in modulating atmospheric CO2 concentrations back to 1.1 Ma. We show that Antarctic atmospheric temperatures are closely linked to changes in SO surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) records. The close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the G/IG cycles of the last 1.1 Ma. However, our data suggest that marine productivity can only explain a fraction of atmospheric CO2 changes (up to around 40–50 ppmv), occurring at glacial maxima in each glacial stage. In this sense, the good correlation of our SST record to the EDC temperature reconstruction suggests that the initial glacial CO2 decrease, as well as the change in the amplitude of the CO2 cycles observed around 400 ka, was most likely driven by physical processes, possibly related to changes in Antarctic sea ice extent, surface water stratification, and westerly winds position.

Understanding Solar Behaviour and its Influence on Climate

The quiet Sun of the Maunder Minimum in the latter part of the 1600's is compared to the hyper-active Sun in the 1900's. Solar influence upon Earth's climate in these times of very different sunspot abundance is investigated. A second thread in this study is the possible influence of Jupiter in the observed variability of solar behaviour. Thirdly, is an analysis of the solar condition right now (late 2008) and its possible implications for climate on Earth; including what might be ahead. Last is a critical examination of IPCC's hypothesis that changing atmospheric CO2 concentration is the dominant contributor to changing climate.

Potential future changes of the terrestrial ecosystem based on climate projections by eight general circulation models

A number of previous modeling studies have assessed the implications of projected CO2‐induced climate change for future terrestrial ecosystems. However, although current understanding of possible long‐term response of vegetation to elevated CO2 and CO2‐induced climate change in some geographical areas (e.g., the high‐latitude regions) has been strengthened by dint of accumulating evidence from these past studies, it is still weak in others. This study examines the responses of global potential natural vegetation distribution, net primary production (NPP), and fire emissions to future changes in atmospheric CO2 concentration and climate using the National Center for Atmospheric Research Community Land Model's dynamic global vegetation model. The model is run to vegetative equilibrium (i.e., with respect to leaf area index (LAI) and vegetation coverage) driven with preindustrial climate and future climate near 2100, respectively, simulated by eight general circulation models (GCMs). The simulated potential vegetation under the preindustrial control mean climate (CO2 concentration held at 275 ppm) is compared with that under the SRESA1B 2100 mean climate (CO2 concentration stabilizes at 720 ppm beyond 2100). Simulated vegetation response ranges from mild changes of the fractional coverage of different plant functional types to the rather dramatic changes of dominant plant functional types. Although such response differs significantly across different GCM climate projections, a quite consistent spatial pattern emerges, characterized by a considerable poleward spread or shift of temperate and boreal forests in the Northern Hemisphere high latitudes, and a substantial degradation of vegetation type in the tropics (e.g., increase of drought deciduous trees coverage at the expense of evergreen trees) especially in portions of West and southern Africa and South America. Despite the widespread degradation of vegetation type in the tropics, NPP, and growing season LAI are predicted to increase under most GCM scenarios over most of the globe. Carbon fluxes to the atmosphere due to fire generally increase too across the globe. Such responses of NPP and fire occurrence result from the synergistic effects of CO2 concentration changes, climate changes, and vegetation changes. In the HadCM‐driven simulation, however, extreme responses are shown in some regions: Deciduous forest is replaced by grasses in large areas in the middle latitudes, and substantial areas in northern South America and southern Africa predominantly covered by evergreen forest are replaced with grasses while NPP and fire emissions reduce drastically (by more than 100%). A future paper will examine how the biosphere response documented here influences the impact of climate change on surface hydrological conditions.

Introduction to the special issue on site characterization for geological storage of CO2

