The Deep Lake surface level indicator is defined as the depth below sea level of the surface of Deep Lake in the Vestfold Hills.
TYPE OF INDICATOR
There are three types of indicators used in this report:
1.Describes the CONDITION of important elements of a system;
2.Show the extent of the major PRESSURES exerted on a system;
3.Determine RESPONSES to either condition or changes in the condition of a system.
This indicator is one of: CONDITION
RATIONALE FOR INDICATOR SELECTION
Deep Lake is the most saline of the lakes of the Vestfold Hills, and due to its salinity, has never been known to completely freeze. It is the only major lake in Antarctica with this characteristic, which makes it a prime candidate for monitoring water levels. This was recognised many years ago, and the water level has been monitored on a monthly basis since 1976. This 25-year long database is one of the longest non-weather records of the natural environment in Antarctica. Significant changes in the water level have been observed over this time.
The water level is related to water balance, that is the difference between inputs by direct precipitation or from melt of snow banks in the drainage basin, and losses, which include evaporation when the lake is ice free and ablation when it ice covered.
Net loss terms are thought to be relatively constant from year to year, and therefore water level is a measure of net precipitation. This may be direct (falling within the drainage basin) or indirect (initially falling elsewhere, but blown into the drainage basin by strong winds).
The water level of Deep Lake is a technologically simple measure of an important parameter. The long existing database should be continued, and means that all data collected can immediately be put into a long-term view.
DESIGN AND STRATEGY FOR INDICATOR MONITORING PROGRAM
Spatial scale: Deep Lake in the Vestfold Hills near Davis Station Antarctica.
Selection of Monitor. One member of the wintering group at Davis each year will be designated the Deep Lake monitor, preferably during pre-departure training. This person should discuss the project with the indicator custodian, and be comfortable with the requirements of the position prior to leaving for Antarctica. In the past, the person responsible for the measurements has often been a non-scientist who otherwise would not normally get off base regularly. This role provides a mechanism by which non-scientists can become involved in a long term scientific program.
If at all possible, there should be a joint visit to Deep Lake by the outgoing and incoming monitors over summer so that details of the location of the pole, method for reading and input of the data into SIMR can be passed on. It is recognised that this may not be possible during changeover, but if the monitors share a longer period together on base, such a visit to the lake should be made.
If the Deep Lake monitor has to leave Davis before winter, or no longer feels he or she is able to fulfil this role, another expeditioner should be designated to maintain continuity of the record.
Frequency: Readings of the surface level of Deep Lake should be taken monthly, preferably within the last few days of any month. A week prior the end of the month, an email will be sent to the Deep Lake monitor reminding him or her that a measurement is due. If no data have been input into the SIMR system by the end of the month, another email will be sent, which will be copied to the Station Leader. This formal monthly reading does not preclude other visitors to the lake recording data. Any expeditioners visiting the lake should be encouraged to record data and pass it on to the designated monitor for inclusion within SIMR. If readings input appear to be in error, the Indicator Custodian will contact the monitor and either work out the problem or request another measurement be made.
Technique: Water level is measured by use of a marked pole located near the edge of the lake, which is in turn tied in to a nearby, accurately surveyed, benchmark. The pole is marked in at 1 cm intervals, and should be read to the closest centimetre. At least two expeditioners should make independent estimates of the water level, which are then compared and a consensus reached. This value, which is a relative, rather than direct measure of the water level of Deep Lake, is input into the SIMR system. While at the lake, note should be taken of the state of the pole. If any change in the position of the pole has occurred since the last visit, an email should be sent to the Indicator Custodian, giving details.
The position of the pole should be checked on an annual basis over summer. This process can be done by surveyors, or, if none are available at Davis, by expeditioners after consultation with the Indicator Custodian and the Mapping Officer, Antarctic Division.
On the 22 Feb 2000, the base or zero reading of the &Tide Pole& at Deep Lake was 51.333 metres below sea level. To derive the water level of Deep Lake below mean sea level, the water level reading on the &Tide Pole& is added to -51.333. Note that this is a negative value so any water level readings will produce a smaller negative number.
The annual cycle in water level can be readily explained, but longer-term variations are more difficult.
The input and output terms are understood, but how these are controlled by the weather is less clear. Analysis of the water level data as well as weather data from Davis station currently underway should clarify the situation.
LINKS TO OTHER INDICATORS
This indicator is linked with weather data from Davis station.