Rajiv Nigam - Academia.edu (original) (raw)

Papers by Rajiv Nigam

THESIS SUBMITTED TO THE ALIGARH MUSLIM UNIVERSITY JN FULFILMENT OF THE REQUIREMENT FOR THE DEGREE... more THESIS SUBMITTED TO THE ALIGARH MUSLIM UNIVERSITY JN FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY By R A J I V NIGAM M. Sc. (Lucknow), M. Phil. (Aligarh) Department of Geology Aligarh Muslim University, A/igarh 1 9 8 1

Continental Shelf Research, 2017

Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera a... more Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera and one 'other genera' of benthic foraminifera from 32 stations off Mangalore-Cochin sector, west coast of India, to study the ecological preferences, especially the effect of depth on external test morphology of benthic foraminifera. It is noticed that cluster B is dominated by rounded-symmetrical forms, cluster C includes both rounded-symmetrical and angularasymmetrical forms, whereas cluster A, is predominantly represented by angularasymmetrical forms. From the spatial distribution of cluster A-C-B, we report that with decreasing depth, there is a gradual tendency among benthic foraminifera to become more symmetrical from angular-asymmetrical,. The observed morphological changes in benthic foraminifera are attributed to the sediment turbulence. The angular-asymmetrical morphogroup could be considered as an indicator of relatively deeper water while roundedsymmetrical forms suggest shallow environment. Therefore, the temporal variation in the relative abundance of these morpho-groups, can be used for paleo-depth reconstruction.

Quaternary International, 2017

Abstract The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera ha... more Abstract The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera has been studied from the shelf and slope of the central-western Bay of Bengal to assess the applicability of temporal changes in benthic foraminiferal morpho-groups (angular asymmetrical and rounded symmetrical) to reconstruct past monsoon changes. We report that the riverine influx and associated processes control the relative abundance of angular asymmetrical (AABF) and rounded symmetrical (RSBF) benthic foraminiferal morpho-groups in the central-western Bay of Bengal. Subsequently, temporal variations in relative abundance of AABF in a gravity core collected from outfall region of the Pennar River, are used to reconstruct decadal scale past monsoon variability during the last ∼1887 years. An increased monsoon discharge is observed during the Medieval Warm Period (MWP) and lower during the Little Ice Age (LIA). The periodic changes with a frequency of ∼123 and ∼238 years are also identified, indicating a close relationship between monsoon and solar activity.

Recent developments in Indian micropaleontology

One of the most challenging problems faced by the mankind today, is the constantly increasing mea... more One of the most challenging problems faced by the mankind today, is the constantly increasing mean annual temperature of the atmosphere of the earth. The gradual increase in the mean annual temperature of the earth's atmosphere during the last century, as a result of ...

Journal of the Geological Society of India, 2021

Fifty two surface sediment samples collected from the region off Goa, central west coast of India... more Fifty two surface sediment samples collected from the region off Goa, central west coast of India from water depths of 15-3300 m were analyzed with special emphasis on foraminiferal content. Rectilinear benthic foraminiferal morphogroup shows a high relative abundance within Oxygen Minimum Zone (OMZ), both shallow marine (50-60 m water depth) and intermediate to deep water (150-1500 m water depth). We gave special emphasis on four rectilinear foraminiferal genera, namely Fursenkoina, Bolivina, Bulimina and Uvigerina to observe their individual distribution among OMZ. We found genus Fursenkoina predominates at the shallow water OMZ, within the water depth zone of 50-60 m. Within 150-1500 m water depth, which is considered as intermediate to deep water OMZ in this region, genus Uvigerina shows its highest abundance above 1000 m water depth, whereas genus Bulimina shows its affinity with deeper water environment (>1000 m water depth). Genus Bolivina does not show any such depth preference, except its higher abundance in only intermediate to deep water OMZ. This depth differentiation among four rectilinear benthic foraminiferal genera presents the basic data for palaeoclimatic study based on the extent and intensity of OMZ along with the palaeobathymetry study.

