ENVIRONMENTAL MONITORING IN A HIGH ARCTIC PROGLACIAL LACUSTRINE WATERSHED IN A WARMING HYDROCLIMATIC REGIME, LINNÉVATNET, SVALBARD

Environmental monitoring in Linnédalen (2003-23) provides a baseline for understanding climate and environmental change in the rapidly warming 21^st century in Svalbard. Process studies also provide the means for directly interpreting the varve record in proglacial Linnévatnet. In turn, the varve record provides a long-term context for the current climate regime.

From 2003 to present, environmental sensors in the 31 km² Linnédalen watershed include an automated weather station, snow depth and stream water temperature sensors, and time-lapse cameras. Moorings with sediment traps and other instrumentation are deployed at stations across Linnévatnet and are recovered and redeployed on an annual basis.

Measurements and observations in the Linnédalen catchment reveal that hydroclimatic processes have accelerated over the past decade as a response to enhanced Atlantification and loss of sea ice in this west coast maritime setting. Linnébreen, a polythermal glacier at the head of the valley, has retreated ~1.6 km from the Little Ice Age maximum. Ice marginal retreat increased from 26m/year (2004 to 2012) to 55 m/year (2012 to 2021). Streamflow duration has increased (74 days in 2005 to 167 in 2016) with late season heavy rainfall events occurring more frequently in recent years. River temperatures reached 15^oC through late July-early August 2020 and lake surface water reached 10^oC, the highest in the period of observation. Since 2013, lake ice formation has occurred later in the autumn, as late as late November or early December. Lake sediment trap analysis and camera imagery shows that peak river discharge occurs in two main modes: the nival flood from spring snowmelt runoff and/or in the late summer and autumn associated with heavy rainfall events. The latter mode has been more persistent in the last decade. The sediment trap and sediment core records in Linnévatnet also document increased annual accumulation due to enhanced regional warmth and rainfall.