Mass Balance Measurements at Ekström Ice Shelf
By Ole Zeising und Filip Heitmann
How much snow falls each year, and how much ice melts at the ice base? These questions are crucial for determining the mass balance of a glacier. Is it losing or gaining mass? Due to external influences, snowfall and melt rates vary from year to year. On a floating ice shelf like the Ekström Ice Shelf in East Antarctica, the melt rate at the ice base is mainly influenced by ocean temperature and flow velocity. Using highly precise measurements with ground-based radar, known as pRES, we can detect very small changes in ice thickness at the bottom of the ice shelf based on two measurements taken at different times. For several years, we have been measuring the melt rates at the Ekström Ice Shelf. Once a year, we travel from Neumayer Station III to various measurement sites using snowmobiles or all-terrain vehicles to determine the spatial distribution of the melt rate. In the central region of the ice shelf, where the ice is about 300 m thick, the melt rate is relatively low at just 0.5 m per year. This is due to cold water in the cavity beneath the ice shelf, which transfers little heat to the ice base. To measure seasonal variations in the melt rate, we also operate the radar autonomously. In this mode, it performs measurements every hour for a full year. The data reveal that the melt rate is higher in winter and spring than in summer and autumn—an effect caused by changing ocean currents due to sea ice formation. Once a year, we dig out the instruments, replace the batteries and memory cards, and bury them again, just slightly less deep.
To determine snow accumulation, we measure the height of bamboo stakes annually. These stakes are placed every 500 m along a 400 km line from Neumayer Station III to the Kottas Mountains inland.
Over time, the bamboo stakes become buried in snow. By comparing their height above the surface, we can determine snow accumulation. If a stake becomes too short, we replace it with a new 4-meter stake to continue the measurement series.
At the end of January, four of us left Neumayer Station III with two all-terrain vehicles, camping equipment, and new bamboo stakes. Every 500 m, we stopped to measure the stake’s height and coordinates digitally before continuing. Under good conditions, we measured around 200 stakes per day—covering about 100 km.
As we traveled further inland, temperatures dropped—from around 0°C at Neumayer Station III to -20°C at night at 1500 m altitude. At the beginning of February, the polar day ended, and for the first time, the sun touched the horizon at night. Every evening, we measured the average snow density of the top meter to calculate the mass of the fallen snow. After four days, we reached the final stake, just a few kilometers before the Kottas Mountains.
