12-14 September, 2011, Lucknow - Earth Science India
12-14 September, 2011, Lucknow - Earth Science India
12-14 September, 2011, Lucknow - Earth Science India
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National Conference on <strong>Science</strong> of Climate Change and <strong>Earth</strong>’s Sustainability: Issues and Challenges ‘A Scientist-People Partnership’<br />
<strong>12</strong>-<strong>14</strong> <strong>September</strong>, <strong>2011</strong>, <strong>Lucknow</strong><br />
GLACIAL-INTERGLACIAL PRODUCTIVITY<br />
FLUCTUATIONS FROM INDIAN ANTARCTIC POLAR<br />
FRONT OF SOUTHERN OCEAN<br />
Sunil Kumar Shukla 1,3 , Xavier Crosta 1 , M. Sudhakar 2 , G.N. Nayak 3<br />
and Olivier Ther 1<br />
1 UMR-CNRS 5805 EPOC, Université Bordeaux 1, Avenue des facultés, 33405 Talence Cedex, France<br />
2 Ministry of <strong>Earth</strong> <strong>Science</strong>s, Govt. of <strong>India</strong>, CGO Complex, New Delhi – 110 003<br />
3 Department of Marine <strong>Science</strong>s, Goa University, Taleigao Plateau, Goa – 403 206<br />
Southern Ocean (SO) plays a pivotal role in regulating glacial-interglacial<br />
variability of atmospheric CO 2 due to deep-water masses protrusion and exchanges of<br />
gases with the atmosphere. The circumpolar connection in the SO permits a global-scale<br />
overturning (thermohaline) circulation to exist. Diatoms are dominant primary<br />
producers in SO and play decisive role in global cycling of silicic acid and carbon.<br />
Their cell sizes determine carbon sequestration efficiency as large cells export<br />
disproportionately large amount of carbon to the ocean floor due to their faster sinking<br />
and slower dissolution. Diatom Fragilariopsis kerguelensis is endemic to SO and its<br />
abundance reaches up to 90% of the total assemblages in surface sediments. Due to its<br />
abundance and good preservation in the sediments, it can be used as a potential proxy to<br />
decipher the cycling of nutrients and productivity fluctuations through glacialinterglacial<br />
cycles in SO. Therefore, we present biometric investigations of F.<br />
kerguelensis from a well dated core SO136-111 from <strong>India</strong>n Antarctic Polar Front<br />
(APF) of SO over the last 40,000 years. Apical length, trans-apical length and valve<br />
area of F. kerguelensis are compared to its absolute and relative abundances as a proxy<br />
for the species productivity, along with sea surface temperature and sea ice duration<br />
reconstructed through diatom-based transfer function by applying modern analogue<br />
technique.<br />
Downcore records demonstrate that F. kerguelensis valves were longer and more<br />
abundant during the Holocene than during the glacial-deglacial period which is opposite<br />
to the records of Atlantic sector of SO. The opposite records in the <strong>India</strong>n and Atlantic<br />
sectors of the Southern Ocean may indicate that different factors regulated diatom<br />
biology in these basins. In the Atlantic sector, longer F. kerguelensis during the last<br />
glacial period may have resulted from greater iron availability from melting ice [Cortese<br />
and Gersonde, 2007]. In the <strong>India</strong>n sector where little ice melt was registered during the<br />
glacial period, longer F. kerguelensis during the Holocene may have resulted from the<br />
prevalence of warmer oceanic conditions and greater upwelling, which is more<br />
favourable for sexually-induced production of long initial cells. Instead of being<br />
opposite records, both these studies argue against the high opal fluxes recorded during<br />
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