Abstract. The source and sinks of carbon dioxide (CO 2 ) and methane (CH 4 ) due to anthropogenic and natural biospheric activities were estimated for the South Asian region (Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka). Flux estimates were based on top-down methods that use inversions of atmospheric data, and bottom-up methods that use field observations, satellite data, and terrestrial ecosystem models. Based on atmospheric CO 2 inversions, the net biospheric CO 2 flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at −104 ± 150 Tg C yr −1 during [2007][2008]. Based on the bottom-up approach, the net biospheric CO 2 flux is estimated to be −191 ± 193 Tg C yr −1 during the period of 2000-2009. This last net flux results from the following flux components: (1) the Net Ecosystem Productivity, NEP (net primary production minus heterotrophic respiration) of −220 ± 186 Tg C yr −1 (2) the annual net carbon flux from land-use change of −14 ± 50 Tg C yr −1 , which resulted from a sink of −16 Tg C yr −1 due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr −1 due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr −1 ; and (4) the net CO 2 emission due to biomass burning of +44.1 ± 13.7 Tg C yr −1 . Including the emissions from the combustion of fossil fuels of 444 Tg C yr −1 for the 2000s, we estimate a net CO 2 landatmosphere flux of 297 Tg C yr −1 . In addition to CO 2 , a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH 4 . Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C-CH 4 yr −1 were released to atmosphere from South Asia during the 2000s. Taking all CO 2 and CH 4 fluxes together, our best estimate of the net land-atmosphere CO 2 -equivalent flux is a net source of 334 Tg C yr −1 for the South Asian region during the 2000s. If CH 4 emissions are weighted by radiative forcing of molecular CH 4 , the total CO 2 -equivalent flux increases to 1148 Tg C yr −1 suggesting there is great potential of reducing CH 4 emissions for stabilizing greenhouse gases concentrations.

The source and sinks of carbon dioxide (CO₂) and methane (CH₄) due to anthropogenic and natural biospheric activities were estimated for the South Asia region (Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka). Flux estimates were based on top-down methods that use inversions of atmospheric data, and bottom-up methods that use field observations, satellite data, and terrestrial ecosystem models. Based on atmospheric CO₂ inversions, the net biospheric CO₂ flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at −104 ± 150 Tg C yr^−1 during 2007–2008. Based on the bottom-up approach, the net biospheric CO₂ flux is estimated to be −191 ± 193 Tg C yr^−1 during the period of 2000–2009. This last net flux results from the following flux components: (1) the Net Ecosystem Productivity, NEP (net primary production minus heterotrophic respiration) of −220 ± 186 Tg C yr^−1 (2) the annual net carbon flux from land-use change of −14 ± 50 Tg C yr^−1, which resulted from a sink of −16 Tg C yr^−1 due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr^−1 due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr^−1; and (4) the net CO₂ emission due to biomass burning of +44.1 ± 13.7 Tg C yr^−1. Including the emissions from the combustion of fossil fuels of 444 Tg C yr^−1 for the decades of 2000s, we estimate a net CO₂ land-to-atmosphere flux of 297 Tg C yr^−1. In addition to CO₂, a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH₄. Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C-CH₄ yr^−1 were released to atmosphere from South Asia during the 2000s. Taking all CO₂ and CH₄ fluxes together, our best estimate of the net land-to-atmosphere CO₂-equivalent flux is a net source of 334 Tg C yr^−1 for the South Asia region during the 2000s. If CH₄ emissions are weighted by radiative forcing of molecular CH₄, the total CO₂-equivalent flux increases to 1148 Tg C yr^−1 suggesting there is great potential of reducing CH₄ emissions for stabilizing greenhouse g...

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Although situated on the same geographical latitude, the two ocean basins (the Bay of Bengal (BoB) and the Arabian Sea (AS)) of the northern Indian Ocean (NIO) experience diverse met-ocean conditions. These ocean basins are the warmest world oceans exhibiting high sea surface temperatures (SST) year-round. Conducive SST, its gradient and coupled interactions of vertical wind shear, absolute vorticity, relative humidity, and potential intensity lead to NIO being host to 7%-10% of all the tropical cyclones (TCs) in the world (Gray, 1979(Gray, , 1998. However, compared to the AS, the BoB witnesses more cyclones, a majority of which propagate in the west-northwest/north-northwest direction (Evan & Camargo 2011;Mohanty 1994). The National Cyclone Risk Mitigation Project (NCRMP) report of India states that during 1891-2000 nearly 308 TCs (out of which 103 were severe) affected the east coast of India. In contrast, only 48 TCs affected the west coast (of which 24 were severe) within the same period. Cyclones in BoB are known to be stronger and more destructive than those in AS (Singh Abstract This study examines the impact of two very severe tropical cyclonic events, Phailin (over the Bay of Bengal) and Ockhi (over the Arabian Sea), on surface ocean pCO 2 and the associated changes in the upper ocean structure using a coupled biogeochemical ROMS model. The primary productivity averaged over the mixed layer is increased from 6.9 to 12.0 (7.2-45.6) mgCm − 3 d −1 in response to Phailin (Ockhi). A decomposition analysis reveals that the mean contribution of temperature-driven changes in inducing pCO 2 variability in response to pre-and post-cyclonic conditions, in case of Phailin (Ockhi), are 5.4 (−8.8) and −7.6 (−58.8) μatm whereas dissolved inorganic carbon (DIC) driven changes are 23.6 (19.5) and 27.8 (78.0) μatm. Although salinity and total alkalinity have a relatively lesser control in inducing pCO 2 variability, salinity's response to the post-Phailin conditions is significant owing to strong salinity stratification in the Bay of Bengal. The enhancement of DIC is more in the near-surface waters than its removal by net biological processes resulting in the dominance of cyclone-induced upwelling and associated vertical mixing driven changes over the enhanced biology-driven changes in controlling pCO 2 variability during both cyclones. Despite comparable magnitudes of environmental forcing during both cyclones, the oceanic response to Phailin is comparatively short-lived and subdued due to stronger stratification in the Bay of Bengal. A relatively large ratio of DIC to total alkalinity in the upper layers of Arabian Sea facilitates a higher pCO 2 response to Ockhi. This makes Ockhi a greater source of CO 2 to the atmosphere.Plain Language Summary Tropical cyclones dissipate large amounts of energy into the upper ocean, enhancing vertical mixing under the influence of strong winds. The enrichment of nutrients and carbon due to upwelling of deeper waters enhance pCO 2 levels making a favorable environment for biological pr...

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