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Mangrove vegetation is an important component of the coastal ecosystem and is associated with near-shore marine habitat in the tropics and subtropics of the world. Indian mangrove vegetation covers about 6749 km2 along the 7516 km long... more
Mangrove vegetation is an important component of the coastal ecosystem and is associated with near-shore marine habitat in the tropics and subtropics of the world. Indian mangrove vegetation covers about 6749 km2 along the 7516 km long coast line, including Island territories (Mandal and Naskar, 2008). The distribution of mangrove areas along the Indian coast is influenced by physical forces such as geomorphology, climate, tidal amplitude and duration and quantity of freshwater inflow (Selvam, 2003). In fact, the geomorphic setting of the mangroves of east coast of India is different from that of the west coast (Ahmed, 1972). The coastal strip of west coast is narrow, and steep in slope as compared to the gentle slope of east coast. Though there are large number of small rivers bringing enormous quantity of sediment to the Arabian Sea along the west coast, deltas are not developed, possibly due to the high-energy conditions of the coast. This topographic set up gives a contrasting pattern of mangrove vegetation in India. Accordingly, the mangrove wetlands of west coast are small, less diverse and less complicated in tidal creek network, while the east coast has larger mangrove wetlands with high species diversity. Besides, beach morphological changes along the west coast are controlled by the southwest monsoon. Therefore it is interesting to ascertain the consequences of mangroves in response to climate changes along the Kerala coast, southwestern India using the sedimentary archives of the coastal plains.
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Abstract The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched... more
Abstract The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted Neogene deposits. Here we report the sedimentary processes, palaeoclimate and sea level records decoded from two borehole cores – Puthenthuruthu and Munrothuruthu borehole cores – retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in SW India, the Ashtamudi estuary, using sedimentology, palynology and stable isotopes as the major proxies. The heavy rainfall event at the latter half of Early Holocene (6117 ± 101 BP) is reflected well in the isotopic signatures of the Puthenthuruthu borehole core. The higher level of lighter isotopes of oxygen and carbon at 10–15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity. This, in turn, was responsible for the development of Bay Head Delta in the fluvial end of the estuary during Early–Middle Holocene period. Palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents. Further, the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies. This was followed by the deposition of littoral sands as Flood Tide Islands within the estuarine basin. The palynological investigations of sediments with radiocarbon age of 4350 ± 90 BP in the Munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules (algal pisolites) embedded in the sediments. The occurrence of pteridophytic spores and a few pollen of Cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view.
Research Interests: Archaeology, Geology, Oceanography, Palynology, Sea Level, and 6 moreQuaternary, Holocene, Facies, Estuary, Fluvial, and Sedimentary Rock
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Cyanobacteria and thecamoebians are the two major constituents of Non Pollen Palynomorphs (NPP) found in the palynological preparations. The former is well represented in the sediment archives while the latter has restricted occurrence in... more
Cyanobacteria and thecamoebians are the two major constituents of Non Pollen Palynomorphs (NPP) found in the palynological preparations. The former is well represented in the sediment archives while the latter has restricted occurrence in the Holocene sequence apart from the conventional organic matter of pollen and spores. Well preserved morphotypes of Gleotrichia and Rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards Early to Middle Holocene coincides with the heavy rainfall and wet climate conditions during the Holocene climate optimum (HCO). Contrary to cyanobacterial diversity, thecamoebians are restricted to Late Holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions. The major elements of thecamoebians identified belong to Arcellaceans, Centropyxids and Cucurbitella types. Abundance of Centropyxids and Arcellaceans in Varapuzha, West Kadungallur, Koonamavu, Pachcha and Ernakulam indicates low humidity and low precipitation. However, the relative abundance of Centropyxids in Mid Holocene at Ernakulam and Koonamavu reflects the early colonization of this type competing with the cyanobacteria, whereas, Arcellaceans are essentially confined to Late Holocene. Dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained. Considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the Holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability. The well preserved cyanobacterial signatures in sediment archives of Kerala coast and their scarcity or even absence elsewhere along the west coast of India indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system.
