Browsing by Author "Dinesh Kumar Naik"

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A strong influence of the precession and northern high latitudinal climate on the monsoon seasonality and productivity in the Andaman Sea
(Elsevier B.V., 2025) Rinu Fathima; R. Saraswat; S. R. Bhadra; Dinesh Kumar Naik; Thejasino Suokhrie
The Indian Monsoon (IM) is a vital component of the global climate system, driving seasonal changes in precipitation, productivity, and circulation in the Indian Ocean. However, despite its significance in affecting the socio-economic conditions of over a billion people living in South Asia, the factors influencing the spatio-temporal variability of IM remain uncertain. The Andaman Sea, a core monsoon region, is a unique and relatively under-sampled basin with limited connectivity to the global ocean. To better understand the stadial-interstadial variability in IM seasonality and associated productivity, we studied the relative abundance of planktic foraminifera from the International Ocean Discovery Program (IODP) Expedition 353 Site U1448 in the Andaman Sea. Our findings reveal a strong stadial-interstadial variability in the monsoon seasonality, with a stronger Indian Summer monsoon (ISM) during the interstadials and a stronger Indian Winter monsoon (IWM) during the stadials. Specifically, the strongest ISM was during the early Holocene, associated with higher insolation, while peak IWM intensity was during the Heinrich Event 1 (H1). Moreover, we observed a strong influence of the high latitudinal millennial scale North Atlantic cold and warm events, such as Younger Dryas (YD), Heinrich Event (H1−10), and Bolling-Allerod (B/A), on the Andaman Sea, with warm events typically leading to stronger ISM and cold events leading to stronger IWM. We also report a strong coupling between ISM and productivity, with stronger ISM associated with higher productivity. A distinct stadial-interstadial variability was observed in the magnetic susceptibility (MS) and Red/Blue (R/B) reflectance ratio which were used to understand the calcium carbonate (CaCO3) and organic carbon (Corg) content variability. The higher CaCO3 and Corg values were observed during the interstadials and lower values during the stadials. Both, ISM and IWM exhibited a significant periodicity of 24 and 21 kyr, respectively and the summer monsoon was in phase with maximum northern hemisphere solar insolation in the precession band with a minor lag of 2.4 kyr, suggesting the dominant role of precession in controlling the monsoon in the Andaman region. This study suggests a precession modulated insolation variability as the major factor controlling IM variability, along with which, internal feedbacks including the glacial boundary conditions, northern hemisphere climate and greenhouse gas concentration also influenced the IM during the last glacial-interglacial cycle. These findings provide crucial insights into the factors affecting IM variability and will aid in improving our understanding of the climate system's complex dynamics. © 2025 Elsevier B.V.
Assessing the ecological preferences of planktic foraminifera from the south-eastern Arabian Sea
(Elsevier Ltd, 2025) Kumari Anjali; Thejasino Suokhrie; R. Saraswat; Sujata Raikar Kurtarkar; Dinesh Kumar Naik; Dharmendra Pratap Singh; Rupal Dubey
The south-eastern Arabian Sea (SEAS) witnesses the confluence of the Arabian Sea and the Bay of Bengal waters along with an influence from both the summer and winter monsoon. As a result, the distinct hydrographic parameters are expected to modulate the diversity and abundance of planktic foraminifera in this region. Hence, 91 surface sediment samples covering a depth range from 25 m to 3150 m were analysed to establish region-specific planktic foraminiferal ecology. Overall, the water depth, seasonal chlorophyll-a and the mixed layer parameters significantly influence the planktic foraminiferal abundance in the SEAS. A total of 31 species of planktic foraminifera belonging to 17 genera were found. We report Globigerina bulloides as the most dominant species, preferring high productivity regions. Globigerina bulloides and Globigerinoides ruber exhibited opportunistic distribution patterns while region-specific preferences were observed for Globigerinita glutinata, N. dutertrei, Globorotalia cultrata and Trilobatus sacculifer. Globigerinita glutinata show a restricted seasonal occurrence while G. hexagonus is reported as a ubiquitous species. The ecological preferences of the planktic foraminifera inferred from the SEAS will help in reconstructing the past climatic conditions from this region. © 2025 Elsevier Ltd
Assessment of Buoyant Plastics in the Andaman and Nicobar Archipelago: Seasonal Dynamics, Source Attribution, Polymer Characterization, and Adverse Impacts
(Springer Science and Business Media Deutschland GmbH, 2025) Pratyush Das; Pratap Kumar Mohanty; Dusmant Maharana; Dinesh Kumar Naik; Mohit Kumar; Jatindra Nath Swain; Bhupendra Singh Kholia
Plastic pollution presents a growing threat to marine ecosystems, with significant impacts on biodiversity and trophic interactions. This study investigated the distribution, abundance, and ecological implications of buoyant plastics in the offshore waters of the Andaman and Nicobar Archipelago over a 12-month period. A total of 178 ship-based visual surveys were conducted, covering 6898 km. The average annual abundance of buoyant plastics was 78.94 ± 14 items km⁻2, with Flexible Packaging Plastics (FPP) and Miscellaneous Plastics (MP) comprising 43.4% and 44.3% of the total plastics, respectively. Seasonal trends revealed the highest abundances during the pre-monsoon period (101.41 ± 20 items km⁻2), likely driven by increased human activities such as fishing and tourism, while the lowest abundances were observed during the winter monsoon (59.36 ± 19 items km⁻2). Notable monthly peaks occurred in January, April, and October. A clear depth gradient was evident, with higher plastic abundances in shallower waters (0–1000 m; 93.48 ± 34 items km⁻2) and reduced concentrations at greater depths (3001–4000 m; 58.39 ± 19 items km⁻2). Plastic ingestion was assessed in 248 large pelagic fish from 13 species. Bigeye Thresher Sharks (42.86%) and Indo-Pacific Blue Marlins (40%) showed the highest ingestion rates. Ingested buoyant plastics ranged up to 78 cm2 in size and predominantly consisted of common polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). These insights reinforce the urgent need for mitigation strategies to address the ecological risks associated with buoyant plastics. © University of Tehran 2025.
