Current Science

Suhas Shetye ¹, Rahul Mohan ¹, Syed A. Jafar ¹, Abhilash Nair ¹, Shramik Patil ¹, Shridhar Jawak ¹, Rajesh Asthana ², Sahina Gazi ¹

Affiliations
1 National Centre for Antarctic and Ocean Research, Headland Sada, Goa 403 804, IN
2 Geological Survey of India, Faridabad 121 001, IN

Abstract

Earlier studies have documented the role of diatoms in reducing the diversity and abundance of other silicadependent organisms, such as radiolaria. Here we hypothesize that diatom burst-driven depletion of dissolved silica (Dsi) in the Antarctic under sea-ice waters affects other silica-biomineralizing organisms. We found intense diatom-dominated, ice-edge phytoplankton bloom in the Enderby basin resulting in severe depletion of Dsi (<5 μM) under the sea ice. We also found siliceous sponge spicules within the surface sediment collected from under the Antarctic sea ice. Dominance of small style spicules (170 spicules/g sediment) under the sea ice along with dissolution seen on them, suggests DSi deficiency in the Antarctic waters. We, therefore, conclude that there is a rapid depletion of DSi due to seasonal diatom blooms under sea ice in the Antarctic waters.

Keywords

Diatoms, Dissolved Silica, Sea Ice, Sponge Spicules.

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Satya Prakash ¹, R. Ramesh ¹, M. S. Sheshshayee ², Rahul Mohan ³, M. Sudhakar ³

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN
2 Department of Crop Physiology, University of Agricultural Sciences, Bengaluru 560 065, IN
3 National Centre for Antarctic and Ocean Research, Vasco-da-Gama, Goa 403 804, IN

Abstract

We report data on nitrate, ammonium and urea uptake rates from the Equatorial and Southern Indian Oceans. Productivity (0.81-2.23 mmol Nm^-2 d^-1) over the Equatorial Indian Ocean was low, but the f-ratio (0.13-0.45) was relatively high. In the Southern Indian Ocean total N-uptake rate varied from 1.7 to 12.3 mmol Nm^-2 d^-1; it was higher in the Antarctic coast (69°S) and lower over most of the Southern Ocean, the lowest being at 58°S. The f-ratio also showed significant spatial variation, but was higher compared to values at the Equatorial Indian Ocean. The mean f-ratio in the Southern Indian Ocean was 0.50. The nitrate-specific uptake rates and f-ratios appear to have increased significantly in the recent past relative to earlier estimates. While productivity in the Southern Ocean is comparable to that in the Equatorial Indian Ocean, higher f-ratios in the former underscore its importance in the uptake of CO₂.

Keywords

Carbon Sequestration, f-Ratio, Nitrogenuptake, Primary Productivity, Southern Ocean.

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Rahul Mohan , Clemente Michael Wong Vui Ling

Abstract

The Asian Forum for Polar Sciences (AFoPS) is a 14- year-old non-governmental organization with its current six members representing national Antarctic/polar research institutions – China, Japan, Republic of Korea, India, Malaysia and Thailand. There are strong ties and collaboration among AFoPS member countries, especially in the aspect of science.

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Badanal Siddaiah Mahesh ¹, Abhilash Nair ¹, Anish Kumar Warrier ², Anirudha Avadhani ¹, Rahul Mohan ¹, Manish Tiwari ¹

Affiliations
1 National Centre for Antarctic and Ocean Research, Headland-Sada, Vasco-da-Gama 403 804, IN
2 Department of Civil Engineering, Manipal Institute of Technology, Manipal University, Manipal 576 104, IN

Abstract

Low altitude coastal lakes along the Antarctic margin often contain both marine and lacustrine sediments as a result of relative sea level changes due to deglaciation. The sediments also record changes in regional climate. A sediment core from a coastal lake in Larsemann Hills, East Antarctica, viz. Stepped Lake (Heart Lake), records distinct changes in C, N, C/N_{atomic ratio}, δ ¹³C_OM, δ ¹⁵N_OM and diatom abundance during the mid-Holocene (8.3 to 4.6 kyr BP). Lower values (C_org ~1%; C/N 8, ¹³C_OM ~ –18‰) during the early Holocene (8.3–4 kyr BP) are consistent with marine conditions, while higher values [C_org 6%; C/N 12; ¹³C_OM ~ –12‰) suggest a shift to lacustrine conditions (5.5–4.6 kyr BP). The diatom community shows similar shift with the major part of Holocene (8.3– 5.5 kyr BP) dominated by sea-ice and open-ocean diatoms while the core-top sections (5.5–4.6 kyr BP) transitions to lacustrine diatoms (Stauroforma inermis). These observations confirm that the basin was marine, and later became isolated as a result of postglacial isostatic uplift after 4.7 kyr BP.

Keywords

Diatoms, Holocene Climate, Larsemann Hills, Stable Isotopes, Sedimentary Organic Matter.

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Rahul Mohan ¹

Affiliations
1 National Centre for Polar and Ocean Research, Headland Sada, Goa 403 804, IN

Abstract

This book by Felix Bast is originally a diary and a travelogue. The author was on a short Antarctic summer trip and has tried to share his polar experiences. It is really admirable that a first-time-visitor to Antarctica was fired with the enthusiasm to chronicle his impressions! Even in his first exposure to Antarctica, the author appreciates the Indian Antarctic programme establishing great facilities in the remotest place on the earth, ‘…indubitably a remarkable achievement’. He recognizes that the pre-expedition training and interactions at Auli-India were useful preparations, ‘…the Antarctic veterans… the interactions I had with them were simply the best part of the whole acclimatization program’. He also rightly points out that ‘Climate change denialism is indeed a form of pseudoscience…’.

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Pallavi P. Choudhari ¹, Shramik M. Patil ¹, Rahul Mohan ¹

Affiliations
1 National Centre for Polar and Ocean Research, Ministry of Earth Sciences, Headland Sada, Vasco-da-Gama, Goa 403 804, IN

Abstract

Coccolithophores are one of the major groups of marine carbonate producers and are the most important pelagic unicellular calcifying organisms which play a pivotal role in the marine biogeochemical cycles. Since past few decades, coccolithophores have gained attention due to their unique role in the global carbon cycle and particularly due to their combined effects on the biological carbon and carbonate counter pumps. Owing to their high diversity, better preservation, fast turnover rate and significant role in the marine biogeochemical cycles, coccolithophores are identified as a potential proxy to reconstruct palaeoceanographic changes. In this review, a broad introduction of the biology and biogeography of extant coccolithophores is discussed with a brief overview on the preservation of the coccoliths and their applications. This includes how coccolith abundance, diversity and morphometric studies are used to reconstruct palaeotemperature, palaeosalinity, palaeoproductivity and palaeocirculation. In addition, implications of coccolithophores in the isotopic studies for the estimation of palaeotemperature and palaeoproductivity are also discussed.

Keywords

Coccolithophores, Nannoplankton, Palaeoceanography, Palaeoclimate, Southern Ocean.

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Rahul Mohan ¹

Affiliations
1 National Centre for Polar and Ocean Research, Headland Sada, Vasco-da-Gama, Goa 403 804, IN

Abstract

No Abstract.

Keywords

No Keywords.

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