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The temperature (Fig 3.2a) through the water column varied very little over depth
and time. The temperature was always between -3 and 3°C, which is substantiated by
previous studies (Laybourn-Parry et al., 2002). Ace Lake's meromictic status greatly affects
the water temperature. The monimolimnion
is reported to start around 10-12m (Gibson.
1999; Laybourn-Parry, unpublished A), but has been reported as high as 7-9m (Hand. 1980:
Bell & Laybourn-Parry,
1999b). An anomalous water temperature peak of 15.7°C was noted
at l Om during the September sampling trip; this temperature is very unlikely and was
probably due to equipment malfunction. The previous maximum temperature recorded in the
lake was 11.42°C (24th Feb, 1992, Rankin et al., 1999). Fluctuations in temperature correlate
well with fluctuations in salinity throughout the mixolimnion during January, March and
July (Fig. 3.16a, b and c). There tends to be an increase in temperature with depth, which
should act to destabilise the stratified layers but proves insufficient to overcome the salinity
gradient (Gibson, 1999; Rankin et al., 1999). The salinity gradient (by virtue of its density)
is the dominant force behind the maintenance of stratification (Gibson, 1999). The
permanent stratification of the lake means that the mixolimnion does not undergo thermal
inversion of its water column during the year, although mixing does occur as demonstrated
by the iso-haline condition of the mixolimnion
during September and November (Fig 3.4a).
Annual temperature fluctuations in Ace Lake are discussed by Hand and Burton (1981) and
Rankin (1999) who suggest that the mixolimnion reaches an isohaline state in winter when it
is cooled to about -1°C. It heats during the spring and summer and heat is transferred to the
thermocline at around 10m, where temperature increases sharply. Temperature at this depth
is balanced between radiative input from heat at the surface and conductive loss to the
surrounding cooler waters (Rankin et al., 1999). This seasonal heat transfer to 1Om results in
the highest temperatures at this depth which are maintained throughout the year (Rankin et
al., 1999). This corresponds with the data from the current work (Fig. 3.2a and 3.16a, b and
c).
Salinity within Ace Lake (Fig 3.4a) tends to remain relatively constant throughout
the year (Bell & Laybourn-Parry, 1999b), due to a balance between an increase in salinity
caused by evaporation and sublimation, and a decrease in salinity caused by melt water
input, both from ice cover melt out and melt stream input from the catchment area (Roberts
89