Nagender Nath Bejugam - Academia.edu (original) (raw)

Papers by Nagender Nath Bejugam

Environmental Monitoring and Assessment, 2011

An area of 0.6 km 2 in the manganese nodule field of the Central Indian Basin was physically dist... more An area of 0.6 km 2 in the manganese nodule field of the Central Indian Basin was physically disturbed and sediments discharged in the near bottom waters to simulate seabed mining and study its impact on benthic ecosystem. An estimated 2-3 tonnes of sedimentary organic carbon (C org) was resuspended into the water column during a 9-day experiment. The majority of the sediment cores from within the disturbed area and areas towards the south showed a ~30% increase in C org content as well as an increase in carbon burial rates after disturbance, though with a reduction in carbon/phosphorus ratios. High specific surface area (SSA~25 m 2 g-1) and low C org /SSA ratios (mostly <0.5) are typical of deep-sea sediments. The increased C org values were probably due to the organic matter from dead biota and the migration and redeposition of fine-grained, organic-rich particles. Spatial distribution patterns of C org contents of cores taken before and after disturbance were used to infer the direction of plume migration and re-sedimentation. A positive relationship was observed between total and labile C org and macrobenthos density and total bacterial numbers prior to disturbance, whereas a negative relationship was seen after disturbance owing to drastic reduction in the density of macrofauna and bacteria. Overall decrease in labile organic matter, benthic biota and redistribution of organic matter suggest that the commercial mining of manganese nodules may have a significant immediate negative effect on the benthic ecosystem inducing changes in benthic community structure.

Marine Georesources & Geotechnology, 2005

Abstract: It is anticipated that in the case of mining of marine minerals, sea floor sediments wi... more Abstract: It is anticipated that in the case of mining of marine minerals, sea floor sediments will be brought up along with the mineral ores and discharged on the surface. These nutrient rich sediments would create a set of different physicochemical conditions at the point of ...

Data in Brief

This data article describes data of magnetic stratigraphy and anisotropy of isothermal remanent m... more This data article describes data of magnetic stratigraphy and anisotropy of isothermal remanent magnetization (AIRM) from “Magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform) reveal changes in the monsoon system” [1]. Acquisition of isothermal magnetization on pilot samples and anisotropy of isothermal remanent magnetization are reported as raw data; magnetostratigraphic data are reported as characteristic magnetization (ChRM).

Palaeogeography, Palaeoclimatology, Palaeoecology

We report a study of the magnetic stratigraphy and the anisotropy of isothermal remanent magnetiz... more We report a study of the magnetic stratigraphy and the anisotropy of isothermal remanent magnetization of Pliocene sediments from International Ocean Discovery Program (IODP) Site U1467 drilled in the Maldives platform (Indian Ocean) during Exp. 359. Magnetic stratigraphy gives a precise record of geomagnetic reversals of the early Pliocene from approximately 5.3 Ma to 3.1 Ma providing a detailed age model in an interval where the biostratigraphic record is scarce. We use the anisotropy of isothermal remanent magnetization (AIRM) to investigate the statistical orientation of fine magnetic particles and provide data on the strength and direction of bottom currents during the early Pliocene. The strength of bottom currents recorded by the AIRM, shows a prominent increase at the top of Chron C3n.1n (about 4.2 Ma), and the current direction (NE - SW) is consistent with that of modern instrumental measurements. Since bottom currents in the Maldives are driven by the monsoon, we speculate that the 4.2 Ma increase of bottom currents could mark the onset of the present-day setting, probably related to the coeval uplift phase of the Himalayan plateau.

Marine Geology

Thirty-two representative deep-sea sediment samples have been studied from three manganese nodule... more Thirty-two representative deep-sea sediment samples have been studied from three manganese nodule-bearing environments in the Central Indian Basin: diatomaceous-radiolarian ooze-clay, pelagic brown clay and calcareous ooze. They have been analysed for major ...

