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Deep Core Studies of the Accumulation and Densification of Snow at Byrd Station and Little America V, Antarctica
Authors: Gow A
Year: 1968
Keywords: RR 197, deep core drilling in ice sheets, ice core, Antarctic glaciology
Periodical/Journal: CRREL Research Report 197
Abstract: Snow and ice cores from two deep drill holes in Antarctica were studied to determine past records of snow accumulation and density variations with depth in the Antarctic ice sheet. Data on the variation of porosity and ice load with depth were also obtained. Byrd Station, located on the inland ice of West Antarctica, was the site of the first drill hole, which reached a depth of 309 m in ice estimated to be about 2500 m thick. Detailed analysis of the core stratigraphy to 88.6 cm-2 annually since 1549 AD. Apart from a small but persistent decline in accumulation between 1839 and 1954 no major variations in snow accumulation were observed. The total absence of melt layers would indicate that surface air temperatures in the vicinity of Byrd Station have not risen above freezing for the last 1900 years - the estimated age of the ice at 309 - m depth. A second hole was drilled at Little America V at a point less than 3 km from the seaward edge of the Ross Ice Shelf. The ice at this location was about 258 m thick and cores were obtained to within 2 to 3 m of the bottom. No saline ice was encountered in any of the cores and all indications are that the bottom of the Ross Ice Shelf at Little America V is melting rather than accreting sea ice. Studies of core stratigraphy to 39 - m depth revealed 105 years of snow deposition; the average rate of accumulation was 22.1 g cm-2 yr-1 . Occasional periods of intensive melt were observed throughout the stratigraphic sequence but no significant deviations in the accumulation record were detected. Three thin layers of debris, tentatively identified as volcanic ash, were observed at depths of 171, 219 and 223 m respectively. These ashes are thought to have been deposited from volcanoes in Marie Byrd Land more than 2000 years ago. Depth-density and surface elevation data show that the Ross Ice Shelf at Little America V is free floating and almost exactly five-sixths submerged. An anomalous increase in the rate of densification of firn below 35 m is attributed to large horizontal stresses in the ice shelf. A Little America firn transformed into ice at 51 to 52 m after only about 150 years. The same transformation at Byrd Station took nearly 300 years and was accomplished at 64-65 m depth. The densification process in polar snow is discussed and a method of predicting depth - density profiles from mean annual accumulation and temperature data is presented together with examples and other useful applications of the data.
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