Marine Pollution Bulletin, 2021

We studied the relationship between organic carbon in sediments (%Corg), bottom water dissolved o... more We studied the relationship between organic carbon in sediments (%Corg), bottom water dissolved oxygen and living benthic foraminifera in a marginal marine upwelling setting from the southeastern Arabian Sea to develop proxy indicator for marine productivity as well as oxygen deficient zones. The surface sediments from 43 stations covering a depth range of 25 to 2980 m were used. The relationship between living benthic foraminifera and ambient environmental parameters (seawater temperature, salinity, dissolved oxygen, organic carbon and Corg/TN and depth) was assessed by multivariate analysis. A majority of the living benthic foraminifera were significantly affected by several ambient parameters. We report that the living benthic foraminiferal assemblage comprising of Epistominella umbonifera, Uvigerina auberiana, Reophax longicollis and Osangularia bengalensis is significantly affected only by %Corg in the sediment. Additionally, we also found that the assemblage including Bolivina obscuranta, Bulimina arabiensis, Bulimina pseudoaffinis and Cancris penangensis is significantly affected only by the bottom water dissolved oxygen. The living benthic foraminifera assemblages can be used to reconstruct marine productivity and dissolved oxygen concentration in the past.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

BMC Research Notes, 2013

Background: Genetic studies of the Foraminifera provide valuable insights into marine speciation ... more Background: Genetic studies of the Foraminifera provide valuable insights into marine speciation and biogeography, yet the discovery of vitally needed new genetic markers for this important group is being severely limited by an extreme lack of genetic data. The establishment of a laboratory culture from a single, asexually reproducing foraminifer, will be essential to provide enough pooled genetic material from these unicellular organisms, to facilitate full genome sequencing and genetic marker discovery, using next-generation sequencing techniques. Findings: The aim of this study was to develop a simple and inexpensive method of culturing benthic foraminifera, via asexual reproduction, in a controlled laboratory environment. Individual specimens of the benthic foraminfer Cornuloculina balkwilli (MacFadyen) were placed in 7 cm plastic beakers, containing 50 ml natural seawater, filtered to 0.2 μm, and kept at 23°C, with a 12-hour light/dark cycle, and fed weekly on a mixed algal diet of Dunaliella tertiolecta and Phaeodactylum tricornutum. Asexually derived cultures were successfully established from 4 specimens of Cornuloculina balkwilli, originally added to the culture vessels as immature specimens. Many thousands of individuals were present after 6 months. Conclusions: The method presented here demonstrates that only basic laboratory equipment is required to establish and maintain a thriving culture of the benthic foraminfer, C. balkwilli, from a single asexually reproducing specimen, providing an excellent source of genetic material for use in next generation sequencing. The method is easily reproducible and will greatly aid in the discovery of critically needed new genetic markers in the Foraminifera. It also highlights C. balkwilli as a good candidate species for use in the field of environmental micropaleontology.

Current Science, 1993

QUATERNARY PERIOD IN INDIA slump structures in clay beds indicate liquefaction of sediments due t... more QUATERNARY PERIOD IN INDIA slump structures in clay beds indicate liquefaction of sediments due to a large earthquake. The radiocarbon dating of a tree trunk found buried at 4 m depth with «$ roots firmly embedded in the clay sediments indi-otes that the tree died 1200 to 1300 ...

Quaternary Research, 2016

We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evapo... more We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evaporation-precipitation (from Mg/Ca and δ18O of surface dwelling planktic foraminifera), productivity (from relative abundance of Globigerina bulloides), carbon burial (from %CaCO3 and organic carbon [%Corg]) and dissolved oxygen at sediment-water interface, covering the entire Holocene, from a core collected from the eastern Arabian Sea. From the multi-proxy record, we define the timing, consequences and possible causes of the mid-Holocene climate transition (MHCT). A distinct shift in evaporation-precipitation (E-P) is observed at 6.4 ka, accompanied by a net cooling of SST. The shift in SST and E-P is synchronous with a change in surface productivity. A concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction. A shift in carbon burial, as inferred from both the %CaCO3 and %Corg, coincides with a change in surface productivity. A simultan...

Early Callovian to Middle Oxfordian foraminiferal assemblages are tagged with precise ammonite oc... more Early Callovian to Middle Oxfordian foraminiferal assemblages are tagged with precise ammonite occurrences for the first time from the Jurassic sediments of Chari Formation exposed at Keera Dome, Kachchh, Western India, with precise dating and marking of the Callovo-Oxfordian boundary. Four ammonite zones and nine subzones are correlated with seven foraminiferal zones, enabling accurate and reliable regional biostratigraphic analysis. Such integrated work will lead to precise dating of the otherwise hard-to-date foraminiferal assemblages from Kachchh.

