Holocene glacier variations and their potential orbital, solar, volcanic and anthropogenic forcings

Abstract

The magnitude of glacier advances generally increased in the Northern Hemisphere and decreased in the Southern Hemisphere over the Holocene. This trend can be explained be the orbital forcings. The exceptions are in some regions of the high Asia. 10–4 ka BP and during the 1th Century CE to the early 13th century CE the glaciers were close by sizes to the modern ones or even smaller. The pattern is confirmed by the upper and Northern tree line advances in the Northern Hemisphere. The period with generally «small glaciers» (5–7 ka) coincides with the lack of the major volcanic eruptions, and with the low solar activity. The Early Holocene moraines cluster in seven groups (from 11.1 to 8.1 ka BP). They coincide with all Early Holocene Bond cycles (11.1, 10.3, 9.4, 8.1 ka) and all major volcanic eruptions (11.0, 9.5–9.7, 9.1–9.3, 8.0–8.1). Due to the coincidence of several eruptions with the Bond cycles (solar minima) it is difficult to distinguish between the solar and volcanic signals in the Early Holocene records. The coupling between the glacial and solar/volcanic forcings in the mid Holocene is less evident, but it become strong again in the last 2 ka (1.4 ka and LIA events). The modern glacier retreat disagrees with the actual orbital forcings and is due to both solar and anthropogenic influence. Glacier variations at the moment do not provide proofs for any cycles or global synchronism through the Holocene. However the lack of such evidences can be also explained by the limitations of these records (discontinuous, incomplete, of low accuracy, showing a mixture of advances triggered by both temperature and precipitation).