Concentrations of carbon dioxide (CO2) in the atmosphere have been rising rapidly as a result of human activities since the Industrial Revolution. From about 280 ppm before the start of this period in history, these values have increased to about 379 ppm in 2005, which is by far higher than the natural range of CO2 determined from ice cores over the last 650,000 years (IPCC 2007). The primary source of this increase is the use of carbon-rich fossil fuels such as coal, oil, and natural gas for energy production. It is widely accepted today that these changes in atmospheric CO2 concentrations are a major contributor to global warming by trapping heat radiating from the earth’s surface, by the so-called greenhouse effect (NAP 2001; IPCC 2007). Several technological options have been proposed to stabilize atmospheric concentrations of CO2 (Pacala and Socolow 2004). One suggested remedy is to separate and capture CO2 from power plants burning fossil fuels and from other stationary industrial sources and to inject the produced CO2 into deep subsurface formations for longterm storage and sequestration (IPCC 2005). The most promising targets for geologic sequestration of the CO2 would be deep saline formations as well as depleted or near-depleted oil and gas reservoirs. Saline formations offer the largest CO2 storage capacity and are widely distributed worldwide. Hydrocarbon reservoirs, on the other hand, are not so common, but have the advantage of having caprocks with proven ‘‘sealing’’ capacity (buoyant fluids remained trapped in place over geologic times), and the injected CO2 may enhance oil or gas production. The scale at which CO2 would have to be sequestered is large. Considering Norway’s North Sea Sleipner project, which is the world’s first industrial-scale CO2 geologic storage operation with an annual injection of about one million tonnes of CO2 since 1996 (e.g., Torp and Gale 2003), Pacala and Socolow (2004) estimate that 3,500 Sleipner-sized capture and storage (CCS) projects, would be needed worldwide over the next 50 years to help stabilize atmospheric CO2 concentrations. While geologic sequestration is a promising method for CO2 mitigation, continued research and development efforts are important to advance the state of the art in many areas so that CCS can be effectively and safely deployed on a global scale (e.g., Litynsky et al. 2006). One challenging research area is the optimization of the methodology to assess the suitability of potential geologic sequestration sites. Careful site characterization is necessary to demonstrate that storage in geologic formations is both feasible, i.e., that the formations have a large enough storage capacity and good injectivity, and effective, i.e., that the formations provide safe long-term containment, without adverse impacts to human health or the environment (Bachu 2000). The importance and objective of site characterization are reiterated in the special report on carbon dioxide capture and storage issued by the intergovernmental panel on climate change (IPCC 2005), which stated that ‘‘site characterization, selection and performance prediction are crucial for successful geological storage. Before selecting a site, the geological setting must be characterized to determine if the overlying cap rock will provide an J. Birkholzer (&) C.-F. Tsang Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 90-1116, Berkeley, CA 94720, USA e-mail: jtbirkholzer@lbl.gov

The role of historical fire disturbance in the carbon dynamics of the pan‐boreal region: A process‐based analysis

Wildfire is a common occurrence in ecosystems of northern high latitudes, and changes in the fire regime of this region have consequences for carbon feedbacks to the climate system. To improve our understanding of how wildfire influences carbon dynamics of this region, we used the process‐based Terrestrial Ecosystem Model to simulate fire emissions and changes in carbon storage north of 45°N from the start of spatially explicit historically recorded fire records in the twentieth century through 2002, and evaluated the role of fire in the carbon dynamics of the region within the context of ecosystem responses to changes in atmospheric CO2 concentration and climate. Our analysis indicates that fire plays an important role in interannual and decadal scale variation of source/sink relationships of northern terrestrial ecosystems and also suggests that atmospheric CO2 may be important to consider in addition to changes in climate and fire disturbance. There are substantial uncertainties in the effects of fire on carbon storage in our simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. To improve the ability to better predict how fire will influence carbon storage of this region in the future, new analyses of the retrospective role of fire in the carbon dynamics of northern high latitudes should address these uncertainties.

Late Quaternary variability of sedimentary nitrogen isotopes in the eastern South Pacific Ocean

We present high‐resolution bulk sedimentary δ15N data from the southern edge of the present‐day oxygen minimum zone of the eastern South Pacific. The record is interpreted as representing changes in water column nitrogen removal during the last 70,000 years. We found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales. These fluctuations were not related to other millennial‐scale changes like the Northern Hemisphere's Dansgaard‐Oeschger climate swings or local changes in primary productivity, so appear to be dictated by the Southern Hemisphere's climate rhythm. This is preliminarily corroborated by an overall agreement between our δ15N data and the sedimentary proxy of ice sheet dynamics in Patagonia, which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern South Pacific intermediate waters. Finally, potential implications on late Quaternary changes in atmospheric CO2 concentrations are discussed.

