Hema Achyuthan

• Ph.D. in Geology
• Professor at Anna University, Chennai

Heavy metals disposed through anthropogenic activities find their way into the oceans and seas through the rivers or through direct fall out from factory effluents. These heavy metals resuspend back into the water column along with the sediments and are known to affect the marine animals. Marine animals like fish, prawn, crab and mussel were collec...

Climate variability, especially monsoonal rainfall, has significantly shaped habitable areas for human populations in South Asia in the past just as it does today. Instances of climate-driven social disruptions and population movements are evident worldwide, as evidenced for example in the Classic Maya and the Indus Valley Civilization (IVC). Howev...

Analysis of plant‐wax biomarkers from sedimentary sequences can enable past environmental and hydrological reconstruction and provide insights into past hominin adaptations. However, biomarker preservation in desert contexts has been considered unlikely given the sparse nature of the vegetation within the landscape. Here we evaluate the preservatio...

The giant clam shells are considered excellent marine bioarchives and have been used in studying current and past climate variabilities. Here, we present the microstructure and growth rate variability of a giant clam shell (T. maxima) collected from the Minicoy Island Lakshadweep, India. We employed FE-SEM, EDX, Raman spectroscopy and petrographic...

The Early to Middle Pleistocene Transition (EMPT) is characterised by major environmental changes and evolutionary innovations within the genus Homo but the scarcity of the African EMPT fossil and archaeological records obscures its palaeoecological context. Here, we present archaeological and faunal evidence from a newly excavated West-Turkana EMP...

The isotopic values of rainfall in the southern parts of India exhibit strong seasonality. Such a contrast in isotopic values arises mainly due to the seasonal reversal of the monsoon winds. During the summer monsoon season, moisture is primarily transported from the Arabian Sea, while during the winter, it is sourced mainly from the Bay of Bengal....

A giant clam shell (Tridacna maxima) collected from the lagoon of Minicoy Island in the southern Lakshadweep Archipelago, India, was used for a high-resolution stable isotope (δ¹⁸O, δ¹³C) analysis. The results reveal a cyclic pattern in δ¹⁸Oshell values, interpreted as combined signatures of seasonal temperature and δ¹⁸Osw fluctuations over the per...

The Holocene arid events and related societal responses are important scientific inquiries due to concerns about their reoccurrences in the future. In the Indian subcontinent, significant number of studies have focussed on understanding the Holocene aridification events at 8.2 and 4.2 ka. Despite these studies, high resolution palaeoclimatic record...

El Niño Southern Oscillation (ENSO) is one of the dominant climate modes influencing global precipitation and temperature. ENSO has a large impact on the monsoonal precipitations over the Indian subcontinent and thereby influences hydrological conditions. Due to dearth of long-term instrumental records of the hydrological parameters on sufficient s...

This study focuses on the immensely debated pre-instrumental centennial–millennial scaled forcing of the late Holocene hydroclimate variability in the Northwest Himalaya (NWH). The Wular Lake is ideally situated close to the modern intertropical convergence zone (ITCZ) in the NWH and fed by the Jhelum River draining the vast Kashmir Valley, which r...

A proper understanding of the paleoclimatic variability in the Southern Peninsular India demands a high-resolution paleoclimate reconstruction record. Hence, in this paper, we compiled all the available paleoclimate records from various locations across the Southern India that receives the southwest and the northeast monsoon. We delineated the sout...

The present study was carried out to determine the characteristics, distribution, and abundance of plastic debris in 25 sediment samples collected from the Poompuhar beach, southeast coast of India. The result reveals that the mean plastic debris abundance was 42 ± 27 particles/m2 dry weight (dw) (1 SD, n = 25) with higher concentrations in the riv...

Acheulean artefacts are widely known from archaeological complexes in India and commonly comprise handaxes, picks and cleavers. These provide information on human occupation and evolution across India, and have been the subject of much research on stone technology. In some of these sites, artefacts are associated with a Pleistocene volcanic ash lay...

South Asia hosts the world’s youngest Acheulean sites, with dated records typically restricted to sub-humid landscapes. The Thar Desert marks a major adaptive boundary between monsoonal Asia to the east and the Saharo-Arabian desert belt to the west, making it a key threshold to examine patterns of hominin ecological adaptation and its impacts on p...

Peninsular Indian Rivers are distinctive in terms of their hydrology and sediment transport characteristics. Many of these rivers have received international attention since last several decades and the evolutionary trajectories of Peninsular rivers are ranging from millions of years to millennia. Hence, this chapter highlights the major research c...

