A first continuous three-year temperature record from the dimictic arctic–alpine Lake Tarfala, northern Sweden

Nina Kirchner,Jakob Kuttenkeuler,Gunhild Rosqvist,Marnie Hancke,Annika Granebeck,Jan Weckström,Kaarina Weckström,Frederik Schenk,Atte Korhola,Pia Eriksson

doi:10.1080/15230430.2021.1886577

Abstract

ABSTRACT Arctic lakes are exposed to warming during increasingly longer ice-free periods and, if located in glaciated areas, to increased inflow of meltwater and sediments. However, direct monitoring of how such lakes respond to changing environmental conditions is challenging not only because of their remoteness but also because of the scarcity of present and previously observed lake states. At the glacier-proximal Lake Tarfala in the Kebnekaise Mountains, northern Sweden, temperatures throughout the water column at its deepest part (50 m) were acquired between 2016 and 2019. This three-year record shows that Lake Tarfala is dimictic and is overturning during spring and fall, respectively. Timing, duration, and intensity of mixing processes, as well as of summer and winter stratification, vary between years. Glacial meltwater may play an important role regarding not only mixing processes but also cooling of the lake. Attribution of external environmental factors to (changes in) lake mixing processes and thermal states remains challenging owing to for example, timing of ice-on and ice-off but also reflection and absorption of light, both known to play a decisive role for lake mixing processes, are not (yet) monitored in situ at Lake Tarfala.

Highlights

Surface freshwater environments in the Arctic comprise mainly lakes (87 percent) and ponds, rivers, streams, and wetland complexes
Based on the three-year lake water temperature record presented here, it is argued that Lake Tarfala is dimictic and that mixing throughout the entire water column occurs in the spring and in the fall
Practical constraints related to the deployment and recovery of the temperature sensors imply that the first mixing captured in the lake water temperature record was the fall over turning in 2016, followed by both spring and fall over turning in 2017 and 2018 and the spring overturning 2019

Summary

Introduction

Surface freshwater environments in the Arctic comprise mainly lakes (87 percent) and ponds, rivers, streams, and wetland complexes. Together, they can cover more than 80 percent of the land surface in some regions of the Arctic (Wrona et al 2013). Currently increasing at 0.2°C/decade on a global average and at rates two to three times higher in the Arctic (Intergovernmental Panel on Climate Change 2018), implies that the period during which lakes are ice covered, between ice-on in autumn and iceoff in spring, decreases (Prowse et al 2011; Benson et al 2012; Šmejkalová, Edwards, and Dash 2016; Lehnherr et al 2018; Sharma et al 2019). This, too, has implications for arctic lakes because they may receive larger amounts of meltwater, sediment, organic matter, and nutrients while glaciers are melting

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Conclusion