Journal of Earth System Science

This paper describes an estimation of endmember compositions followed by the assessment of those ... more This paper describes an estimation of endmember compositions followed by the assessment of those results by log-ratio variance analysis. As an appraisal, it deals only with the first objective of an endmember analysis namely, to identify endmembers if they exist by estimating their compositions. Following the creation of the endmember estimates, the computation of an array of log-ratio variances was a key innovation in this type of study. Log-ratio variances revealed intrinsic linear associations between the dominant elements on each of the estimated endmember compositions, largely confirming the endmember analysis. The dataset under study contained the concentrations of 16 elements in 93 samples of deep-sea manganese nodules from the Central Indian Ocean Basin. Many previous analyses of these nodules were undertaken to assess the economic potential of the deposits. This study by contrast, quantified the interelement associations that account for the nodule compositions. Four endmembers were identified. The elements loaded on each were: (1) Mn, Zn, Ni, Cu, Mn-rich, (2) Fe, Ti, P, Co, Fe-rich, (3) Si, Al, Na, K, clay minerals, (3) Mg, ultramafic material, possibly including Mn, Cr, V, Ca, Na. These latter elements were also detected by their log-ratio variances to be associated with Mg on the 4th endmember.

$Research paper thumbnail of Kinetic and equilibrium based fractionation study of Pb in continental shelf sediment of India$

Marine pollution bulletin, Jan 5, 2017

Two independent analytical methods (kinetic and sequential extraction protocols) were used to und... more Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0±0.6 to 30.4±0.1mg·kg(-1) and 15.9±0.3 to 36.7±0.4mg·kg(-1) in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~24% of total Pb) than the western shelf sediments (~14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in...

Palaeogeography, Palaeoclimatology, Palaeoecology, 2016

Abstract Here, we present planktonic foraminiferal, benthic foraminiferal and other proxy profile... more Abstract Here, we present planktonic foraminiferal, benthic foraminiferal and other proxy profiles from well-dated sediment cores in the Andaman Sea showing changes in climate and oceanography at Dansgaard-Oeschger (D/O) and Heinrich scales. The large temporal variations in the abundances of total benthic foraminifera, Globigerina rubescens and Neogloboquadrina dutertrei suggest substantial changes in the surface to bottom hydrography of the Andaman Sea. G. rubescens abundance minima during the last glacial cycle correspond to warm interstadials (D/O events 1 to 14) while maxima correspond to Heinrich events (H1 to H4), the last glacial maximum (LGM) and the Younger Dryas. D/O events are marked by very low G. rubescens and high N. dutertrei abundances which indicate freshened surface water related to increased direct precipitation (over evaporation) and strengthened Irrawaddy outflow. Lower abundance of N. dutertrei (and higher abundance of G. rubescens) during North Atlantic Heinrich events, the deglacial, the YD and the mid- to late-Holocene reflect reduced influx of fresh water as a result of weakened summer monsoon freshwater input. The timing of these Andaman Sea monsoonal changes indicate a strong teleconnection to North Atlantic climate change.

$Research paper thumbnail of Effects of bottom water dissolved oxygen variability on copper and lead fractionation in the sediments across the oxygen minimum zone, western continental margin of India$

The Science of the total environment, Jan 3, 2016

This study describes the effect of varying bottom-water oxygen concentration on geochemical fract... more This study describes the effect of varying bottom-water oxygen concentration on geochemical fractionation (operational speciation) of Cu and Pb in the underneath sediments across the oxygen minimum zone (Arabian Sea) in the west coast of India. Both, Cu and Pb were redistributed among the different binding phases of the sediments with changing dissolved oxygen level (from oxic to hypoxic and close to suboxic) in the bottom water. The average lability of Cu-sediment complexes gradually decreased (i.e., stability increased) with the decreasing dissolved oxygen concentrations of the bottom water. Decreasing bottom-water oxygen concentration increased Cu association with sedimentary organic matter. However, Pb association with Fe/Mn-oxyhydroxide phases in the sediments gradually decreased with the decreasing dissolved oxygen concentration of the overlying bottom water (due to dissolution of Fe/Mn oxyhydroxide phase). The lability of Pb-sediment complexes increased with the decreasing bo...

Marine pollution bulletin, Jan 15, 2016

Sediment texture controls the spatial distribution of sedimentary organic matter (SOM) in the Vem... more Sediment texture controls the spatial distribution of sedimentary organic matter (SOM) in the Vembanad Lake. Influences of marine derived organic matter (OM) on SOM decreased inner-wards in the northern part of the lake. However, SOM from the southern part of the lake was dominated by terrestrial OM. Marine-derived OM showed the highest affinity for the clay-sized fraction (<2μm) of the sediment in the northern part of the lake. However, aged and humified soil-derived OM was predominant in the clay-sized fractions from the southern part. Alteration of sediment texture led to a change in the distribution pattern of SOM in the lake after bund construction. Human intervention and changes in land-use pattern were also found to influence the SOM content in the southern part of the lake.

