Cyclonic circulation and upwelling in Lake Baikal

Abstract

We investigated upwelling events in the pelagic area of Lake Baikal that developed during summer stratification (July-November) using a combination of in situ and satellite observations. These upwellings appear in the centres of local cyclonic macrovortices with compensatory downwelling located on their periphery in coastal areas. The average duration of upwelling events was 5 weeks, with an observed maximum of 16 weeks. The most stable upwellings in Southern Baikal and over the Academician Ridge covered areas of up to 4,400 km 2 (59 % of Southern Baikal's surface) and 1,550 km 2 , respectively. Water was ascending in the upwelling zones at velocities of 1 9 10 -4 to 1.2 9 10 -2 cm s -1 . Temperature differences of 1-4°C and 2-13°C were observed between the downwelling and upwelling zones in the epilimnion and metalimnion, respectively. On the surface of the lake, water temperature can drop 4-7°C for water ascending from depths of 10-75 m, but the observed thickness of the layer within which water was ascending reached a depth of 280 m in August-September and 380 m in October; i.e. the ascending water included the entire upper layer (0-300 m). Geostrophic currents reached up to 24-38 cm s -1 on the boundary between up-and downwelling zones (usually 5-7 km offshore), but did not exceed 6-10 cm s -1 in the centres of upwelling zones.Comparison with other large lakes of the world is carried. This study is important for understanding the upwelling process that develops in Lake Baikal during summer stratification and can influence the heterogeneity of nutrients and primary production.

Coexistence of two Cyclotella diatom species in the plankton of Lake Baikal

“…The temperatures had to fall below 11 °C for C. minuta to begin cell division and below 6 °C for C. baicalensis . Figure shows changes in 1998, but three other years (1996, 1997 and 1999) were similar (see also Troitskaya et al ., for 1999). In August 1998, surface temperatures over the whole south basin were too high for cell division of either species.…”

Insights into the transfer of silicon isotopes into the sediment record

“…This ice cover plays a key role in regulating seasonal diatom productivity (as discussed in Sect. 2) with blooms developing following the (1) reductions in ice cover in spring and (2) after mixed-layer stratification in summer (Shimaraev et al, 1994;Popovskaya, 2000;Granin et al, 2000;Jewson et al, 2009;Troitskaya et al, 2014). These blooms are also coincident with periods of overturn in the upper waters of the lake (e.g.…”

“…In the upper waters (above ca. 200-300 m), both convective and wind forced mixing occurs twice a year (Shimaraev et al, 1994;Troitskaya et al, 2014) during spring and autumn overturn periods. These overturn periods follow (precede) ice-off (on) respectively and are separated by a period of summer surface water stratification (e.g.…”

Temperature gradient affects differentiation of gene expression and SNP allele frequencies in the dominant Lake Baikal zooplankton species

“…Each location has also been characterized by multiyear averages of August–September temperature at the surface, 10 m and 50 m from the nearest 1–3 stations available from the Limnological Institute Baikal Water Temperature database (Shimaraev, Troitskaya, & Gnatovsky, ; M. N. Shimaraev, personal communication ). Multiyear averages of temperatures from several nearby locations better characterize temperature regimes experienced by zooplankton in each region of Baikal than the snapshot data from the sampling date which are strongly influenced by local wind and upwelling conditions (Shimaraev & Domysheva, ; Troitskaya et al., ).…”