M. Kocherla - Academia.edu (original) (raw)

Papers by M. Kocherla

Materials Today: Proceedings

Abstract Vechur breed is the smallest cattle of the world and the milk has natural abundant A2 fo... more Abstract Vechur breed is the smallest cattle of the world and the milk has natural abundant A2 form of β-casein proteins and hence milk and clarified butter become premier products for the farmer, fetching high returns. This indirectly accounts for the routine uniform composition of the dung, which can be utilized as a resource for extracting value-added products, thus initiating a circular economy at the microscale. X-ray fluorescence (XRF) showed very high amounts of bio-metals like calcium, zinc and copper along with 21% silica enriched to 90% after burning. It was found that pure dung without any earthly contact is the best source, since earthly contact mixes up minerals like orthoclase which can cause phase change and structural alterations. Opaline silica supported Cu(II) was prepared by a simple sol–gel method. X-ray diffraction was generously employed to identify phase changes at each stage namely: acid treatment, combustion and metal incorporated precipitation, which showed the composite was a para-crystalline silica (opaline silica). Weight loss studies were carried out using thermogravimetry which collaborated well with XRF. Surface morphology showed irregular structure with particle dimensions of 700 nm. 87% of cell line survived in the MTT cytotoxic assay. The prepared composite showed anti-microbial activity against five pathogens and also exhibited excellent free radical scavenging activity against five radicals. This study escorts the concept of circular economy, synthesizing (easy scale up) a versatile composite with potential microcidal environmental applications from raw cow dung, a biowaste.

Palaeogeography, Palaeoclimatology, Palaeoecology

Marine Pollution Bulletin, 2021

This study investigates the influence of upwelling induced seasonal hypoxia in the sediment-water... more This study investigates the influence of upwelling induced seasonal hypoxia in the sediment-water interface on the distribution, bioavailability and geochemical partitioning of selected trace metals in surficial sediments along the southwest coast of India based on two successive cruises. The first cruise was during the southwest monsoon (SWM) season when coastal waters exhibited intermittent bottom hypoxia due to upwelling. The second cruise during the northeast monsoon (NEM) season was characterised by a uniformly warm and well-oxygenated water column in the study region. The results showed that grain size, organic carbon and Fe are the major factors influencing the distribution of trace metals in the surface sediments. Based on the geochemical indices (contamination factor, enrichment factor and geo-accumulation factor), the study region appears to be moderately contaminated by Ni, Cr, and Pb. Based on the ecological risk assessment criteria, the enrichment of Pb, Cr and Ni may cause adverse effects on the benthic organisms. The fractionation studies demonstrated that the major pathway of metal deposition in the sediment is lithogenic. The data also showed that labile and organic fractions are the second dominant forms, while other fractions (exchangeable and carbonate) are insignificant. The consistency in the reactive Fe concentrations during SWM and NEM could be due to the absence of Fe dissolution in sediments under mild reducing condition (intermittent hypoxia). In addition to the above, an enrichment of organic matter also leads to increased deposition of trace metals in sediments. Conversely, the secondary phase enrichment factor and risk assessment code calculated based on the metal fractionation data indicated low risk and contamination along the southwest coast of India except for Zn that showed moderate contamination in some transects. The study provides the need for regular geochemical assessment to control metal pollution in the coastal environment, which is a major resource of the fishery.