Mid-Pleistocene Transition altered upper water column structure in the Bay of Bengal
(Elsevier B.V., 2023) Sudhira R. Bhadra; Rajeev Saraswat; Sanjeev Kumar; Sangeeta Verma; Dinesh Kumar Naik
The unique water column structure and seasonal change in the hydrodynamics make the Bay of Bengal an interesting area to understand the effect of monsoon on the water column stratification. We have reconstructed a 1.45 Myr record of planktic foraminifera assemblages and a 1.16 Myr (MIS 47- MIS 8) record of the difference in the stable oxygen isotopic ratio (Δδ18O) between the mixed layer dwelling Globigerinoides ruber and thermocline dweller Neogloboquadrina dutertrei from the IODP Site U1446 to understand the change in water column stratification and its relationship with the monsoon. From the glacial-interglacial shift in Δδ18O and mixed layer and thermocline assemblages, we infer a stronger stratification during the warm interstadials and comparatively weaker stratification during the cold stadials. The strengthened summer monsoon induced high direct rainfall and riverine influx inhibited mixing in the upper layer and created a shallow thermocline during the interstadials. We report a large variability in Δδ18O prior to the mid-Pleistocene transition (MPT). Interestingly, the glacial-interglacial shift in Δδ18O significantly decreased post MPT. A stronger upwelling and deeper mixed layer during the stadial periods reduced the glacial-interglacial shift in Δδ18O post mid-Pleistocene transition. The strengthened summer monsoon during the post MPT period increased the stratification in the Bay of Bengal. © 2023 Elsevier B.V.
Sediment-associated microplastics in Chilika lake, India: Highlighting their prevalence, polymer types, possible sources, and ecological risks
(Elsevier B.V., 2024) Mohit Kumar; Dinesh Kumar Naik; Dusmant Maharana; Moumita Das; Ekta Jaiswal; Amiya Shankar Naik; Neha Kumari
The primary objective of this research was to assess microplastics (MPs) in the sediments of Chilika lake. MPs were extracted from 22 sediment samples using the density separation method combined with vacuum pump filtration. A stereo-zoom microscope and Raman spectroscopy were employed to identify the sediment-associated MPs. The total MPs collected from all 22 sites was 440 ± 3.53 particles kg−1 wet sediments, with sizes ranging between 50 and 500 μm. In terms of morphology, fibers and fragments emerged as the dominant MP types, with counts of 210 ± 1.66 and 175 ± 1.76 particles kg−1 wet sediments, respectively. Raman spectroscopy verified the presence of various MP polymers in the sediments, predominantly HDPE (37 %), followed by PS (20 %), PET (18 %), PA (11 %), PP (7 %), and PC (7 %). A notable color variation was observed in MPs; black being the most prevalent (38.8 %), succeeded by blue (19.5 %), green (11.8 %), white (11.5 %), red (10.6 %), and transparent (7.5 %). ANOVA results indicated significant (p > 0.05) variations in MP abundance across the 22 sampling locations. However, principal component analysis (PCA) and multiple regression analysis indicated that water quality parameters did not significantly influence MP abundance, yet it was found that MP retention was higher in fine-grained sediments like clay and silt. The leading sources of MPs in Chilika lake were found to be aquafarming, trailed by river and sewage discharges, fishing activities, antifouling coatings and tourism. Additionally, the pollution load index (PLI) was employed to gauge the ecological risks, categorizing the lake under risk category 1, which implies a minimal level of MPs pollution. This research aims to serve as an early warning system for MPs pollution in productive brackish water habitats globally, including Chilika lake, guiding policymakers towards appropriate management strategies and preventive measures. © 2024 Elsevier B.V.