Water and soil resources response to rising levels of atmospheric CO 2 concentration and to changes in precipitation and air temperature

Summary The quantification of the diverse responses of soils and terrestrial fresh water to elevated levels of greenhouse gases and to climate change is crucial for the proper management of natural ecosystems in the future. Despite previous experiments and simulations, there is still a need for the evaluation of the impact of these global changes at the watershed level. The main objective of this paper is to examine the effects of increasing CO2 concentrations and rainfall changes associated with changes in average daily rainfall intensity, and surface air temperature on loads of water, NO3–N and sediments from watersheds exhibiting different environmental conditions. The interactively coupled (CO2–climate–landuse) Soil and Water Assessment Tool (SWAT) was used to predict the effect of variations in precipitation and rainfall intensity (a 10%, 20% and 40% increase or decrease) or surface air temperature (an increase of 0.5 and 3.5 °C in the mean winter temperature) associated with an increase of CO2 concentration from 330 to 950 ppm in two agricultural watersheds in Iowa and Texas. Over a 100-year simulated period: (1) precipitation changes primarily affected flow and sediment discharges while temperature and changes in atmospheric CO2 concentration had a smaller effect; (2) CO2 concentration was the main controlling factor of NO3–N loads; and (3) global changes in the humid watershed had a greater effect on the water and soil resources than in the semi-arid. In particular, increasing precipitations in the humid watershed significantly increased the median and interquartile of outputs of all the variables under consideration. In contrast, changes in surface air temperature had only a slight impact on loads. However higher temperatures in the more humid site tended to reduce the highest loads. These results demonstrate that changes in CO2 concentration and climate, particularly an increase in precipitation, had significant effects on the soil and fresh water resources. The magnitude of these effects differed according to the watershed’s characteristics. Finally, the general applicability of these results and the limits of the approach are discussed.

Interaction Between Atmospheric CO2 and Glucosinolates in Broccoli

Total and individual glucosinolate contents of broccoli cv Marathon were assessed at ambient CO2 (430-480 ppm) and elevated atmospheric CO2 (685-820 ppm) to determine the ecological relationship between changing atmospheric CO2 concentrations and phytochemicals. Elevated atmospheric CO2 concentration had a differing effect on individual glucosinolates and glucosinolate groups. Total glucosinolate content increased at elevated atmospheric CO2 concentration as a result of a strong increase in both methylsulfinylalkyl glucosinolates glucoraphanin and glucoiberin. In contrast, indole glucosinolates simultaneously decreased, predominantly because of a reduction of glucobrassicin and 4-methoxy-glucobrassicin contents. We conclude that changes in N content and N/S ratios as well as alterations in photochemical processes at elevated atmospheric CO2 concentration can influence total and individual glucosinolates contents of Brassicaceae, as demonstrated in the greenhouse, for broccoli.

ENSO amplitude changes in climate change commitment to atmospheric CO2 doubling

Simulations from six climate system models are analyzed to investigate the ENSO amplitude changes in response to a transient increase of the atmospheric CO2. It is found that the ENSO amplitude amplifies as the CO2 concentration increases, then weakens once the concentration is held fixed at 2xCO2 level in the Meteorological Research Institute (MRI) model simulation, but with no significant sensitivity in the other five models. By comparing the MRI and the Geophysical Fluid Dynamical Laboratory (GFDL) models, both of which simulate ENSO reasonably well for the unperturbed climate, we investigate the origin of the sensitivity or lack of sensitivity of the ENSO amplitude to changes in atmospheric CO2 concentration. It is found that in the MRI model the oceanic sensitivity to the equatorial zonal wind stress is significantly decreased in the doubled CO2 period compared to the transient period. Moreover, the vertical stratification at upper levels is weaker in the former period than in the latter period. However, these changes in the GFDL model are negligible.

The past 20 years of ecology and evolution

The past 20 years of ecology and evolution

Cenozoic continental climatic evolution of Central Europe

Continental climate evolution of Central Europe has been reconstructed quantitatively for the last 45 million years providing inferred data on mean annual temperature and precipitation, and winter and summer temperatures. Although some regional effects occur, the European Cenozoic continental climate record correlates well with the global oxygen isotope record from marine environments. During the last 45 million years, continental cooling is especially pronounced for inferred winter temperatures but hardly observable from summer temperatures. Correspondingly, Cenozoic cooling in Central Europe is directly associated with an increase of seasonality. In contrast, inferred Cenozoic mean annual precipitation remained relatively stable, indicating the importance of latent heat transport throughout the Cenozoic. Moreover, our data support the concept that changes in atmospheric CO2 concentrations, although linked to climate changes, were not the major driving force of Cenozoic cooling.