Peninsular India is a combination of various terranes and illustrates an amazing diversity of landscape features due to spatial differences in lithology, geological history, topography, and hydrology. It is generally considered as a tectonically stable region. The tropical rivers and its associated landforms in this region are the key features of t...

The Bay of Bengal covers a vast expanse of area, it being warmer, holds signatures of climate change. Its impact and the parameters have been studied in terms of rise in temperature, sea level change, increased rainfall, drought, heat waves, the intensity of tropical cyclones, ocean acidification and ocean productivity. In the last 45 years, sea su...

The region around the coastal Chennai area, India, is drained by three major rivers that rise from the remnants of the Eastern Ghats and receive dominantly the northeast rains. These rivers meander short distances, deposit sediments into the Bay of Bengal and preserve signatures of past phases of sedimentation and incision. In this study, detailed...

Atmospheric CO2 rise in post‐industrial era has resulted in decline in surface ocean pH, commonly known as “ocean acidification (OA),” which has become a threat to marine calcifiers. Instrumental records of ocean pH and its reconstruction utilizing boron isotope (δ¹¹B) composition of corals demonstrate a long‐term OA trend characterized by large sp...

The loess-paleosol proxy records from mid-latitude Asia have been instrumental in the reconstruction of regional paleoclimate evolution and its relationship with global climatic changes. The present study explores the discrete occurrence of a loess and paleosol sequence (LPS) in the Southern Zanskar Range (SZR), NW Himalaya. Stratigraphic variation...

Marine sediment deposited on the ocean floor and near coastal areas, the western coastal regions of India provide records of monsoonal shifts and productivity. To understand the paleoproductivity in the northern Indian Ocean, we analyzed carbon, hydrogen, nitrogen, sulfur, total organic carbon (TOC) and calcium carbonate (CaCO 3) in a deep-sea sedi...

Lake systems act as a significant source of freshwater supply for the local population living in the Kashmir Valley. The water level in Kashmir Himalayan lakes is predominantly controlled by melt water generated from seasonal snowmelt and high-altitude glaciers. Heavy metal contamination poses a serious threat of vulnerability to these freshwater e...

Terrestrial loess palaeosol sequences (LPS) are the most extensive paleoclimate archives documenting dynamic sedimentary processes in response to glacial (cold-dry) and interglacial (warm-wet) phases. In the present study, we provide chrono-stratigraphy and paleoenvironmental implications of a 600 cm LPS outcrop from the Kashmir Valley, Western Him...

Multi-proxy analysis of lake sediments provides high-resolution and reliable palaeoclimate records. The present study aims to investigate the palaeoenvironmental changes and eutrophic evolution of the Wular Lake, Kashmir Valley spanning the last ~ 500 years. Based on the multi-proxy analysis and supported by radiocarbon chronology, two prominent en...

Kashmir valley receives the rainfall owing to the dominant westerly winds and experiences less impact of the southwest monsoonal rains (SWM). In this valley, loess and loess paleosols occur as a thin veneer covering the landscape. The loess paleosols form an important proxy for paleoclimate reconstruction and understanding the late Quaternary paleo...

Freshwater lakes and sediments need to be monitored continuously for environmental assessment and geochemical explorations. Lake sediments are major sinks for organic matter and for all geochemical elements. In the present study, total organic matter (TOC), nitrogen (TN), and geochemical analysis of major oxides was carried out on Yercaud Lake surf...

Freshwater lakes and sediments need to be monitored continuously for environmental assessment and geochemical explorations. Lake sediments are major sinks for organic matter and for all geochemical elements. In the present study, total organic matter (TOC), nitrogen (TN), and geochemical analysis of major oxides was carried out on Yercaud Lake surf...

The Thar Desert, located in western South Asia, marks a major global biogeographic boundary and a major adaptive threshold for the eastward expansions of modern humans from Africa across Asia. Examining the framework of palaeoenvironmental change in this region, both in terms of the regional manifestation of global climate change and the physical g...

This study examines the catchment and source morphodynamics of the Palar River, Southern Peninsular India. Here, we applied a multidisciplinary approach (Remote sensing Techniques, Lineament Analysis, Geochemistry and Ground Penetration Radar) for a better understanding of its evolution during Holocene times. The linea-ments present in the Palar Ri...

Inevitable use of plastic materials in our day-to-day life has led to the entry of microplastic into aquatic environments, which are plastics less that than 5 mm. Microplastic is of great concern in recent years due to its impact on humans and aquatic organisms since they absorb organic contaminants and pathogens from the surrounding media due to h...

