Abstract
Abstract. During the anomalously hot summer in 2012, surface air temperatures in Western Siberia were 5 to 15 °C higher than those observed during the previous period of > 30 yr. This unusual climate phenomenon provided an opportunity to examine the effects of short-term natural heating of water in thermokarst ponds and lakes in discontinuous permafrost zones and compare these observations to previous field results obtained when the temperature was normal during the summer of 2010 in the same region. In 2012, thermokarst bodies of water shrank significantly, water levels dropped approximately 50 cm in large lakes and small (< 10–100 m2) ponds, and shallow soil depressions disappeared. Based on samples from ~ 40 bodies of water collected previously and in 2012, first-order features of changes in chemical composition in response to increased water temperatures (from 14.1 ± 2.2 to 23.8 ± 2.3 °C in 2010 and 2012, respectively) were established. In these thermokarst bodies of water that covered a full range of surface areas, the average conductivity and pH were almost unchanged, whereas dissolved organic carbon (DOC), Cl- and SO42- concentrations were higher by a factor of ~ 2 during summer 2012 compared to periods with normal temperatures. Similarly, most divalent metals and insoluble trivalent and tetravalent elements were more concentrated by a factor of 1.7–2.4 in the summer of 2012 than normal periods. The average concentrations of dissolved CO2 and CH4 during the hot summer of 2012 increased by factors of 1.4 and 4.9, respectively. For most of the trace elements bound to colloids, the degree of colloidal binding decreased by a factor of 1.44 ± 0.33 (for an average of 40 elements) during the hot summer of 2012 compared to normal periods. Increases in CO2 and CH4 concentrations with the decreasing size of the body of water were well-pronounced during the hot summer of 2012. The concentrations of CO2 and CH4 rose by factors of 5 and 150, respectively, in small (≤ 102 m2) compared to large (≥ 104 m2) thermokarst (thaw) lakes. Taken together, these trends suggest that, for a conservative scenario of lake size distribution, lake water warming at high latitudes will produce (1) a significant increase in methane emission capacity from thaw lake surfaces; (2) decreased molecular sizes of trace element complexes and potential bioavailability of metal micronutrients in water columns; and (3) relatively conservative responses by CO2, DOC and trace element concentrations.
Highlights
Othbawse)rvlaatkioendsydnuarminigcsTfieihnldeasntuCadciretyisvoeolfsytphdeehrvmeeolrokepairnsgt ( called permafrost system are of crucial importance for quantitative and predictive modeling of greenhouse gas (GHG) emissions from these lakes to the atmosphere, which is one of the most significant environmental threats of permafrost warming at high latitudes (Schuur et al, 2008; O’Connor et al, 2010)
We addressed our objectives via concerted biogeochemical sampling of 40 thaw lakes in a pristine region of western Siberia where a heat wave occurred in June–July 2012, unprecedented over several decades of available meteorological records
Our study site, which is located in the central part of Western Siberia (63.5◦ N, 75.4◦ E, 20 km from the Khanymey settlement), lies on a discontinuous permafrost tundra over Neocene sand and clay deposits that are covered by a layer of peat that is 1–2 m thick (Fig. 1 and ground photos in the Electronic Supporting Information, ESM-1)
Summary
Othbawse)rvlaatkioendsydnuarminigcsTfieihnldeasntuCadciretyisvoeolfsytphdeehrvmeeolrokepairnsgt ( called permafrost system are of crucial importance for quantitative and predictive modeling of greenhouse gas (GHG) emissions from these lakes to the atmosphere (van Huissteden et al, 2011), which is one of the most significant environmental threats of permafrost warming at high latitudes (Schuur et al, 2008; O’Connor et al, 2010). Pokrovsky et al.: Greenhouse gases and trace metal concentration in thaw lakes warming scenarios were (i) substituting “space for time” by considering ecosystem changes along a latitude or landscape profile, for example, from sporadic to continuous permafrost (Frey et al, 2007) or corresponding to different degrees of permafrost coverage (Petrone et al, 2006), and (ii) artificial soil heating experiments (Melillo et al, 2002; Kirschbaum, 2004) or water table level manipulation (Blodau et al, 2008b; Reiche et al, 2009) These approaches are certainly useful for making straightforward predictions of the evolution of river – ocean and soil – atmosphere fluxes during climate warming, it is impossible to apply these two methods to model the main landscape features of arctic and subarctic wetlands, i.e., thermokarst (thaw) lakes and soils subsidences in permafrost regions. The first objective of this study was to quantify changes in thaw lake chemical composition during the anomalously hot summer of 2012 and compare these results to the normal period investigated during summer 2010 in the same region (Shirokova et al, 2013)
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