My research interests lie in the fields of paleoclimatic reconstruction, especially the reconstruction of monsoon using natural archives. I also work on the isotopic analysis of precipitation to understand the moisture dynamical processes. Additionally, I employ the eddy-covariance based technique to quantify the atmosphere-biosphere carbon exchange and energy fluxes in natural ecosystems. The study of greenhouse gases in the urban environment is another component of my research. Phone: +91(0)20 2590 4427 Address: Dr. Homi Bhabha Road
Pashan
Pune-411008
India
Earlier proxy-observational studies, and a sole modeling study, suggest that the Indian Ocean Dip... more Earlier proxy-observational studies, and a sole modeling study, suggest that the Indian Ocean Dipole (IOD), an important global climate driver, exhibited multi-scale temporal variability during the Last Millennium (LM; CE 0851-1849, with relatively high number of strong positive IOD events during the Little Ice Age (LIA; CE 1550-1749), and strong negative IOD events during the Medieval Warm Period (MWP; CE 1000-1199). Using nine model simulations from the PMIP3, we study the IOD variability during the LM after due validation of the simulated current day (CE 1850-2005) IOD variability. Majority of the models simulate relatively higher number of positive IOD events during the MWP, and negative IOD events in the LIA, commensurate with simulated background conditions. However, higher number of strong positive IOD events are simulated relative to the negative IODs during the LIA, in agreement with proxy-observations, apparently owing to increased coupled feedback during positive IODs. Plain Language Summary The Indian Ocean Dipole (IOD) is a natural climate phenomenon in the tropical Indian Ocean with significant global impacts. Positive IOD (pIOD) events are apparently occurring more frequently in recent decades, which may also be due to under-sampling associated with limited observations span. Analyzing outputs for last millennium (CE 850-1850) from climate models, validated for historical period, helps in generating relatively longer-period the paleo-IOD records. Our analysis of simulations of the last thousand years from multiple models indicates relatively more positive (negative) IOD events in medieval warm period-CE 1000-1200 (Little Ice Age-CE 1550-1749). While during the ICA, background conditions similar to a negative IOD were simulated, models also simulate an increase in relativelystronger positive IOD events in its latter part, in agreement with a proxy-climate record. The simulated centennial changes in positive and negative IOD frequencies are associated with changes in coupled oceanatmospheric feedback mechanisms.
The ecosystem-atmosphere exchanges of terrestrial ecosystems are key drivers of global carbon, wa... more The ecosystem-atmosphere exchanges of terrestrial ecosystems are key drivers of global carbon, water, and energy cycles which are crucial to be measured accurately and represented in bottom-up biogeochemically and biogeophysically coupled ecosystem, Earth system, and climate models for improving the model predictions and impact assessment of climate change on these ecosystems. The diverse natural ecosystems in India are poorly represented in these models due to the absence any of integrated data-model framework and intercomparison study so far. To partially address this, we have used flux-tower measurements in this study to simulate the gross primary productivity (GPP), sensible (H), and latent heat fluxes (LE) of a moist semi-evergreen deciduous forest in the Kaziranga National Park in subtropical Northeast India using a process-based model ISAM. The model is calibrated using two years of measurement which improves its performance when subsequently run to simulate these fluxes for a year. The model produced annual GPP, mean maximum H, and LE are 2432.26 gC m − 2 y − 1 , 29 and 82 W m − 2 respectively as compared to their measured values i.e. 2398.47 gC m − 2 y − 1 , 26 and 73 W m − 2 correspondingly. Additionally, we report the calibrated model biogeochemical and biogeophysical parameters which will be useful to simulate the fluxes in this forest using the aforementioned models.
Forecasting the global warming of the post-industrial period requires knowledge of natural variat... more Forecasting the global warming of the post-industrial period requires knowledge of natural variations in climatic parameters, especially temperature in preceding times. Due to its stable time resolution and known physiochemical formation process, tree ring cellulose isotope datasets have immense potential to yield climatic variability information. The first standardized site-independent temperature reconstruction model from tree-ring cellulose oxygen isotope data is demonstrated here using data from a montane site in the western Himalayas. This model does not require any statistical calibration and can be directly compared with instrumental or modelled data. The resulting temperature amplitude is dependent on moisture availability and this input is needed to modulate the reconstruction. The present work tests the possibility of input of carbon isotope discrimination as a proxy of relative humidity. This input achieved amplitude control but additional frequency components were introduced to the reconstruction.
