Earlier ice breakup induces changepoint responses in duration and variability of spring mixing and summer stratification in dimictic lakes

Abstract

Reductions in ice cover duration and earlier ice breakup are two of the most prevalent responses to climate warming in lakes in recent decades. In dimictic lakes, the subsequent periods of spring mixing and summer stratification are both likely to change in response to these phenological changes in ice cover. Here, we used a modeling approach to simulate the effect of changes in latitude on long-term trends in duration of ice cover, spring mixing, and summer stratification by "moving" a well-studied lake across a range of latitudes in North America (35.2 N to 65.7 N). We found a changepoint relationship between the timing of ice breakup vs. spring mixing duration on 09 May. When ice breakup occurred before 09 May, which routinely occurred at latitudes < 47 N, spring mixing was longer and more variable; when ice breakup occurred after 09 May at latitudes > 47 N, spring mixing averaged 1 day with low variability. In contrast, the duration of summer stratification showed a relatively slower rate of increase when ice breakup occurred before 09 May (< 47 N) compared to a 109% faster rate of increase when ice breakup was after 09 May (> 47 N). Projected earlier ice breakup can result in important nonlinear changes in the relative duration of spring mixing and summer stratification, which can lead to mixing regime shifts that influence the severity of oxygen depletion differentially across latitudes.

Earlier ice loss accelerates lake warming in the Northern Hemisphere

“…In all, 16% of lakes experience stratification in the ice-off month, and 82% experience stratification onset in the subsequent 1–3 months. In addition, 14% of lakes experience incomplete overturn (when the number of days between the ice-off date and onset of stratification is <3 days 43 ) at least once during the study period (see Methods section). The extended stratification period thereby could contribute to excess lake warming in spring and summer.…”

“…20 ). The occurrence of incomplete overturn of a lake is defined as when the lake’s mixing duration (the number of days between the ice-off date and onset of stratification) is <3 days 43 .…”

Holocene Temperature Variations in Semi-Arid Central Mongolia—A Chronological and Sedimentological Perspective From a 7400-year Lake Sediment Record From the Khangai Mountains

“…In most cases enhanced primary productivity results in the consumption of dissolved CO 2 and the incorporation of dissolved HCO 3 − (Meyers, 2003;Leng and Marshall, 2004;Lamb et al, 2006), but in high-altitude and high-latitude lakes also ice cover can determine the availability of dissolved CO 2 (Striegl et al, 2001;Neumann et al, 2004). Studies of highlatitude lakes showed that a shortening of the ice cover period results in longer mixing of the lake during spring with a slower rate until summer stratification sets in, and vice versa if the ice cover period was longer (Couture et al, 2015;Pilla and Williamson, 2021). Therefore, we suggest at Shireet Naiman Nuur, where ice coverage is in the order of 7 months, that more dissolved CO 2 is available during shorter ice periods with longer mixing, resulting in more negative δ 13 C TOC values, (Laskar et al, 2004) and total solar irradiance (TSI) (Steinhilber et al, 2009) i.e., from 7.4 ± 0.3 to 4.3 ± 0.2 (Figure 6).…”

Nonlinear dynamics, resilience, and regime shifts in aquatic communities and ecosystems: an overview

“…A well‐established trend for inland waters is the shorter duration of seasonal ice cover, raising questions about how changes in winter ice affect seasonal phenology. Modeling this process along a latitudinal gradient for an exemplar lake reveals a change‐point between the date of ice breakup and the variability of the spring mixing period, with effects extending to summer stratification (Pilla and Williamson 2022). In this study, climate and latitudinal seasonality interact to produce differential impacts foreshadowing the types of complex effects that will result from warming.…”