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My research interest mainly focuses on past climatic changes and their impact on land surface processes at various timescales. I evaluate weathering and climate linkage by investigating geochemical and isotopic signatures of sedimentary records and river water samples. I assess these couplings in the Himalayan river basins, which play a dominant role in global biogeochemical and climatic cycles. Some of the key findings from my PhD work are summarized below.
Climate-weathering linkage during the last glacial and interglacial periods
Geochemical study of sediment cores from the Arabian Sea shows no major shift in provenances during the mid-Holocene period. However, trends of multiple weathering indices point to fluctuating chemical weathering patterns during the Meghalayan stage.
In contrast, the recent intensification of chemical weathering from ~1600 yr BP to the present is not synchronous with any significant change in the southwest (SW) monsoon during this period. However, this weathering change is consistent with the rise in C4 vegetation, possibly due to sustained agricultural practices in the SW monsoon-dominated region. The human-induced increase in C4 vegetation with shallow root systems may promote efficient sediment transport and hence, intense erosion of young soils with the faster dissolution kinetics. Whereas the temporal trends of the Sr-Nd isotopic composition and other weathering indices for the sedimentary records from the upper Indus basin show intensification of chemical weathering during Bølling–Allerød (warm and humid) climate event, establishing a strong coupling between weathering and climate.
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Impact of seasonal climate change on chemical weathering
This study assessed the climatic sensitivity of chemical weathering at the seasonal scale using time-series water chemistry, dissolved major ions, silica and strontium concentrations, data of Brahmaputra River, one of the largest Himalayan rivers. Although the elemental abundances and their ratios for the Brahmaputra mainstream show seasonal changes, the estimated silicate-derived fraction, based on inverse model calculations, of cations for monsoon and non‐monsoon seasons are statistically indifferent. Observations from this study suggest that the weathering in the Brahmaputra basin is not limited by runoff/water‐rock interaction time and is more regulated by rapid weathering at around eastern syntaxis with relatively steeper slopes and intense mechanical erosion than the upper reaches of the basin.
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Mid to late-Holocene variability in the Indian summer monsoon
This study used oxygen isotopic data (δ18O) of a speleothem sample from eastern India to reconstruct the mid-Holocene variability of the Indian summer monsoon (ISM), which reveals the impact of the Indian Ocean on short-term extreme climate events over the ISM regime. On the contrary, the North Atlantic (NA) climatic changes control the long-term trends of ISM variability. The δ18O data identify the occurrence of a super drought event spanning ~200 years at around 6.5 kyr BP along with other two well-known global drought events, e.g. the 4.2 and the 8.2 kyr events. This super-drought event is synchronous to the negative Indian Ocean Dipole (IOD). This study also shows that the broad declining nature of ISM during the middle to late Holocene is linked to south-ward migration of the Inter-tropical convergence zone and/or change in NA climatic conditions.
Further, I am interested in understanding the paleo-hydrological condition using the trace elemental ratio of the cave calcite deposits.
Paleo-oceanic redox condition
While my primary research interest is to understand the climate-weathering linkage, I am also interested in understanding the paleo-oceanic redox state and the depositional environment using the sediment geochemical data.
One of our studies, based on the variations on Al-normalized ratios (Ba/Al, TOC/Al and S/Al) and enrichment factors of redox-sensitive elements (U and Mo) of the Arabian Sea, have identified a shift in oceanic (bottom water) redox state from oxic to anoxic bottom water condition since ~ 4.2 kyr BP. The timing of this change is synchronous to the earlier reported drought phase at the beginning of the Meghalayan stage, underscoring climatic control on the bottom water redox state.
