scholarly journals Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry

2013 ◽  
Vol 10 (7) ◽  
pp. 5009-5017 ◽  
Author(s):  
M. Roland ◽  
P. Serrano-Ortiz ◽  
A. S. Kowalski ◽  
Y. Goddéris ◽  
E. P. Sánchez-Cañete ◽  
...  
Keyword(s):  
Atmospheric Turbulence ◽  
Co2 Exchange ◽  
Biological Behavior ◽  
Co2 Uptake ◽  
Carbonate Precipitation ◽  
Carbonate Weathering ◽  
Diel Pattern ◽  
Weathering Rates ◽  
Carbonate Geochemistry ◽  
Co2 Concentrations

Abstract. CO2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or nighttime CO2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO2 exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO2 during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO2 production. At night, ventilation ceases and the depleted CO2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil–atmosphere CO2 exchanges in dry regions \\mbox{with carbonate soils}.

scholarly journals Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry

2013 ◽  
Vol 10 (1) ◽  
pp. 1207-1227 ◽  
Author(s):  
M. Roland ◽  
P. Serrano-Ortiz ◽  
A. S. Kowalski ◽  
Y. Goddéris ◽  
E. P. Sánchez-Cañete ◽  
...  
Keyword(s):  
Atmospheric Turbulence ◽  
Co2 Exchange ◽  
Biological Behavior ◽  
Carbonate Precipitation ◽  
Carbonate Weathering ◽  
Diel Pattern ◽  
Weathering Rates ◽  
Carbonate Geochemistry ◽  
Co2 Concentrations ◽  
Exchange Patterns

Abstract. CO2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during daytime or nighttime CO2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO2 exchange patterns. We found that by rapidly depleting soil CO2 during daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO2 production. At night, ventilation ceases and the depleted CO2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil-atmosphere CO2 exchanges in dry regions with carbonate soils.

scholarly journals Can seasonal and interannual variation in landscape CO<sub>2</sub> fluxes be detected by atmospheric observations of CO<sub>2</sub> concentrations made at a tall tower?

2014 ◽  
Vol 11 (3) ◽  
pp. 735-747 ◽  
Author(s):  
T. L. Smallman ◽  
M. Williams ◽  
J. B. Moncrieff
Keyword(s):  
Interannual Variation ◽  
Atmospheric Transport ◽  
Co2 Exchange ◽  
Atmospheric Co2 ◽  
Co2 Uptake ◽  
Post Harvest ◽  
Co2 Concentrations ◽  
Prevailing Wind Direction ◽  
Atmospheric Co2 Concentrations ◽  
Tall Tower

Abstract. The coupled numerical weather model WRF-SPA (Weather Research and Forecasting model and Soil-Plant-Atmosphere model) has been used to investigate a 3 yr time series of observed atmospheric CO2 concentrations from a tall tower in Scotland, UK. Ecosystem-specific tracers of net CO2 uptake and net CO2 release were used to investigate the contributions to the tower signal of key land covers within its footprint, and how contributions varied at seasonal and interannual timescales. In addition, WRF-SPA simulated atmospheric CO2 concentrations were compared with two coarse global inversion models, CarbonTrackerEurope and the National Oceanic and Atmospheric Administration's CarbonTracker (CTE-CT). WRF-SPA realistically modelled both seasonal (except post harvest) and daily cycles seen in observed atmospheric CO2 at the tall tower (R2 = 0.67, rmse = 3.5 ppm, bias = 0.58 ppm). Atmospheric CO2 concentrations from the tall tower were well simulated by CTE-CT, but the inverse model showed a poorer representation of diurnal variation and simulated a larger bias from observations (up to 1.9 ppm) at seasonal timescales, compared to the forward modelling of WRF-SPA. However, we have highlighted a consistent post-harvest increase in the seasonal bias between WRF-SPA and observations. Ecosystem-specific tracers of CO2 exchange indicate that the increased bias is potentially due to the representation of agricultural processes within SPA and/or biases in land cover maps. The ecosystem-specific tracers also indicate that the majority of seasonal variation in CO2 uptake for Scotland's dominant ecosystems (forests, cropland and managed grassland) is detectable in observations within the footprint of the tall tower; however, the amount of variation explained varies between years. The between years variation in detectability of Scotland's ecosystems is potentially due to seasonal and interannual variation in the simulated prevailing wind direction. This result highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude.

scholarly journals Can seasonal and interannual variation in landscape CO<sub>2</sub> fluxes be detected by atmospheric observations of CO<sub>2</sub> concentrations made at a tall tower?

