HOLOCENE CLIMATE IN GREENLAND BASED ON 3 DEEP ICE CORES AND 2 TEMPERATURE PROFILES

Oxygen isotope variations spanning the Holocene derived from ice-core records for 3 sites in Greenland (Dye-3, GRIP, and NorthGRIP) show strong similarities. This suggests that the dominant influence on oxygen isotope variations reflected in the ice-sheet records was regional climatic change. Differences in detail between the records probably reflect geographical gradients in atmospheric isotope ratios. Palaeotemperature estimates have been obtained from the records using three approaches: (a) inferences based on the measured relationship between mean annual oxygen isotope ratio of snow and of mean annual surface temperature over Greenland, (b) modelled inversion of the borehole temperature profile either constrained by the dated isotopic profile, or (c) using Monte Carlo simulation techniques. The third of these approaches was adopted to reconstruct Holocene temperature variations for the Dye 3 and GRIP temperature profiles, which yields remarkably compatible results. A new record of Holocene isotope variations obtained from the NorthGRIP ice-core matches the Dye-3 and GRIP short-term isotope records, shows similar long-term trends to the Dye-3 and GRIP inverted temperature data. The NorthGRIP isotope record reflects: (a) a generally stronger isotopic signal than is found in the Dye-3 and GRIP records; (b) several short-lived temperature fluctuations during the first 1,500 years of the Holocene; (c) a marked cold event at ca. 8.2 ka BP (the "8.2 ka BP event"); (d ) optimum temperatures for the Holocene between ca. 8.6 and 4.3 ka BP, a signal that is 0.6? stronger than for the GRIP profile; (e) a clear signal for the Little Ice Age; and (f) a clear signal of climate warming during the last century. These data suggest that the NorthGRIP stable isotope record responded in a sensitive manner to temperature fluctuations during the Holocene. While the GRIP and NorthGRIP Holocene temperatures seem to have recovered fast from the glacial environment, the Dye-3 temperatures were only back to normal after 7 ka BP.