A ~400 ka supra-Milankovitch cycle in the Na, Mg, Pb, Ni, and Co records of a ferromanganese crust from the Vityaz fracture zone, central Indian ridge R. Banerjee1, S. M. Gupta1, H. Miura2, and D. V. Borole1 1Geological Oceanography Division, National Institute of oceanography, CSIR, Dona Paula, Goa 403 004, India 2Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
Received: 21 May 2010 – Accepted: 25 June 2010 – Published: 09 July 2010
Abstract. A ~400 ka (kilo years) supra-Milankovitch cycle, recorded in the sodium, magnesium,
lead, nickel and cobalt contents of a 32 mm thick ferromanganese crust from Vityaz
fracture zone, central Indian ridge is reported here. To arrive at the geological ages, we
used both 230Thexeccs and
Co-chronometric datings. The correlation coefficient between the 230Thexeccs
based dates and Co-chronometric dates for the top 0–8 mm is very high (r=0.9734, at
99.9% significance). The cobalt chronometric age for the bottom most oxide layer of this
crust is computed as 3.5 Ma. Red-fit and multi-taper spectral analyses of time series data
revealed the existence of the significant ~400 ka cycle, representing the changes in
the hydrogeochemical conditions in the ocean due to the Earth's orbital eccentricity related
summer insolation at the equator. This is the first report of such cycle from a hydrogenous
ferromanganese crust from equatorial Indian ocean.
Citation: Banerjee, R., Gupta, S. M., Miura, H., and Borole, D. V.: A ~400 ka supra-Milankovitch cycle in the Na, Mg, Pb, Ni, and Co records of a ferromanganese crust from the Vityaz fracture zone, central Indian ridge, Clim. Past Discuss., 6, 1311-1335, doi:10.5194/cpd-6-1311-2010, 2010.