δ18O, δD and d-excess signatures of ground ice in permafrost in the Beiluhe Basin on the Qinghai-Tibet Plateau, China

摘要

In this paper,stable isotope (δ18O,δD) investigations were completed in ground ice from a deep borehole in the Beiluhe Basin on northern Qinghai-Tibet Plateau to unravel the isotopic variations of ground ice and their possible source water.The δ18O and δD of ground ice show distinctive characteristics compared with precipitation and surface water.The near-surface ground ice is highly enriched in heavier isotopes (δ18O and δD),which were gradually depleted from top to bottom along the profile.It is suggestive of different origin and ice formation process.According to isotopic variations,the ice profile was divided into three sections:the near-surface ground ice at 2.5 m is frozen by the active-layer water which suffered evaporation.It is possible that ground ice between 3 and 4.2 m is recharged by the infiltration of snowmelt.From 5 to 6 m,the ground ice show complex origin and formation processes.Isotopic variations from 6 to 11.1 m and 20.55 m indicate different replenishment water.The calculated slope of freezing line (S=6.4) is larger than the experimental value (5.76),and is suggestive of complex origin and formation process of ground ice.