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Non-pollen palynomorphs (NPP) are organic-walled microfossils that one frequently come across in palynological preparations during pollen analysis. Like pollen and spores they are more resistant to corrosion, and as such they too get... more
Non-pollen palynomorphs (NPP) are organic-walled microfossils that one frequently come across in palynological preparations during pollen analysis. Like pollen and spores they are more resistant to corrosion, and as such they too get preserved but not destroyed during ...
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Abstract Signatures of monsoon variability preserved in the Late Quaternary sediments of southwestern India have been decoded and addressed using biological proxies along with geochronological data. Barring sediments beyond the threshold... more
Abstract Signatures of monsoon variability preserved in the Late Quaternary sediments of southwestern India have been decoded and addressed using biological proxies along with geochronological data. Barring sediments beyond the threshold for conventional 14C dating, Late Pleistocene sequences have been recognized both in Konkan and Kerala basins. Konkan area has only subsurface continental/lacustrine Late Pleistocene, whereas Kerala coast has mixed facies. The landscape as well as the vegetation cover has been substantially modified and the fossil contents and related palaeoenvironment provided ample evidence to demonstrate the landscape and vegetation dynamics since Late Pleistocene. Evidence of Myristica swamps until Late Pleistocene and its subsequent replacement by riparian forest towards Late Holocene in Konkan has been a significant impact of monsoon variations on the tropical rain forests. The prevalence of such freshwater swamps and a sensitive habitat indicated that Konkan had enjoyed an extended period of rainfall due to the combined effects of both SW and NE monsoons until the Late Pleistocene. The tropical rainforest cover along Kerala coast has shrunken considerably and pieces of evidence suggest that the entire terrain west of Sahyadri (Western Ghats) was under dense forest cover during the Holocene Climatic Optimum (9.0–6.0 k yrs BP) when the region had witnessed heavy precipitation much higher than that of the present. The forest land has been converted into major wetlands and present ecology is unsuitable to support evergreen forests and it can be concluded that coastal plains and associated landforms were covered by thick tropical evergreen forests which got destroyed by flooding towards Middle Holocene. Development of a chain of wetland system all along Kerala coast, loss of sheltered habitat and mangrove cover, and loss of sensitive freshwater Myristica swamps are some of the significant aspects brought in while addressing the monsoon variability in southwestern India.
Research Interests: Archaeology, Geology, Pleistocene, Quaternary, Monsoon, and 3 moreHolocene, Evergreen Forest, and Swamp
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Fossil evidence indicates that mangrove species have had their first appearance in the Late Cretaceous(70 65 Ma) and they have evolved around the Tethys seaway after the plate tectonics and the movement of the continents when Tethys Sea... more
Fossil evidence indicates that mangrove species have had their first appearance in the Late Cretaceous(70 65 Ma) and they have evolved around the Tethys seaway after the plate tectonics and the movement of the continents when Tethys Sea was fast closing as the massive continental fragments continued to shift and jostle across the globe. The oldest geological record of Acrostichum and Nypa palm offers good examples as these species prefer low-salinity requirements and have wide ecological tolerance. Such environmental and habitat preferences must have been the probable reason for their initial adaptation to mangrove habitat and a wider distribution. The open sea link must have also provided enough coastal areas for the establishment of mangrove ecosystem and subsequent spreading of the mangroves into newer areas by Early to Middle Eocene(ca 50–40 Ma). However, the mangroves started acquiring the present geographical positions towards OligoceneMiddle Miocene period. The fossil record and the modern analogues of Kandelia, Nypa and Pelliciera indicate that their biogeographical preferences have been shifted due to oceanic reorganization wherein the latter is now confined only to Atlantic East Pacific mangrove realm despite it was earlier widespread in the Tethys Sea. Although Rhizophora and Avicennia differ only at the species level and common occurrence of Acrostichum aureum, the present mangrove distribution shows the contrast in the biogeography of many genera due to geomorphic barriers and climatic changes. The Himalayan uplift and establishment of Asian summer monsoon system towards Late Neogene has also affected the coastal dynamics considerably which in turn modified the distribution of mangrove vegetation of the Indian subcontinent. The loss of sensitive habitats, disjunct distribution of a few species and local extinction of significant taxa has affected the overall biogeography of mangroves in South and SE Asia.