Palk Strait forms a part of the prograding micro delta, and the benthic foraminifera assemblages are influenced both by the fresh and marine water influxes. To delineate the various benthic foraminifera species 40 sea bottom water and sediment samples at a water depth range of 0.5 to 6.5 m were collected during May 2015 from the near-shore environm...

This study presents major element geochemistry, mineral magnetism and textural analysis of lake-bottom sediments collected from the Wular Lake located in the Kashmir Valley (northwest Himalaya). Connected to the Jhelum River, Wular Lake basin occupies ~ 75% watershed area of the valley, covering ~ 10,196 km2, and makes it the major depo-centre for...

The rise and fall of human cultures are strongly modulated by the strong environmental changes taking place during the Holocene. Here, we use the sedimentological and geochemical records of a core taken in the Arabian Sea, west of Kerala, to identify potential factors that may reflect on-land history of local civilizations, in particular the Harapp...

The rise and fall of human cultures are strongly modulated by the strong environmental changes taking place during the Holocene. Here, we use the sedimentological and geochemical records of a core taken in the Arabian Sea, west of Kerala, to identify potential factors that may reflect on-land history of local civilizations, in particular the Harapp...

This work is based on a marine sediment core retrieved from 250 m column of water depth near the landfall island Andaman isalands.

Surface sediments were collected from Wular Lake, located in Bandipora district of Kashmir Valley, NW Himalaya to investigate the environmental risk assessment using trace element concentrations. The surface sediments of the lake reveal higher concentration of Cl, Cr, Ni, Cu, Co, Pb, Zn and Th. In order to estimate the impact of metal pollution on...

We present a comprehensive record of Holocene (11,590–628 cal. yr BP) climate and hydrographic changes around the Wular Lake located in Kashmir Valley, India. Based on the multi-proxy investigations, we have identified three phases of wet climate conditions that prevailed from the commencement of the Holocene Epoch – 9000 cal. yr BP, 8100–6650 cal....

Integrating multiproxy results (geochemistry, mineral magnetism, grain size, and C/N ratio variability supported by ¹⁴ C AMS dating), obtained from a 1.4-m sediment core retrieved from high-altitude Anchar Lake, Kashmir Valley, NW Himalaya, we present a 6000-years record of paleoenvironmental and paleolimnological shifts. Phase 1 (6000–4700 cal. yr...

This present study provides an overview of the C/N ratio and organic matter (OM) contents in surface sediments of four lakes that occur in the Kashmir Valley. Valleys are depressed areas of land that influence climate and weather at both global and local scales. The oval-shaped intermontane valley is dotted with numerous freshwater lakes of various...

The Young Toba Tuff (YTT) ash containing biotite flakes was once spread over the Indian peninsula, and is now exposed at several sites in the Sagileru river basin in Andhra Pradesh. The ash beds form a distinct marker horizon in the landscape and have been recognized in a variety of sedimentary sequences associated with middle Paleolithic archaeolo...

This study reports the spatial distributions of diatom assemblages and potential relationships between diatom diversity and environmental variables (C/N ratio, CaCO3%, clay mineralogy) using multivariate analyses in surface sediments of the Akkulam-Veli Lake. Surface sediment samples were collected at 19 sites throughout the lake to analyse diatom...

Loess paleosols have been often studied to reconstruct late Quaternary past climate changes. In the present study, textural analysis, TOC, CaCO3 content, micromorphology and clay mineralogy of the three loess paleosol profiles from three sites (Choori, Alochibagh and Burzahama) from Kashmir valley are presented. Based on the dates of Burzahama sect...

The volcanic ash layers exposed in th Sagileru and Gundalakamma basin have been often correlated to the YTT ash of ~74 ka. However, the ash deposit associated with the Middle Palaeolithic assemblage in Sagileru river basin and at Ainavolu in Gundlakamma basin are reworked and redeposited. and hence these deposits cannot be used as stratigraphic mar...

Paleoclimate investigations and reconstruction using the lake sediment cores of Kashmir Valley have been rarely attempted. The basin is influenced by Indian Summer Monsoon, Westerlies and the local katabatic winds. In the present study, an 80 cm undisturbed sediment core was retrieved from the Manasbal Lake situated in North western Himalaya. Sedim...

