Subglacial water pressure and ice-speed variations at Johnsons Glacier, Livingston Island, Antarctic Peninsula

To study subglacial hydrological condition and its influence on the glacier dynamics, we drilled Johnsons Glacier on Livingston Island in the Antarctic Peninsula region. Subglacial water pressure was recorded in boreholes at two locations over 2 years, accompanied by high-frequency ice-speed measurements during two summer melt seasons. Water pressure showed two different regimes, namely high frequency and large amplitude variations during the melt season (January-April) and small fluctuations near the overburden pressure the rest of the year. Speed-up events were observed several times in each summer measurement period. Ice motion during these events substantially contributed to total glacier motion, for example, fast ice flow over 1 week accounted for similar to 70% of the total displacement over a 25-day long measurement period. We did not find a clear relationship between subglacial water pressure and ice speed. This was probably because subglacial hydraulic conditions were spatially inhomogeneous and thus our borehole data did not always represent a large-scale subglacial condition. Ice temperature measurements in the boreholes confirmed the existence of a cold ice layer near the glacier surface. Our data provide a basis to better understand the dynamic and hydrological conditions of relatively unstudied glaciers in the Antarctic Peninsula region.