A sink for atmospheric carbon dioxide in the northeast Indian Ocean (original) (raw)
Related papers
Environmental controls on the seasonal carbon dioxide fluxes in the northeastern Indian Ocean
Indian Journal of …, 2010
Total carbon dioxide (TCO 2) and computations of partial pressure of carbon dioxide (pCO 2) had been examined in Northerneastern region of Indian Ocean. It exhibit seasonal and spatial variability. North-south gradients in the pCO 2 levels were closely related to gradients in salinity caused by fresh water discharge received from rivers. Eddies observed in this region helped to elevate the nutrients availability and the biological controls by increasing the productivity. These phenomena elevated the carbon dioxide draw down during the fair seasons. Seasonal fluxes estimated from local wind speed and air-sea carbon dioxide difference indicate that during southwest monsoon, the northeastern Indian Ocean acts as a strong sink of carbon dioxide (-20.04 mmol m-2 d-1). Also during fall intermonsoon the area acts as a weak sink of carbon dioxide (-4.69 mmol m-2 d-1). During winter monsoon, this region behaves as a weak carbon dioxide source with an average sea to air flux of 4.77 mmol m-2 d-1. In the northern region, salinity levels in the surface level are high during winter compared to the other two seasons. Northeastern Indian Ocean shows significant intraseasonal variability in carbon dioxide fluxes that are mediated by eddies which provide carbon dioxide and nutrients from the subsurface waters to the mixed layer.
Journal of Oceanography, 2013
Your article is protected by copyright and all rights are held exclusively by The Oceanographic Society of Japan and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
Limnology, 2019
Surface water partial pressure of carbon dioxide [pCO 2 (water)], total alkalinity (TA), dissolved inorganic carbon (DIC), and air-water CO 2 flux were measured in two estuaries of the Bay of Bengal namely Mahanadi and Dhamra. Though the annual average air-water CO 2 fluxes at the Mahanadi and the Dhamra Estuaries were − 3.9 ± 21.4 (mean ± standard deviation) µmol m −2 h −1 and − 2.9 ± 11.6 µmol m −2 h −1 , respectively, the intra-annual variation of air-water CO 2 fluxes in the two estuaries was contrasting. Nonetheless, from the perspective of net primary productivity, the surface water of both the estuaries were found autotrophic throughout the study period with varying rates at different seasons and highest during summer months. Mahanadi Estuary acted as a CO 2 source toward atmosphere during monsoon months, whereas, Dhamra Estuary acted as a source during pre-monsoon months. On the contrary, Mahanadi and Dhamra Estuaries acted as CO 2 sink during pre-monsoon months and monsoon months, respectively. The salinity in Mahanadi Estuary was much lower compared to Dhamra, which indicated significant freshwater discharge rich in organic carbon, and the remineralization of this carbon to DIC during summer and monsoon months explained the CO 2 source character. Whereas, in Dhamra, reduced freshwater flow and high turbidity were held accountable for net heterotrophic character of the water column during the post-monsoon months. The annual data set of air-water CO 2 fluxes from these two estuaries produced from this study could be utilized in future to fill the data gap and upscale the Indian estuaries scenario from the perspective of blue carbon budgeting.
Seasonal controls on surface pCO2 in the central and eastern Arabian Sea
Journal of Earth System Science, 2000
The variability in partial pressure of carbon dioxide (pCO 2) and its control by biological and physical processes in the mixed layer (ML) of the central and eastern Arabian Sea during inter-monsoon, northeast monsoon, and southwest monsoon seasons were studied. The ML varied from 80-120 m during NE monsoon, 60-80 m and 20-30 m during SW-and inter-monsoon seasons, respectively, and the variability resulted from different physical processes. Significant seasonal variability was found in pCO 2 levels. During SW monsoon, coastal waters contain two contrasting regimes; (a) pCO 2 levels of 520-685 "atm were observed in the SW coast of India, the highest found so far from this region, driven by intense upwelling and (b) low levels of pCO 2 (266 "atm) were found associated with monsoonal fresh water influx. It varied in ranges of 416-527 "atm and 375-446 "atm during inter-and NE monsoon, respectively, in coastal waters with higher values occurring in the north. The central Arabian Sea pCO 2 levels were 351-433, 379-475 and 385-432 "atm during NE-inter and SW monsoon seasons, respectively. The mixed layer pCO 2 relations with temperature, oxygen, chlorophyll a and primary production revealed that the former is largely regulated by physical processes during SW-and NE monsoon whereas both physical and biological processes are important in inter-monsoon. Application of Louanchi et al (1996) model revealed that the mixing effect is the dominant during monsoons, however, the biological effect is equally significant during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons.
