New profiling and mooring records help to assess variability of Lake Issyk-Kul and reveal unknown features of its thermohaline structure

Abstract

Abstract. This article reports the results of 3 field campaigns conducted in Lake Issyk-Kul in 2015, 2016, and 2017. Vertical CTD profiles were obtained and water samples collected at the total of 75 stations. 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 3 mooring stations in the eastern littoral region of the lake, yielding 147 days 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 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 the depth of 70–120 m, from where salinity slightly decreased downwards. The data from the moored thermistor chains support previously published hypothesis about 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 substantiate this hypothesis by estimates based on simple model assumptions.

Modeling subgrid lake energy balance in ORCHIDEE terrestrial scheme using the FLake lake model

“…Missing processes could also explain part of the errors such as the impact of water salinity, which could present seasonal and interannual variations linked to human activities and water level changes. In our evaluation, among the 15 lakes presenting the largest errors, three of them are saline lakes (Issyk-Kul, Urmia and Natron) with high salinity levels, and which can present salt crust regularly (Zavialov et al, 2018, Sima et al, 2013, Tebbs et al, 2013. Salinity impacts surface albedo and evaporation (which is lower compared to those of freshwater), and consequently the surface temperature and its seasonal evolution.…”

Variation of bacterial communities along the vertical gradient in Lake Issyk Kul, Kyrgyzstan

“…Table 1) and, in total, analysed 43 water samples. Sampling and measurement of physical and chemical variables were performed only from lake water samples using methods previously described (Zavialov et al ., 2018). Briefly, water samples were taken using HydroBios 5 L Niskin bottles at all stations at different depth levels from the surface to the bottom.…”

“…This lake arouses great scientific interest because of its geophysical and ecological characteristics. Being the sixth deepest lake in the world and tenth‐largest by volume, it reveals surprisingly high rates (below 11 years) of deep‐water renewal (Hofer et al ., 2002; Peeters et al ., 2003), which maintain the lake water column well‐oxygenated down to its deepest parts (Zavialov et al ., 2018). Despite the absence of any outflows, the lake water's salinity of 6 g/kg is relatively low, suggesting the lake to become endorheic relatively recently, possibly due to tectonic processes (Romanovsky, 2002).…”