$Research paper thumbnail of Determination of rare earth, major and trace elements in authigenic fraction of Andaman Sea (Northeastern Indian Ocean) sediments by Inductively Coupled Plasma-Mass Spectrometry$

Microchemical Journal, 2010

Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment cor... more Downcore variation of rare-earth elements (REEs) in the authigenic Fe-Mn oxides of a sediment core (covering a record of last ~40 kyr) from the Andaman Sea, a part of Indian Ocean show distinctive positive Ce and Eu anomalies. These positive Ce anomalies (Ce*=1.1~1.8) are ascribed to be due to oxidation of deep sea sediments. The large positive Eu anomalies (i.e., Eu* >1.8 to 3.2) occur within a time span near the glacial/interglacial transition (~7,000-14,000 yr BP) which could be due to the past hydrothermal activity or to the effects arising from sea level changes. During glacial times, the Andaman Sea was almost completely isolated due to low sea level, leading to a reduction in sediment supply from the Ayeyarwady river. The variations of metal abundances (i.e., Ca, Al, Mn, and Fe) in the authigenic fraction provided independent information to evaluate the water column physicochemical changes during the glacial/interglacial transition period. The studied sediment core record changes in riverine inputs and reflect depositional changes related to sea level fluctuations and climatic events over the past 40 kyr in the Andaman Sea.

... These concentrations are less than those of 33-52 pp~n ill ECMI nod-ules (Tables 1 and 2). Th... more ... These concentrations are less than those of 33-52 pp~n ill ECMI nod-ules (Tables 1 and 2). The REE concentrations are ... acquire their REE e~lrichments ~ostdel~osi-tionally (Kolodny, 1983; McArthur and LV~llsh, 1984; Elderfield and Paggett, 1986), so~neti~nes reaching eight ...

Pteropods, popularly known as “sea butterflies” are marine gastropods made up of highly susceptib... more Pteropods, popularly known as “sea butterflies” are marine gastropods made up of highly susceptible form of CaCO3 known as aragonite. Occurrence and abundance of pteropod is a subject of renewed interest owing to the fact that they are the most vulnerable among the major plankton producers of CaCO3 in the current levels of atmospheric carbon dioxide (CO2) resulting from ocean acidification. Before the industrial period, the atmospheric CO2 concentrations is nearly 280 ppm but the impact of industrial and land use activities of human beings, the current atmospheric concentrations are now approaching 380 ppm. As a result of rising atmospheric CO2 concentrations in the last 100 years have led to greater uptake of CO2 by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate which greatly affects the carbonate shelled organism, especially the aragonitic shells (pteropods). The present study has evaluated aragonitic pteropo...

Considering the potential of elemental data in marine sediments as diagnostic tools of various ge... more Considering the potential of elemental data in marine sediments as diagnostic tools of various geological and oceanographic processes, sediment geochemical data from the Indian Ocean region has been reviewed in this article. Emphasis is laid on the literature, where, the processes have been deciphered from geochemical studies and obviously avoiding the literature with mere description of spatial variation. Sediment geochemistry is primarily used in deciphering provenance. Therefore, a section is devoted to infer various sources of lithogenic sediments to the Indian Ocean region. Considering the size and very high discharge rates of rivers debouching northern Indian Ocean, studies involving clay mineralogical, major, trace elemental data, porewater chemistry, isotope geochemistry, rare-earth element fractionation and patterns to delineate the southern limits of influence of Ganges-Brahmaputra river system are described. Other sources of sediments to the northern and central Indian Oc...

Distribution of 10Be in systematically collected (degree + degree interval at 10 to 16 degrees S;... more Distribution of 10Be in systematically collected (degree + degree interval at 10 to 16 degrees S; 73.5 to 76.5 degrees E) surficial siliceous ooze, siliceous clay and pelagic clay sediments (top 2 cm) from the abyssal Central Indian Basin and the Andaman Sea is used to evaluate sources and to decipher the transport pathways of sediment particles, demarcate sediment depocenters and erosional areas. While sup(10)Be concentrations display a wide variation (0.12-5.56 x 10 sup(9) atoms g sup(-1)) with an average of 3.58 x 10 sup(9) atoms g sup(-1) in the Central Indian Basin, the values in the Andaman Sea are uniform with an average of 1.49 x 10 sup(9) atoms g sup(-1). The sup(10)Be/sup(9)Be values in the Central Indian Basin sediments range between 0.06 and 2.99 x 10 sup(-8) atoms atoms sup(-1) and average to approx. 1.56 x 10 sup(-8) atoms atoms sup(-1). Correlation of sup(10)Be data with some selected major (Al, Mn, Ti) and trace (Rb and Ba) elements suggest that large part of the iso...