Marine Pollution Bulletin, 2020

Despite being located at the same latitudes, the Bay of Bengal oxygen deficient zone (ODZ) is mar... more Despite being located at the same latitudes, the Bay of Bengal oxygen deficient zone (ODZ) is markedly different than the Arabian Sea ODZ. The uptake of oxygen in the Bay of Bengal does not lead to denitrification as in the Arabian Sea. This difference in ODZ of the Bay of Bengal and the Arabian Sea is expected to support different benthic fauna. We report that the living benthic foraminifera in the Bay of Bengal ODZ are markedly different than that in the Arabian Sea ODZ. Only four species (Brizalina spathulata, Eubuliminella exilis, Uvigerina peregrina and Rotaliatinopsis semiinvoluta) dominant in the Bay of Bengal ODZ have also been reported from the Arabian Sea oxygen deficient waters. The difference in living benthic foraminifera dominant in the ODZ of the Bay of Bengal and the Arabian Sea, is attributed to the lack of denitrification and associated processes in the Bay of Bengal.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Water column measurements suggest shoaling of aragonite saturation depths (ASD) throughout the wo... more Water column measurements suggest shoaling of aragonite saturation depths (ASD) throughout the world oceans, due to increase in greenhouse gas concentration. Past records of aragonite saturation state under different climatic conditions are required to assess the impact of climatic changes on shoaling/deepening of ASD. The preservation state of organisms having aragonite skeletons, is used to assess the past changes in aragonite saturation depths, with respect to the modern ASD. Here for the first time, we delineate and discuss the factors that affect the modern aragonite compensation depth (ACD) in the eastern Arabian Sea by using pteropod abundance in the surface sediments. A total of 78 spade core-top samples collected along seven latitudinal transects, covering the continental shelf, slope and abyssal region of the eastern Arabian Sea were used. Pteropods were picked from coarse fraction (≥63 μm). Based on the pteropod preservation, we report that in the eastern Arabian Sea, ACD lies at a water depth of ≤525 m, which matches with the chemically defined aragonite saturation depth. We further report that the ACD shoals from north to south. The zone of high pteropod abundance coincides with low %C org. The increase in pteropod abundance in the outer shelf region coincides with the drop in dissolved oxygen concentration. The deeper limit of pteropod abundance lies in the center of the oxygen minimum zone with higher %C org. Therefore, we suggest that the pteropod abundance in the eastern Arabian Sea is not always related with the lower dissolved oxygen, but is strongly influenced by %C org. This first report of the pteropod based aragonite compensation depth estimates from the eastern Arabian Sea will help in assessing future changes in ACD under the influence of anthropogenic greenhouse gas emissions.

THESIS SUBMITTED TO THE ALIGARH MUSLIM UNIVERSITY JN FULFILMENT OF THE REQUIREMENT FOR THE DEGREE... more THESIS SUBMITTED TO THE ALIGARH MUSLIM UNIVERSITY JN FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY By R A J I V NIGAM M. Sc. (Lucknow), M. Phil. (Aligarh) Department of Geology Aligarh Muslim University, A/igarh 1 9 8 1

Continental Shelf Research, 2017

Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera a... more Q-mode and R-mode cluster analyses have been carried out on the census counts data of 68 genera and one 'other genera' of benthic foraminifera from 32 stations off Mangalore-Cochin sector, west coast of India, to study the ecological preferences, especially the effect of depth on external test morphology of benthic foraminifera. It is noticed that cluster B is dominated by rounded-symmetrical forms, cluster C includes both rounded-symmetrical and angularasymmetrical forms, whereas cluster A, is predominantly represented by angularasymmetrical forms. From the spatial distribution of cluster A-C-B, we report that with decreasing depth, there is a gradual tendency among benthic foraminifera to become more symmetrical from angular-asymmetrical,. The observed morphological changes in benthic foraminifera are attributed to the sediment turbulence. The angular-asymmetrical morphogroup could be considered as an indicator of relatively deeper water while roundedsymmetrical forms suggest shallow environment. Therefore, the temporal variation in the relative abundance of these morpho-groups, can be used for paleo-depth reconstruction.

Quaternary International, 2017

Abstract The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera ha... more Abstract The effect of ambient conditions on living (Rose-Bengal stained) benthic foraminifera has been studied from the shelf and slope of the central-western Bay of Bengal to assess the applicability of temporal changes in benthic foraminiferal morpho-groups (angular asymmetrical and rounded symmetrical) to reconstruct past monsoon changes. We report that the riverine influx and associated processes control the relative abundance of angular asymmetrical (AABF) and rounded symmetrical (RSBF) benthic foraminiferal morpho-groups in the central-western Bay of Bengal. Subsequently, temporal variations in relative abundance of AABF in a gravity core collected from outfall region of the Pennar River, are used to reconstruct decadal scale past monsoon variability during the last ∼1887 years. An increased monsoon discharge is observed during the Medieval Warm Period (MWP) and lower during the Little Ice Age (LIA). The periodic changes with a frequency of ∼123 and ∼238 years are also identified, indicating a close relationship between monsoon and solar activity.

