Abstract
Abstract. This article reports the results of three field campaigns conducted in Lake Issyk-Kul in 2015, 2016, and 2017. During the campaigns, CTD profiling and water sampling were performed at 34 locations all over the lake. A total of 75 CTD profiles were obtained. Some biogeochemical and thermohaline parameters at the lake surface were also mapped at high horizontal resolution along the ship's track. In addition, thermistor chains were deployed at three mooring stations in the eastern littoral region of the lake, yielding 147-day-long records of temperature data. The measurements revealed that – while the thermal state of the active layer, as well as some biogeochemical characteristics, were subject to significant interannual variability mediated by atmospheric forcing – the haline structure of the entire lake was remarkably stable at the interannual scale. Our data do not confirm the reports of progressive warming of the deep Issyk-Kul waters as suggested in some previous publications. However, they do indicate a positive trend of salinity in the lake's interior over the last 3 decades. A noteworthy newly found feature is a weak but persistent salinity maximum below the thermocline at a depth of 70–120 m, from where salinity slightly decreased downwards. The data from the moored thermistor chains support the previously published hypothesis about the significant role of the submerged ancient riverbeds on the eastern shelf in advecting littoral waters into the deep portion of the lake during differential cooling period. We hypothesize that the less saline littoral water penetrating into the deep layers due to this mechanism is responsible for the abovementioned features of salinity profile, and we substantiate this hypothesis by estimates based on simple model assumptions.
Highlights
With its volume of 1730 km3, Lake Issyk-Kul is the tenthlargest lake by volume on Earth overall and the secondlargest mountain lake
The official navigation map published by the USSR General Staff in 1978 indicated 663 m; Hofer et al (2002) suggested 650 m; a value of 668 m was given by Giralt et al (2002) and a number of other publications; and some authors (e.g., Alamatov and Mikkola, 2011), as well as assorted sources on the Internet, including the Russian-language Wikipedia, give a value of 702 m
The most plausible is the maximum depth of 668 m, as it was established based on high-quality echo-sounding data (De Batist et al, 2001)
Summary
With its volume of 1730 km, Lake Issyk-Kul is the tenthlargest lake by volume on Earth overall and the secondlargest mountain lake. It is the sixth-deepest lake of the world. Even until recently, the information on the maximum depth of the lake in the available literature has been contradictory. The most plausible is the maximum depth of 668 m, as it was established based on high-quality echo-sounding data (De Batist et al, 2001). As an enclosed terminal water body, Lake Issyk-Kul is sensible to climate change in its catchment area. Some summarizing estimates of the water budget components can be found in Romanovsky (2002) and Kulenbekov and Merkel (2012), for example; there are large uncertainties
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