Fluid permeability measurements taken on vertical component of sea ice during the SIPEX II voyage of the Aurora Australis, 2012

Brief description

A 9 cm diameter Kovacs corer was used to drill holes partially through the ice. The core was removed, creating a pressure head in the hole. Packers made of ABS tubing wrapped with foam to create a tight seal were inserted into the holes to block the horizontal component of flow. A "Levelogger", which is a pressure transducer for monitoring well-water, created by Solinst, was then inserted into each hole to record the change in water level over time. Each Levelogger was fitted into a plastic holder to keep it upright during measurement, which is a requirement for accurate data from the device. The temperature at the bottom of the core was measured immediately after removal, and the bottom 2 centimetres were removed for melting and subsequent measurement of salinity. The measurements of salinity and temperature enable calculation of the brine volume fraction. Solinst Levelogger software was then used to compensate for local barometric changes recorded using a Solinst Barologger. Following each measurement an auger was used to drill through the bottom of each hole to measure the ice thickness and freeboard in each hole. A full core was taken at each worksite for crystallographic study, immediately adjacent to where permeability measurements were taken. A temperature profile was taken on each of these cores immediately after extraction. Cores were then moved to a -20 degree C cold room for further processing. A thin vertical section, approximately 3mm thick, was taken from each of the cores stored for analysis. These sections were placed between a pair of cross polarised plates and photographed. Each photo was labelled with the core and date it was taken, and was photographed with a meter stick for scale. After the thin sections were photographed, the remaining samples were melted to measure salinity. Some of the melted sea ice was saved for later O18 analysis to distinguish samples containing snow-ice. Recorded values required to determine permeability are contained within the Master_Core_List.xls Excel spreadsheet, found in the Permeability worksheet. This worksheet is generated directly from notebook data, and contains the date, start and end time for each permeability record, the core number assigned, the depth of the partial sackhole, the levelogger serial number used, the station (site), the temperature 2cm from the bottom of the removed core, the bulk salinity from the bottom 2cm of the removed core, as well as the measured freeboard and thickness at each site. This worksheet also contains a column to indicate which crystal structure the crystallographic core taken from this site and depth had, as well as which crystallographic core this came from. Finally, the worksheet contains notes, and a column to indicate whether we believe this data is somehow bad. Please see the notes section for reasons why a data point was determined invalid. Typically was due to heavy rafting beneath the flow or too quick an influx of water to properly measure. All permeability data can be found both in the original binary .xle format used by Solinst levelogger software, as well as exported into comma separated value (CSV) files. These files are located in the datalogger_data directory. Binary files are contained in the raw folder, organised into sub folders by station number. The CSV files are located in the csv folder, again organised into sub folders by station number. Photos of the crystallography cores can be found in the crystallography folder, separated into subfolders labelled with the site and core number. Each photo also contains a tag indicating the core number, site taken, date, and what depth range this covers. Tags may not contain a depth range for cores less than 1 meter. Please see the meter stick in each photo for scale. Scans of the original notebooks from which the Permeability worksheet were created are provided in the scanned_notebook directory.

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Progress Code: completed

Statement: Please see the Permeability worksheet in the Master_Permeability.xls spreadsheet for individual data points marked bad, as well as notes regarding why they were bad. In general, these data points were marked bad for one of three reasons. The first occurred when the sack hole was drilled too deep. Within the bottom few centimetres of ice the ice became too permeable to block the horizontal component of flow and insert the pressure transducer before the hole had filled to freeboard. Inserting the packer and deploying the pressure transducer typically took between 5 and 10 seconds, which on occasion was not fast enough. The second problem we encountered was a bottom slush layer below sites 7 and 8. At the beginning of each day a hole was drilled into the slush layer to verify the fluid flowed in and equalized with the freeboard as quickly as would be expected in the ocean. Additional data analysis, potentially including modelling work, will be required to determine the effect of this slush layer on the values recorded. The third problem occurred due to the rafted nature of floes. On occasion, attempts to auger through the ice for thickness measurement resulted in the discovery of a raft below the ice. In particular this was a problem at site 3. Following the discovery of this problem the presence of rafting became criteria in determining an appropriate worksite. Auger holes were created while scouting for worksites to look for rafting. Potential worksites with rafting were rejected in favour of another area.