Role of biology in the air–sea carbon flux in the Bay of Bengal and Arabian Sea
A physical-biological-chemical model (PBCM) is used for investigating the seasonal cycle of air–sea carbon flux and for assessing the effect of the biological processes on seasonal time scale in the Arabian Sea (AS) and Bay of Bengal (BoB), where the surface waters are subjected to contrasting physical conditions. The formulation of PBCM is given in Swathi et al (2000), and evaluation of several ammonium-inhibited nitrate uptake models is given in Sharada et al (2005). The PBCM is here first evaluated against JGOFS data on surface pCO 2 in AS, Bay of Bengal Process Studies (BoBPS) data on column integrated primary productivity in BoB, and WOCE I1 data on dissolved inorganic carbon (DIC) and alkalinity (ALK) in the upper 500 meters at 9 • N in AS and at 10 • N in BoB in September–October. There is good qualitative agreement with local quantitative discrepancies. The net effect of biological processes on air–sea carbon flux on seasonal time scale is determined with an auxiliary computational experiment, called the abiotic run, in which the biological processes are turned off. The difference between the biotic run and abiotic run is interpreted as the net effect of biological processes on the seasonal variability of chemical variables. The net biological effect on air–sea carbon flux is found to be highest in southwest monsoon season in the northwest AS, where strong upwelling drives intense new production. The biological effect is larger in AS than in BoB, as seasonal upwelling and mixing are strong in AS, especially in the northeast, while coastal upwelling and mixing are weak in BoB.
Journal of Marine Research, 1999
As part of a cooperative effort of the Joint Global Ocean Flux Study (JGOFS) and of the World Ocean Circulation Experiment (WOCE) program, we have measured total CO 2 (TCO 2) and total alkalinity (TA) along three sections in the northern Indian Ocean. One section through the Gulf of Aden to the Arabian Sea is parallel to the coast of Yemen. One section is across the Arabian Sea along the nominal 9N latitude and the other section is across the Bay of Bengal along the nominal 10N latitude. The measurements were performed on board R/V Knorr in September-October 1995. The primary purpose of this work is to understand the penetration of anthropogenic CO 2 along these ocean sections. Here, we present a novel approach to the calculation of anthropogenic CO 2 in the ocean based upon the fundamentals of water-sources mixing. Consequently, we rst describe the observations and mixing of water-sources before we describe the quanti cation of anthropogenic CO 2 concentrationsin these waters. The data show large spatial variations in surface seawater of both total CO 2 (up to 50 µmol kg 2 1) and total alkalinity (up to 40 µmol kg 2 1). The variations are mainly associated with physical processes characterized by water masses of different temperature and salinity. For example, at depths we observed low TCO 2 concentration at longitude 54E 6 2E associated with the low-salinity water mass owing northward. The contrasts between the sections across the Arabian Sea and the Bay of Bengal emphasize the large property differences between the two ocean basins. Multiparametric analyses on the data clearly show the relative contributions of different water-sources in each of the ocean sections. The mixing coefficients calculated from the multiparametric analyses are further used to quantify anthropogenic CO 2 concentrations in each water-source. The results indicate that the surface water-sources contain 47.8, 42.1 and 50.4 µmol kg 2 1 in the Gulf of Aden, the Arabian Sea and the Bay of Bengal, respectively. In the surface waters there is slightly more anthropogenic CO 2 across the Bay of Bengal than across the Arabian Sea. In contrast, anthropogenic CO 2 has penetrated signi cantly deeper in the Gulf of Aden than in the Arabian Sea and in the Bay of Bengal.