Marine and Petroleum Geology, 2019

The vast area, varying climate regimes, diverse source terrain lithology of the mainland India ge... more The vast area, varying climate regimes, diverse source terrain lithology of the mainland India generate complex weathering and erosional patterns and leads to diverse sediment distribution and dispersal on the surrounding continental margins of India. Thus, to delineate the sources, distribution and sediment dispersal pathways around India, 254 sediment cores from the eastern and western continental margins of India were investigated for physical properties using non-destructive, whole core logging technique combined with grain-size analyses. The distribution of magnetic susceptibility, gamma ray density and grainsize traces the sources in the Indian landmass which contribute sediments to the margins and demarcates their extent of influence. The results from the magnetic susceptibility distribution indicate that the dominant influx of modern high susceptibility sediment into the margins of India originates from the weathering of Deccan Basalts and its subsequent transportation by Narmada and Tapti Rivers in the west coast and Krishna and Godavari Rivers in the east coast. Though the Himalayan sources are the second largest supplier of magnetic minerals to the shelf, their contribution, when compared to the Deccan sediments is not significant. The lack of present-day sedimentation in the outer shelf regions of margins of India is evident from the gamma ray density distribution and is confirmed by the discrete sample grain-size

CURRENT SCIENCE, VOL. 102, NO. 8, 25 APRIL 2012 1205 *e-mail: kocherla@nio.org 30. Dollar, S. J. ... more CURRENT SCIENCE, VOL. 102, NO. 8, 25 APRIL 2012 1205 *e-mail: kocherla@nio.org 30. Dollar, S. J. and Tribble, G. W., Recurrent storm disturbance and recovery: a long-term study of coral communities in Hawaii. Coral Reefs, 1993, 12, 223–233. 31. Arthur, R., Done, T. J., Marsh, H. and Harriott, V., Local processes strongly influence post-bleaching benthic recovery in the Lakshadweep Islands. Coral Reefs, 2006, 25, 427–440. 32. Pearson, R. G., Recovery and recolonization of coral reefs. Mar. Ecol. Prog. Ser., 1981, 4, 122–138. 33. Briggs, J. C., Tropical diversity and conservation. Conserv. Biol., 1996, 10, 713–718. 34. Briggs, J. C., The marine East Indies: centre of origin? Global Ecol. Biogeogr. Lett., 1992, 2, 149–156. 35. Krishnan, P. et al., Elevated sea surface temperature during May 2010 induces mass bleaching of corals in the Andaman. Curr. Sci., 2011, 10, 111–117.

Acta Geologica Sinica - English Edition, 2013

Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcite... more Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydrate bearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India in the water depths of 1691 m. X-Ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals (i.e. pyrite). Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates possibly indicating that they are formed authigenically in situ in the gas hydrate influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane (AOM). Therefore the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.

Marine and Petroleum Geology, 2021

We conducted rock magnetic, mineralogical, sedimentological and geochemical analyses on a sedimen... more We conducted rock magnetic, mineralogical, sedimentological and geochemical analyses on a sediment core (MD161/Stn-11) retrieved from a complex marine sedimentary system of Krishna-Godavari (K-G) basin to delineate the control of mass transport deposits (MTD's) and methane-induced diagenesis on the sediment magnetic record. Four sediment magnetic zones (Z-I, Z-II, Z-III, Z-IV) were defined based on rock magnetic signatures. The sediment magnetic signal is mainly carried by complex magnetic mineral assemblages of detrital (titanomagnetite, titanohematite) and diagenetic (pyrite) minerals. Changes in rock magnetic properties are mainly controlled by fluctuations in supply of detrital magnetic particles, onset of MTD's and differential rate of methane-influenced magnetic minerals diagenesis in the studied sediment core. Downcore reduction in magnetic susceptibility followed by subsequent precipitation of iron sulfides within sediment magnetic zone (Z-I) representing the period of normal sedimentation can be attributed to diagenetic dissolution caused by anaerobic oxidation of methane coupled to sulfate reduction. Decline in magnetic susceptibility and increase in sediment grain size within MTD-rich sediment intervals (Z-II, Z-III, Z-IV) is linked to loss of finer magnetic grains due to diagenetic dissolution and dilution caused by increase in concentration of diamagnetic minerals. Lower values of magnetic grain size diagnostic (ARM/IRM) parameter indicate loss of finer and selective retention of coarser magnetic particles due to diagenetic dissolution beyond 12 mbsf. Elevated content of total organic carbon (TOC) content in Z-III and Z-IV can be attributed to the efficient preservation of labile organic matter due to rapid sediment deposition. A conceptual model is presented to explain the control of mass transport deposit and magnetic mineral diagenesis on the sediment magnetic record. Highlights ► Delineated the control of geological and methane-induced diagenetic processes on the sediment magnetic record from the Bay of Bengal. ► Established the linkage between sediment magnetism, mass transport deposits, preservation of organic carbon, sediment gran size, and magnetic mineral diagenesis Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. in a rapidly depositing marine sedimentary system. ► A conceptual model summarizing the control of steady and non-steady sedimentation on the sediment magnetic record is developed.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2018

