・Liping Zhu 5)Study of primary production magnitude under the thermocline (20-25 m) and the continuous supporting mechanism of production in Lake Pumayum Co, Tibetan Plateau AbstractTo study the primary production magnitude under the thermocline (20-25 m) and the continuous supporting mechanism of the production in Lake Pumayum Co (a high alpine lake) located on the southern Tibetan Plateau Thus, the subsurface primary production maximum appears to have formed in the 27-45 m water layer of the lake. Moreover, although this high alpine lake is generally classifi ed as oligotrophic and is located well above the forest line, primary production in the subsurface layer probably continued to exceed the mesotrophic magnitude.2) Because of the transport and supply mechanisms of nutrients supporting such high production under the thermocline, there can be deep intrusion of river water (5℃ ) colder than the lake epilimnion (10-13℃ ). This possibility is supported by the high average abundances of silt and clay, sinking terrestrial plant-derived organic carbon, and sinking soil-derived organic carbon in the 27-45 m water layer, as compared with the 0-27 m layer.The supply of nutrients in the 27-45 m water layer is believed to be several times higher than that of the 0-27 m