On the multi-century Southern Hemisphere response to changes in atmospheric CO2-concentration in a Global Climate Model

The transient response of the Southern Hemisphere to climate change is examined using an intermediate complexity climate model. Unlike previous studies, the Southern Ocean response on the centennial to multi-centennial time-scale is assessed in some detail. It is shown that changes in atmospheric CO2-concentrations lead to an increase in the strength of the Antarctic Circumpolar Current (ACC) by ∼20 Sv by 2750 for an atmospheric CO2-concentration of 750 ppm. This increase is predominantly the result of an enhanced steric height gradient. The increase in the strength of the ACC induces changes in its steering around topographic features. This change in ACC pathway causes increased surface flow of colder waters into some regions (reducing the rate of warming) and increased surface flow of warmer waters into others (increasing the rate of warming). This meridional shifting of the ACC causes changes in atmospheric temperature in the Southern Hemisphere to be nonuniform. It is also shown that the strength and location of the Antarctic Bottom Water (AABW) overturning cell is affected by increased atmospheric CO2. For a CO2-concentration scenario increasing gradually to 750 ppm, AABW production initially decreases, then recovers and eventually increases. New production zones form, which extend AABW production all the way from the Weddell Sea eastward into the Ross Sea. These new production zones are the result of increased areas of atmosphere-ocean interactions, due to decreased sea-ice coverage, although the overturned waters are now warmer and fresher due to climate change. A new production zone of Antarctic Intermediate water is also established in the Southeast Pacific Ocean, poleward of its present-day location.

Did Humankind Prevent a Holocene Glaciation?

Recently, W.F. Ruddiman (2003, Climatic Change, Vol. 61, pp. 261–293) suggested that the anthropocene, the geological epoch of significant anthropospheric interference with the natural Earth system, has started much earlier than previously thought (P. I. Crutzen and E. F. Stoermer, 2000, IGBP Newsletter, Vol. 429, pp. 623–628). Ruddiman proposed that due to human land use, atmospheric concentrations of CO2 and CH4 began to deviate from their natural declining trends some 8000 and 5000 years ago, respectively. Furthermore, Ruddiman concluded that greenhouse gas concentrations grew anomalously thereby preventing natural large-scale glaciation of northern North America that should have occurred some 4000–5000 years ago without human interference. Here we would like to comment on (a) natural changes in atmospheric CO2 concentration during the Holocene and (b) on the possibility of a Holocene glacial inception. We substantiate our comments by modelling results which suggest that the last three interglacials are not a proper analogue for Holocene climate variations. In particular, we show that our model does not yield a glacial inception during the last several thousand years even if a declining trend in atmospheric CO2 was assumed.

Transient simulation of the last glacial inception. Part II: sensitivity and feedback analysis

The sensitivity of the last glacial-inception (around 115 kyr BP, 115,000 years before present) to different feedback mechanisms has been analysed by using the Earth system model of intermediate complexity CLIMBER-2. CLIMBER-2 includes dynamic modules of the atmosphere, ocean, terrestrial biosphere and inland ice, the last of which was added recently by utilising the three-dimensonal polythermal ice-sheet model SICOPOLIS. We performed a set of transient experiments starting at the middle of the Eemiam interglacial and ran the model for 26,000 years with time-dependent orbital forcing and observed changes in atmospheric CO2 concentration (CO2 forcing). The role of vegetation and ocean feedback, CO2 forcing, mineral dust, thermohaline circulation and orbital insolation were closely investigated. In our model, glacial inception, as a bifurcation in the climate system, appears in nearly all sensitivity runs including a run with constant atmospheric CO2 concentration of 280 ppmv, a typical interglacial value, and simulations with prescribed present-day sea-surface temperatures or vegetation cover—although the rate of the growth of ice-sheets growth is smaller than in the case of the fully interactive model. Only if we run the fully interactive model with constant present-day insolation and apply present-day CO2 forcing does no glacial inception appear at all. This implies that, within our model, the orbital forcing alone is sufficient to trigger the interglacial–glacial transition, while vegetation, ocean and atmospheric CO2 concentration only provide additional, although important, positive feedbacks. In addition, we found that possible reorganisations of the thermohaline circulation influence the distribution of inland ice.

