Low CO2 evasion rate from the mangrove surrounding waters of Sundarban

Abstract. Globally, water bodies adjacent to mangroves are considered sources of atmospheric CO2. We directly measured the partial pressure of CO2 in water, pCO2(water), and other related biogeochemical parameters with very high (1-min) temporal resolution at Dhanchi Island in India’s Sundarbans during the post-monsoon season. We used elemental, stable isotopic, and optical signatures to investigate the sources of dissolved inorganic carbon (DIC) and organic matter (OM) in these waters. Diel mean pCO2(water) was marginally oversaturated in creeks (efflux, 69 ± 180 µmol m−2 h−1) and undersaturated along the island boundary and in the main river (influx, −17 ± 53 and −31 ± 73 µmol m−2 h−1, respectively) compared to the atmospheric CO2 concentration. The possibility in earlier studies of over- or underestimating the CO2 flux because of an inability to capture tidal minima and maxima was minimized in the present study, which confirmed that the waters surrounding mangroves in this region can act as a sink or a very weak source of atmospheric CO2. δ13C values for DIC suggest a mixed DIC source, and a three-end-member stable isotope mixing model and optical signatures of OM suggest negligible riverine contribution of freshwater to OM. We conclude that the CO2 sink or weak source character was due to a reduced input of riverine freshwater [which usually has high pCO2(water)] and the predominance of pCO2-lean water from the coastal sea, which eventually increases the buffering capacity of the water as evidenced by the Revelle factor. Up-scaling the CO2 flux data for all seasons and the entire estuary, we propose that the CO2 evasion rate observed in this study is much lower than the recently estimated world average. Mangrove areas having such low emissions should be given due emphasis when up-scaling the global mangrove carbon budget from regional observations.

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Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans

Biogeochemistry ◽

10.1007/s10533-021-00769-9 ◽

2021 ◽

Author(s):

Anirban Akhand ◽

Abhra Chanda ◽

Kenta Watanabe ◽

Sourav Das ◽

Tatsuki Tokoro ◽

...

Keyword(s):

Bay Of Bengal ◽

Dissolved Inorganic Carbon ◽

Monsoon Season ◽

Buffering Capacity ◽

Marine Water ◽

High Temporal Resolution ◽

Post Monsoon Season ◽

Biogeochemical Parameters ◽

Northern Bay Of Bengal ◽

The Sundarbans

AbstractGlobally, water bodies adjacent to mangroves are considered significant sources of atmospheric CO2. We directly measured the partial pressure of CO2 in water [pCO2(water)] and related biogeochemical parameters with high temporal resolution, covering both diel and tidal cycles, in the mangrove-surrounding waters around the northern Bay of Bengal during the post-monsoon season. Mean pCO2(water) was marginally oversaturated in two creeks (470 ± 162 µatm, mean ± SD) and undersaturated in the adjoining estuarine stations (387 ± 58 µatm) compared to atmospheric pCO2, and was considerably lower than the global average. We further estimated the pCO2(water) and buffering capacity of all possible sources of the mangrove-surrounding waters and concluded that their character as a CO2 sink or weak source is due to the predominance of marine water from the Bay of Bengal with low pCO2 and high buffering capacity. Marine water with high buffering capacity suppresses the effect of pCO2 increase within the mangrove system and lowers the CO2 evasion even in creek stations. The δ13C of dissolved inorganic carbon (DIC) in the mangrove-surrounding waters indicated that the DIC sources were a mixture of mangrove plants, pore-water, and groundwater, in addition to marine water. Finally, we showed that the CO2 evasion rate from the estuaries of the Sundarbans is much lower than the recently estimated world average. Our results demonstrate that mangrove areas having such low emissions should be considered when up-scaling the global mangrove carbon budget from regional observations.

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Challenges in Linking Atmospheric CO2 Concentrations to Fluxes at Local and Regional Scales

Australian Journal of Botany ◽

10.1071/bt9920697 ◽

1992 ◽

Vol 40 (5) ◽

pp. 697 ◽

Cited By ~ 71

Author(s):

MR Raupach ◽

OT Denmead ◽

FX Dunin

Keyword(s):

