Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

A Time Series of Environmental Tracer Data from Deep, Meromictic Lake Lugano, Switzerland

W. Aeschbach-Hertig, C.P. Holzner, M. Hofer, M. Simona, A. Barbieri and R. Kipfer
Limnology and Oceanography
Vol. 52, No. 1 (Jan., 2007), pp. 257-273
Stable URL: http://www.jstor.org/stable/40006079
Page Count: 17
  • More info
  • Cite this Item
A Time Series of Environmental Tracer Data from Deep, Meromictic Lake Lugano, Switzerland
Preview not available

Abstract

An 11-yr (1990-2001) time series of tritium-helium-3 (³H-³He) apparent water ages as well as one sulfur hexafluoride (SF₆) profile were used to study the development of the vertical mixing dynamics of the deep, meromictic northern basin of Lake Lugano. The density stratification of the water column was dominated by an increase in dissolved ions with depth, which remained approximately constant during the 1990s. The deep-water temperature increased steadily during this period, passing a threshold above which cooling of the surface water could force convection. However, increasingly mild winter temperatures prevented the occurrence of a turnover until 2005. The maximum apparent ³H-³He water age increased from about 16 yr in 1990 to 23 yr in 2001. The maximum apparent SF₆ age in 2001 was 12.8 yr. The large difference between the apparent ³H-³He and SF₆ ages is at least partly due to nonlinear effects of mixing, causing SF₆ ages to underestimate the true mean deep-water residence time, whereas ³H-³He ages overestimate it. The decreasing concentrations of ³H and ³He are more reliable indicators of the continuous deep-water exchange in the lake than are the apparent ages. Budget calculations using the tracer concentrations reveal an annual renewal of the deep water below 100 m in depth by about 8% and enable the calculation of long-term mean profiles of the effective vertical turbulent diffusivity ${\rm{K}}_{\rm{z}} $ No trend in the mixing intensity during the 1990s could be determined. The radiogenic He flux into the lake is comparable to estimates of the whole crustal degassing flux.

Page Thumbnails

  • Thumbnail: Page 
257
    257
  • Thumbnail: Page 
258
    258
  • Thumbnail: Page 
259
    259
  • Thumbnail: Page 
260
    260
  • Thumbnail: Page 
261
    261
  • Thumbnail: Page 
262
    262
  • Thumbnail: Page 
263
    263
  • Thumbnail: Page 
264
    264
  • Thumbnail: Page 
265
    265
  • Thumbnail: Page 
266
    266
  • Thumbnail: Page 
267
    267
  • Thumbnail: Page 
268
    268
  • Thumbnail: Page 
269
    269
  • Thumbnail: Page 
270
    270
  • Thumbnail: Page 
271
    271
  • Thumbnail: Page 
272
    272
  • Thumbnail: Page 
273
    273