• ARCHANA M NAIR

      Articles written in Journal of Earth System Science

    • Stable water isotope signatures of dual monsoon precipitation: A case study of Greater Cochin region, south-west coast of India

      T D ANEESH REJI SRINIVAS AJIT T SINGH T R RESMI ARCHANA M NAIR B L REDKAR

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      Precipitation samples of various spatio-temporal scales were collected from coastal, midland and urban regions of Greater Cochin, Ernakulam district, Kerala for a period of 1 yr (2015–2016). The collected samples were analysed for stable water isotopes (SWI) ($\delta\rm{D}$ and $\delta^{18}\rm{O}$), to understand these variations in the precipitation source and the factors governing its isotopic characteristics during precipitation. The $\delta^{18}O$ in rainwater varies from -8.73 per thousand to 0.29 per thousand in urban, -12.21 per thousand to 2.59 per thousand in midland and -9.99 per thousand to 0.97 per thousand in lowland regions. Spatio-temporal variations in SWI were observed in various regions, suggesting altitude and continental effect followed by the establishment of a regional overall local meteoric water line (LMWL) $\delta\rm{D}$ = $8.06 (\pm0.15)\delta^{18}O + 12.5 (\pm0.68)$. Among the coastal, midland and urban regions, the highest slope ($\sim8.3$) and intercept($\sim13.0$) were observed in the urban region, which designates the variations in temperature along spatial and different layers of the atmosphere in the urban region, resulting in the deviation of isotopic characteristics.The overall deuterium excess ($d$-excess) value is $\sim10$ per thousand during the south-west monsoon (June–September), suggesting a moisture source of marine origin. A $d$-excess of $\sim13$ per thousand is observed during the north-east monsoon, indicating a moisture source from the continental contribution (October–December). The results of the moisture source obtained from the $d$-excess value are also supported by back-trajectory analysis. Thus, the present study on isotopic characterisation of precipitation and its controlling factor may enhance our understanding of the Indian monsoon and its dynamics in the west coast region of India.

    • Landform evolution of Tharsis Montes and Olympus Mons of Mars: Insights from morphometric, hypsometric and chronologic evidences

      ADNAN AHMAD ARCHANA M NAIR

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      We studied the growth and evolutionary history of four major volcanoes of the Tharsis Province based on morphometry, age and hypsometric studies. Shield volcanoes of Tharsis volcanic province demonstrate marginally dissimilar landform evolutionary trends. Arsia Mons is distinct with a single caldera of large diameter and showed the highest asymmetry in the apron development. A convex hypsometric curve of Arsia Mons indicates tectonic dominance in its evolution. Olympus Mons, on the other hand, is concave in shape, suggesting an erosion dominated landform. Olympus Mons shows the highest symmetry in its morphology as a cone, while Ascraeus Mons and Pavonis Mons display a deviation from the symmetry due to the development of aprons. We determined the age of the caldera and the surrounding region of the four major shield volcanoes of Tharsis Province using the crater counting technique. Chronological studies using the crater counting technique indicate that the significant part of the Tharsis volcanic province belongs to the Late Amazonian period ( <  300 Ma). Hypsometric studies indicate that Tharsis Montes are tectonically active, while Olympus Mons dominantly showed erosional activity in the recent past. Accordingly, the investigation of Tharsis Montes is a critical way to improve the understanding of evolutionary pathways of volcanic landforms of the Martian surface.

      $\bf{Highlights}$

      $\bullet$ We studied the landform evolution of four major shield volcanoes of Tharsis volcanic province.

      $\bullet$ Morphometric, chronologic and hypsometric analysis was carried out to understand the evolutionary trend.

      $\bullet$ Hypsometric curve analysis showed that the landform evolution of Arsia Mons is dominantly tectonic.

      $\bullet$ Chronological analysis shows that majority of the Tharsis volcanic province belongs to the Late Amazonian period.

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