Towards critical white ice conditions in lakes under global warming

Abstract

The quality of lake ice is of uppermost importance for ice safety and under-ice ecology, but its temporal and spatial variability is largely unknown. Here we conducted a coordinated lake ice quality sampling campaign across the Northern Hemisphere during one of the warmest winters since 1880 and show that lake ice during 2020/2021 commonly consisted of unstable white ice, at times contributing up to 100% to the total ice thickness. We observed that white ice increased over the winter season, becoming thickest and constituting the largest proportion of the ice layer towards the end of the ice cover season when fatal winter drownings occur most often and light limits the growth and reproduction of primary producers. We attribute the dominance of white ice before ice-off to air temperatures varying around the freezing point, a condition which occurs more frequently during warmer winters. Thus, under continued global warming, the prevalence of white ice is likely to substantially increase during the critical period before ice-off, for which we adjusted commonly used equations for human ice safety and light transmittance through ice.

Blooms also like it cold

“…Light is often a limiting factor for phytoplankton growth during winter months when the photoperiod is shorter. The absence or presence of ice cover can strongly affect the light quantity and quality, depending on ice characteristics (Lundberg et al 2007; Cavaliere et al 2021; Weyhenmeyer et al 2022). There are many taxon‐specific traits that enable survival/growth during low‐light conditions including shifts from a photochemically active state to a heterotrophic state adapted to low light (i.e., mixotrophy, e.g., Spirulina ; Vonshak et al 2000), optimizing light absorption efficiency and photosynthetic capacity via pigment packing and increased chlorophyll a (Chl a ) content (Hawes and Schwarz 2001; Palmer et al 2013; Lewis et al 2019), and shifting light absorption toward the blue‐green spectrum under ice (Rochet et al 1986).…”

Causes and consequences of changing oxygen availability in lakes

“…While some northern temperate lakes exhibit winter oxygen depletion and even anoxia under ice (Prowse andStephenson 1986, Ellis andStefan 1989), some of the highest oxygen saturation levels ever observed (>300%) were recorded in amictic lakes in Antarctica (Wharton et al 1986, Craig et al 1992. As lake ice cover in many regions is rapidly changing (Sharma et al 2021), it is vital to quantify the effects of shorter ice duration (Smits et al 2021), more intermittent ice cover (Sharma et al 2020), and changing ice quality (Weyhenmeyer et al 2022) on under-ice depth profiles, especially as shorter durations of ice cover may result in higher oxygen conditions in lake bottom layers (Flaim et al 2020).…”

Under‐ice plankton community response to snow removal experiment in bog lake

“…As lake ice duration shortens, it is projected that average lake ice thickness could decline by $0.35 m for 1300 of the world's largest lakes in coming years (Li et al 2021) due to rapidly warming winter air temperatures (Shatwell et al 2019). It is also predicted that as winters warm, the relative thickness of white ice to black ice will increase (Weyhenmeyer et al 2022). Concomitant with warming winters are projected changes in winter snowpack.…”