Figure 6.7. The evolution of climate indicators from the NH (panels a to d), and from Antarctica (panels e to g), over the period 64 to 30 ka. (a) Anhysteretic remanent magnetisation (ARM), here a proxy of the northward extent of Atlantic MOC, from an ocean sediment core from the Nordic Seas (Dokken and Jansen, 1999); (b) CH₄ as recorded in Greenland ice cores at the Greenland Ice Core Project (GRIP), Greenland Ice Sheet Project (GISP) and North GRIP (NGRIP) sites (Blunier and Brook, 2001; Flückiger et al., 2004; Huber et al., 2006); CH₄ data for the period 40 to 30 ka were selected for the GRIP site and for 64 to 40 ka for the GISP site when sample resolution is highest in the cores; (c) surface temperature estimated from nitrogen isotope ratios that are influenced by thermal diffusion (Huber et al., 2006); (d) d¹⁸O, a proxy for surface temperature, from NGRIP (2004) with the D-O NH warm events 8, 12, 14 and 17 indicated; (e) d¹⁸O from Byrd, Antarctica (Blunier and Brook, 2001) with A1 to A4 denoting antarctic warm events; (f) nss-Ca²⁺, a proxy of dust and iron deposition, from Dome C, Antarctica (Röthlisberger et al., 2004); and (g) CO₂ as recorded in ice from Taylor Dome, Antarctica (Indermühle et al., 2000). The Heinrich events (periods of massive ice-rafted debris recorded in marine sediments) H3, H4, H5, H5.2, and H6, are shown. All data are plotted on the Greenland SS09sea time scale (Johnsen et al., 2001). CO₂ and CH₄ are well mixed in the atmosphere. CH₄ variations are synchronous within the resolution of ±50 years with variations in Greenland temperature, but a detailed analysis suggests that CH₄ rises lag temperature increases at the onset of the D-O events by 25 to 70 years (Huber et al., 2006). CO₂ co-varied with the antarctic temperature, but the exact synchronisation between Taylor Dome and Byrd is uncertain, thus making the determination of leads or lags between temperature and CO₂ elusive. The evolution of Greenland and antarctic temperature is consistent with a reorganisation of the heat transport and the MOC in the Atlantic (Knutti et al., 2004).