Modeling Earth Systems and Environment, May 30, 2023
The present study targets modeling the mangrove's gross primary productivity (GPP) throug... more The present study targets modeling the mangrove's gross primary productivity (GPP) through path analysis using Sentinel-2 satellite-derived optical indices and climatic factors. The formulated objectives were executed in the Pichavaram mangrove regions of India. The bio-physical related Near Infrared vegetation (NIRv), chlorophyll-related red edge symmetry (RES), pigment-related Structure Insensitive Pigment Index (SIPI), and water-content related Modified Normalized Difference Water Index (MNDWI) along with precipitation and temperature z-score values were found to be the appropriate causal variables for modeling the GPP of mangroves. The path model applied in the present study helped to understand the direct and indirect influences of optical indices and climatic factors on estimating GPP. Using the path analysis technique, the concurrent inputs of Sentinel-2 optical indices and climatic factors accurately estimated the GPP of mangroves (R 2 = 0.76), RMSE = 0.58 g Cm −2 day −1 , p < 0.01). Another remarkable outcome of the study was the synchronization of the period of the peak growing season of mangroves with the duration between the downward zero-crossing and upward zero-crossing of the z-score quantifier depicting the temperature and precipitation effect. This statistical correspondence with phenological aspects creates a scope for modeling the phenology of mangroves. The path model decomposition outcomes of the present investigation facilitate the refinement of parameterization of the light-use efficiency models.
Reef building corals are known to provide high resolution records of ocean-atmospheric variables ... more Reef building corals are known to provide high resolution records of ocean-atmospheric variables for the last several centuries. The most important parameter is the sea surface temperature, which is accurately recorded by the oxygen isotopic composition as well as by a few trace elemental ratios such as, Sr/Ca, Mg/Ca, U/Ca, etc. Determination of the sea surface temperature has enabled the palaeocenographers to study a variety of oceanic processes, such as the El Niño and Southern Oscillation, ocean circulation, air-sea gas exchange, Indian Ocean dipole, etc. Monsoon is an important atmospheric process in which sea surface temperature plays an active role in governing the moisture production and modulation of the wind circulation. Apart from temperature reconstruction, the corals have also been used to study the monsoon processes by some investigators, viz. the estimation of rainfall. In this article, we review the available coral records, specifically for studying the Indian summer monsoon rainfall variability. The study reveals that the coral records only from a few specific regions show promise in this endeavour.
Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO 2) and met... more Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO 2) and methane (CH 4) are the most important, owing to their maximum contribution to the net radiative forcing of the Earth. India is undergoing rapid economic development, where fossil fuel emissions have increased drastically in the last three decades. Apart from the anthropogenic activities, the GHGs dynamics in India are governed by the biospheric process and monsoon circulation; however, these aspects are not well addressed yet. Towards this, we have measured CO 2 and CH 4 concentration at Sinhagad, located on the Western Ghats in peninsular India. The average concentrations of CO 2 and CH 4 observed during the study period are 406.05 ± 6.36 and 1.97 ± 0.07 ppm (µ ± 1σ), respectively. They also exhibit significant seasonal variabilities at this site. CH 4 (CO 2) attains its minimum concentration during monsoon (post-monsoon), whereas CO 2 (CH 4) reaches its maximum concentration during premonsoon (post-monsoon). CO 2 poses significant diurnal variations in monsoon and post-monsoon. However, CH 4 exhibits a dual-peak like pattern in pre-monsoon. The study suggests that the GHG dynamics in the western region of India are significantly influenced by monsoon circulation, especially during the summer season.
Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are incr... more Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are increasing since the dawn of the industrial era. After years of growth, atmospheric CH 4 achieved a steady state in the late 1990s and early 2000s but then grew rapidly in the 2010s at a rate of 7.18 ppb/yr (E. G. Nisbet et al., 2019). It was also observed that, along with the increase, the CH 4 carbon isotope ratio (denoted as 13 4 CH) shifted toward more negative values. This change in 13 4 CH , in association with the increased concentration, is a matter of intense study because it can elucidate the causative factors like, increase in biogenic emissions (wetlands, ruminants, waste) or a reduction in the atmospheric sink of CH 4 through OH oxidation. If such growth rate continues in the coming decades, it could negate or even reverse the effect of climate mitigation by reduced CO 2 emission (E. G. Nisbet et al., 2019). In this context, some investigators
Evapotranspiration denotes the transport of water vapor between an ecosystem and atmosphere compr... more Evapotranspiration denotes the transport of water vapor between an ecosystem and atmosphere comprising the biotic (transpiration) and abiotic (evaporation) components. Additionally, the water vapor transports the energy used for its vaporization, the latent heat. In the present study we compare the ecohydrological cycle of a mangrove on the Bay of Bengal coast in southeast India with a broadleaf deciduous forest in northeast India using eddy covariance flux measurement for the very first time. Similar to a semi-arid ecosystem the evapotranspiration from mangrove is dominated by the dry sensible heat flux throughout the year, except pre-monsoon when it behaves like a well-watered ecosystem with evapotranspiration dominating the sensible heat flux. Such behavior is in stark contrast with the broadleaf deciduous forest which provides stronger evapotranspirative heating than sensible heat throughout the year including the dry seasons. The evaporative fraction remains consistently much lower at the mangrove than the broadleaf deciduous forest. Compared to the broadleaf deciduous forest, the mangrove ecosystem remains tighter coupled with the atmosphere. Transpiration contributes the larger share to the evapotranspiration of mangrove even in the dry seasons, whereas transpiration and evaporation contribute maximum to the evapotranspiration of broadleaf deciduous forest periodically through the year. Based on principal component analysis we show that both transpiration and evaporation at the mangrove are most strongly coupled with salinity, much different from the broadleaf deciduous forest where transpiration and evaporation are most tightly coupled with root-zone soil moisture and wind speed, respectively. The salinity regulation of transpiration has an important implication for the carbon cycle of mangrove and its appropriate parameterization in ecosystem and climate models.
Tropical forest ecosystems play a significant role in controlling the global carbon cycle. Severa... more Tropical forest ecosystems play a significant role in controlling the global carbon cycle. Several biometeorological parameters control the carbon dynamics of a forest ecosystem. We have studied the biometeorological processes of a tropical semi-deciduous forest in northeast India to understand the dynamics of the net ecosystem exchange (NEE). On a monthly scale, it is observed that mostly the leaf area index, incoming radiation, vapor pressure deficit, and air temperature control the carbon transfer processes. Furthermore, the diurnal patterns of rainfall and associated cloudiness during the monsoon season indirectly control the carbon uptake by modulating the incoming radiation. The pre-monsoon season is the most preferred, while the winter season is the least favorite time for carbon uptake by this forest. The respiration component of the studied forest ecosystem is higher than the other similar ecosystems in India. The estimated annual NEE of the forest was +177 and-31 gC m − 2 yr − 1 for 2016 and 2018, respectively. The forest's annual gross primary productivity (GPP) for 2016 and 2018 was estimated as 2693 and 2564 gC m − 2 yr − 1 , respectively.
the region in 2010 and caused widespread coral bleaching throughout the Lakshadweep Archipelago. ... more the region in 2010 and caused widespread coral bleaching throughout the Lakshadweep Archipelago. Even though several other negative excursions in δ 18 O shell values follow, the cyclicity in the isotope signal and the growth rates become again more regular in the distal part of the shell, indicating a gradual recovery of the bivalve after the initial thermal stress event. The results reveal that even short high-temperature events can significantly perturb the biology of giant clams and require long recovery phases. This information is particularly significant for conservation efforts for this endangered bivalve group in a world with ongoing global warming.
The rapid conversion of tropical rainforests into monoculture plantations of rubber (Hevea brasil... more The rapid conversion of tropical rainforests into monoculture plantations of rubber (Hevea brasiliensis) in Southeast Asia (SEA) necessitates understanding of rubber tree physiology under local climatic conditions. Frequent fog immersion in the montane regions of SEA may affect the water and carbon budgets of the rubber trees and the plantation ecosystems. We studied the effect of fog on various plant physiological parameters in a mature rubber plantation in southwest China over 3 years. During the study period, an average of 141 fog events occurred every year, and the majority occurred during the dry season, when the temperature was relatively low. In addition to the low temperature, fog events were also associated with low vapor pressure deficit, atmospheric water potential, relative humidity and frequent wet-canopy conditions. We divided the dry season into cool dry (November-February) and hot dry (March-April) seasons and classified days into foggy (FG) and non-foggy (non-FG) days. During the FG days of the cool dry season, the physiological activities of the rubber trees were suppressed where carbon assimilation and evapotranspiration showed reductions of 4% and 15%, respectively, compared to the cool dry non-FG days. Importantly, the unequal declines in carbon assimilation and evapotranspiration led to enhanced crop water productivity (WP c) on cool dry FG days but insignificant WP c values were found between FG and non-FG days of the hot dry season. Our results suggest that, by regulating plant physiology, fog events during the cool dry season significantly reduce water demand and alleviate water stress for the trees through improved WP c .
The present study targets modeling the mangrove's gross primary productivity (GPP) through path a... more The present study targets modeling the mangrove's gross primary productivity (GPP) through path analysis using Sentinel-2 satellite-derived optical indices and climatic factors. The formulated objectives were executed in the Pichavaram mangrove regions of India. The bio-physical related Near Infrared vegetation (NIRv), chlorophyll-related red edge symmetry (RES), pigment-related Structure Insensitive Pigment Index (SIPI), and water-content related Modified Normalized Difference Water Index (MNDWI) along with precipitation and temperature z-score values were found to be the appropriate causal variables for modeling the GPP of mangroves. The path model applied in the present study helped to understand the direct and indirect influences of optical indices and climatic factors on estimating GPP. Using the path analysis technique, the concurrent inputs of Sentinel-2 optical indices and climatic factors accurately estimated the GPP of mangroves (R 2 = 0.76), RMSE = 0.58 g Cm −2 day −1 , p < 0.01). Another remarkable outcome of the study was the synchronization of the period of the peak growing season of mangroves with the duration between the downward zero-crossing and upward zero-crossing of the z-score quantifier depicting the temperature and precipitation effect. This statistical correspondence with phenological aspects creates a scope for modeling the phenology of mangroves. The path model decomposition outcomes of the present investigation facilitate the refinement of parameterization of the light-use efficiency models.
The isotopic composition of precipitation was studied over a terrestrial environment in western I... more The isotopic composition of precipitation was studied over a terrestrial environment in western India and an island region in the Bay of Bengal. We have examined the precipitation isotopes' response to the surface temperature and the tropospheric warming during the monsoon season. We observed that tropospheric temperature and surface temperature are positively correlated over the ocean while they are negatively correlated over the land. As a result, the precipitation isotopes in these environments show the opposite behavior to surface temperature variability. Despite this difference, precipitation isotopes in both environments respond positively to the tropospheric temperature variability, though the relationship is weaker in the terrestrial environment. The precipitation isotopic response to tropospheric temperature may provide an alternative to the precipitation and precipitation isotope relation widely used in past monsoon reconstruction.
Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are incr... more Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are increasing since the dawn of the industrial era. After years of growth, atmospheric CH 4 achieved a steady state in the late 1990s and early 2000s but then grew rapidly in the 2010s at a rate of 7.18 ppb/yr (E. G. Nisbet et al., 2019). It was also observed that, along with the increase, the CH 4 carbon isotope ratio (denoted as 13 4 CH) shifted toward more negative values. This change in 13 4 CH , in association with the increased concentration, is a matter of intense study because it can elucidate the causative factors like, increase in biogenic emissions (wetlands, ruminants, waste) or a reduction in the atmospheric sink of CH 4 through OH oxidation. If such growth rate continues in the coming decades, it could negate or even reverse the effect of climate mitigation by reduced CO 2 emission (E. G. Nisbet et al., 2019). In this context, some investigators
The isotopic composition of precipitation is known to be a function of various ocean-atmospheric ... more The isotopic composition of precipitation is known to be a function of various ocean-atmospheric parameters, such as temperature, rainfall, humidity, sea surface condition, etc.
• Methane concentration and isotopic values were measured the first time in India. • Methane conc... more • Methane concentration and isotopic values were measured the first time in India. • Methane concentration but not the isotopic values shows seasonality in Pune. • Isotopic analysis shows waste sector is the significant source of methane in Pune. • No lockdown effect was found on methane records.
We present precipitation isotope data (δ2H and δ18O values) from 19 stations across the tropics c... more We present precipitation isotope data (δ2H and δ18O values) from 19 stations across the tropics collected from 2012 to 2017 under the Coordinated Research Project F31004 sponsored by the International Atomic Energy Agency. Rainfall samples were collected daily and analysed for stable isotopic ratios of oxygen and hydrogen by participating laboratories following a common analytical framework. We also calculated daily mean stratiform rainfall area fractions around each station over an area of 5° x 5° longitude/latitude based on TRMM/GPM satellite data. Isotope time series, along with information on rainfall amount and stratiform/convective proportions provide a valuable tool for rainfall characterisation and to improve the ability of isotope-enabled Global Circulation Models to predict variability and availability of inputs to fresh water resources across the tropics.
DIverse plant remains recovered from an archaeoIogicaI site of ChaIcothIc-Early HIstoric age in t... more DIverse plant remains recovered from an archaeoIogicaI site of ChaIcothIc-Early HIstoric age in the BhaIrabdanga area of Pakhanna (1atitude 23.25 'N, longitude 87.23'E), situated on the west bank of the Damodar river, Bankura district, West Bengal, Indla, include food grains, wood charcoals, and palynomorphs. Radio-carbon dating of the recovered biological remains reveaI the age of the site as (3 320±400) to (2 080±80) yr BP. The food graIns were Identified as Oryza sativa L. and Vigna mun 口 o L, and seeds of 日 rassica cf. ...