Recent developments in Indian micropaleontology

One of the most challenging problems faced by the mankind today, is the constantly increasing mea... more One of the most challenging problems faced by the mankind today, is the constantly increasing mean annual temperature of the atmosphere of the earth. The gradual increase in the mean annual temperature of the earth's atmosphere during the last century, as a result of ...

Journal of the Geological Society of India, 2021

Fifty two surface sediment samples collected from the region off Goa, central west coast of India... more Fifty two surface sediment samples collected from the region off Goa, central west coast of India from water depths of 15-3300 m were analyzed with special emphasis on foraminiferal content. Rectilinear benthic foraminiferal morphogroup shows a high relative abundance within Oxygen Minimum Zone (OMZ), both shallow marine (50-60 m water depth) and intermediate to deep water (150-1500 m water depth). We gave special emphasis on four rectilinear foraminiferal genera, namely Fursenkoina, Bolivina, Bulimina and Uvigerina to observe their individual distribution among OMZ. We found genus Fursenkoina predominates at the shallow water OMZ, within the water depth zone of 50-60 m. Within 150-1500 m water depth, which is considered as intermediate to deep water OMZ in this region, genus Uvigerina shows its highest abundance above 1000 m water depth, whereas genus Bulimina shows its affinity with deeper water environment (>1000 m water depth). Genus Bolivina does not show any such depth preference, except its higher abundance in only intermediate to deep water OMZ. This depth differentiation among four rectilinear benthic foraminiferal genera presents the basic data for palaeoclimatic study based on the extent and intensity of OMZ along with the palaeobathymetry study.

Marine Pollution Bulletin, 2021

We studied the relationship between organic carbon in sediments (%Corg), bottom water dissolved o... more We studied the relationship between organic carbon in sediments (%Corg), bottom water dissolved oxygen and living benthic foraminifera in a marginal marine upwelling setting from the southeastern Arabian Sea to develop proxy indicator for marine productivity as well as oxygen deficient zones. The surface sediments from 43 stations covering a depth range of 25 to 2980 m were used. The relationship between living benthic foraminifera and ambient environmental parameters (seawater temperature, salinity, dissolved oxygen, organic carbon and Corg/TN and depth) was assessed by multivariate analysis. A majority of the living benthic foraminifera were significantly affected by several ambient parameters. We report that the living benthic foraminiferal assemblage comprising of Epistominella umbonifera, Uvigerina auberiana, Reophax longicollis and Osangularia bengalensis is significantly affected only by %Corg in the sediment. Additionally, we also found that the assemblage including Bolivina obscuranta, Bulimina arabiensis, Bulimina pseudoaffinis and Cancris penangensis is significantly affected only by the bottom water dissolved oxygen. The living benthic foraminifera assemblages can be used to reconstruct marine productivity and dissolved oxygen concentration in the past.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

BMC Research Notes, 2013

Background: Genetic studies of the Foraminifera provide valuable insights into marine speciation ... more Background: Genetic studies of the Foraminifera provide valuable insights into marine speciation and biogeography, yet the discovery of vitally needed new genetic markers for this important group is being severely limited by an extreme lack of genetic data. The establishment of a laboratory culture from a single, asexually reproducing foraminifer, will be essential to provide enough pooled genetic material from these unicellular organisms, to facilitate full genome sequencing and genetic marker discovery, using next-generation sequencing techniques. Findings: The aim of this study was to develop a simple and inexpensive method of culturing benthic foraminifera, via asexual reproduction, in a controlled laboratory environment. Individual specimens of the benthic foraminfer Cornuloculina balkwilli (MacFadyen) were placed in 7 cm plastic beakers, containing 50 ml natural seawater, filtered to 0.2 μm, and kept at 23°C, with a 12-hour light/dark cycle, and fed weekly on a mixed algal diet of Dunaliella tertiolecta and Phaeodactylum tricornutum. Asexually derived cultures were successfully established from 4 specimens of Cornuloculina balkwilli, originally added to the culture vessels as immature specimens. Many thousands of individuals were present after 6 months. Conclusions: The method presented here demonstrates that only basic laboratory equipment is required to establish and maintain a thriving culture of the benthic foraminfer, C. balkwilli, from a single asexually reproducing specimen, providing an excellent source of genetic material for use in next generation sequencing. The method is easily reproducible and will greatly aid in the discovery of critically needed new genetic markers in the Foraminifera. It also highlights C. balkwilli as a good candidate species for use in the field of environmental micropaleontology.

