Lacustrine diatom oxygen isotopes as palaeo precipitation proxy -
Holocene environmental and snowmelt variations recorded at Lake Bolshoye
Shchuchye, Polar Urals, Russia
Abstract
The diatom oxygen isotope composition
(δ18Odiatom) from lacustrine sediments
helps tracing the hydrological and climate dynamics in individual lake
catchments, and is generally linked to changes in temperature and
δ18Olake. Lake Bolshoye Shchuchye
(67°53’N; 66°19’ E; 186 m a.s.l) is the largest and deepest freshwater
reservoir in the Polar Urals, Arctic Russia. Its
δ18Odiatom record generally follows a
decrease in summer insolation and the northern hemisphere (NH)
temperature history. However, it displays exceptional, short-term
variations exceeding 5‰, especially in Mid and Late Holocene. This
centennial-scale variability occurs contemporaneously with and similarly
to Holocene NH glacier advances. However, larger Holocene glacier
advances in the Lake Bolshoye Shchuchye catchment are unknown and have
not left any significant imprint on the lake sediment record. As Lake
Bolshoye Shchuchye is deep and voluminous, about 30−50% of its volume
needs to be exchanged with isotopically different water within decades
to account for these shifts in the
δ18Odiatom 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. Here, we propose snow melt and influx
changes being the dominant mechanism responsible for the observed
short-term changes in the δ18Odiatom
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.