The paleomonsoonal variations and their impact on the weathering patterns in the source regions o... more The paleomonsoonal variations and their impact on the weathering patterns in the source regions of sediments of the Andaman Sea were investigated from a 21 kyr sedimentary record using environmental magnetic, clay mineralogical and geochemical techniques. The sediment provenance of the study area determined from the geochemical discrimination diagrams and available Nd records indicates that the Western Andaman Sea receives a considerable contribution from the Indo-Burman Ranges (IBR) and local sources compared to the central and eastern Andaman Sea. The results illustrate a strong Indian Summer Monsoon (ISM) during the late glacial (16-13 kyr), early (10.5-8.5 kyr) and middle Holocene (5-3.5 kyr) and a weak ISM during the Younger Dryas (12.9-11.7 kyr) and late Holocene (3.5-0 kyr) periods. The mineral magnetic grain size parameters (ARM/SIRM, SIRM/LF, ARM/ LF) show finer grain sizes during the strong ISM periods indicating the increased chemical weathering while cold and dry periods are marked by an increase in magnetic grain size indicating the shift from chemical to physical weathering in the source regions. The results from our study are in agreement with the global and local records of paleoclimate and weathering and exhibit a close correlation with the solar insolation data suggesting the major role played by the solar forcing on the ISM variability.

Marine Chemistry, 2018

Results of a study on phosphorus (P) cycling in the Eastern Arabian Sea provides convincing evide... more Results of a study on phosphorus (P) cycling in the Eastern Arabian Sea provides convincing evidence of present-day phosphogenesis in the study area. This finding contrasts with previous reports of the occurrence of only old phosphorites along the Indian margin. Extensive benthic P regeneration is observed in the sediments that are deposited on topographic highs in the western Indian continental margin, which is impinged by a perennial oxygen minimum zone (OMZ). The phosphate flux from the sediments ranged between 1.1 and 22 mmol m-2 yr-1. Among the P reservoirs, biogenic P (P bio) is the major pool of P within the upper 30 cm of sediment. P released from organic matter decomposition and fish debris dissolution mainly controls benthic P regeneration while the role of redox cycling of iron is weak. The change in authigenic P (P auth) with depth in the sediment and concomitant decrease in porewater dissolved inorganic phosphate (DIP), solid phase P bio and organic P (P org) content collectively indicate the transformation of P from labile phases to an authigenic phase. Molar C org /P org and C org /P reactive ratios also support the notion of ongoing phosphogenesis in the area. The content of carbonate fluroapatite (CFA) is elevated especially in one of the three study sites as a result of in-situ precipitation and a contribution from eolian and water column authigenesis. The estimated burial efficiency of P at the sediment-water interface at two locations is only about 2%, which is much less than in the western Arabian Sea also indicating extensive P regeneration.

Geochemistry, Geophysics, Geosystems, 2017

In this study, we integrate environmental magnetic, sedimentological, and geochemical records of ... more In this study, we integrate environmental magnetic, sedimentological, and geochemical records of sediment core of Hole NGHP‐01‐10D overlying methane hydrate deposits to decipher the controls on the evolution of fracture‐filled gas‐hydrate system in the Krishna‐Godavari (K‐G) basin. Four distinct sedimentary units have been identified, based on the sediment magnetic signatures. An anomalous zone of enhanced magnetic susceptibility (Unit III: 51.9–160.4 mbsf) coinciding with the gas hydrate bearing intervals is due to the presence of magnetite‐rich detrital minerals brought‐in by the river systems as a result of higher sedimentation events in K‐G basin and has no influence over hydrate formation. A strong to moderate correlation between magnetite concentration and chromium reducible sulfur (CRS) content indicates significant influence of sulfidization on the magnetic record and could be further exploited as a proxy to decipher paleo‐H2S seepage events. Analysis of high‐resolution seis...

Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off... more Many coastal regions of India were affected by the tsunami caused by a magnitude 9 earthquake off Sumatra on 26th December 2004. This report presents the observations of post-tsunami reconnaissance survey conducted by the National Institute of Oceanography, Dona Paula, Goa, India, along the most affected coastal stretch of Tamil Nadu, Pondicherry and southern Andhra Pradesh. The surveyed coastal tract is about 450 km long and lies between Vedaranyam (Tamil Nadu) in the south and Krishnapatnam (Andhra Pradesh) in the north. The objective of the study was to observe and document the readily available and perishable data, which contains information about the nature and impact of the phenomenon. This information is expected to be helpful for planning, preparedness and identifying further research needs. To fulfill the above objective, the survey covered various aspects of tsunami such as run-up, inundation, tsunami transported sediments, tsunamigenic structural failures and other damage...

Marine and Petroleum Geology, 2014

The mineralogical and stable isotopic composition of authigenic carbonates from the KrishnaeGodav... more The mineralogical and stable isotopic composition of authigenic carbonates from the KrishnaeGodavari (KG) and Mahanadi Basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of India in the Bay of Bengal. Authigenic carbonate cements, (micro) nodules, bioturbation casts and tubes from 12 core locations drilled during the Indian National Gas Hydrate Program (NGHP) Expedition 01 were investigated for this study. Three main processes responsible for authigenic carbonate precipitation are identified: organoclastic sulfate reduction, anaerobic oxidation of methane and methanogenesis. Evidence of vigorous methane seepage is indicated in carbonates recovered at Sites 7, 10, 12 (KG Basin) and 19 (Mahanadi Basin). These methane-derived carbonates display typical paragenetic carbonate mineralogies (aragonite, high-Mg calcite with >15 Mol% MgCO 3 , Ca-rich dolomite). Two separate horizons of methane derived-carbonates are correlated between 4 drill holes (up to~16 km apart). The upper horizon has been dated with 14 C (40,100e51,600 a BP 1950) and clearly indicates that methane seepage has been much more vigorous in the past, possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin.

Marine and Petroleum Geology, 2015

The Krishna-Godavari and Mahanadi rivers drain the east coast of India and deposit the sediment l... more The Krishna-Godavari and Mahanadi rivers drain the east coast of India and deposit the sediment load into the Krishna-Godavari and Mahanadi offshore basins along the western margin of the Bay of Bengal. Here we report the bulk major, trace and rare earth element (REE) compositions and clay mineralogy of the fine grained sediments from the cores collected on board JOIDES Resolution and Marion Dufresne as part of India's gas hydrate program. The geochemical composition and clay mineralogy of sediments have been used to constrain the provenance. The results show that the Mahanadi sediments are primarily derived from the felsic rocks belonging to the late Archean-early Proterozoic Peninsular Gneissic Complexes, whereas the Krishna-Godavari sediments are derived from the mixing of late Archean-early Proterozoic Peninsular Gneissic Complexes and late Cretaceous Deccan basalt sources. This paper presents the first comparative analysis of provenance of the Krishna-Godavari (K-G) and Mahanadi offshore basin sediments. The sediment geochemistry enables distinction of specific contributing sources, which could potentially be related to modern climatic and geomorphological conditions. The present study could also provide the opportunity for high resolution paleoclimatic analysis using clay mineralogical contents and weathering indices (Haughton et al., 1991).