Current Science, 1993

QUATERNARY PERIOD IN INDIA slump structures in clay beds indicate liquefaction of sediments due t... more QUATERNARY PERIOD IN INDIA slump structures in clay beds indicate liquefaction of sediments due to a large earthquake. The radiocarbon dating of a tree trunk found buried at 4 m depth with «$ roots firmly embedded in the clay sediments indi-otes that the tree died 1200 to 1300 ...

Quaternary Research, 2016

We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evapo... more We reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evaporation-precipitation (from Mg/Ca and δ18O of surface dwelling planktic foraminifera), productivity (from relative abundance of Globigerina bulloides), carbon burial (from %CaCO3 and organic carbon [%Corg]) and dissolved oxygen at sediment-water interface, covering the entire Holocene, from a core collected from the eastern Arabian Sea. From the multi-proxy record, we define the timing, consequences and possible causes of the mid-Holocene climate transition (MHCT). A distinct shift in evaporation-precipitation (E-P) is observed at 6.4 ka, accompanied by a net cooling of SST. The shift in SST and E-P is synchronous with a change in surface productivity. A concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction. A shift in carbon burial, as inferred from both the %CaCO3 and %Corg, coincides with a change in surface productivity. A simultan...

Early Callovian to Middle Oxfordian foraminiferal assemblages are tagged with precise ammonite oc... more Early Callovian to Middle Oxfordian foraminiferal assemblages are tagged with precise ammonite occurrences for the first time from the Jurassic sediments of Chari Formation exposed at Keera Dome, Kachchh, Western India, with precise dating and marking of the Callovo-Oxfordian boundary. Four ammonite zones and nine subzones are correlated with seven foraminiferal zones, enabling accurate and reliable regional biostratigraphic analysis. Such integrated work will lead to precise dating of the otherwise hard-to-date foraminiferal assemblages from Kachchh.

Marine Pollution Bulletin, 2020

Despite being located at the same latitudes, the Bay of Bengal oxygen deficient zone (ODZ) is mar... more Despite being located at the same latitudes, the Bay of Bengal oxygen deficient zone (ODZ) is markedly different than the Arabian Sea ODZ. The uptake of oxygen in the Bay of Bengal does not lead to denitrification as in the Arabian Sea. This difference in ODZ of the Bay of Bengal and the Arabian Sea is expected to support different benthic fauna. We report that the living benthic foraminifera in the Bay of Bengal ODZ are markedly different than that in the Arabian Sea ODZ. Only four species (Brizalina spathulata, Eubuliminella exilis, Uvigerina peregrina and Rotaliatinopsis semiinvoluta) dominant in the Bay of Bengal ODZ have also been reported from the Arabian Sea oxygen deficient waters. The difference in living benthic foraminifera dominant in the ODZ of the Bay of Bengal and the Arabian Sea, is attributed to the lack of denitrification and associated processes in the Bay of Bengal.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2017

Water column measurements suggest shoaling of aragonite saturation depths (ASD) throughout the wo... more Water column measurements suggest shoaling of aragonite saturation depths (ASD) throughout the world oceans, due to increase in greenhouse gas concentration. Past records of aragonite saturation state under different climatic conditions are required to assess the impact of climatic changes on shoaling/deepening of ASD. The preservation state of organisms having aragonite skeletons, is used to assess the past changes in aragonite saturation depths, with respect to the modern ASD. Here for the first time, we delineate and discuss the factors that affect the modern aragonite compensation depth (ACD) in the eastern Arabian Sea by using pteropod abundance in the surface sediments. A total of 78 spade core-top samples collected along seven latitudinal transects, covering the continental shelf, slope and abyssal region of the eastern Arabian Sea were used. Pteropods were picked from coarse fraction (≥63 μm). Based on the pteropod preservation, we report that in the eastern Arabian Sea, ACD lies at a water depth of ≤525 m, which matches with the chemically defined aragonite saturation depth. We further report that the ACD shoals from north to south. The zone of high pteropod abundance coincides with low %C org. The increase in pteropod abundance in the outer shelf region coincides with the drop in dissolved oxygen concentration. The deeper limit of pteropod abundance lies in the center of the oxygen minimum zone with higher %C org. Therefore, we suggest that the pteropod abundance in the eastern Arabian Sea is not always related with the lower dissolved oxygen, but is strongly influenced by %C org. This first report of the pteropod based aragonite compensation depth estimates from the eastern Arabian Sea will help in assessing future changes in ACD under the influence of anthropogenic greenhouse gas emissions.