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The coastal lands of southern Kerala, SW India in the vicinity of Achankovil and Thenmala Shear Zones reveal a unique set of geomorphic features like beach ridges, runnels, chain of wetlands, lakes, estuaries, etc. The chain of wetlands... more
The coastal lands of southern Kerala, SW India in the vicinity of Achankovil and Thenmala Shear Zones reveal a unique set of geomorphic features like beach ridges, runnels, chain of wetlands, lakes, estuaries, etc. The chain of wetlands and water bodies that are seen in the eastern periphery of the coastal lands indicates the remnants of the upper drainage channels of the previously existed coastal plain rivers of Late Pleistocene age that are later broadened due to coastal erosion under the transgressive phase. The terrain evolutionary model developed from the results of the study shows that the Late Pleistocene transgressive events might have carved out a major portion of the land areas drained by the coastal plain rivers and as a result the coastal cliff has been retreated several kilometers landwards. The NNE-SSW trending beach ridges located close to the inland wetlands indicate the extent of shoreline shift towards eastwards during Late Pleistocene period. The present beach pa...
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Abstract The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched... more
Abstract The southern Kerala coast in SW India has experienced dramatic changes in climate and sea level during Holocene. These changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted Neogene deposits. Here we report the sedimentary processes, palaeoclimate and sea level records decoded from two borehole cores – Puthenthuruthu and Munrothuruthu borehole cores – retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in SW India, the Ashtamudi estuary, using sedimentology, palynology and stable isotopes as the major proxies. The heavy rainfall event at the latter half of Early Holocene (6117 ± 101 BP) is reflected well in the isotopic signatures of the Puthenthuruthu borehole core. The higher level of lighter isotopes of oxygen and carbon at 10–15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity. This, in turn, was responsible for the development of Bay Head Delta in the fluvial end of the estuary during Early–Middle Holocene period. Palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents. Further, the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies. This was followed by the deposition of littoral sands as Flood Tide Islands within the estuarine basin. The palynological investigations of sediments with radiocarbon age of 4350 ± 90 BP in the Munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules (algal pisolites) embedded in the sediments. The occurrence of pteridophytic spores and a few pollen of Cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view.
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Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been... more
Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coasta...
Research Interests: Geology, Climate Change, Soil, Carbon, Rivers, and 15 moreCarbon Cycle, Medicine, Multidisciplinary, India, Lakes, Atmosphere, Peat, Holocene, Wetland, Rain, PLoS one, Grassland, Time Factors, Seasons, and Geologic Sediments
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ABSTRACT
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The palaeobotanical and palynological data along with physical proxies obtained from Konkan, western India, have been addressed while ascertaining the vegetation response to monsoon variations since Late Pleistocene (∼53,000 yrs BP). The... more
The palaeobotanical and palynological data along with physical proxies obtained from Konkan, western India, have been addressed while ascertaining the vegetation response to monsoon variations since Late Pleistocene (∼53,000 yrs BP). The retrieved plant fossil assemblage, being a sensitive indicator of climate changes, has important implications in palaeoclimate study of the Late Pleistocene as it is the first of its kind in the entire 7500 km long coastline of India. The plant fossil assemblage of the lacustrine sediments forms potential evidence for the prevalence of wet evergreen forest in the Late Pleistocene (∼44,000 yrs BP). This scenario was attributed to prevalence of an extended period of rainfall of both the Southwest (SW) and Northeast (NE) monsoon in Konkan, although the Indian subcontinent was under the influence of active tectonic processes. Numerous fossil plant taxa are now confined to freshwater Myristica swamps of Southeast Asia in general and that of southwestern India in particular suggesting that these areas maintain a similar monsoon trend to that existing prior to 44,000 yrs BP. On the other hand, the NE monsoon did not reappear during the Early Holocene, when the SW monsoon became strong along the Konkan coast. Many of the plant species of the fossil assemblage have been displaced from Konkan as a response to weakening of the monsoons since the Late Pleistocene and towards the Last Glacial Maximum (LGM). The aridity/reduced rainfall since Late Pleistocene, including the LGM, and limited terrestrial accumulation in the Early Holocene suggests an ecological shift and subsequent replacement of evergreen forest cover and a possible break in sedimentation. Palynological evidence of the Late Holocene (<3000 yrs BP) fluvio-lacustrine sediments reveals that the evergreen forest could not reappear/rejuvenate in Konkan due to such climatic stress, in contrast to southwestern India and Sri Lanka where extended rainfall was still prevalent. The hypothesis of an extended period of monsoonal rains prior to 44,000 yrs BP in the present humid tropical parts of Konkan holds significance, as data on paleosols and vertebrate fossils from the semi-arid/arid parts of western India indicate relatively wet climate and wetland flood plains.
