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The thesis presents observations on the CO2 mixing ratio and the carbon isotopic ratio (13C/12C i.e. δ13) of atmospheric CO2 from the Indian region, for the period 2008 - 2011. An experimental system was established at the Centre for Earth Sciences, Indian Institute of Science, Bangalore. The experimental protocol involves collection of air samples, extraction of CO2 from the air samples collected, and finally the measurement of the CO2 mixing ratio and isotopic ratios of the extracted CO2 using pressure gauge readings and the dual inlet peripheral of the isotope ratio mass spectrometer, IRMS MAT 253. The isotopic ratios measured are scaled to VPDB and corrected for their N2O contribution. The experimental set up is calibrated with primary carbonate standards (NBS19) and an air CO2 reference mixture. The analytical precision (reproducibility of paired samples) obtained for the atmospheric CO2 measurement is ±7 µ mol.mol-1, ±0.05‰ and ±0.17‰ for the mixing ratio, δ 13C and δ 18Oof atmospheric CO2 respectively. The present study lays emphasis on the CO2 mixing ratio and the δ 13C of atmospheric CO2. There are very few atmospheric CO2 monitoring stations in India. There exists only one long-term monitoring station, Cabo de Rama, on the west coast of India. Of late, a few new stations for measuring atmospheric trace gases have been in operation, with the major focus being on remote locations. Urban stations in India have never been monitored before for both the mixing ratio and the δ13C of atmospheric CO2 together. Monitoring urban stations in India is crucial today as they have become prime emitters of CO2 due to industrial activity. The emission from the sources varies seasonally and is influenced by factors like the Indian monsoon. The Indian subcontinent is surrounded by the Arabian Sea, the Indian Ocean and the Bay of Bengal which act differentially in terms of CO2 uptake or release. There is also a differential transport of CO2 to and from the open ocean. Thus, understanding the spatial pattern of CO2 in the marine region close to the Indian subcontinent is essential to understand the oceanic uptake/release of CO2. As part of this thesis, an urban area was monitored during 2008 - 2011 and the marine region was observed during the southwest monsoon of 2009. The temporal variation of the CO2 mixing ratio and δ13C of atmospheric CO2 was observed over an urban station, Bangalore (12° 58′ N, 77° 38′ E, masl= 920 m), India. Since Bangalore is one of the developing urban cities in India, it is interesting to monitor Bangalore air to understand the impact of anthropogenic emissions on atmospheric CO2 variability. The region has four distinct seasons, dry summer (March – May), southwest monsoon (June – September), post monsoon (October – November) and winter (December – February). Thus, it is also an ideal location to identify the effect of different seasons on the contribution of CO2 from various sources. Air samples were collected from the Indian Institute of Science campus, Bangalore, during 2008 - 2011. Both the diurnal and seasonal variations of the mixing ratio and δ13C of CO2 were observed in Bangalore. On the diurnal scale, a higher mixing ratio with lighter carbon isotopes (negative value) of δ13C of CO2 was recorded in the air-CO2 analyzed during the early morning compared to the late afternoon samples. The observations suggest that coal combustion, biomass burning and car exhausts are possible sources for CO2 identified based on the Keeling plot method. The nocturnal boundary layer (NBL) is found to influence the buildup of CO2 concentration in the early morning. The presence of the NBL in the early morning prevents the mixing of locally produced air with the CO2 from the free atmosphere above. Thus, the free air contribution of CO2 is reduced during the early morning rather than in the afternoon. The effect of seasonal variability in the height of the NBL on the air CO2 mixing ratio and the 13C of atmospheric CO2 were documented in the present study. On a seasonal scale, the free air contribution of CO2 was found to be higher during the southwest monsoon and winter compared to the dry hot summer and post monsoon period. On a seasonal time scale, a sinusoidal pattern in both the mixing ratio and δ13C has been recorded in the observations. While compared with nearby CO2 monitoring stations like the coastal station, Cabo de Rama, and the Open Ocean station, Seychelles, maintained by CSIRO Australia and NOAA-CMDL respectively, Bangalore recorded higher amplitudes of seasonal variation. Seasonal scale variations have revealed an additional source i.e. emission from the cement industry along with other sources identified from diurnal variations. The emission of CO2 from these different sources is not constant; rather it was found to vary with different seasons. The enhanced biomass burning during the dry season drives the δ13C of atmospheric CO2 towards more negative values, while during the southwest monsoon; the increased biosphere cover pushes the δ13C value of atmospheric CO2 towards positive values. The effect of La Nina in 2011 is also prominent in the observation. The study also intends to identify the spatial variability of both the mixing ratio and δ 13C air-CO2 close to the urban station, Bangalore based on the simultaneous sampling of air from three locations, Bangalore and two coastal stations, Mangalore and Chennai, which