GEOCHEMICAL JOURNAL, 2007

Several cores from Krishna-Godavari (Western Bay of Bengal) and Goa (Eastern Arabian Sea) basins ... more Several cores from Krishna-Godavari (Western Bay of Bengal) and Goa (Eastern Arabian Sea) basins have been studied for pore water sulfate concentrations in order to understand and contrast diagenetic processes. K-G sediments differ markedly from Goa sediments in pore water sulfate gradients and depth-integrated sulfate reduction rates. Significantly higher sulfate reduction rates in K-G sediments (3.6 to15.8 nmol cm-2 day-1), compared to that in Goa sediments (0.011 to 0.65 nmol cm-2 day-1), can be attributed to higher sedimentation rates. Lower exposure time to oxygen for the organic matter in K-G sediments has preserved reactive organic compounds required for sulfate reducers and possibly methanogens. Authigenic carbonates with depleted carbon isotopic composition (δ 13 C =-48 to-50) at the base of the sulfate reduction zone in a core from K-G suggests anaerobic methane oxidation (AMO) process. The possibility, that the underlying methane gas hydrate zone is acting as a methane source for sulfate reduction can not be negated specially in light of the existing geophysical studies. Both methane and the fermentation products of organic matter degradation served as a substrate for sulfate reduction. However, a clear understanding of there relative importance needs further investigation.

Geochemistry, Geophysics, Geosystems, 2009

We report evidence of paleo–cold seep associated activities, preserved in methane‐derived carbona... more We report evidence of paleo–cold seep associated activities, preserved in methane‐derived carbonates in association with chemosynthetic clams (Calyptogena sp.) from a sediment core in the Krishna‐Godavari basin, Bay of Bengal. Visual observations and calculations based on high‐resolution wet bulk density profile of a core collected on board R/V Marion Dufresne (May 2007) show zones of sharp increase in carbonate content (10–55 vol %) within 16–20 meters below seafloor (mbsf). The presence of Calyptogena clam shells, chimneys, shell breccias with high Mg calcite cement, and pyrite within this zone suggest seepage of methane and sulfide‐bearing fluid to the seafloor in the past. Highly depleted carbon isotopic values (δ13C ranges from −41 to −52‰ VPDB) from these carbonates indicate carbon derived via anaerobic oxidation of methane. Extrapolated mean calendar age (∼58.7 ka B.P.) of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the U‐Th based depositional a...

Chemical Geology, 2012

The inner shelf off west coast of India, is covered with late Holocene to recent organic rich, si... more The inner shelf off west coast of India, is covered with late Holocene to recent organic rich, silty-clay dominant sediments. High TOC content and sedimentation rates result in high sulfate reduction rates in this region (Mazumdar et al., 2009). In the present study, we have investigated the nature of pyrite and C-Fe-S geochemistry in a sediment core (covering the last 378 y) at a water depth of 17 m off Goa, west coast, India, to understand the diagenetic and palaeoclimatic/oceanographic processes. The chromium reducible sulfur (CRS) and highly reactive iron (Fe HR) profiles show significant fluctuations and a negative correlation with δ 34 S CRS , which is attributed to relative availability of highly reactive and less reactive iron bearing minerals close to the sediment water interface. Low δ 34 S CRS corresponding to high CRS content characterizes early diagenetic pyritization near the sediment-water interface, whereas high δ 34 S CRS and low CRS content indicate late diagenetic pyritization of less reactive iron during burial. High OBS/CRS ratios suggest the important role played by the labile organic compound in binding sulfur in the sediment. Partitioning of stable sulfur isotopes into organic and iron bound phases is apparently linked to Fe HR and labile organic matter availability. We have proposed Fe HR profile and Fe HR /Fe T ratios as a potential tool to understand runoff /monsoonal fluctuations in a shallow marine depositional setting. To develop this tool into a potential paleoclimatic/ oceanographic proxy and to link it to other proxies within a chronological framework, needs high resolution sampling and age dating.