Abstract
Lake Tanganyika, the deepest and most voluminous lake in Africa, has warmed over the last century in response to climate change. Separate analyses of surface warming rates estimated from in situ instruments, satellites, and a paleolimnological temperature proxy (TEX86) disagree, leaving uncertainty about the thermal sensitivity of Lake Tanganyika to climate change. Here, we use a comprehensive database of in situ temperature data from the top 100 meters of the water column that span the lake’s seasonal range and lateral extent to demonstrate that long-term temperature trends in Lake Tanganyika depend strongly on depth, season, and latitude. The observed spatiotemporal variation in surface warming rates accounts for small differences between warming rate estimates from in situ instruments and satellite data. However, after accounting for spatiotemporal variation in temperature and warming rates, the TEX86 paleolimnological proxy yields lower surface temperatures (1.46 °C lower on average) and faster warming rates (by a factor of three) than in situ measurements. Based on the ecology of Thaumarchaeota (the microbes whose biomolecules are involved with generating the TEX86 proxy), we offer a reinterpretation of the TEX86 data from Lake Tanganyika as the temperature of the low-oxygen zone, rather than of the lake surface temperature as has been suggested previously. Our analyses provide a thorough accounting of spatiotemporal variation in warming rates, offering strong evidence that thermal and ecological shifts observed in this massive tropical lake over the last century are robust and in step with global climate change.
Highlights
Climate change is altering the thermal characteristics of lakes worldwide, leading to a broad range of impacts on ecosystem processes [1]
The models fit to in situ temperature observations in the upper water column of Lake Tanganyika accounted for 44–89% of the variation in temperature depending on the depth to which the model was fit (S2 Fig)
Though our statistical approach to the incomplete space-time matrix of in situ observations from Lake Tanganyika has limitations, it reveals consistent patterns of spatial variation in warming that illustrate a need to assess the spatial dimensions of warming within large lakes
Summary
Climate change is altering the thermal characteristics of lakes worldwide, leading to a broad range of impacts on ecosystem processes [1]. Despite recognition that climate change has important direct and indirect effects on lake ecosystems, monitoring of long-term thermal changes in lakes remains limited. Compared with temperate and arctic lakes, long-term, in situ lake temperature data sets are rare in the tropics. Satellite remote sensing of lake surface temperatures can redress the latitudinal bias of temperature monitoring for large lakes. Remote sensing typically yields comparable results to in situ monitoring [9,10], but is presently limited to only three decades of imagery. Paleolimnological temperature proxies can expand the temporal scales of lake temperature measurement, but the expense of core collection and analysis limits the spatial scope of this approach. Assessment programs should simultaneously consider multiple independent methods to cover longer timescales and allow maximal spatial and temporal resolution
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