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Publications
Publications
Peer-Reviewed Articles
J.A. Wassenburg, A. Samanta, L. Sha, H. Lee, D. Scholz, H. Cheng, B. Stoll, Y. A. Brahim, A. Budsky and S.F.M. Breitenbach, 2024. Trace element partitioning controls on cave drip water compositions through prior calcite and aragonite precipitation. Communications Earth & Environment, 5, 488. [Online version]
A.M. Lone, S.P. Singh, R.A. Shah, H. Achyuthan, N. Ahmad, A. Qasim, G.R. Tripathy, A. Samanta, and P. Kumar, 2022. The late Holocene hydroclimate variability in the Northwest Himalaya: Sedimentary clues from the Wular Lake, Kashmir Valley. Journal of Asian Earth Sciences, 229, 105184. [Online version]
A. Samanta, G.R. Tripathy, B.N. Nath, R. Bhushan, R. Panchang, N. Bharti, and A. Shrivastava, 2022. Holocene variability in chemical weathering and ocean redox state: A reconstruction using sediment geochemistry of the Arabian Sea. Journal of Asian Earth Sciences, 224, 105029. [Online version]
A. Samanta, G.R. Tripathy, A.T. Pradeep, and A. Mandal, 2021. Major ion chemistry of two cratonic rivers in the Tropics: Weathering rates and their controlling factors. Hydrological Processes, 35, 2, e14035. [Online version]
A. Samanta, G.R. Tripathy, and R. Das, 2019. Temporal variations in water chemistry of the (lower) Brahmaputra river: Implications to seasonality in mineral weathering. Geochemistry, Geophysics, Geosystems, 20, 2769-2785. [Online version]
M. Joshi, A. Samanta, G.R. Tripathy, and S. Rajamani, 2017. Formation and stability of prebiotically relevant vesicular systems in terrestrial geothermal environments. Life, 7, 51, 1-14. [Online version]
Conference Presentations (Abstract)
J.A. Wassenburg, A. Samanta, L. Sha, H. Lee, D. Scholz, H. Cheng, Y.A. Brahim, A. Budsky, and S.F.M. Breitenbach, 2024. Effects of prior calcite and prior aragonite precipitation on cave dripwater compositions. EGU General Assembly, Vienna, Austria. [Online version]
A. Samanta, G.R. Tripathy, R. Panchang, B.N. Nath, R. Bhushan, and N. Bharti, 2022. Linkage between chemical erosion and human-induced vegetation pattern during the late Holocene period. EGU General Assembly, Vienna, Austria. [Online version]
A. Samanta and R. Das, 2021. Evaluation of the concentration-discharge relationship for the Brahmaputra river. Goldschmidt, Lyon, France. [Online version]
A. Samanta and G.R. Tripathy, 2020. Runoff-independent chemical weathering in the Brahmaputra river basin. 36th International Geological Congress, Delhi.
A. Mandal, G.R. Tripathy, A. Samanta, A. Pradeep, 2020. Evidence of sulfide oxidation in the Damodar and Subarnarekha river basins. 36th International Geological Congress, Delhi.
G.R. Tripathy, A. Samanta, A.T. Pradeep, and A. Mandal, 2018. Sulfide oxidation in mining-dominated river basins and its impact on long-term carbon cycle. Humboldt (AvH) Kolleg, Aurangabad, India.
A. Samanta and G.R. Tripathy, 2017. Evidence of pyrophosphate bearing dolomitic veins in Paleoproterozoic rocks: Link between life evolution and hydrothermal activity. Presented during May 2017, Virtual Poster Showcase, American Geophysical Union, Washington, DC.
Book Contributions
A. Samanta, 2015. Ductile sheared quartz vein shows a top-to-right shear. Central Indian Suture Zone. Jabalpur, Madhya Pradesh, India. In: Mukherjee, S. (Ed) Atlas of Structural Geology, Elsevier.
A. Samanta, 2015. Isoclinally folded chert layers with closures in two directions. Central Indian Suture Zone. Jabalpur, Madhya Pradesh, India. In: Mukherjee, S. (Ed) Atlas of Structural Geology, Elsevier.
A. Samanta, 2015. A folded layer of chert with closures at two directions. Central Indian Suture Zone. Jabalpur, Madhya Pradesh, India. In: Mukherjee, S. (Ed) Atlas of Structural Geology, Elsevier.
Geological Field Trips
Zanskar Valley, Himalaya | PhD
Aravalli Supergroup (Paleoproterozoic) | PhD
Large Igneous Province: Deccan Traps (Cretaceous) | MSc
Archean Ultramafic-mafic Complex: Nuasahi and Sukinda | MSc
Oceanographic Expedition
Indian Ocean Expedition, 2021 (SK - 373: ORV Sagar Kanya) | PhD
Cave Visits for Monitoring
Ondal and Yongyeon Caves, Republic of Korea | PDF
Santana, Morro, Couto, Laje Branca, Alambari de Baixo and Caverna do Diabo Caves, Brazil | 5th S4 Speleothem Summer School
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