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Title: | δ¹³C depleted oceans before the Termination 2: More nutrient-rich deep-water formation or light-carbon transfer? |
Authors: | Banakar, Virupaxa K. |
Keywords: | Equatorial Indian Ocean;Foraminifera- δ¹³C;Glacial termination-2;Deep-water circulation;Role of atmosphere |
Issue Date: | Sep-2005 |
Publisher: | CSIR |
Abstract: | Carbon-isotopes (δ¹³C) composition of benthic foraminifera has been extensively used to understand the link between deep-water circulation and climate. Equatorial Indian Ocean δ¹³C records of planktic- and benthic-foraminifera together show an unexplained shift in the long-term mean oceanic- δ¹³C around the penultimate glacial termination (T2: 132 ka). The time-series planktic- and benthic- species δ¹³C records exhibit two distinct mean- δ¹³C levels. The low mean- δ¹³C characterises the pre-T2 period (250 ka – 132 ka), while the post-T2 (~95 ka – Present) period records high mean- δ¹³C, generating a one-time shift of ~0.4 ‰ within the last ~250 kyr time-period. This shift is a result of consistently higher- δ¹³C in post-T2 glacial (and interglacial) periods as compared to the pre-T2 glacial (and interglacial) periods, and begins around the T2 (~132 ka), lasts until ~95 ka, and sustained through the T1. The normally observed glacial-interglacial δ¹³C variations of ~0.3 ‰ occur as secondary fluctuations around the long-term primary mean-levels in the Indian Ocean, as well as in other oceans. The T2- δ¹³C shift appears to be an inherent feature of the world oceans although with certain timing offsets. Therefore, it should represent a fundamental change in deep-ocean circulation (nutrient) dynamics. But, the leading hypotheses of circulation-driven oceanic distribution of δ¹³C fail to explain the observed mean- δ¹³C shift. Therefore it is proposed that, in addition to changes in deep-water circulation, the oceans before T2 were characterised by significantly lower- δ¹³C than after. Such low- δ¹³C mean-ocean during the pre-T2 period might have been the result of significantly increased transfer of terrestrial light-carbon to the ocean reservoir due to changes in global wind patterns. |
Page(s): | 249-258 |
URI: | http://hdl.handle.net/123456789/1560 |
ISSN: | 0379-5136 |
Appears in Collections: | IJMS Vol.34(3) [September 2005] |
Files in This Item:
File | Description | Size | Format | |
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IJMS 34(3) 249-258.pdf | 735.52 kB | Adobe PDF | View/Open |
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