A high resolution multi-proxy record of pronounced recent environmental change at Baker Lake, Nunavut

Abstract

Arctic aquatic systems are considered to be especially sensitive to anthropogenic disturbance, which can have cascading effects on biological communities as aquatic food-web structure is altered. Bio-indicators that respond to major limnological changes can be used to detect and infer major environmental change, such as climate warming, with the use of paleolimnological techniques. A multiproxy approach was used to quantify recent environmental changes at Baker Lake, Nunavut, Arctic Canada. Analyses of fossilized remains of chironomids and diatoms were conducted on a sediment core of 20 cm in length sampled at 0.5-cm intervals. A new surface sediment training set of subfossil chironomid assemblages from 65 lakes across the eastern Canadian Arctic generated a robust (r jack 2 = 0.79) surface water paleotemperature transfer function. The transfer function was applied to stratigraphic intervals from the Baker Lake sediment core to generate a paleotemperature reconstruction of sub-decadal resolution. The surface water temperature reconstruction inferred a 2°C increase in mid-summer surface water temperature for Baker Lake over the last 60 years, which was corroborated by the local instrumental record spanning the period of 1950-2007 AD. The chironomid record shows a recent decline of several cold-water taxa and appearance of warm-water indicators. This shift in community structure began circa 1906 AD, and intensified after 1940 AD. The corresponding fossil diatom record showed an increase in small planktonic Cyclotella taxa over the past 60 years, intensifying in the last 5 years, which also suggests a warmer climate and longer ice-free periods. The shifts in the diatom assemblages began later than the shifts in the chironomid assemblages, and were of lower magnitude, reflecting differences in the mechanisms in which these two indicators respond to environmental change.

Chironomid-environment relations in northern North America

“…Likewise, each was identified to have a strong influence on the first axes (Table 2). We chose to generate chironomid-based transfer functions for reconstructing mean July air temperature rather than August as this is a variable commonly used for paleoenvironmental reconstructions (Larocque and Hall 2003;Medeiros et al 2012). Dissolved organic carbon (DOC) was also found to explain a significant Included are the nine significant environmental variables and the added variance they each explain as identified through forward selection in RDA.…”

Temperature change as a driver of spatial patterns and long‐term trends in chironomid (Insecta: Diptera) diversity

“…By comparing subfossil chironomid assemblages to their modern‐day distribution patterns, quantitative reconstructions of changes in their past environment can be made. For instance, chironomids have been used to quantitatively reconstruct past changes in temperature (Brooks, Davies, Mather, Matthews, & Lowe, ; Heiri et al, ; Medeiros, Friel, Finkelstein, & Quinlan, ), water depth (Engels, Cwynar, Shuman, & Rees, ; Nazarova, Bleibtreu, Hoff, Dirksen, & Diekmann, ), salinity (Dickson, Bos, Pellatt, & Walker, ), hypolimnetic oxygen (Quinlan & Smol, ) and several other environmental variables. Subfossil chironomids encountered in lake sediment records can additionally be used to track changes in past species richness or evenness of the fauna through time (e.g.…”

Review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages

“…Bioturbation and other processes will mix the top few centimetres of sediment, acting as a low-pass filter. The smooth changes in chironomid assemblages at Baker Lake (Medeiros et al, 2012) may indicate the importance of such processes in this large deep lake. Stratigraphy can potentially be further compromised as chironomids can burrow several centimetres into the sediment (Charbonneau and Hare, 1998).…”

“…Chrysophyte stomatocysts have also been used to reconstruct summer calcium concentrations (Hernández-Almeida et al, 2015b), which might reflect summer mixing and so were correlated with summer wind. High-resolution chironomid head capsule stratigraphies have been used to reconstruct summer air (e.g., Larocque et al, 2009a;Luoto and Ojala, 2016;Zhang et al, 2017a) and water (Medeiros et al, 2012) temperature. Highresolution pollen records have been used to reconstruct summer air temperature (Kamenik et al, 2009).…”