Thermal Heads for Melt Drilling to Subglacial Lakes: Design and Testing.

Antarctic subglacial lakes are often considered suitable analogues to extraterrestrial subglacial aqueous environments. Recently, an environmentally friendly RECoverable Autonomous Sonde (RECAS) was designed at the Polar Research Center of Jilin University (JLU) to sample the water of subglacial lakes without contamination. In this regard, the development of a fast-penetration thermal head is the key issue for RECAS. Two different prototypes were designed and tested at the JLU ice-well to determine the optimal design and operation parameters of the thermal heads. Practical top and bottom thermal heads were then designed based on one of the prototypes, which can penetrate ice at an average rate of 1.88 m/h. The test results for the RECAS thermal heads show that the rate of penetration (ROP) can be 1.80-1.95 m/h in -10°C ice, and the axial load on the thermal head only affects the ROP when it is lower than a specified threshold. The decrease of the ice temperature from -10°C to -30°C leads to a decrease of 17% in the ROP. The bottom thermal head can drill into dirty ice, and a simple collector positioned above the head can collect solid particles suspended in the melted ice. The top thermal head exhibited a long lifetime and stable heating performance after being powered in water for 2 weeks. In addition, the ice temperature near the borehole was monitored to evaluate the range of heat disturbance caused by the thermal head.

Kilimanjaro ice core records: evidence of holocene climate change in tropical Africa.

Six ice cores from Kilimanjaro provide an approximately 11.7-thousand-year record of Holocene climate and environmental variability for eastern equatorial Africa, including three periods of abrupt climate change: approximately 8.3, approximately 5.2, and approximately 4 thousand years ago (ka). The latter is coincident with the "First Dark Age," the period of the greatest historically recorded drought in tropical Africa. Variable deposition of F- and Na+ during the African Humid Period suggests rapidly fluctuating lake levels between approximately 11.7 and 4 ka. Over the 20th century, the areal extent of Kilimanjaro's ice fields has decreased approximately 80%, and if current climatological conditions persist, the remaining ice fields are likely to disappear between 2015 and 2020.