Radiolarian monsoonal index Pyloniid group responds to astronomical forcing in the last approx. 500,000 y ears: Evidence from the Central Indian Ocean

Abstract

Pyloniid radiolarians, oceanic micro-zooplanktons (surface water dwelling), are sensitive to monsoon sea surface temperature and salinity, and their variation down a core may provide an insight into the proxy climatic changes in the tropical Indian Ocean. In the present study, the Pyloniid's percentage distribution at approx. 5 kyr intervals during the last approx. 500 kyr (plus or minus 10 kyr) years exhibited sinusoidal changes in a biostratigraphically dated sediment core (AAS-2/3; 7.49 degrees S, 80.01 degrees E, water depth approx 5463 m) from the central tropical Indian Ocean. Characteristic of Pyloniid variation in time suggest several short and long term periodic changes in the proxy monsoonal record. Fourier Transform Spectral Analysis of Pyloniid percentages revealed the triplet peaks of the earth's orbital cycles at the eccentricity (405-, 129- and 95-kyr), obliquity (41- and 30-kyr) and precessional (23-, 19- and 17- kyr) bands. The results suggest that the Pyloniid group of radiolarians, a proxy index for the south-west monsoon, exhibit cyclic changes at the earth's orbital precession, obliquity and eccentricity cycles in the last 500 kyr