Geo-Marine Letters, 2015

Mineralogical and elemental analyses of 20 ferromanganese (FeMn) coated pumice samples from the C... more Mineralogical and elemental analyses of 20 ferromanganese (FeMn) coated pumice samples from the Central Indian Ocean Basin (CIOB) indicate that todorokite is the major mineral phase, whereas vernadite occurs only rarely. Based on major, trace and rare earth elements (REEs) as well as Ce anomalies, the sources of the FeMn oxides were identified to be either hydrogenous, hydrothermalplume fallout, diagenetic or a combination of these. Plots of Fe/Mn vs. Ce or Co reveal a distinct demarcation of the diagenetic, hydrogenous and plume fallout samples. Five samples are interpreted to be of hydrothermal origin because these show negative Ce anomalies and low Co/Zn ratio (0.5 to 1.1), and are masked by diagenesis. The relative contributions of hydrogenous, hydrothermal and diagenetic inputs were assessed in terms of ternary mixing patterns using REE mass balance equations. Furthermore, the hypothetical Ce anomaly (Ce/Ce*) was calculated using ternary mixing calculations for hydrogenous: hydrothermal:diagenetic end-members to ascertain the input to FeMn oxides on the pumice samples. This revealed a distinction between hydrogenous and hydrothermal components but diagenetic and plume fallout components could not be distinguished because this scheme comprises a three end-member calculation. A conservative estimate indicates the hydrothermal component to vary between 24% and 72%. The growth rates of the oxides, as estimated from published empirical methods, range between 3 and 47 mm/10 6 years. Fe/Mn ratios yielded a maximum age of 5-7 Ma and a minimum of 0.04-0.1 Ma. This suggests that the commencement of accretion of the FeMn oxides generally precedes the age of the Krakatau 1883 eruption, which is commonly considered as being the prime source of pumice to CIOB. This is the first evidence of hydrothermal influence in the formation of FeMn oxides on CIOB pumice.

Eolian dust deposited in the Chinese Loess Plateau [CLP] is considered as derived from the dry an... more Eolian dust deposited in the Chinese Loess Plateau [CLP] is considered as derived from the dry and semidry areas of the western to central China and Mongolia-western Siberia. These eolian sediments are major component of Quaternary loess-paleosoil sequence and late Tertiary Red Clay formation, and provide continuous archives of continental climate change spanning the last 22 Ma (Guo et al., 2002). It is paleoceanographic implication

In order to study the impact of placer mining on shallow coastal waters, a simulated sand mining ... more In order to study the impact of placer mining on shallow coastal waters, a simulated sand mining experiment was carried out in Kalbadevi, Ratnagiri, west coast of India, which is recognized as one of the future sand mining sites. Water column characteristics such as Total Suspended Matter (TSM), Dissolved Oxygen (DO) and nutrients (phosphate, nitrite, nitrate and silicate) were studied in different stages of the experiment (pre mining, during mining, post mining) in view of their essential nature in regulating the coastal ecosystem. The test mining experiment was conducted on a stable platform, anchored from three sides at a water depth of 8 meter. The water samples were collected from three locations viz., the Suction point (S), the Discharge point (D) and the Reference Point (R) at two depths of 1 m and 3 m at different time intervals for a period of 5 hours. At the discharge point, DO concentration attained the baseline condition shortly after the experiment that is similar to the values, observed at the reference point. During the early stages of experiment, phosphate concentration increased but attained baseline condition after the experiment probably related to the upward movement of bottom nutrient rich sediments due to suction. Nitrite and nitrate concentration decreased in the early stage of disturbance but increased with the progress of time. Initial decrease could be attributed to the denitrification brought about by the disturbance and the later increase could be probably due to new production. In the early stage of the experiment, silicate shows decrease in concentration than the reference point but attains baseline condition in the later stages of the experiment. TSM increased drastically (from 21 mg/l to 40 mg/l) at the discharge point during test mining, may due to the coarse nature of sediment where as the TSM values at Suction and Reference points remained below 20 mg/l through out the experiment. All the parameters showed sudden response to the disturbance but attained base level condition soon after the experiment.