Earlier proxy-observational studies, and a sole modeling study, suggest that the Indian Ocean Dip... more Earlier proxy-observational studies, and a sole modeling study, suggest that the Indian Ocean Dipole (IOD), an important global climate driver, exhibited multi-scale temporal variability during the Last Millennium (LM; CE 0851-1849, with relatively high number of strong positive IOD events during the Little Ice Age (LIA; CE 1550-1749), and strong negative IOD events during the Medieval Warm Period (MWP; CE 1000-1199). Using nine model simulations from the PMIP3, we study the IOD variability during the LM after due validation of the simulated current day (CE 1850-2005) IOD variability. Majority of the models simulate relatively higher number of positive IOD events during the MWP, and negative IOD events in the LIA, commensurate with simulated background conditions. However, higher number of strong positive IOD events are simulated relative to the negative IODs during the LIA, in agreement with proxy-observations, apparently owing to increased coupled feedback during positive IODs. Plain Language Summary The Indian Ocean Dipole (IOD) is a natural climate phenomenon in the tropical Indian Ocean with significant global impacts. Positive IOD (pIOD) events are apparently occurring more frequently in recent decades, which may also be due to under-sampling associated with limited observations span. Analyzing outputs for last millennium (CE 850-1850) from climate models, validated for historical period, helps in generating relatively longer-period the paleo-IOD records. Our analysis of simulations of the last thousand years from multiple models indicates relatively more positive (negative) IOD events in medieval warm period-CE 1000-1200 (Little Ice Age-CE 1550-1749). While during the ICA, background conditions similar to a negative IOD were simulated, models also simulate an increase in relativelystronger positive IOD events in its latter part, in agreement with a proxy-climate record. The simulated centennial changes in positive and negative IOD frequencies are associated with changes in coupled oceanatmospheric feedback mechanisms.
The ecosystem-atmosphere exchanges of terrestrial ecosystems are key drivers of global carbon, wa... more The ecosystem-atmosphere exchanges of terrestrial ecosystems are key drivers of global carbon, water, and energy cycles which are crucial to be measured accurately and represented in bottom-up biogeochemically and biogeophysically coupled ecosystem, Earth system, and climate models for improving the model predictions and impact assessment of climate change on these ecosystems. The diverse natural ecosystems in India are poorly represented in these models due to the absence any of integrated data-model framework and intercomparison study so far. To partially address this, we have used flux-tower measurements in this study to simulate the gross primary productivity (GPP), sensible (H), and latent heat fluxes (LE) of a moist semi-evergreen deciduous forest in the Kaziranga National Park in subtropical Northeast India using a process-based model ISAM. The model is calibrated using two years of measurement which improves its performance when subsequently run to simulate these fluxes for a year. The model produced annual GPP, mean maximum H, and LE are 2432.26 gC m − 2 y − 1 , 29 and 82 W m − 2 respectively as compared to their measured values i.e. 2398.47 gC m − 2 y − 1 , 26 and 73 W m − 2 correspondingly. Additionally, we report the calibrated model biogeochemical and biogeophysical parameters which will be useful to simulate the fluxes in this forest using the aforementioned models.
Forecasting the global warming of the post-industrial period requires knowledge of natural variat... more Forecasting the global warming of the post-industrial period requires knowledge of natural variations in climatic parameters, especially temperature in preceding times. Due to its stable time resolution and known physiochemical formation process, tree ring cellulose isotope datasets have immense potential to yield climatic variability information. The first standardized site-independent temperature reconstruction model from tree-ring cellulose oxygen isotope data is demonstrated here using data from a montane site in the western Himalayas. This model does not require any statistical calibration and can be directly compared with instrumental or modelled data. The resulting temperature amplitude is dependent on moisture availability and this input is needed to modulate the reconstruction. The present work tests the possibility of input of carbon isotope discrimination as a proxy of relative humidity. This input achieved amplitude control but additional frequency components were introduced to the reconstruction.
