NOAA/WDS Paleoclimatology - GRIP Ice Core 40KYr Methane Data

Records of the variation in atmospheric methane concentration have been obtained from ice cores for the past 1,000 years and for the period 8,000-220,000 yr BP, but data for the intervening period, spanning most of the present interglacial period (Holocene), are patchy. Here we present a continuous, high-resolution record of atmospheric methane from 8,000 to 1,000 yr BP, from the GRIP ice core in central Greenland. Unlike most other climate proxies from ice cores (such as oxygen isotope composition and electrical conductivity), methane concentrations show significant variations - up to 15% - during the Holocene. We have proposed that variations in the hydrological cycle at low latitudes are the dominant control on past levels of atmospheric methane. This is now supported by the observation that the lowest methane concentrations in our new record occur in the mid-Holocene, when many tropical lakes dried up. The concentration increases during the Late Holocene, probably owing to an increasing contribution from northern wetlands.