Phase lag of Antarctic and Greenland temperature in the last glacial and link between CO2 variations and Heinrich Events

Fundamental for the understanding of processes involved in climate change is the knowledge about its temporal and spatial evolution. Of special interest is the relation between high-latitude polar sites since they are a major component in climate change. Ice cores are a unique climate archive with a high temporal resolution which directly record the atmospheric composition of trace gases. We have established coherent time scales for two Antarctic cores with respect to the GRIP time scale over the period from 50kyr BP to the Holocene by using the global CH4 signal recorded in Antarctic (Byrd Station and Vostok ) and Greenland (GRIP ice core, Summit) ice cores. The atmospheric CO2 evolution is best recorded in Antarctic ice cores. The glacial CO2 variations (back to ∼50kyr BP) can now be linked to northern hemispheric climate change (Dansgaard-Oeschger events, Heinrich events). Variations of the atmospheric CO2 concentration during Dansgaard-Oeschger (D-O) events were generally less than ∼10ppmv. Rather, atmospheric CO2 varied parallel to Heinrich events, especially to the ones which start with a very long lasting D-0 event (∼20ppmv). D-0 cycles represent as well fast and abrupt changes in the Northern Hemisphere temperature, but there seem to be no significant CO2 increases parallel to short D-O cycles. We suggest that either the dynamics of the D-O cycles are distinctly different from that of H-events or that the response time for CO2 to reach a new equilibrium is too long compared to the time scale of the shorter D-O cycles. A central issue in climate dynamics is to understand how the Northern and Southern Hemisphere temperatures couple during climatic events. It was shown that some of the fast temperature changes observed in Greenland during the last glacial have a concomitant in the temperature signal of Antarctica. With the CH4 synchronisation we are able to show that long-lasting Greenland warming events around 36 and 45kyr BP (D-O events 8 and 12) lag their Antarctic counterpart by 2–3kyr (comparing the starting points of corresponding warmings). On average, Antarctic climate change leads that of Greenland by 1–2.5kyr over the period 47–23kyr BP. The CH4 changes are in phase with Greenland climatic fluctuations and thus also lag the Antarctic climate change. The observed time lag questions a coupling between northern and southern polar regions via the atmosphere and favours a connection via the ocean. Here we confirm a mechanism described in climate models: when the North Atlantic deep water formation switches on, heat is extracted from the Southern Hemisphere where cooling occurs. This interhemispheric coupling is clearly identified for interstadial events 8 and 12 as well as during the termination of the last glacial