Modeling Earth Systems and Environment, May 30, 2023
The present study targets modeling the mangrove&#39;s gross primary productivity (GPP) throug... more The present study targets modeling the mangrove&#39;s gross primary productivity (GPP) through path analysis using Sentinel-2 satellite-derived optical indices and climatic factors. The formulated objectives were executed in the Pichavaram mangrove regions of India. The bio-physical related Near Infrared vegetation (NIRv), chlorophyll-related red edge symmetry (RES), pigment-related Structure Insensitive Pigment Index (SIPI), and water-content related Modified Normalized Difference Water Index (MNDWI) along with precipitation and temperature z-score values were found to be the appropriate causal variables for modeling the GPP of mangroves. The path model applied in the present study helped to understand the direct and indirect influences of optical indices and climatic factors on estimating GPP. Using the path analysis technique, the concurrent inputs of Sentinel-2 optical indices and climatic factors accurately estimated the GPP of mangroves (R 2 = 0.76), RMSE = 0.58 g Cm −2 day −1 , p &lt; 0.01). Another remarkable outcome of the study was the synchronization of the period of the peak growing season of mangroves with the duration between the downward zero-crossing and upward zero-crossing of the z-score quantifier depicting the temperature and precipitation effect. This statistical correspondence with phenological aspects creates a scope for modeling the phenology of mangroves. The path model decomposition outcomes of the present investigation facilitate the refinement of parameterization of the light-use efficiency models.
Reef building corals are known to provide high resolution records of ocean-atmospheric variables ... more Reef building corals are known to provide high resolution records of ocean-atmospheric variables for the last several centuries. The most important parameter is the sea surface temperature, which is accurately recorded by the oxygen isotopic composition as well as by a few trace elemental ratios such as, Sr/Ca, Mg/Ca, U/Ca, etc. Determination of the sea surface temperature has enabled the palaeocenographers to study a variety of oceanic processes, such as the El Niño and Southern Oscillation, ocean circulation, air-sea gas exchange, Indian Ocean dipole, etc. Monsoon is an important atmospheric process in which sea surface temperature plays an active role in governing the moisture production and modulation of the wind circulation. Apart from temperature reconstruction, the corals have also been used to study the monsoon processes by some investigators, viz. the estimation of rainfall. In this article, we review the available coral records, specifically for studying the Indian summer monsoon rainfall variability. The study reveals that the coral records only from a few specific regions show promise in this endeavour.
Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO 2) and met... more Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO 2) and methane (CH 4) are the most important, owing to their maximum contribution to the net radiative forcing of the Earth. India is undergoing rapid economic development, where fossil fuel emissions have increased drastically in the last three decades. Apart from the anthropogenic activities, the GHGs dynamics in India are governed by the biospheric process and monsoon circulation; however, these aspects are not well addressed yet. Towards this, we have measured CO 2 and CH 4 concentration at Sinhagad, located on the Western Ghats in peninsular India. The average concentrations of CO 2 and CH 4 observed during the study period are 406.05 ± 6.36 and 1.97 ± 0.07 ppm (µ ± 1σ), respectively. They also exhibit significant seasonal variabilities at this site. CH 4 (CO 2) attains its minimum concentration during monsoon (post-monsoon), whereas CO 2 (CH 4) reaches its maximum concentration during premonsoon (post-monsoon). CO 2 poses significant diurnal variations in monsoon and post-monsoon. However, CH 4 exhibits a dual-peak like pattern in pre-monsoon. The study suggests that the GHG dynamics in the western region of India are significantly influenced by monsoon circulation, especially during the summer season.
Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are incr... more Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are increasing since the dawn of the industrial era. After years of growth, atmospheric CH 4 achieved a steady state in the late 1990s and early 2000s but then grew rapidly in the 2010s at a rate of 7.18 ppb/yr (E. G. Nisbet et al., 2019). It was also observed that, along with the increase, the CH 4 carbon isotope ratio (denoted as 13 4 CH) shifted toward more negative values. This change in 13 4 CH , in association with the increased concentration, is a matter of intense study because it can elucidate the causative factors like, increase in biogenic emissions (wetlands, ruminants, waste) or a reduction in the atmospheric sink of CH 4 through OH oxidation. If such growth rate continues in the coming decades, it could negate or even reverse the effect of climate mitigation by reduced CO 2 emission (E. G. Nisbet et al., 2019). In this context, some investigators
Evapotranspiration denotes the transport of water vapor between an ecosystem and atmosphere compr... more Evapotranspiration denotes the transport of water vapor between an ecosystem and atmosphere comprising the biotic (transpiration) and abiotic (evaporation) components. Additionally, the water vapor transports the energy used for its vaporization, the latent heat. In the present study we compare the ecohydrological cycle of a mangrove on the Bay of Bengal coast in southeast India with a broadleaf deciduous forest in northeast India using eddy covariance flux measurement for the very first time. Similar to a semi-arid ecosystem the evapotranspiration from mangrove is dominated by the dry sensible heat flux throughout the year, except pre-monsoon when it behaves like a well-watered ecosystem with evapotranspiration dominating the sensible heat flux. Such behavior is in stark contrast with the broadleaf deciduous forest which provides stronger evapotranspirative heating than sensible heat throughout the year including the dry seasons. The evaporative fraction remains consistently much lower at the mangrove than the broadleaf deciduous forest. Compared to the broadleaf deciduous forest, the mangrove ecosystem remains tighter coupled with the atmosphere. Transpiration contributes the larger share to the evapotranspiration of mangrove even in the dry seasons, whereas transpiration and evaporation contribute maximum to the evapotranspiration of broadleaf deciduous forest periodically through the year. Based on principal component analysis we show that both transpiration and evaporation at the mangrove are most strongly coupled with salinity, much different from the broadleaf deciduous forest where transpiration and evaporation are most tightly coupled with root-zone soil moisture and wind speed, respectively. The salinity regulation of transpiration has an important implication for the carbon cycle of mangrove and its appropriate parameterization in ecosystem and climate models.
