Millenial scale variations of the isotopic composition of atmospheric oxygen over Marine Isotopic Stage 4

During rapid events of the last glacial period (DO events), dramatic changes are recorded at high and low latitudes. Without a precise common timescale, links between changes in Greenland temperature and changes in biosphere productivity, hydrology regimes and sea level are difficult to establish. The composition of atmospheric oxygen (δ18Oatm) is influenced by global sea level changes, the global hydrologic cycle and the biosphere productivity. Since δ18Oatm is measured in ice cores it gives the opportunity to investigate the underlying processes with no timescale uncertainty. Here, we present the first high resolution (50 yrs) record of the isotopic composition of atmospheric oxygen (δ18Oatm) measured in the air trapped in a Greenland ice core (NorthGRIP). Our record covers a sequence of DO events (18-19-20) corresponding to the Marine Isotopic Stage 4, ∼ 75 to 60 ka ago. Our measurements reveal rapid changes of δ18Oatm associated with the DO events. With a few additional measurements of the third isotope of oxygen (17O) during the DO event 19, we exclude the hypothesis that sea level changes are responsible for the isotopic variations. They originate more likely from large changes in relative humidity and latitudinal repartition of the continental vegetation over the DO events.