Abstract
One of the most important physical characteristics driving lifecycle events in lakes is stratification. Already subtle variations in the timing of stratification onset and break-up (phenology) are known to have major ecological effects, mainly by determining the availability of light, nutrients, carbon and oxygen to organisms. Despite its ecological importance, historic and future global changes in stratification phenology are unknown. Here, we used a lake-climate model ensemble and long-term observational data, to investigate changes in lake stratification phenology across the Northern Hemisphere from 1901 to 2099. Under the high-greenhouse-gas-emission scenario, stratification will begin 22.0 ± 7.0 days earlier and end 11.3 ± 4.7 days later by the end of this century. It is very likely that this 33.3 ± 11.7 day prolongation in stratification will accelerate lake deoxygenation with subsequent effects on nutrient mineralization and phosphorus release from lake sediments. Further misalignment of lifecycle events, with possible irreversible changes for lake ecosystems, is also likely.
Highlights
One of the most important physical characteristics driving lifecycle events in lakes is stratification
We show that climate change during the twentyfirst century will have a considerable influence on stratification phenology, with lakes across the Northern Hemisphere stratifying sooner and maintaining their stratification for longer
Our long-term daily simulations suggest that thermal stratification in Northern Hemisphere lakes during the historic period typically begins between March and July and ends between June and December (Fig. 1)
Summary
One of the most important physical characteristics driving lifecycle events in lakes is stratification. The vast majority of lakes worldwide are located in the Northern Hemisphere, notably north of the mid-temperate climate zone[1] Lakes in these northern regions experience strong seasonality in climatic forcing, and, as a result, exhibit a pronounced seasonal variation in temperature[2]. In all but very shallow lakes (or some very deep lakes where stratification can be almost permanent), a stratified regime develops as heating outcompetes the effects of mixing— commonly referred to as the onset of stratification. On a global scale, the influence of climate change on stratification phenology remains largely unexplored This knowledge gap is of considerable concern given the high vulnerability of lake ecosystems, and the threatened biodiversity that they currently support, to climate change. Our results show that the duration of the thermally stratified period will increase within a warming world, with lakes situated at higher latitudes projected to experience the greatest relative change
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