Observations of a deep-mixing event in Crater Lake, Oregon

Abstract

We present observations of the evolution of a deep-mixing event in a deep, temperate lake. The observations were obtained from thermistors mounted on a long-term mooring in the lake. The event seems to have originated near 150-m depth and resulted in a plume or layer of cold water from the upper half of the lake that descended to the lake bottom (590 m) over a 3-d period. Net mixing associated with this event resulted in an overall vertical heat exchange of nearly 1015 J and a volume exchange of 0.7-3.2 km3 (4-18% of the lake volume) between the upper and lower portions of the lake. The deep water displaced during the event is estimated to have carded 0.32.5 x 106 mol of nitrate to the upper lake, which accounts for a significant portion of the average annual nitrate flux (~2-4 x 106 mol yr-1) thought to be upwelled in this highly oligotrophic system.