Lacustrine diatom oxygen isotopes as Holocene palaeo precipitation proxy for the Polar Urals, Russia

Abstract

<p>The diatom oxygen isotope composition (δ<sup>18</sup>O<sub>diatom</sub>) from lacustrine sediments is a reliable proxy to trace hydrological and climate dynamics in individual lake catchments, and is generally linked to lake temperature and water isotope variations. Diatom oxygen isotopes are excellent recorders of these changes, especially in high-latitudes where carbonates are widely absent.</p><p>In this study, Lake Bolshoye Shchuchye (67°53'N; 66°19' E; 186 m a.s.l) is explored being the largest and deepest freshwater reservoir in the Polar Urals, Arctic Russia. The recent isotope geochemistry helps identifying Lake Bolshoye Shchuchye as a well-mixed monomictic lake, covered more than half of the year by ice, and with negligible evaporative effects. Its Holocene δ<sup>18</sup>O<sub>diatom</sub> record generally follows a decrease in summer insolation and the northern hemisphere (NH) temperature history interpreted as Holocene cooling. However, it is overprinted by short-term variations in δ<sup>18</sup>O<sub>diatom</sub> exceeding 5‰, especially in Mid and Late Holocene. This centennial-scale variability is similar to Holocene NH glacier advances. However, presently glaciers in the Lake Bolshoye Shchuchye catchment are not known, nor have left any significant imprint on the lake sedimentary record. As the lake is deep (max water depth 160 m) and voluminous, about 30−50% of its volume need to be exchanged with isotopically different water within decades to account for the short-term shifts in the δ<sup>18</sup>O<sub>diatom</sub> record. A plausible source of water with light isotope composition inflow is snow, known to be transported in surplus by snow redistribution from the windward to the leeward side of the Polar Urals. We propose snow melt and influx changes being the dominant mechanism responsible for the observed short-term changes in the δ<sup>18</sup>O<sub>diatom</sub> record. This is the first time such drastic, centennial-scale hydrological changes in a catchment have been identified in Holocene lacustrine diatom oxygen isotopes, which, for Lake Bolshoye Shchuchye, are interpreted as proxy for summer temperatures and palaeo precipitation.</p>