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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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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