are equidistant from Bangalore. Samples were collected during the southwest monsoon and winter of 2010 - 2011. The observations documented a similar source of CO2 for all the three stations irrespective of the season. The factor responsible for the variability in the mixing ratio and the δ 13C of air CO2 among these stations is the differential transport of air from the marine region and its mixing with locally produced air. To identify the variability of atmospheric CO2 over the marine region, the atmosphere over the Bay of Bengal was monitored during the southwest monsoon of 2009 as part of the Continental Tropical Convergence Zone (CTCZ) Cruise expedition. The ocean surface water was also monitored simultaneously for the δ18O of water and the δ13C of dissolved inorganic carbon measurement. The combined observations of both air and water have shown the transport of continental air to the marine region and its uptake by the ocean during the period. The variability of atmospheric-CO2 is also observed during special events like the solar eclipse. During the annular solar eclipse of 15th January, 2010 an unusually depleted source value was identified for Bangalore air. The role of the boundary layer and a change in photosynthesis were identified as possible factors affecting air CO2 composition. In conclusion, the thesis has provided the first observations on air CO2 variability from an urban station in India. The observations have identified the possible sources of CO2 and have demonstrated the role of climatic phenomena like the Atmospheric Boundary Layer, Indian Monsoon, and La Nina in controlling the behaviour of sources and sinks and thus affecting the air CO2 variability over land and ocean. The seasonal scale variation based on day-to-day variability in the afternoon samples has revealed the important contribution of emissions from the cement industry whose contribution was absent in the diurnal variability. Thus, it is evident from this study that the timing of air sampling is crucial while identifying the sources. The per capita emission of individual urban stations in India is different; thus, it is essential to monitor more urban stations to identify sources and their different contributions. In future, the simultaneous monitoring of both continental and marine air over both the Arabian Sea and the Bay of Bengal will enable us to understand the long range transport of atmospheric CO2. The long term monitoring of CO2 from the Indian region can give us a better perspective on the effect of the Indian monsoon on air CO2 variability and vice versa.

The thesis presents observations on the CO2 concentration and carbon isotopes in air CO2 (δ13C) to constrain the inter-annual variability of carbon inventory over the Southern Ocean between the years 2011-2013. Based on the observation, the region of CO2 venting was identified over the Southern Ocean. Further, isotopic characterization allowed inferring about the possible sources of CO2 degassing and contribution from the dissolved inorganic carbon (DIC) that exsolved to generate CO2. It is concluded that the origin CO2 is mainly from the degassing of CO2 available from the dissociation of DIC or organic degradation. Live Foraminiferal samples of Globigerina bulloides from towing were captured, separated and analysed for δ18O and δ13C from various locations across the Southern Ocean between 10°N−60°S. A large similarities in the estimated values (deduced from simultaneous composition of ocean water 18O, δ13C in DIC and temperature i.e. SST under equilibrium condition) and measured δ18O and δ13C values were observed until 40°S from the equator, and hence it was concluded that the calcification depth of G. bulloides is confined to a depth of ~75-200m till 40°S latitude. However, further south (>40oS) disequilibrium from the estimates was detected. A number of possible reasons were cited for the observed disequilibrium such as (1) Deeper depth habitat (2) Partial dissolution (3) Non-equilibrium calcification (4) Oceanic Suess Effect and (5) Genetic Variability. A box model of isotopic mass balance was presented in this study to explain the pattern of enrichment in the 13C values of sea water DIC with latitude (up to about 43°S). The model shows that a steady state of the carbon isotope ratio of water is achieved in a relatively short time of ~5000 days. Rainwater isotope in the open marine condition across the latitudinal transects over Southern Ocean marking zone of precipitation and evaporation is another element of this thesis. A variation with excess lighter isotopes in rainwater was observed in high latitude rain in this study. Observed isotopic depletion is attributed to rainout process over the ocean. The average rainout fraction over the Southern Ocean in the region of zone of precipitation is ~44%, while it drops to ~25% in the zone of evaporation. Second part of the thesis presents a novel method of isotope thermometry which is called “clumped isotope (13C18O16O16O-2 in the calcite structure) thermometry”. A revision in the thermometry equation relating 47 vs T in synthetic carbonates precipitates and otoliths was proposed. The revised calibration was used on fish otoliths from the modern and past environment to estimate the temperatures. Together with the clumped isotope, conventional stable isotopes in the shell carbonates were measured to effectively reconstruct the seasonal fresh water fraction at seasonal time scales.