2013 ◽  
Vol 10 (8) ◽  
pp. 14301-14331
Author(s):  
T. L. Smallman ◽  
M. Williams ◽  
J. B. Moncrieff
Keyword(s):  
Interannual Variation ◽  
Co2 Exchange ◽  
Atmospheric Co2 ◽  
Co2 Uptake ◽  
Post Harvest ◽  
Terrestrial Ecosystem Model ◽  
Co2 Concentrations ◽  
Atmospheric Co2 Concentrations ◽  
Source Sink ◽  
Tall Tower

Abstract. The Weather Research and Forecasting (WRF) meteorological model has been coupled to the Soil Plant Atmosphere (SPA) terrestrial ecosystem model, hereafter known as WRF-SPA. SPA generates realistic land-atmosphere exchanges through fully coupled hydrological, carbon and energy cycles. Here we have used WRF-SPA to investigate regional scale observations of atmospheric CO2 concentrations made over a multi-annual period from a tall tower in Scotland. WRF-SPA realistically models both seasonal and daily cycles, predicting CO2 at the tall tower (R2 = 0.67, RMSE = 3.5 ppm, bias = 0.58 ppm), indicating realistic transport, and appropriate source sink distribution and magnitude of CO2 exchange. We have highlighted a consistent post harvest increase in model-observation residuals in atmospheric CO2 concentrations. This increase in model-observation residuals post harvest is likely related to a lack of an appropriate representation of uncultivated components (~ 36% of agricultural holding in Scotland) of agricultural land (e.g., hedgerows and forest patches) which continue to photosynthesise after the crop has been harvested. Through the use of ecosystem specific CO2 tracers we have shown that tall tower observations here do not detect a representative fraction of Scotland's ecosystem CO2 uptake. Cropland CO2 uptake is the dominant ecosystem signal detected at the tall tower, consistent with the dominance of cropland in the area surrounding the tower. However cropland is over-represented in the atmospheric CO2 concentrations simulated to be at the tall tower, relative to the simulated surface cropland CO2 uptake. Observations made at the tall tower were able to detect seasonal variation in ecosystem CO2 uptake, however a majority of variation was only detected for croplands. We have found evidence that interannual variation in weather has a greater impact than interannual variation of the simulated land surface CO2 exchange on tall tower observations for the simulated years. This highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude.

scholarly journals Greenhouse gas flux measurements in a forestry-drained peatland indicate a large carbon sink

2011 ◽  
Vol 8 (11) ◽  
pp. 3203-3218 ◽  
Author(s):  
A. Lohila ◽  
K. Minkkinen ◽  
M. Aurela ◽  
J.-P. Tuovinen ◽  
T. Penttilä ◽  
...  
Keyword(s):  
Carbon Sink ◽  
Accumulation Rate ◽  
Peat Soil ◽  
Net Ecosystem Exchange ◽  
Flux Measurement ◽  
Co2 Exchange ◽  
Co2 Uptake ◽  
Flux Measurements ◽  
Ch4 And N2o ◽  
Carbon Dioxide Co2