Tropical forest ecosystems play a significant role in controlling the global carbon cycle. Severa... more Tropical forest ecosystems play a significant role in controlling the global carbon cycle. Several biometeorological parameters control the carbon dynamics of a forest ecosystem. We have studied the biometeorological processes of a tropical semi-deciduous forest in northeast India to understand the dynamics of the net ecosystem exchange (NEE). On a monthly scale, it is observed that mostly the leaf area index, incoming radiation, vapor pressure deficit, and air temperature control the carbon transfer processes. Furthermore, the diurnal patterns of rainfall and associated cloudiness during the monsoon season indirectly control the carbon uptake by modulating the incoming radiation. The pre-monsoon season is the most preferred, while the winter season is the least favorite time for carbon uptake by this forest. The respiration component of the studied forest ecosystem is higher than the other similar ecosystems in India. The estimated annual NEE of the forest was +177 and-31 gC m − 2 yr − 1 for 2016 and 2018, respectively. The forest's annual gross primary productivity (GPP) for 2016 and 2018 was estimated as 2693 and 2564 gC m − 2 yr − 1 , respectively.
the region in 2010 and caused widespread coral bleaching throughout the Lakshadweep Archipelago. ... more the region in 2010 and caused widespread coral bleaching throughout the Lakshadweep Archipelago. Even though several other negative excursions in δ 18 O shell values follow, the cyclicity in the isotope signal and the growth rates become again more regular in the distal part of the shell, indicating a gradual recovery of the bivalve after the initial thermal stress event. The results reveal that even short high-temperature events can significantly perturb the biology of giant clams and require long recovery phases. This information is particularly significant for conservation efforts for this endangered bivalve group in a world with ongoing global warming.
The rapid conversion of tropical rainforests into monoculture plantations of rubber (Hevea brasil... more The rapid conversion of tropical rainforests into monoculture plantations of rubber (Hevea brasiliensis) in Southeast Asia (SEA) necessitates understanding of rubber tree physiology under local climatic conditions. Frequent fog immersion in the montane regions of SEA may affect the water and carbon budgets of the rubber trees and the plantation ecosystems. We studied the effect of fog on various plant physiological parameters in a mature rubber plantation in southwest China over 3 years. During the study period, an average of 141 fog events occurred every year, and the majority occurred during the dry season, when the temperature was relatively low. In addition to the low temperature, fog events were also associated with low vapor pressure deficit, atmospheric water potential, relative humidity and frequent wet-canopy conditions. We divided the dry season into cool dry (November-February) and hot dry (March-April) seasons and classified days into foggy (FG) and non-foggy (non-FG) days. During the FG days of the cool dry season, the physiological activities of the rubber trees were suppressed where carbon assimilation and evapotranspiration showed reductions of 4% and 15%, respectively, compared to the cool dry non-FG days. Importantly, the unequal declines in carbon assimilation and evapotranspiration led to enhanced crop water productivity (WP c) on cool dry FG days but insignificant WP c values were found between FG and non-FG days of the hot dry season. Our results suggest that, by regulating plant physiology, fog events during the cool dry season significantly reduce water demand and alleviate water stress for the trees through improved WP c .
