Stable isotopic and carbonate stratigraphy of the late Pliocene and Pleistocene of Hole 704A: eastern subantarctic South Atlantic

Abstract

We studied the stable isotopic and carbonate stratigraphy of ODP Hole 704A to reconstruct the paleoceanographic evolution of the eastern subantarctic sector of the South Atlantic Ocean. Site 704 is well positioned with respect to latitude (46°52.8′S, 7°25.3′E) and bathymetry (2532 m) to monitor past migrations in the position of Polar Front Zone (PFZ) and changes in deep-water circulation during the late Pliocene-Pleistocene. Several important changes occurred in proxy palaeoceanographic indicators across the Gauss/Matuyama boundary at 2.47 Ma: (1) accumulation rates of biogenic sedimentary components increased by an order of magnitude; (2) planktonic δ18O values increased by an average of 0.5‰; (3) the amplitude of the benthic δ18O signal increased; (4) the accumulation rate of ice-rafted detritus increased several fold and (5) carbon isotopic ratios of benthic foraminifers decreased by 0.5‰, as did the δ13C of the fine-fraction carbonate by 1.5‰, but no change occurred in planktonic foraminiferal δ13C values. Most of the these changes are consistent with more frequent expansions and contractions of the PFZ over Site 704 after 2.47 Ma, bringing cold, nutrient rich waters to 47°S that stimulated both carbonate and siliceous productivity. The synchronous increase in δ18O values and ice-rafted detritus accumulation in Hole 704A indicates that the 2.4 Ma paleoceanographic event included ice volume growth on both Antarctica and Northern Hemisphere continents. -from Authors