A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case stud from Hardangerjokulen, central southern Norway

Abstract

At Hardangerjøkulen, central southern Norway, detailed knowledge of the number, age and magnitude of Holocene glacier fluctuations is used to reconstruct variations in equilibrium-line altitude (ELA) for the last 10 000 years. Present and past ELAs are based on an accumulation-area ratio (AAR) of 0.7 and are adjusted for land uplift. A synchronous relationship between advanced glacier positions and the highest pinetree limits ( Pinus sylvestris L.) is demonstrated for the early to mid-Holocene in southern Scandinavia, which indicates that warm summers were compensated for by high winter precipitation. Based on pine-tree limit fluctuations as a measure of mean ablation-season temperature, Holocene variations in winter precipitation at Hardangerjøkulen have been calculated by substitution in the close exponential relationship between mean ablation-season temperature and winter precipitation at the ELA of Norwegian glaciers. Setting the winter precipitation during the period 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 summer temperature of c. 1.35°C warmer than at present, and may be regarded as a climatic analogue for the increase in precipitation which may accompany greenhouse warming of the atmosphere during the next century. These early-Holocene 'greenhouse centuries' ended abruptly within 30-50 years, and changed into a climatic regime dominated by dry winters and by summers only a little warmer than at present. The transition is synchronous with the most notable δ 18 O minimum recorded in Greenland ice cores at 8210 ± 30 years ago (before AD 1990), and is tentatively suggested as a Holocene analogue for the climatic instability (which may have been) recorded in the GRIP ice core during the last interglacial period (the Eemian).

Simulating the evolution of Hardangerjøkulen ice cap in southern Norway since the mid-Holocene and its sensitivity to climate change

“…2300-1300 BP), reconstructed precipitation in western Norway is slightly lower than the general increasing mass balance trend applied here (Dahl and Nesje, 1996;Bjune et al, 2005). At the same time, glacier reconstructions from southern Hardangerjøkulen indicate a slight decrease in glacier size .…”

“…K −1 (Giesen and Oerlemans, 2010) and no change in precipitation, the air temperature increase responsible for the ice cap disappearance after the Finse event must have been at least 1.5 K. Reconstructed summer temperature after the Finse event suggest a sharp increase of 1.0-1.2 K (Dahl and Nesje, 1996). A 10 % precipitation decrease would compensate for this difference, since the sensitivity to precipitation for Hardangerjøkulen is around +0.3 m w.e.…”

“…At 4000 BP, proxy studies suggest a drop in summer temperatures to 0.5 • C lower than present combined with a drier climate (Dahl and Nesje, 1996;Bjune et al, 2005;Velle et al, 2005b;Seppä et al, 2005). Dahl and Nesje (1996) reconstructed Holocene summer temperatures for southern Norway based on former pinetree limits.…”

“…At 4000 BP, proxy studies suggest a drop in summer temperatures to 0.5 • C lower than present combined with a drier climate (Dahl and Nesje, 1996;Bjune et al, 2005;Velle et al, 2005b;Seppä et al, 2005). Dahl and Nesje (1996) reconstructed Holocene summer temperatures for southern Norway based on former pinetree limits. Using a well-established empirical relationship between summer temperature and winter precipitation at the ELA of Norwegian glaciers (Liestøl in Sissons, 1979;Sutherland, 1984), they estimated winter precipitation for the Hardangerjøkulen area from lake sediment-derived ELAs.…”

A high-resolution diatom record of late-Quaternary sea-surface temperatures and oceanographic conditions from the eastern Norwegian Sea

“…Glaciers redeveloped in western Norway at about 5100 14 C yr BP (c. 6000 cal. yr BP) (Nesje & Dahl 1993;Dahl & Nesje 1996), a similar time to glacial re-advance in Iceland (Stötter et al 1999). Temperature reconstructions from pollen data in NW Finland and other terrestrial records in northern Norway all indicate the onset of cooling after the mid-Holocene period of maximum warmth at around 6500 cal.…”