The present study targets modeling the mangrove's gross primary productivity (GPP) through path a... more The present study targets modeling the mangrove's gross primary productivity (GPP) through path analysis using Sentinel-2 satellite-derived optical indices and climatic factors. The formulated objectives were executed in the Pichavaram mangrove regions of India. The bio-physical related Near Infrared vegetation (NIRv), chlorophyll-related red edge symmetry (RES), pigment-related Structure Insensitive Pigment Index (SIPI), and water-content related Modified Normalized Difference Water Index (MNDWI) along with precipitation and temperature z-score values were found to be the appropriate causal variables for modeling the GPP of mangroves. The path model applied in the present study helped to understand the direct and indirect influences of optical indices and climatic factors on estimating GPP. Using the path analysis technique, the concurrent inputs of Sentinel-2 optical indices and climatic factors accurately estimated the GPP of mangroves (R 2 = 0.76), RMSE = 0.58 g Cm −2 day −1 , p < 0.01). Another remarkable outcome of the study was the synchronization of the period of the peak growing season of mangroves with the duration between the downward zero-crossing and upward zero-crossing of the z-score quantifier depicting the temperature and precipitation effect. This statistical correspondence with phenological aspects creates a scope for modeling the phenology of mangroves. The path model decomposition outcomes of the present investigation facilitate the refinement of parameterization of the light-use efficiency models.
The isotopic composition of precipitation was studied over a terrestrial environment in western I... more The isotopic composition of precipitation was studied over a terrestrial environment in western India and an island region in the Bay of Bengal. We have examined the precipitation isotopes' response to the surface temperature and the tropospheric warming during the monsoon season. We observed that tropospheric temperature and surface temperature are positively correlated over the ocean while they are negatively correlated over the land. As a result, the precipitation isotopes in these environments show the opposite behavior to surface temperature variability. Despite this difference, precipitation isotopes in both environments respond positively to the tropospheric temperature variability, though the relationship is weaker in the terrestrial environment. The precipitation isotopic response to tropospheric temperature may provide an alternative to the precipitation and precipitation isotope relation widely used in past monsoon reconstruction.
Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are incr... more Carbon dioxide (CO 2) and methane (CH 4), the two most important greenhouse gases (GHGs) are increasing since the dawn of the industrial era. After years of growth, atmospheric CH 4 achieved a steady state in the late 1990s and early 2000s but then grew rapidly in the 2010s at a rate of 7.18 ppb/yr (E. G. Nisbet et al., 2019). It was also observed that, along with the increase, the CH 4 carbon isotope ratio (denoted as 13 4 CH) shifted toward more negative values. This change in 13 4 CH , in association with the increased concentration, is a matter of intense study because it can elucidate the causative factors like, increase in biogenic emissions (wetlands, ruminants, waste) or a reduction in the atmospheric sink of CH 4 through OH oxidation. If such growth rate continues in the coming decades, it could negate or even reverse the effect of climate mitigation by reduced CO 2 emission (E. G. Nisbet et al., 2019). In this context, some investigators
The isotopic composition of precipitation is known to be a function of various ocean-atmospheric ... more The isotopic composition of precipitation is known to be a function of various ocean-atmospheric parameters, such as temperature, rainfall, humidity, sea surface condition, etc.
• Methane concentration and isotopic values were measured the first time in India. • Methane conc... more • Methane concentration and isotopic values were measured the first time in India. • Methane concentration but not the isotopic values shows seasonality in Pune. • Isotopic analysis shows waste sector is the significant source of methane in Pune. • No lockdown effect was found on methane records.
We present precipitation isotope data (δ2H and δ18O values) from 19 stations across the tropics c... more We present precipitation isotope data (δ2H and δ18O values) from 19 stations across the tropics collected from 2012 to 2017 under the Coordinated Research Project F31004 sponsored by the International Atomic Energy Agency. Rainfall samples were collected daily and analysed for stable isotopic ratios of oxygen and hydrogen by participating laboratories following a common analytical framework. We also calculated daily mean stratiform rainfall area fractions around each station over an area of 5° x 5° longitude/latitude based on TRMM/GPM satellite data. Isotope time series, along with information on rainfall amount and stratiform/convective proportions provide a valuable tool for rainfall characterisation and to improve the ability of isotope-enabled Global Circulation Models to predict variability and availability of inputs to fresh water resources across the tropics.
DIverse plant remains recovered from an archaeoIogicaI site of ChaIcothIc-Early HIstoric age in t... more DIverse plant remains recovered from an archaeoIogicaI site of ChaIcothIc-Early HIstoric age in the BhaIrabdanga area of Pakhanna (1atitude 23.25 'N, longitude 87.23'E), situated on the west bank of the Damodar river, Bankura district, West Bengal, Indla, include food grains, wood charcoals, and palynomorphs. Radio-carbon dating of the recovered biological remains reveaI the age of the site as (3 320±400) to (2 080±80) yr BP. The food graIns were Identified as Oryza sativa L. and Vigna mun 口 o L, and seeds of 日 rassica cf. ...
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