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Résumé/Abstract Fossil pneumatophores (breathing roots) of Avicennia are recovered and reported from the lignite beds exposed in Kolamb well-section near Malvan, Konkan area of western Maharashtra. The accrued palynoflora is dominated... more
Résumé/Abstract Fossil pneumatophores (breathing roots) of Avicennia are recovered and reported from the lignite beds exposed in Kolamb well-section near Malvan, Konkan area of western Maharashtra. The accrued palynoflora is dominated bymangroves (Avicennia, ...
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Abstract: The pneumatophore bearing lignites of Kolamb in Malvan (Maharashtra, west coast of India) have yielded a rich mycoflora of higher marine fungi. Out of a dozen hypomycetes known from the submerged parts of mangrove plants, more... more
Abstract: The pneumatophore bearing lignites of Kolamb in Malvan (Maharashtra, west coast of India) have yielded a rich mycoflora of higher marine fungi. Out of a dozen hypomycetes known from the submerged parts of mangrove plants, more than 8 species ...
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Cyanobacteria and thecamoebians are the two major constituents of Non Pollen Palynomorphs (NPP) found in the palynological preparations. The former is well represented in the sediment archives while the latter has restricted occurrence in... more
Cyanobacteria and thecamoebians are the two major constituents of Non Pollen Palynomorphs (NPP) found in the palynological preparations. The former is well represented in the sediment archives while the latter has restricted occurrence in the Holocene sequence apart from the conventional organic matter of pollen and spores. Well preserved morphotypes of Gleotrichia and Rivularia are the best forms of cyanobacteria found in almost all the studied profiles and their abundance towards Early to Middle Holocene coincides with the heavy rainfall and wet climate conditions during the Holocene climate optimum (HCO). Contrary to cyanobacterial diversity, thecamoebians are restricted to Late Holocene in most of the studied profiles and their occurrence is correlated with the prevailing dry and stressful environmental conditions. The major elements of thecamoebians identified belong to Arcellaceans, Centropyxids and Cucurbitella types. Abundance of Centropyxids and Arcellaceans in Varapuzha, West Kadungallur, Koonamavu, Pachcha and Ernakulam indicates low humidity and low precipitation. However, the relative abundance of Centropyxids in Mid Holocene at Ernakulam and Koonamavu reflects the early colonization of this type competing with the cyanobacteria, whereas, Arcellaceans are essentially confined to Late Holocene. Dominance of cyanobacteria and its proliferation is directly related to freshwater influx of the rainfall as well as the local hydrological regimes associated with the active aquifers controlled by the geomorphological features of the region in which the wetland system sustained. Considering the signatures of cyanobacteria and thecamoebians observed in the sediment archives their occurrence in the wetlands during the Holocene corresponds to the hydrodynamic regimes brought in by the freshwater influx as a result of monsoon variability. The well preserved cyanobacterial signatures in sediment archives of Kerala coast and their scarcity or even absence elsewhere along the west coast of India indicates that they are exclusively adapted to the wetland habitats where the hydrodynamic regimes are regularly controlled by fresh water influx in the form of extended rainy days of the monsoon system.
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... a profile has its implications in understanding the different aspects of the coastal and climaticchanges. ... deposits and organic matter mainly derived from Late Pleistocene to Late Holocene mangroves are ... occur in the intertidal... more
... a profile has its implications in understanding the different aspects of the coastal and climaticchanges. ... deposits and organic matter mainly derived from Late Pleistocene to Late Holocene mangroves are ... occur in the intertidal zone, they are directly related to the sea level at the ...
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Cyanobacteria tolerate extreme hydrological regimes, and their mucilaginous filaments account for binding and preservation of delicate structures. As the hydrological set-up is controlled by rainfall, they serve as biomarkers to... more
Cyanobacteria tolerate extreme hydrological regimes, and their mucilaginous filaments account for binding and preservation of delicate structures. As the hydrological set-up is controlled by rainfall, they serve as biomarkers to distinguish palaeoenvironmental ...