12th International Earth Science Olympiad (IESO) at Mahidol University, Kanchanburi Campus, Thailand _

In the Thar Desert, India, calcretes occur in several geomorphic environments and have been classified based on their form, induration, chemistry and associations with parent material. These calcretes have been dated from late Neogene-Early Pleistocene (hardpan calcretes) to 5 ka (nodular calcretes). The calcretes consist of CaCO3 (40–75%) with SiO...

The Palar River basin is one of the major rivers in southern peninsular India. Morphometric analysis coupled with drainage network analysis was carried out for the Palar River basin to understand its drainage characteristics and the drainage network geometry with reference to tectonics. The morphometric analysis has been carried out using 'bearing,...

A multiproxy study involving sedimentology, palynology, radiocarbon dating, stable isotopes, and geochemistry was carried out on the Parsons Valley Lake deposit, Nilgiris, India, to determine palaeoclimatic fluctuations and their possible impact on vegetation since the late Pleistocene. The 72-cm-deep sediment core that was retrieved reveals five d...

Following the line of approach enumerated in the tsunami toolkit of Chague-Goff et al. (2011), ‘Expanding the proxy toolkit to help identify past events - Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, Earth Sci. Rev. 107 (1-2), 107–122’, measurements of elemental and mineral magnetic properties coupled with textural...

In the present study, the lake floor sediments of the Karlad lake, located at higher elevation in Wayanad region of north Kerala, were analyzed for textural characteristics, organic matter, calcium carbonate, major oxides and trace elements. This study was carried out to infer the chemical composition, provenance and intensity of chemical weatherin...

This present study describes the geochemistry of fluvial sediments of the Palar River (lower reaches), Southern Peninsular India, with an aim to evaluate their provenance, weathering and tectonic setting. The bulk sediment chemistry is influenced by grain size. The river sediments are enriched with SiO2 and depleted in Al2O3, K2O, CaO, Na2O, MgO, P...

Lake sedimentation represents a collective record of atmospheric and surface processes operating over the catchment areas. Magnetic minerals along with heavy metal assemblages can selectively represent the ongoing impact of dominant environmental processes over the catchment regions. Lake bottom sediments collected from Anchar Lake were investigate...

The Asian continent is endowed with one of the most dynamic meteorological phenomenon the 'Asian Monsoon', which year after year is anticipated with great anxiety as the Asian countries depend on the monsoonal waters for agriculture and other economic purposes. There has therefore been a great emphasis on understanding and predicting future trends...

A study involving grain size analysis was carried out from the Parsons valley lake deposit, Nilgiris, India to determine the depositional environments and paleoflood events since late Pleistocene period (∼29,838 cal yr BP). A 72 cm lacustrine core was collected from the lake and eight organic rich sediment samples were AMS radiocarbon dated. The st...

Earlier studies on the ferricrete of Sriperumbudur Formation were focused on their types of occurrences and mode of formation. However, in the present study, an attempt is made to understand the physico-chemical changes across seven saprolite-ferricrete profiles developed over sedimentary protolith after upliftment to decipher the paleoenvironmenta...

In this chapter, the depositional environment of the high level gravels is reinterpreted.

In this review, the shifts in organic matter (OM) accumulation and C:N ratios in lake sediments to reconstruct paleoclimate and paleo-environmental changes since the early Holocene period are presented. The C:N proxy data of total OM reflect wet climatic conditions during early Holocene (10 to 8.2 kyrs BP) due to enhanced southwest monsoon. This wa...

Assessing the organic matter (OM) content, its source and the nutrient loading in lake sediments helps limnologists to maintain the desired trophic status of lakes. The present study aims at investigating the spatial distribution and source of OM, CaCO3 content, total nitrogen (TN) and carbon to nitrogen (C/N ratio) in the lake sediments of three f...

Intermontane basin sedimentation occurred during Pliocene-Pleistocene in the Karewa Basin which formed after the continent-continent collision resulting in the formation of Himalayan orogenic belt around Eocene. These are elongated, narrow, thrust bounded basins which have formed during the late stages of orogeny. Situated at a height of 1700–1800...

Anchar Lake, a mono-basined freshwater lake in Kashmir Valley, has experienced major sediment deterioration due to changes in the local catchment and anthropogenic inputs during the recent past. The present study was conducted to evaluate the major, trace element concentrations and environment risk assessment in the surface sediments of Anchar Lake...

The present-day Palar River and its palaeochannels located in the southern peninsular India were investigated with a multidisciplinary approach. The main aim of the study was to reconstruct the palaeoenvironment history of the Palar River basin and to delineate the role of monsoon fluctuations that played a major role in the geomorphological evolut...

