Thaw depth was measured using a steel probe in the Imnavait Creek watershed, near Toolik Lake, Alaska. The thaw grid includes measurements made from the valley bottom (on both sides of the stream), up the hillslope to the hilltop (watershed boundary). The thaw grid is near Imnavait water tracks 7 and 8, and measurements have been made from the 2003 season until present. Two surveys are conducted each summer, on 2 July and on 11 August (plus or minus 1-2 days on either side of those dates).
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Starting in 2003, thaw depth has been measured in the Imnavait Creek watershed several times during the summer season, and after after 2010 the surveys were made twice a year as close to 2 July and 11 August as possible (plus or minus 1-2 days). The UTM grid (stakes are in a grid at every 100 meters) was used to locate the starting points, and a tape measure was used to mark points every 25 m in between the UTM stakes. The grid covers the watershed from the valley bottom on both sides of the stream (in wet sedge tundra), up the hillslope of moist acid tussock tundra, to the top of the hillslope on the eastern watershed boundary in hilltop heath tundra. At each of 97 sites on the grid a ruled stainless steel rod was inserted in non-tussock microhabitat (that is, not on top of a tussock but in the space between tussocks) until the frozen layer was reached, and the distance was measured to the top of the upper soil organic mat (beneath the uppermost moss layer if present). Three measurements are made at each site (point on the grid) within a 50 cm radius of each location point. The measurements for all sites are averaged to arrive at an annual value of thaw depth for 2 July and for 11 August.
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1/26/2010 JMK- Updated to add the 2009 Data
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