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Orbital frequencies in radiolarian assemblages of the central Indian Ocean: implications on the Indian summer monsoon

DRS at CSIR-National Institute of Oceanography

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Title Orbital frequencies in radiolarian assemblages of the central Indian Ocean: implications on the Indian summer monsoon
 
Creator Gupta, S.M.
 
Subject palaeo studies
radiolarian ooze
sediments
quaternary
temporal variations
monsoon
summer
 
Description Radiolarian distribution in surface sediments and its relationships with overlying surface oceanography provided impetus for down-core faunal variation related to changes in monsoon intensity due to the Earth's orbital eccentricity in the geologic past. In present study, a high resolution (delta t=4.75 ka) radiolarian distribution for the last 485 ka in a core (AAS 2/3) from the central Indian Ocean Basin revealed orbital and sub-orbital cycles. Relationships between temporal distribution of: (1) high-salinity Pyloniids and Didymocyrtis; (2) low-salinity Spongodiscids and Spongaster; (3) transitional Euchitoniids; and (4) southern Anthocyrtidium assemblages, and the orbital forcing (ETP, i.e. the normalized sum of the Earth's eccentricity, tilt and precession), and the May-July insolation were analyzed. Spectral analyses revealed significant cycles of Pyloniids (400-, 126-, 95-, 54-, 41-, 31-, 23-, 19-, 17-, and 15-ka), Spongaster (95-, 41-, 29-, 23-, 19-, 17-, and 15-ka), Euchitoniids (126-, 95-, 51-, 31-, 21-, 18-, and 17-ka), and Anthocyrtidium (400-, 69-, 41-, 31-, 23-, 19-, and 15-ka). Cross-spectral analysis between Pyloniids and ETP suggested coherent Pyloniid cycles lagging ETP by 9 ka at 100-ka eccentricity, while both were in-phase (less than 2 ka) at 41-ka tilt and 23-ka precession cycles. Coherent Spongaster cycles led ETP by 38 ka at 100-ka eccentricity, 15 ka at 41-ka tilt, 5 ka at 23-ka precession cycles. Coherent Anthocyrtidium cycles led ETP by 14 ka at 100-ka eccentricity, 10 ka at 31-ka tilt, and were in-phase at 41-ka tilt as well as 23- and 19-ka precession cycles. Similarly, a radiolarian monsoon index defined as the normalized sum of Pyloniids, Didymocyrtis, Spongodiscids, Spongaster, Euchitoniids, and Anthocyrtidium (PDSSEA) led ETP at 54- and 23-ka cycles, while both were nearly in-phase at 41-, 31- and 15-ka cycles. Coherent PDSSEA cycles led insolation during May-July at 8 degrees S (core-site) at 23-ka precession, lagged 100-, 54- and 29-ka cycles and were in-phase at 41-ka tilt and 15-ka sub-orbital cycles. The results suggest that radiolarian assemblages exhibit proxy-monsoon cycles due to the Earth's orbital eccentricity at 400-, 126- and 95-ka, tilt at 54-, 41- and 31-ka, next to precession at 23-, 19- and 17-ka as well as insolation forcings at the core-site during the Late Quaternary.
 
Date 2008-07-18T05:45:19Z
2008-07-18T05:45:19Z
2003
 
Type Journal Article
 
Identifier Palaeogeography, Palaeoclimatology, Palaeoecology, Vol.197; 1-16p.
http://drs.nio.org/drs/handle/2264/1258
 
Language en
 
Rights Copyright [2003]. It is tried to respect the rights of the copyright holders to the best of the knowledge. If it is brought to our notice that the rights are violated then the item would be withdrawn.
 
Publisher Elsevier