Boundary Layer ◽

Planetary Boundary Layer ◽

Co2 Flux ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Wheat Crop ◽

Turbulent Transfer ◽

Near Surface ◽

Scalar Dispersion ◽

Source Sink

We describe relationships between atmospheric CO2 concentration variations and CO2 source-sink distributions, at two important scales between the single plant and the whole earth: the vegetation canopy and the atmospheric planetary boundary layer. For both these scales, it is shown how knowledge of turbulence and scalar dispersion can be applied to infer CO2 source-sink distributions or fluxes from concentration measurements. At the canopy scale, the turbulent transfer of CO2 and other scalars is non-diffusive close to any point source or sink in the canopy, but diffusive at greater distances. This distinction leads to a physically tenable description of turbulent transfer, and thence to an 'inverse method' for finding the vertical profiles of sources and sinks in the canopy from measured concentration profiles. The method is tested with data from a wheat crop. At the scale of the planetary boundary layer, we consider the daily CO2 concentration drawdown (the depression of the near-surface CO2 concentration below the free-atmosphere value) of typically 20-40 ppm. This is determined by both the regionally averaged CO2 uptake at the surface and the growth of the daytime convective boundary layer (CBL). It is shown that, for a column of air which fills the CBL and is moved across the landscape by the mean wind, the net cumulative surface CO2 flux (in mol m-2) is given to a good approximation by h(t)[Cm(t) - C+]/V, where h(t) is CBL depth, Cm(t) the CO2 concentration in the CBL column in mol mol-1, C+ the concentration above the CBL, V the molar volume and time t is measured from the time at which Cm = C+ in the morning, typically about 0800 hours local time. The resulting CO2 flux estimates are regionally averaged over the trajectory followed by the column. This 'CBL budget method' for inferring surface fluxes is compared with direct measurements of CO2 fluxes, with satisfactory results. The technique has application to scalars other than CO2.

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Carbon balance of China constrained by CONTRAIL aircraft CO2 measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-7683-2014 ◽

2014 ◽

Vol 14 (6) ◽

pp. 7683-7709

Author(s):

F. Jiang ◽

H. M. Wang ◽

J. M. Chen ◽

T. Machida ◽

L. X. Zhou ◽

...

Keyword(s):

Transport Model ◽

Carbon Sink ◽

Terrestrial Ecosystem ◽

Co2 Flux ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Inversion Method ◽

Climate Factors ◽

Mean Climate ◽

Atmospheric Co2 Concentrations

Abstract. Terrestrial CO2 flux estimates in China using atmospheric inversion method are beset with considerable uncertainties because very few atmospheric CO2 concentration measurements are available. In order to improve these estimates, nested atmospheric CO2 inversion during 2002–2008 is performed in this study using passenger aircraft-based CO2 measurements over Eurasia from the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project. The inversion system includes 43 regions with a focus on China, and is based on the Bayesian synthesis approach and the TM5 transport model. The terrestrial ecosystem carbon flux modeled by the BEPS model and the ocean exchange simulated by the OPA-PISCES-T model are considered as the prior fluxes. The impacts of CONTRAIL CO2 data on inverted China terrestrial carbon fluxes are quantified, the improvement of the inverted fluxes after adding CONTRAIL CO2 data are rationed against climate factors and evaluated by comparing the simulated atmospheric CO2 concentrations with three independent surface CO2 measurements in China. Results show that with the addition of CONTRAIL CO2 data, the inverted carbon sink in China increases while those in South and Southeast Asia decrease. Meanwhile, the posterior uncertainties over these regions are all reduced. CONTRAIL CO2 data also have a large effect on the inter-annual variation of carbon sinks in China, leading to a better correlation between the carbon sink and the annual mean climate factors. Evaluations against the CO2 measurements at three sites in China also show that the CONTRAIL CO2 measurements have improved the inversion results.

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Distributions of surface water CO2 and air-sea flux of CO2 in coastal regions of the Canadian Beaufort Sea in late summer

Biogeosciences Discussions ◽

10.5194/bgd-5-5093-2008 ◽

2008 ◽

Vol 5 (6) ◽

pp. 5093-5132 ◽

Cited By ~ 6

Author(s):

A. Murata ◽

K. Shimada ◽

S. Nishino ◽

M. Itoh

Keyword(s):