Despite a strong link between climate and society, our knowledge of the intensity and timing of past Indian summer monsoon (ISM) variations coupled with environmental shifts and short extreme events is limited. Here we review the Holocene summer monsoon fluctuations using retrieved lake and ocean sediment cores from southern India. The results sugg...

Morphotectonic analysis of landscape using remote sensing and GIS is an effective way of deducing the pattern and spatial variation of neotectonic activity in the drainage basin. In the present study, we have undertaken geomorphologic, morphometric indices analyses and Optically stimulated luminescence (OSL) dating to investigate the neotectonic ac...

Lakes and wetlands are dynamic geomorphic units of a landscape that hold geochemical signatures of sediment provenance and paleo-environmental shifts and are major sinks for organic matter accumulation. The source of organic matter is diverse in lake sediments and varies widely with the type and size of the lake and hence it is important to underst...

Lake sediments are major sink for carbon and trace elements. Lake water and sediments need to be monitored continuously for environmental and geochemi-cal explorations. In the present study, sediment characteristics , source and distribution of trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb and Zn) of Yercaud fresh water lake sediments , South India, sit...

In this paper, a study on the surface and deeper waters of the Yercaud Lake, Tamil Nadu, South India, was carried out to understand the geochemistry of the lake waters and also to determine its utility for agricultural purposes. Totally, 50 surface and deep water samples were collected from Yercaud Lake. Major ion and heavy metals were measured. Th...

This paper examines the difference in the geophysical and chemical characteristic of the volcanic ash and thermal fly ash to evaluate environmental pollution. Natural volcanic ash (VA) samples from Sagirelu, Cuddapah dist., Andhra Pradesh and thermal fly ash (FA) samples from the Thermal Power Station, Ennore, Chennai, were collected, analysed and...

In the present study, sediment samples were collected from different locations and diverse environments around Chennai city to evaluate the environmental conditions and the health of the water bodies. The grain size analysis of the sediment samples reveals that sand is the dominant fraction deposited in high-energy coastal environments followed by...

This paper presents a detailed sediment chemistry investigation of the Manasbal Lake, Srinagar, Jammu and Kashmir, India, which is one of the high altitude lakes in the Kashmir Valley. 22 Lake Floor sediment samples covering the entire lake were collected and analyzed for textural characteristics, CaCO3, Organic matter, TOC, TN contents, C/N ratio,...

Late Pleistocene palaeoenvironments in the Thar Desert (India), located at the eastern extent of the Saharo-Arabian desert belt, have fluctuated considerably as a result of the varying range and intensity of the Indian summer monsoon. Phases of widespread Pleistocene aridity are well documented in the Thar Desert, but research focusing on humid pro...

The present study was conducted on the Manasbal Lake (34°14′N: 74°40′E) to assess the geochemical characteristics of the lake bottom sediments, its environmental implications and its response in the local catchment area. This study tracks the spatial distribution of grain size, geochemical analysis, C/N ratio, calcium carbonate (CaCO3) and organic...

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along S-N transects covering the entire surface area of the lake. Textural studies indica...

Freshwater bodies such as lakes and ponds are sinks and major depocentres that preserve signatures of geochemical and biological variations derived principally from the surrounding rocks and soils. Here, we present the data collected on two lake sediment cores and lake floor sediment samples collected from Pookode and Vellayani, Kerala, South India...

The late Quaternary loess and loess-like deposits in Kashmir Valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region. We present a loess-like paleosol located along the margin of the Manasbal Lake, Ganderbal, which was studied in detail for understanding the pedological processes and reconstructing...

Diatoms constitute one of the most diverse and ecologically important groups of phytoplankton. Diatom variations within the lake are often used as an important tool for lake environmental monitoring. Furthermore, because the diatom silica cell walls do not decompose, diatoms in lake and marine sediments are often used to interpret conditions that p...

The East Coast of Tamil Nadu, Chennai to Cuddalore, is a narrow sandy strip with promontories of different bedrocks such as granite, granite gneiss, charnockite and sandstone.In this work, tafoni, spheroidal weathering, weathering rind and red soil formed over different rock types have been studied. Detailed mineralogy, micromorphology and geochemi...

Stable isotope analysis has been performed on a coral collected from the Minicoy Island to investigate its potential as a proxy for southwest monsoonal variability. The X-Ray picture of the porites coral collected revealed about 24 annual bands (1989-2013). The mean annual extension over this period is ca. 7.7mm/year. Stable carbon (δ 13 C) and oxy...