Physical Limnology

Weekly CTD profile measurements of conductivity, specific conductance, temperature, depth, density, and salinity from Lake Hoare, McMurdo Dry Valleys, Antarctica during the 2012-2013 austral summer


As part of the McMurdo Dry Valleys Long Term Ecological Research (LTER) project, we investigated relationships between wind conditions and barotropic seiches within Lake Hoare, located in Taylor Valley, Antarctica, during the 2012-2013 austral summer. Temporal changes in the water column were measured using a rugged, handheld, CastAway CTD (conductivity-temperature-depth probe, manufactured by SonTek), deployed through the Lake Hoare Limno Hole (note, this is a separate instrument from the SeaBird CTD used as part of the MCM LTER core limnological monitoring program). The CastAway CTD directly measures temperature, electrical conductivity, and pressure at 5 Hz as it free-falls through the water column at a rate of approximately 1 m s-1 on the downward cast and approximately 0.3 m s-1 on the upward cast. The device calculates salinity and density using the International Equation of State for Seawater, called EOS-80. This data package provides 27 profiles of depth, temperature, conductivity, specific conductance, salinity, and density collected between November 25, 2012 and January 21, 2013. In general, three profiles were collected over a ten-minute-period every seven days for 57 days. Five profiles were collected prior to the arrival of spring melt, four profiles were collected during the arrival of spring melt on December 7, 2012, and 18 profiles were collected after the arrival of spring melt continuing into late summer.

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A description of the CastAway CTD methods and equations can be downloaded from the manufacture, SonTek, at the following URL:

The following procedure was used at the Lake Hoare Limno Hole:

  1. Ice was cleared from the Limno Hole.
  2. The CTD was connected to a 50-m-long nylon line attached to a hand reel with a diameter of 9.5 cm.
  3. The CTD was powered on, placed on the ice adjacent to the Limno Hole, and allowed several minutes to determine its location using its onboard GPS.
  4. The CTD was suspended 10 cm below the water surface and held in place for approximately 10 seconds.
  5. The CTD was allowed to free fall through the water column to the lake bottom on the downward cast at a rate of approximately 1 m s-1. Once the line on the surface became slack, the researcher smoothly reeled in the line for an upward cast at a rate of approximately 0.3 m s-1 (approximately 1 revolution of the reel per second).
  6. Data were sent to a laptop computer via bluetooth connection.
  7. Data were viewed and exported to CVS format using the program CastAway CTD v1.5 (SonTek, January 30, 2012).

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Funding provided by the National Science Foundation Grants #OPP-1115245 and #OPP-1637708 for Long Term Ecological Research.


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