Surface Water ◽

Dissolved Inorganic Carbon ◽

High Capacity ◽

Coastal Region ◽

Chemical Properties ◽

Late Summer ◽

Co2 Flux ◽

Beaufort Sea ◽

Atmospheric Co2 ◽

Co2 Sink

Abstract. To quantify the air-sea flux of CO2 in a high-latitude coastal region, we conducted shipboard observations of atmospheric and surface water partial pressures of CO2 (pCO2) and total dissolved inorganic carbon (TCO2) in the Canadian Beaufort Sea (150° W–127° W; 69° N–73° N) in late summer 2000 and 2002. Surface water pCO2 was lower than atmospheric pCO2 (2000, 361.0 μatm; 2002, 364.7 μatm), and ranged from 250 to 344 μatm. Accordingly, ΔpCO2, which is the driving force of the air-sea exchange of CO2 and is calculated from differences in pCO2 between the sea surface and the overlying air, was generally negative (potential sink for atmospheric CO2), although positive ΔpCO2 values (source) were also found locally. Distributions of surface water pCO2, as well as those of ΔpCO2 and CO2 flux, were controlled mainly by water mixing related to river discharge. The air-sea fluxes of CO2 were −15.0 and −16.8 mmol m−2 d−1 on average in 2000 and 2002, respectively, implying that the area acted as a moderate sink for atmospheric CO2. The air-to-sea net CO2 flux in an extended area of the western Arctic Ocean (411 000 km2) during the ice-free season (=100 days) was calculated as 10.2±7.7 mmol m−2 d−1, equivalent to a regional CO2 sink of 5.0±3.8 Tg C. The estimated buffer factor was 1.5, indicating that the area is a high-capacity CO2 sink. These CO2 flux estimates will need to be revised because they probably include a bias due to the vertical gradients of physical and chemical properties characteristic in the region, which have not yet been adequately considered.

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Sensitivity of the air–sea CO2 exchange in the Baltic Sea and Danish inner waters to atmospheric short term variability

Biogeosciences Discussions ◽

10.5194/bgd-11-16993-2014 ◽

2014 ◽

Vol 11 (12) ◽

pp. 16993-17042

Author(s):

A. S. Lansø ◽

J. Bendtsen ◽

J. H. Christensen ◽

L. L. Sørensen ◽

H. Chen ◽

...

Keyword(s):

Baltic Sea ◽

Co2 Flux ◽

Co2 Concentration ◽

Co2 Exchange ◽

Atmospheric Co2 ◽

The Baltic Sea ◽

Short Term ◽

Transfer Velocity ◽

The Baltic ◽

Short Term Variability

Abstract. Minimising the uncertainties in estimates of air–sea CO2 exchange is an important step toward increasing the confidence in assessments of the CO2 cycle. Using an atmospheric transport model makes it possible to investigate the direct impact of atmospheric parameters on the air–sea CO2 flux along with its sensitivity to e.g. short-term temporal variability in wind speed, atmospheric mixing height and the atmospheric CO2 concentration. With this study the importance of high spatiotemporal resolution of atmospheric parameters for the air–sea CO2 flux is assessed for six sub-basins within the Baltic Sea and Danish inner waters. A new climatology of surface water partial pressure of CO2 (pCO2) has been developed for this coastal area based on available data from monitoring stations and underway pCO2 measuring systems. Parameterisations depending on wind speed were applied for the transfer velocity to calculate the air–sea CO2 flux. Two model simulations were conducted – one including short term variability in atmospheric CO2 (VAT), and one where it was not included (CAT). A seasonal cycle in the air–sea CO2 flux was found for both simulations for all sub-basins with uptake of CO2 in summer and release of CO2 to the atmosphere in winter. During the simulated period 2005–2010 the average annual net uptake of atmospheric CO2 for the Baltic Sea, Danish Straits and Kattegat was 287 and 471 Gg C yr-1 for the VAT and CAT simulations, respectively. The obtained difference of 184 Gg C yr-1 was found to be significant, and thus ignoring short term variability in atmospheric CO2 does have a sizeable effect on the air–sea CO2 exchange. The combination of the atmospheric model and the new pCO2 fields has also made it possible to make an estimate of the marine part of the Danish CO2 budget for the first time. A net annual uptake of 2613 Gg C yr-1 was found for the Danish waters. A large uncertainty is connected to the air–sea CO2 flux in particular caused by the transfer velocity parameterisation and the applied pCO2 climatology. However, the present study underlines the importance of including short term variability in the atmospheric CO2 concentration in future model studies of the air–sea exchange in order to minimise the uncertainty.

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Carbon balance of China constrained by CONTRAIL aircraft CO2 measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-10133-2014 ◽

2014 ◽

Vol 14 (18) ◽

pp. 10133-10144 ◽

Cited By ~ 7

Author(s):

F. Jiang ◽

H. M. Wang ◽

J. M. Chen ◽

T. Machida ◽

L. X. Zhou ◽

...

