Subglacial discharge controls seasonal variations in the thermal structure of a glacial lake in Patagonia.

Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Despite its importance, seasonal lake temperature variations are poorly understood because taking long-term measurements near the front of calving glaciers is challenging. To investigate the thermal structure and its seasonal variations, we performed year-around temperature and current measurement at depths of 58-392 m in Lago Grey, a 410-m-deep glacial lake in Patagonia. The measurement revealed critical impacts of subglacial discharge on the lake thermal condition. Water below a depth of ~100 m showed the coldest temperature in mid-summer, under the influence of glacial discharge, whereas temperature in the upper layer followed a seasonal variation of air temperature. The boundary of the lower and upper layers was controlled by the depth of a sill which blocks outflow of dense and cold glacial meltwater. Our data implies that subglacial discharge and bathymetry dictate mass loss and the retreat of lake-terminating glaciers. The cold lakewater hinders underwater melting and facilitates formation of a floating terminus.

Thermohaline structure and circulation beneath the Langhovde Glacier ice shelf in East Antarctica.

Basal melting of ice shelves is considered to be the principal driver of recent ice mass loss in Antarctica. Nevertheless, in-situ oceanic data covering the extensive areas of a subshelf cavity are sparse. Here we show comprehensive structures of temperature, salinity and current measured in January 2018 through four boreholes drilled at a ~3-km-long ice shelf of Langhovde Glacier in East Antarctica. The measurements were performed in 302-12 m-thick ocean cavity beneath 234-412 m-thick ice shelf. The data indicate that Modified Warm Deep Water is transported into the grounding zone beneath a stratified buoyant plume. Water at the ice-ocean interface was warmer than the in-situ freezing point by 0.65-0.95°C, leading to a mean basal melt rate estimate of 1.42 m a-1. Our measurements indicate the existence of a density-driven water circulation in the cavity beneath the ice shelf of Langhovde Glacier, similar to that proposed for warm-ocean cavities of larger Antarctic ice shelves.

A modified measurement method of electrical properties for ZnO microvaristors by direct measurements.

Zinc oxide (ZnO) materials are fine ceramics with non-linear electrical properties. Their non-linear electrical properties appear from a double Schottky barrier formed in the grain boundaries (GBs). These microparticles are not easy to measure directly with electrical microprobes due to their small size (i.e., 50-100 µm). We developed a direct measurement process with two Cu cables of small diameter. In this paper, we have developed an amplified method of the previous measurement system, which can measure not only one ZnO microvaristor directly but also a group of microvaristors in a series connection. The I-V characteristics of the microvaristors were measured with the modified method, and we found non-linear properties in each particle while measuring I-V characteristics. Their fine structures were also investigated, and the non-linear I-V characteristics showed a direct relationship with the number of the GBs of the samples. Moreover, varistor voltage was calculated for a single GB for the I-V measurements for ZnO microvaristors connected in a series connection.