A NEW APPROACH TO CALCULATING HOLOCENE WINTER PRECIPITATION BY COMBINING GLACIER EQUILIBRIUM-LINE ALTITUDES AND PINE-TREE LIMITS - A CASE-STUDY FROM HARDANGERJOKULEN, CENTRAL SOUTHERN NORWAY

At Hardangerjokulen, central southern Norway, detailed knowledge of th e number, age and magnitude of Holocene glacier fluctuations is used t o reconstruct variations in equilibrium-line altitude (ELA) for the la st 10000 years; Present and past ELAs are based on an accumulation-are a ratio (AAR) of 0.7 and are adjusted for land uplift. A synchronous r elationship between advanced glacier positions and the highest pine-tr ee limits (Pinus sylvestris L.) is demonstrated for the early to mid-H olocene in southern Scandinavia, which indicates that warm summers wer e compensated for by high winter precipitation. Based on pine-tree lim it fluctuations as a measure of mean ablation-season temperature, Holo cene variations in winter precipitation at Hardangerjokulen have been calculated by substitution in the close exponential relationship betwe en mean ablation-season temperature and winter precipitation at the EL A of Norwegian glaciers. Setting the winter precipitation during the p eriod AD 1961-1990 at 100%, mean values varied from about 65 to c. 175 %. The wettest phase, at c. 8500-8300 cal. BP, experienced a mean summ er temperature of c. 1.35 degrees C warmer than at present, and may be regarded as a climatic analogue for the increase in precipitation whi ch may accompany greenhouse warming of the atmosphere during the next century. These early-Holocene 'greenhouse centuries' ended abruptly wi thin 30-50 years, and changed into a climatic regime dominated by dry winters and by summers only a little warmer than at present. The trans ition is synchronous with the most notable delta(18)O minimum recorded in Greenland ice cores at 8210+/-30 years ago (before AD 1990), and i s tentatively suggested as a Holocene analogue for the climatic instab ility (which may have been) recorded in the GRIP ice core during the l ast interglacial period (the Eemian).