Limnological evolution of Zelma Lake, a recently drained thermokarst lake in Old Crow Flats (Yukon, Canada)

Abstract

Evidence from remote sensing studies suggests that the frequency of thermokarst lake drainage events is increasing in response to climate change, but the consequences of these changes on the limnology of remaining waterbodies remain unknown. Here, we utilize a multiparameter paleolimnological record and post-drainage water isotope and chemistry monitoring to characterize the limnological evolution of Zelma Lake in Old Crow Flats, Yukon. During the early part of the record (~1678 to 1900 CE), analysis of geochemical variables and algal pigments indicate relatively stable limnological conditions. Abruptly beginning at~1900, Zelma Lake experienced a 40 year phase of reduced production, likely resulting from thermokarst shoreline expansion and associated increases in turbidity and low light availability. This was followed by~70 years of increasing production, likely from the stabilization of shorelines combined with a warming climate. Zelma Lake catastrophically drained in June 2007. Post-drainage conditions were characterized by intense eutrophication marked by increases in nutrient and major ion concentrations and the unprecedented occurrence of okenone and diatoxanthin pigments. Comparison to the post-drainage paleolimnological record from another thermokarst lake in Old Crow Flats indicates that a sharp increase of production is likely a common outcome of thermokarst lake drainage, yet intensity differs owing to site-specific catchment characteristics.Key words: climate change, thermokarst lakes, paleolimnology, limnology, lake drainage.Résumé : La preuve obtenue des études de télédétection suggère que la fréquence des évé-nements de drainage de lacs thermokastiques augmente en réponse au changement climatique, mais les conséquences de ce changement sur la limnologie des plans d'eau restant ne sont pas connues. Ici, nous utilisons un rapport paléolimnologique à multiples paramètres et la surveillance isotopique et chimique de l'eau postdrainage afin de caractériser l'évolu-tion limnologique du lac Zelma, à Old Crow Flats au Yukon. Pendant la première période faisant l'objet du rapport (~1678 à 1900 notre ère), l'analyse des variables géochimiques et des pigments algaires indiquent des conditions limnologiques relativement stables. Brusquement débutant~1900, le lac Zelma a subi une phase de 40 ans de production réduite, probablement en raison de l'expansion du rivage thermokarstique et des augmentations de la turbidité et de la faible luminosité disponible qui y sont associées. Il s'en suivit~70 ans de production accrue, probablement en raison de la stabilisation du rivage combinée avec le réchauffement du climat. Le lac Zelma s'est vidé de façon catastrophique en juin 2007.

Holocene pore‐ice δ18O and δ2H records from drained thermokarst lake basins in the Old Crow Flats, Yukon, Canada

“…Our DTLB record from WP283 exhibits a δ 18 O increase of ~2.7‰ through time immediately preceding lake drainage. This relict δ 18 O signature may reflect evaporative enrichment of residual lake waters following a partial drainage scenario (Figure 5B), which is known to occur presently in the Old Crow Flats 53 . The WP283 record also shows an ~5.0‰ decrease in d‐excess below the silt–peat interface.…”

Monitoring 13 years of drastic catchment change and the hydroecological responses of a drained thermokarst lake

“…Within days, the lake had lost well over 80% of its water volume, exposing over half of the lakebed (Wolfe and Turner 2008). Our previous studies at Zelma Lake showed that nutrient and ion concentrations increased and became highly variable during 2007-2011, and the lake transitioned to anoxic conditions as indicated by the presence of okenone, a carotenoid pigment produced by purple-sulfur bacteria, within the lakebed sediment (Tondu et al 2017). During this time, the intermittent and remnant water bodies within the Zelma Lake basin underwent reduced residence time with ongoing lateral drainage through the new outlet in addition to evaporation.…”

Paleolimnology of thermokarst lakes: a window into permafrost landscape evolution

“…Notably, organic matter content at Zelma Lake does indeed increase following observed drainage in 2007 (the sediment core was obtained in 2010) providing additional support for the use of Fig. 6b, although other evidence suggests that aquatic productivity during the post-drainage phase has been much greater than prior to expansion (Tondu et al 2017). It is notable that the timing of these drainage events, based on 210 Pb chronologies extrapolated downcore (where available), is highly variable, suggesting episodic occurrence.…”