The formation conditions of subglacial Lake Vostok’s accreted ice based on its stable water isotope composition

In this paper, we present a new dataset on the stable water isotopic composition (δD and δ18O) in a sequence of subglacial Lake Vostok’s accreted ice (3538–3769 m) measured along three parallel ice cores. The high precision of the new data has allowed us to characterize the formation conditions of different sections of the ice. The whole lake ice interval may be divided into 3 zones: 1) “zone 0”, 3538.8–3549.8 m, is under the strong influence of the local water formed from melted meteoric ice likely entering from under the glacier on the lake’s west coast; 2) “zone 1” (accreted ice 1), 3549.8–3607.4 m, is experiencing significant variability due to the slightly different effective fractionation coefficient in the course of “water inclusions” in the ice matrix during the freezing process; 3) “zone 2” (accreted ice 2), 3607.4–3768.8 m, is under the influence of glacial melt water from the northern part of the lake and the hydrothermal flux from the lake’s bottom. We defined the exact boundary between the accreted ice 1 and ice 2, which corresponds to a sharp isotopic excursion at a depth of 3607.4 m. In this work, we present for the first time data on the “17O-excess” parameter in the lake ice and water, which allowed us to make a direct calculation of the equilibrium fractionation coefficient for oxygen 17 during water freezing.