Abstract. Drainage for forestry purposes increases the depth of the oxic peat layer and leads to increased growth of shrubs and trees. Concurrently, the production and uptake of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) change: due to the accelerated decomposition of peat in the presence of oxygen, drained peatlands are generally considered to lose peat carbon (C). We measured CO2 exchange with the eddy covariance (EC) method above a drained nutrient-poor peatland forest in southern Finland for 16 months in 2004–2005. The site, classified as a dwarf-shrub pine bog, had been ditched about 35 years earlier. CH4 and N2O fluxes were measured at 2–5-week intervals with the chamber technique. Drainage had resulted in a relatively little change in the water table level, being on average 40 cm below the ground in 2005. The annual net ecosystem exchange was −870 ± 100 g CO2 m−2 yr−1 in the calendar year 2005, indicating net CO2 uptake from the atmosphere. The site was a small sink of CH4 (−0.12 g CH4 m−2 yr−1) and a small source of N2O (0.10 g N2O m−2 yr−1). Photosynthesis was detected throughout the year when the air temperature exceeded −3 °C. As the annual accumulation of C in the above and below ground tree biomass (175 ± 35 g C m−2) was significantly lower than the accumulation observed by the flux measurement (240 ± 30 g C m−2), about 65 g C m−2 yr−1 was likely to have accumulated as organic matter into the peat soil. This is a higher average accumulation rate than previously reported for natural northern peatlands, and the first time C accumulation has been shown by EC measurements to occur in a forestry-drained peatland. Our results suggest that forestry-drainage may significantly increase the CO2 uptake rate of nutrient-poor peatland ecosystems.

scholarly journals Short-term Effects of Grazing Exclusion on Net Ecosystem CO2 Exchange and Net Primary Production in a Pannonian Sandy Grassland

2012 ◽  
Vol 40 (2) ◽  
pp. 67 ◽  
Author(s):  
Szilard CZOBEL ◽  
Orsolya SZIRMAI ◽  
Zoltan NEMETH ◽  
Csaba GYURICZA ◽  
Judit GAZI ◽  
...  
Keyword(s):  
Carbon Sequestration ◽  
Primary Production ◽  
Net Primary Production ◽  
Plant Productivity ◽  
Co2 Exchange ◽  
Co2 Uptake ◽  
Aboveground Phytomass ◽  
Grazing Exclusion ◽  
Sequestration Potential ◽  
Sandy Grassland

Using portable, non-destructive own developed chambers (d=60 cm) and infrared gas analyses, the in situ field investigation was performed to study the seasonal and inter-annual dynamics of the stand level CO2-flux and production of sandy grassland that has been extensively grazed for decades. Furthermore, NEE measurements and biomass samples were used to identify the initial effects of grazing exclusion on CO2 exchange, aboveground phytomass and potential plant productivity in years of significantly different precipitation levels. A considerable inter-annual variation in all of the studied parameters was found both in the non-grazed and grazed stands. As a result of the grazing exclusion the CO2 uptake potential of the non-grazed stand increased by 13% compared to the grazed stand. It was more significant in the extreme dry year (220%), however, in wet year slightly lower average carbon sequestration was detected at the non-grazed stand (-13%), than that of the grazed area. Significant carbon sequestration potential was only detected during wet periods in both stands. The rate of CO2 uptake was found to be nearly six times higher in the non-grazed stand in the wet year than in the previous extremely dry year. The drought in 2003 significantly reduced the CO2 uptake of both stands, leading to lower annual net primary production and potential plant productivity. The annual net primary production dropped by almost 40% in the extremely dry year but then it rose by nearly two and a half times in the subsequent year with adequate rainfall.

scholarly journals O<sub>2</sub> : CO<sub>2</sub> exchange ratio for net turbulent flux observed in an urban area of Tokyo, Japan, and its application to an evaluation of anthropogenic CO<sub>2</sub> emissions

2020 ◽  
Vol 20 (9) ◽  
pp. 5293-5308
Author(s):  
Shigeyuki Ishidoya ◽  
Hirofumi Sugawara ◽  
Yukio Terao ◽  
Naoki Kaneyasu ◽  
Nobuyuki Aoki ◽  
...  
Keyword(s):  
Fuel Consumption ◽  
Urban Area ◽  
Co2 Emission ◽  
Co2 Flux ◽  
Co2 Exchange ◽  
Co2 Fluxes ◽  
Diurnal Cycles ◽  
Co2 Concentrations ◽  
Human Respiration ◽  
Two Peaks