Keyword(s):

Transport Model ◽

Carbon Sink ◽

Terrestrial Ecosystem ◽

Co2 Flux ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Inversion Method ◽

Climate Factors ◽

Terrestrial Carbon ◽

Atmospheric Co2 Concentrations

Abstract. Terrestrial carbon dioxide (CO2) flux estimates in China using atmospheric inversion method are beset with considerable uncertainties because very few atmospheric CO2 concentration measurements are available. In order to improve these estimates, nested atmospheric CO2 inversion during 2002–2008 is performed in this study using passenger aircraft-based CO2 measurements over Eurasia from the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project. The inversion system includes 43 regions with a focus on China, and is based on the Bayesian synthesis approach and the TM5 transport model. The terrestrial ecosystem carbon flux modeled by the Boreal Ecosystems Productivity Simulator (BEPS) model and the ocean exchange simulated by the OPA-PISCES-T model are considered as the prior fluxes. The impacts of CONTRAIL CO2 data on inverted China terrestrial carbon fluxes are quantified, the improvement of the inverted fluxes after adding CONTRAIL CO2 data are rationed against climate factors and evaluated by comparing the simulated atmospheric CO2 concentrations with three independent surface CO2 measurements in China. Results show that with the addition of CONTRAIL CO2 data, the inverted carbon sink in China increases while those in South and Southeast Asia decrease. Meanwhile, the posterior uncertainties over these regions are all reduced (2–12%). CONTRAIL CO2 data also have a large effect on the inter-annual variation of carbon sinks in China, leading to a better correlation between the carbon sink and the annual mean climate factors. Evaluations against the CO2 measurements at three sites in China also show that the CONTRAIL CO2 measurements may have improved the inversion results.

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Sensitivity of the air–sea CO2 exchange in the Baltic Sea and Danish inner waters to atmospheric short-term variability

Biogeosciences ◽

10.5194/bg-12-2753-2015 ◽

2015 ◽

Vol 12 (9) ◽

pp. 2753-2772 ◽

Cited By ~ 7

Author(s):

A. S. Lansø ◽

J. Bendtsen ◽

J. H. Christensen ◽

L. L. Sørensen ◽

H. Chen ◽

...

Keyword(s):

Baltic Sea ◽

Co2 Flux ◽

Co2 Concentration ◽

Co2 Exchange ◽

Atmospheric Co2 ◽

The Baltic Sea ◽

Short Term ◽

Transfer Velocity ◽

The Baltic ◽

Short Term Variability

Abstract. Minimising the uncertainties in estimates of air–sea CO2 exchange is an important step toward increasing the confidence in assessments of the CO2 cycle. Using an atmospheric transport model makes it possible to investigate the direct impact of atmospheric parameters on the air–sea CO2 flux along with its sensitivity to, for example, short-term temporal variability in wind speed, atmospheric mixing height and atmospheric CO2 concentration. With this study, the importance of high spatiotemporal resolution of atmospheric parameters for the air–sea CO2 flux is assessed for six sub-basins within the Baltic Sea and Danish inner waters. A new climatology of surface water partial pressure of CO2 (pCO2w) has been developed for this coastal area based on available data from monitoring stations and on-board pCO2w measuring systems. Parameterisations depending on wind speed were applied for the transfer velocity to calculate the air–sea CO2 flux. Two model simulations were conducted – one including short-term variability in atmospheric CO2 (VAT), and one where it was not included (CAT). A seasonal cycle in the air–sea CO2 flux was found for both simulations for all sub-basins with uptake of CO2 in summer and release of CO2 to the atmosphere in winter. During the simulated period 2005–2010, the average annual net uptake of atmospheric CO2 for the Baltic Sea, Danish straits and Kattegat was 287 and 471 Gg C yr−1 for the VAT and CAT simulations, respectively. The obtained difference of 184 Gg C yr−1 was found to be significant, and thus ignoring short-term variability in atmospheric CO2 does have a sizeable effect on the air–sea CO2 exchange. The combination of the atmospheric model and the new pCO2w fields has also made it possible to make an estimate of the marine part of the Danish CO2 budget for the first time. A net annual uptake of 2613 Gg C yr−1 was found for the Danish waters. A large uncertainty is connected to the air–sea CO2 flux in particular caused by the transfer velocity parameterisation and the applied pCO2w climatology. However, as a significant difference of 184 Gg C yr−1 is obtained between the VAT and CAT simulations, the present study underlines the importance of including short-term variability in atmospheric CO2 concentration in future model studies of the air–sea exchange in order to minimise the uncertainty.

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