Sea-air CO2 fluxes in the Indian Ocean between 1990 and 2009
2013
The Indian Ocean (44 • S-30 • N) plays an important role in the global carbon cycle, yet it remains one of the most poorly sampled ocean regions. Several approaches have been used to estimate net sea-air CO 2 fluxes in this region: interpolated observations, ocean biogeochemical models, atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Indian Ocean sea-air CO 2 fluxes between 1990 and 2009. Using all of the models and inversions, the median annual mean sea-air CO 2 uptake of −0.37 ± 0.06 PgC yr −1 is consistent with the −0.24 ± 0.12 PgC yr −1 calculated from observations. The fluxes from the southern Indian Ocean (18-44 • S; −0.43 ± 0.07 PgC yr −1 ) are similar in magnitude to the annual uptake for the entire Indian Ocean. All models capture the observed pattern of fluxes in the Indian Ocean with the following exceptions: underestimation of upwelling fluxes in the northwestern region (off Oman and Somalia), overestimation in the northeastern region (Bay of Bengal) and underestimation of the CO 2 sink in the subtropical convergence zone. These differences were mainly driven by lack of atmospheric CO 2 data in atmospheric inversions, and poor simulation of monsoonal currents and freshwater discharge in ocean biogeochemical models. Overall, the models and inversions do capture the phase of the observed seasonality for the entire Indian Ocean but overestimate the magnitude. The predicted sea-air CO 2 fluxes by ocean biogeochemical models (OBGMs) respond to seasonal variability with strong phase lags with reference to climatological CO 2 flux, whereas the atmospheric inversions predicted an order of magnitude higher seasonal flux than OBGMs. The simulated interannual variability by the OBGMs is weaker than that found by atmospheric inversions. Prediction of such weak interannual variability in CO 2 fluxes by atmospheric inversions was mainly caused by a lack of atmospheric data in the Indian Ocean. The OBGM models suggest a small strengthening of the sink over the period 1990-2009 of −0.01 PgC decade −1 . This is inconsistent with the observations in the southwestern Indian Ocean that shows the growth rate of oceanic pCO 2 was faster than the observed atmospheric CO 2 growth, a finding attributed to the trend of the Southern Annular Mode (SAM) during the 1990s.
Air-water CO 2 flux was measured from the gradient of fCO 2 (water) and fCO 2 (air) in the Hooghly-Matla estuary to offshore transition zone. An average gas transfer velocity of 10.2 cm h-1 was evaluated in this region. fCO 2 (air) ranged between 275.08 µatm to 459.07 µatm and fCO 2 (water) varied from 149.1 µatm to 299.2 µatm. Wind velocity and bathymetry (depth) were observed to be the main controlling factors for exchange of CO 2 between the atmosphere and water phase. Seawater is found to have a greater influence at the marine end of the estuary. Apart from physical mixing in this freshwater-sea water interacting zone, the study of fCO 2 and pH reflects a possible influence of biological activity as well. A maximum efflux rate of 24.56 µmol m-2 h-1 and influx rate of-41.61 µmol m-2 h-1 is determined during high wind velocity. The overall region surveyed was found to behave as a sink during the study period with an average (daytime) influx rate of-14.03 µmol m-2 h-1 .
Carbon dioxide emissions from Indian monsoonal estuaries
Geophysical Research Letters, 2012
Estuaries are known to be strong source for atmospheric CO 2 , however, little information is available from Indian estuaries. In order to quantify CO 2 emissions from the Indian estuaries, samples were collected at 27 estuaries all along the Indian coast during discharge (wet) period. The emissions of CO 2 to the atmosphere from Indian estuaries were 4-5 times higher during wet than dry period. The pCO 2 ranged between ~300 and 18492 μatm which are within the range of world estuaries. The mean pCO 2 and particulate organic carbon (POC) showed positive relation with rate of discharge suggesting availability of high quantities of organic matter that led to enhanced microbial decomposition. The annual CO 2 fluxes from the Indian estuaries, together with dry period data available in the literature, amounts to 1.92 TgC which is >10 times less than that from the European estuaries. The low CO 2 fluxes from the Indian estuaries are attributed to low flushing rates and less human settlements along the banks of the Indian estuaries.
Atmospheric Environment, 2011
This study reveals that landesea breezes, atmospheric stability and influence of net ecosystem metabolism for the conversion of organic carbon to atmospheric CO 2 are the major driving forces behind the variation of atmospheric CO 2 at the landeocean boundary, northeast coast of India. The seasonal variation of partial pressure of CO 2 (pCO 2 ) and its efflux from the coastal water were several fold higher in the pre-monsoon (1807.9 AE 757.03 m atm; 579.03 AE 172.9 mM m À2 h À1 ) than in the monsoon (1070.5 AE 328.5 m atm; 258.96 AE 185.65 mM m À2 h À1 ) and the post-monsoon (615.7 AE 121.6 m atm; 53.27 AE 19.24 mM m À2 h À1 ). The mean photic zone productivity to column respiration ratio was 0.12 AE 0.08, revealing predominance of heterotrophic processes. Community respiration was at minimum during monsoon (38.82 AE 8.63 mM C m À2 d À1 ) but was at maximum (173.8 AE 111.8 mM C m À2 d À1 ) during pre-monsoon and intermittent (125.07 AE 11.97 mM C m À2 d À1 ) during post-monsoon. Diurnal variations of atmospheric CO 2 concentration were determined by local air circulations and atmospheric stability. Seasonal variations of atmospheric CO 2 bear a significant signature of biological processes occurring in the coastal water by means of airesea exchange, markedly affected by the net ecosystem metabolism. Important predictors of coastal atmospheric CO 2 in decreasing order of explained variability are wind direction, stability, CO 2 efflux and wind velocity.