Abstract. In order to examine O2 consumption and CO2 emission in a megacity, continuous observations of atmospheric O2 and CO2 concentrations, along with CO2 flux, have been carried out simultaneously since March 2016 at the Yoyogi (YYG) site located in the middle of Tokyo, Japan. An average O2 : CO2 exchange ratio for net turbulent O2 and CO2 fluxes (ORF) between the urban area and the overlaying atmosphere was obtained based on an aerodynamic method using the observed O2 and CO2 concentrations. The yearly mean ORF was found to be 1.62, falling within the range of the average OR values of liquid and gas fuels, and the annual average daily mean O2 flux at YYG was estimated to be −16.3 µmol m−2 s−1 based on the ORF and CO2 flux. By using the observed ORF and CO2 flux, along with the inventory-based CO2 emission from human respiration, we estimated the average diurnal cycles of CO2 fluxes from gas and liquid fuel consumption separately for each season. Both the estimated and inventory-based CO2 fluxes from gas fuel consumption showed average diurnal cycles with two peaks, one in the morning and another one in the evening; however, the evening peak of the inventory-based gas consumption was much larger than that estimated from the CO2 flux. This can explain the discrepancy between the observed and inventory-based total CO2 fluxes at YYG. Therefore, simultaneous observations of ORF and CO2 flux are useful in validating CO2 emission inventories from statistical data.

Sources and Sinks of Atmospheric CO2

1992 ◽  
Vol 40 (5) ◽  
pp. 407 ◽  
Author(s):  
JA Taylor ◽  
J Lloyd
Keyword(s):  
Climate Change ◽  
Biomass Burning ◽  
Transport Model ◽  
Atmospheric Co2 ◽  
Tropical Rainforests ◽  
Co2 Uptake ◽  
Tracer Transport ◽  
Intergovernmental Panel ◽  
Co2 Concentrations ◽  
Atmospheric Co2 Concentrations

The biosphere plays an important role in determining the sources, sinks, levels and rates of change of atmospheric CO2 concentrations. Significant uncertainties remain in estimates of the fluxes of CO2 from biomass burning and deforestation, and uptake and storage of CO2 by the biosphere arising from increased atmospheric CO2 concentrations. Calculation of probable rates of carbon sequestration for the major ecosystem complexes and global 3-D tracer transport model runs indicate the possibility that a significant net CO2 uptake (> 1 Pg C yr-1), a CO2 'fertilisation effect', may be occurring in tropical rainforests, effectively accounting for much of the 'missing sink'. This sink may currently balance much of the CO2 added to the atmosphere from deforestation and biomass burning. Interestingly, CO2 released from biomass burning may itself be playing an important role in enhanced carbon storage by tropical rainforests. This has important implications for predicting future CO2 concentrations. If tropical rainforest destruction continues then much of the CO2 stored as a result of the CO2 'fertilisation effect' will be rereleased to the atmosphere and much of the 'missing sink' will disappear. These effects have not been considered in the IPCC (Intergovernmental Panel on Climate Change) projections of future atmospheric CO2 concentrations. Predictions which take account of the combined effects of deforestation, the return of carbon previously stored through the CO2 'fertilisation effect' and the loss of a large proportion of the 'missing sink' as a result of deforestation, would result in much higher predicted concentrations and rates of increase of atmospheric CO2 and, as a consequence, accelerated rates of climate change.

scholarly journals Ikaite crystals in melting sea ice – implications for <i>p</i>CO<sub>2</sub> and pH levels in Arctic surface waters

2012 ◽  
Vol 6 (2) ◽  
pp. 1015-1035 ◽  
Author(s):  
S. Rysgaard ◽  
R. N. Glud ◽  
K. Lennert ◽  
M. Cooper ◽  
N. Halden ◽  
...  
Keyword(s):  
Sea Ice ◽  
Surface Waters ◽  
Elevated Temperatures ◽  
Co2 Exchange ◽  
The Arctic ◽  
Co2 Uptake ◽  
Surface Mixed Layer ◽  
Chemical Transformations ◽  
X Ray Diffraction ◽  
Antarctic Sea Ice

Abstract. A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (CaCO3·6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from an actively melting 1.7 km2 (0.5–1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures gradually disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice flow thickness by ca. 0.2 m per week and resulted in an estimated 1.6 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 11 mmol m−2 sea ice d−1 or to 3.5 ton km−2 ice floe week−1.

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