Direct dating of the oxygen-isotope record of the last deglaciation by 14C accelerator mass spectrometry

Abstract

Major trends of Quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen-isotope analysis1,2. δ18O records from deep-sea sediments show that the net glacial build-up occurs relatively slowly3, but that the end of an ice age occurs quickly, in less than 10,000 yr, implying a nonlinear response4,5 to simple Milankovitch theory6. The latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the Northern Hemisphere centred around 11,000 yr ago, a view supported by early studies7. Later work has produced conflicting dates, the main source of confusion being problems with obtaining accurate and reliable dates. Here, by using accelerator mass spectrometry, we have measured 14C for various species of foraminifera to produce a reliable timescale for the oxygen-isotope record. Our results show that, at the end of the last ice age, continental ice sheets began to melt more than 4,000 yr before the Northern Hemisphere maximum of summer calorific radiation.