The interactive effects of elevated CO2, temperature and initial size on growth and competition between a native C3 and an invasive C3 grass

A controlled environment experiment was conducted to determine the impact of enhanced carbon dioxide and temperature on competition between the C3 grasses Austrodanthonia eriantha and Vulpia myuros. Plants were grown in mixtures and monocultures to compare the responses both with and without an interspecific competitor. Temperature and CO2 were set at current levels (350 ppm CO2; 20 °C day and 10 °C night temperature), in factorial combination with enhanced levels (700 ppm CO2; 23 °C day and 13 °C night temperature). To examine the potential impact of initial seedling size on competition under elevated CO2 and temperature, the two species were combined in mixtures of differing initial sizes. Above-ground growth of all plants was enhanced by increased CO2 and temperature alone, however the combined temperature and CO2 treatment showed a sub-additive effect, where growth was less than expected based on the responses to each factor independently. Austrodanthonia in mixture with Vulpia plants of the same initial size experienced a 27 reduction in growth. Austrodanthonia grown in the presence of an initially larger Vulpia plant experienced a 58 reduction in growth. When the Vulpia plant was initially smaller than Austrodanthonia, growth of the Austrodanthonia was reduced by 16%. The growth of Vulpia appeared to be largely unaffected by the presence of Austrodanthonia. Variation in the CO2 and temperature environment did not affect the pattern of these interspecific interactions, although there was some evidence to suggest that the degree of suppression of Austrodanthonia by Vulpia was less under elevated CO2. These results do not support the initial advantage hypothesis, as Vulpia was always able to suppress Austrodanthonia, regardless of the initial relative sizes of the competitors. Furthermore, the lack of an effect of changing the CO2 or temperature environment on the direction of interspecific competition suggests that the competitiveness of the invasive Vulpia will be minimally affected by changes in atmospheric CO2 concentration or temperature.

Increase of photosynthesis and starch in potato under elevated CO2 is dependent on leaf age

Potato plants (Solanum tuberosum cv. Bintje) were grown in open top chambers under ambient (400 microL L(-1)) and elevated CO2 (720 microL L(-1)). After 50 days one half of each group was transferred to the other CO2 concentration and the effects were studied in relation to leaf age (old, middle-aged and young leaves) in each of the four groups. Under long-term exposure to elevated CO2, photosynthesis increased between 10% and 40% compared to ambient CO2. A subsequent shift of the same plants to ambient CO2 caused a 20-40% decline in photosynthetic rate, which was most pronounced in young leaves. After shifting from long-term ambient to elevated CO2, photosynthesis also increased most strongly in young leaves (90%); these experiments show that photosynthesis was downregulated in the upper young fully expanded leaves of potato growing long-term under elevated CO2. Soluble sugar content in all leaf classes under long-term exposure was stable irrespective of the CO2 treatment, however under elevated CO2 young leaves showed a strongly increased starch accumulation (up to 400%). In all leaf classes starch levels dropped in response to the shift from 720 to 400 microL L(-1) approaching ambient CO2 levels. After the shift to 720 microL L(-1), sucrose and starch levels increased, principally in young Leaves. There is clear evidence that leaves of different age vary in their responses to changes in atmospheric CO2 concentration.

Invasion of anthropogenic CO2 recorded in planktonic foraminifera from the northern Gulf of Aqaba

The stable carbon isotopic composition of the planktonic foraminifera Globigerinoides sacculifer and G. ruber (white) and sedimentary organic matter from the northern Gulf of Aqaba have been investigated to estimate changes in δ13CDIC in surface waters during the last 1,000 years. The high sedimentation rates at the core sites (about 54 cm/Kyear) provide high temporal resolution (~10 years). Recent sediments at the top of the cores reflect conditions younger than 1950. The δ13C records of the planktonic foraminifera from three multicores display similar trends, showing a uniform and consistent pattern before the 1750s, and a gradual decrease of approximately 0.63‰ over the last two centuries. This decrease seems to track the decrease of δ13CDIC in surface waters, which is mainly caused by the increase of anthropogenic input of 13C-depleted CO2 into the atmosphere. Similarly, a trend towards lighter values of the carbon isotopic composition of sedimentary organic matter (δ13Corg) during the last 200 years supports the interpretation obtained from the planktonic foraminiferal δ13C. Furthermore, direct measurements of seawater show that δ13C of the dissolved inorganic carbon (DIC) in the northern Gulf of Aqaba has decreased by about 0.44‰ during the period 1979–2000. The average annual decrease is 0.021‰, which is similar to that observed globally. The δ13C values of planktonic foraminifera combined with organic matter δ13C from marine sediments are good indicators for reconstructing past changes in atmospheric CO2 concentrations from the northern Gulf of Aqaba.