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.

Disappearance of the last tropical glaciers in the Western Pacific Warm Pool (Papua, Indonesia) appears imminent.

The glaciers near Puncak Jaya in Papua, Indonesia, the highest peak between the Himalayas and the Andes, are the last remaining tropical glaciers in the West Pacific Warm Pool (WPWP). Here, we report the recent, rapid retreat of the glaciers near Puncak Jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y. Photographs and measurements of a 30-m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a ∼5.4-fold increase in the thinning rate, which was augmented by the strong 2015-2016 El Niño. At the current rate of ice loss, these glaciers will likely disappear within the next decade. To further understand the mechanisms driving the observed retreat of these glaciers, 2 ∼32-m-long ice cores to bedrock recovered in mid-2010 are used to reconstruct the tropical Pacific climate variability over approximately the past half-century on a quasi-interannual timescale. The ice core oxygen isotopic ratios show a significant positive linear trend since 1964 CE (0.018 ± 0.008‰ per year; P < 0.03) and also suggest that the glaciers' retreat is augmented by El Niño-Southern Oscillation processes, such as convection and warming of the atmosphere and sea surface. These Papua glaciers provide the only tropical records of ice core-derived climate variability for the WPWP.

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.

Temperature profile for glacial ice at the South Pole: implications for life in a nearby subglacial lake.

Airborne radar has detected approximately 100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of -9 degrees C, which is 7 degrees C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km(3)) and at lower temperatures (-20 degrees C to -35 degrees C) than has heretofore been possible.