Hydrophysical processes in Lake Baikal in its transition from subtropical to modern climates

Abstract

During the past 5 million years significant changes have taken place in the Lake Baikal ecosystem. The climate changed from subtropical, with average annual air temperatures (T air ) of 15-10°C, to a moderate one with T air of $0°C. The modern hydrophysical regime of the lake has been formed with increase in depth, and gradual cooling of the water body from deepwater temperatures (T dw ) of 15-10°C to below 4°C. The processes of cooling of Lake Baikal water in its transition from subtropical climate with deep temperatures greater than those of maximal density (T md ) are similar to modern processes of deepwater cooling of the Mediterranean type of MEDOC convection. Such intensive mechanisms of vertical exchange (MVE) are similar to autumn homothermy in Lake Baikal. However, they are higher than T md . Inverse thermal stratification began to occur in surface layers in cold periods of the year after the deep water had cooled to T md . The character of water exchange also changed; instead of a monomictic lake with warm water from surface to bottom, the lake has become dimictic with lower water below 4°C, i.e. vertical mixing now occurs not once but twice a year. Winter ice cover began about a million years ago.

The endemic Cladophorales (Ulvophyceae) of ancient Lake Baikal represent a monophyletic group of very closely related but morphologically diverse species

“…, Macdonald et al. , Yokoyama and Goto , Sherstyankin and Kuimova , Schön and Martens , Karanovic and Sitnikova ), while algae have largely been ignored in evolutionary studies, with the exception of diatoms (Mann , Flower , Edlund and Soninkhishig , Kulikovskiy et al. ).…”

“…, Karanovic and Sitnikova ). During the last 5 My, the lake passed through several climate changes, from a subtropical (~5 Mya), a transitional stage (from ~2.6 to 2.4 Mya), to the current cold‐temperate climate (Sherstyankin and Kuimova ). Although the origin of the species and the timing of their radiation has not been investigated in all groups, it has been suggested that the cooling of the lake during the Pleistocene (~2 Mya) produced many of the species assemblages that are present to date (Sherbakov , Mats et al.…”

“…Research on speciation in Lake Baikal and other ancient lakes has focused on animals (Martens 1997, Hausdorf et al 2003, Macdonald et al 2005, Yokoyama and Goto 2005, Sherstyankin and Kuimova 2006, Sch€ on and Martens 2012, Karanovic and Sitnikova 2017, while algae have largely been ignored in evolutionary studies, with the exception of diatoms (Mann 1999, Flower 2005, Edlund and Soninkhishig 2009, Kulikovskiy et al 2012. Our data show that the morphologically and taxonomically diverse endemic Cladophorales of Lake Baikal represent a monophyletic group of closely related taxa nested within the morphologically simple genus Rhizoclonium.…”

“…Lake Baikal has shifted from a subtropical to a temperate climate during the past 5 million years (Sherstyankin and Kuimova 2006), which led to shifts in community composition and diversification in selected groups of organisms (Sherbakov 1999). Several rapid evolutionary radiations have been linked to historical events of drastic changes in environmental conditions providing settings of ecological opportunity with newly available niches (Yoder et al 2010, Genner and Turner 2011, Hou et al 2011, Sch€ on and Martens 2012.…”

Molecular analyses of ostracod flocks from Lake Baikal and Lake Tanganyika

“…Geological and climatic reconstructions provide further detailed information on the time of origin of these lakes and on changing environmental conditions over the millions of years of their history (e.g. for Lake Baikal (LB): Karabanov et al, 2004;Sherstyankin & Kuimova, 2006, for LT: Cohen et al, 1993, 1997Lezzar et al, 1996;Nicholson, 1999;Scholz et al, 2003). Molecular research on evolution and speciation of ancient lake taxa has mainly focused on cichlid fish (see Seehausen, 2006, andKoblmüller et al, 2008, for more recent reviews on cichlids), although molecular analyses on invertebrates such as crabs (Marijnissen et al, 2006(Marijnissen et al, , 2008, snails (West & Michel, 2000;Wilson et al, 2004;Albrecht et al, 2006Albrecht et al, , 2008Hauswald et al, 2008;Schultheiß et al, 2008), sponges (Schröder et al, 2002) and amphipods (Macdonald et al, 2005) have meanwhile also been published.…”