Deep‐water renewal in Lake Issyk‐Kul driven by differential cooling

Abstract

During two field campaigns on Lake Issyk-Kul in March and August 2001, 179 high-resolution conductivitytemperature-depth profiles were measured, along with profiles of dissolved oxygen and light transmission. On the basis of this extensive data set, we investigated the large-scale vertical advective processes responsible for deepwater renewal in Lake Issyk-Kul. At some locations sampled in March, variable peak structures in the tracer profiles were observed that indicate horizontally localized intrusions. These intrusions have their origin in density plumes that propagate along the bottom of the channels in the eastern shelf region. The cold dense water at the bottom of the channels is most likely generated by differential cooling of the water in the shallow shelf regions during winter. During summer, vertical advective processes appear to be limited to the upper 200 m, where upwelling in the open water leads to a doming structure. The August data support the results of earlier investigations that suggested that dynamic forcing by a basinwide gyre is responsible for the upwelling in the open water. Lake Issyk-Kul, which is located at an altitude of 1,606 m in the Tien Chan mountains of northeast Kyrgyzstan, is one of the largest (1740 km 3 ) and deepest (668 m) lakes in the world. It is a closed basin lake and is slightly saline, with 6 g kg Ϫ1 of dissolved ionic substances (Tsigelnaya 1995). Despite its depth, the lake has large, shallow shelf regions, predominantly in the east and west (Fig. 1a). Twenty-seven percent of the lake (by area) is shallower than 50 m. During previous periods of low lake level, the area of the lake was therefore considerably less than it is now. The river valleys that were cut into the land surrounding the lake at this time were later submerged as the lake level rose and are now easily recognizable on the bathymetric map of Lake Issyk-Kul (Fig. 1a) as channels cut into what are now the shallow regions of the lake (Tsigelnaya 1995).More than 50% of the water volume of the lake is located below 200 m depth. Hence, the exchange between surface and deep water is an important factor in determining the distribution of dissolved substances in the lake and must be taken into account in assessing the ecological impact of pollutants and nutrients possibly introduced by spills (associ-

Cyclonic circulation and upwelling in Lake Baikal

“…The thickness of the upwelling zone layer in large lakes of the world can vary from 10 to 20 m in Lake Onega (17 m, Boyarinov and Petrov 1991) to several tens of metres in Lake Tanganyika (60-66 m, Corman et al 2010) and up to hundreds of metres in Lake Issyk-Kul (100-200 m, Romanovskiy and Shabunin 1981;Kipfer and Peeters 2002;Peeters et al 2003) and Lake Baikal (300-400 m, present paper). The temperature differences between up-and downwelling zones on the water surface of temperate lakes is similar, varying within 5-8°C in July-September (Romanovskiy and Shabunin 1981, present paper) and decreasing by up to 1-1.5°C in OctoberNovember (Romanovskiy and Shabunin 1981, Fig.…”

“…The authors found that upwellings in the pelagic area of the lake lead to an increase in dissolved oxygen in the surface layer Shabunin 1981, 2002) that is inversely distributed during summer stratification (Karmanchuk 2002). Later, in a study of vertical water exchange using temperature, conductivity, pressure, dissolved oxygen and light transmission data, Kipfer and Peeters (2002) and Peeters et al (2003) described upwelling in the upper 200-m layer of the water in the central part of Lake Issyk-Kul. Corman et al (2010) analysed upwellings in Lake Tanganyika induced by longitudinal winds and their influence on changes in water temperature and concentrations of nutrients and phytoplankton.…”

“…Afanaseva (1977) also showed that vertical movements of water in an upwelling zone can transport nauplii of the copepod Epishura baikalensis from deep water layers to the surface water. Based on phytoplankton measurements and SeaWiFS satellite observations in -2003, Heim et al (2005 concluded that reduced chlorophyll a concentrations along the eastern shore of Northern Baikal were associated with upwelling events. Notably, chlorophyll a concentrations can increase after upwelling relaxation, as was noted by Verbolov et al (1992) during complex hydrophysical studies at a site near Cape Elokhin (the western shore of Northern Baikal) in August 1988.…”

The physics of the warming of Lake Tanganyika by climate change

“…In contrast, 80% of the lake's volume (14,960 km 3 or 459 m averaged over the lake surface) is cooler than 24uC, and 76% is cooler than 23.85uC (potential temperatures). Deep cool water formation is not likely driven by evaporative cooling under current conditions occurring offshore (Peeters et al 2003), but is more likely driven by cooling in shallow inshore areas, where surface cooling is more rapid than offshore (Wells and Sherman 2001), followed by convective downflows along the bottom, starting at the lake margins. Such cooling of the hypolimnion by marginal downflows does not require overturn mixing, although these downflows may entrain larger volumes, and does not disrupt stratification, but instead maintains it.…”

Consideration of Water Uses for Its Sustainable Management, the Case of Issyk-Kul Lake, Kyrgyzstan

“…It is situated at an altitude of 1607 m above sea level and surrounded by high mountain ranges: the Kungey Ala-Too Range in the north with the highest peaks reaching 4770 m, and the Teskey Ala-Too Range in the south with peaks exceeding 5200 m [22][23][24], see in Figure 1. The total area equals approximately 22,080 km 2 , of which the lake occupies 6236 km 2 , the coastal zone called zone dissipation runoff occupies 3092 km 2 , and other part of the basin (12,752 km 2 ) is occupied by mountain areas.…”