11/14/2023 0 Comments Lake turnover water temperature![]() High-frequency measurements reveal otherwise undetectable deep water dynamics during a noted period of warming in the world’s lakes. Here we show how seasonal changes in the timing of overturn and stratification link surface warming trends to deep water temperatures in a large dimictic lake using three decades of nearly continuous subsurface water temperature observations in Lake Michigan. weekly, monthly, etc.), or of insufficient duration for long-term analysis. Therefore, our understanding of how our largest lakes are responding to climate change at depth has been formed either by translating what has been observed at the lake surface or by subsurface observations that are limited in vertical resolution (depth), temporal frequency (e.g. Measurements of hypolimnetic water temperatures suitable for long-term trend analysis are limited to a few studies in deep lakes 10, 12, 14, 23, 24, 25, 26, 27, 28, although, projected connections between climate change induced thermal structure changes and mixing regime shift have been demonstrated through numerical modeling 15, 29. Therefore, direct observations of subsurface thermal structure are imperative to the interpretation of climate impacts on the majority of Earth’s freshwater 2. However, these trends in surface temperatures are not easily translated into the more complex deep subsurface conditions, where stratification, thermocline depth, and density gradient influence subsurface mixing. There has been an improved understanding of year-round or seasonal surface trends from satellite remote sensing in recent years that demonstrates the physical drivers of surface warming and the spatial and temporal variation of LSWT warming and overturn in the Laurentian Great Lakes 20, 21, 22. Most of our understanding of large lake warming trends comes from observations of summer LSWT due to data availability restrictions in satellite measurements, buoy deployment schedules, and seasonal ice conditions 6, 7, 16, 17, 18, 19. Subsurface conditions in the largest lakes, hereby referred to as large lakes, are a missing piece in the global climate change narrative. from dimictic to monomictic mixing conditions 2, 3, 15. Subsurface waters in deep lakes can provide an important signal because they integrate conditions across years, providing a climate memory 14, and can help identify the potential for ecological and thermal shifts, e.g. While an abundance of surface measurements reveal surface warming in response to climate change 13, subsurface observations are relatively sparse and may tell a story that is more indicative of long-term climate change impacts. Several lakes appear to be warming faster than ocean temperatures (0.12 ☌/decade) and regional air temperatures (0.25 ☌/decade), including the world’s largest lakes 6, 7, 10, 11, 12. As air temperatures trend upward, global lake surface water temperatures (LSWT) have warmed by an average of 0.21 ☌/decade 5, 6, 7, 8, 9. ![]() Because of the sensitivity to changing conditions, along with the ability to integrate climate conditions across the watershed and produce measurable signals of climate-impacted parameters, lakes have been identified as ideal climate change sentinels 2, 3, 4. ![]() Shifts in the thermal regimes of large lakes will have profound impacts on the ecosystems of the world’s surface freshwater.Įighty-four percent of Earth’s non-frozen, surface freshwater is found in the 10 largest lakes 1. Relationships from the data show a shortened winter season results in higher subsurface temperatures and earlier onset of summer stratification. This unique data set reveals that deep water temperatures are rising in the winter and provides precise measurements of the timing of fall overturn, the point of minimum temperature, and the duration of the winter cooling period. ![]() We present an analysis of three decades of high frequency (3-hourly and hourly) subsurface water temperature data from Lake Michigan. While the response of lake surface water temperatures to climate change is well documented from satellite and summer in situ measurements, our understanding of how water temperatures in large lakes are responding at depth is limited, as few large lakes have detailed long-term subsurface observations. Most of Earth’s fresh surface water is consolidated in just a few of its largest lakes, and because of their unique response to environmental conditions, lakes have been identified as climate change sentinels.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |