The Little Ice Age in the Himalaya: a review of glacier advance driven by Northern Hemisphere temperature change

Northern Hemisphere cooling between 1400 and 1900 in the Common Era (CE) resulted in the expansion of glaciers during a period known as the Little Ice Age (LIA). Early investigation of recent advances of Himalayan glaciers assumed that these events were synchronous with LIA advances identified in Europe, based on the appearance and position of moraines and without numerical age control. However, applications of Quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred. This paper reviews geochronological evidence for the last advance of glaciers in the Himalaya. The 66 ages younger than 2,000 years old (0 CE to 2000 CE) calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300–1600 CE, slightly earlier than the coldest period of Northern Hemisphere air temperatures. The timing of LIA advances varied spatially, likely influenced by variations in topography and meteorology across and along the mountain range. Palaeoclimate proxies indicate cooling air temperatures from 1300 CE leading to a southward shift in the Asian monsoon, increased Westerly winter precipitation, and generally wetter conditions across the range around 1400 CE and 1800 CE. The last advance of glaciers in the Himalaya during a period of variable climate resulted from cold Northern Hemisphere air temperatures and was sustained by increased snowfall as atmospheric circulation reorganised in response to cooling during the LIA

Spatial variability in mass change of glaciers in the Everest region, central Himalaya, between 2000 and 2015

The mass balance of the majority of Himalayan glaciers is currently negative, and has been for several decades. Region wide averaging of mass change estimates has masked any catchment or glacier scale variability in glacier recession, thus the role of a number of glaciological processes in glacier wastage remains poorly understood. In this study, we quantify surface lowering and mass loss rates for the ablation areas of 32 glaciers in different catchments across the Everest region, and specifically examine the role of glacial lakes in glacier mass change. We then assess how future ice loss is likely to differ depending on glacier hypsometry. Spatially variable ice loss is observed within and between the Dudh Koshi and Tama Koshi catchments and glaciers that flow onto the Tibetan Plateau. Surface lowering rates on glaciers flowing onto the Tibetan Plateau are 54 and 19 % greater than those flowing southward into the Dudh Koshi and Tama Koshi catchments, respectively. Surface lowering rates of up to −3.78 ± 0.26 m a-1 occurred on some lacustrine terminating glaciers, although glaciers with small lakes showed rates of lowering comparable with those that terminate on land. We suggest that such a range reflects glacial lakes at different stages of development, and that rates of mass loss are likely to increase as glacial lakes expand and deep water calving begins to occur. Hypsometric data reveal a coincidence of the altitude of maximum surface lowering and the main glacier hypsometry in the Dudh Koshi catchment, thus a large volume of ice is readily available for melt. Should predicted CMIP5 RCP 4.5 scenario warming (0.9–2.3 °C by 2100) occur in the study area, 19–30, 17–50 and 14–37 % increases in the total glacierised area below the Equilibrium Line Altitude will occur in the Dudh Koshi and Tama Koshi catchments, and on the Tibetan Plateau. Comparison of our data with a conceptual model of Himalayan glacier shrinkage confirms the presence of three distinct process regimes, with all glaciers in our sample now in a state of accelerating mass loss and meltwater storage

Silicon mirror suspensions for gravitational wave detectors

One of the most significant limits to the sensitivity of current, and future, long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their suspensions. This paper reports results of analytical and experimental studies of the limits to thermal noise performance of cryogenic silicon test mass suspensions set by two constraints on suspension fibre dimensions: the minimum dimensions required to allow conductive cooling for extracting incident laser beam heat deposited in the mirrors; and the minimum dimensions of fibres (set by their tensile strength) which can support test masses of the size envisaged for use in future detectors. We report experimental studies of breaking strength of silicon ribbons, and resulting design implications for the feasibility of suspension designs for future gravitational wave detectors using silicon suspension fibres. We analyse the implication of this study for thermal noise performance of cryogenically cooled silicon suspensions

Forward modelling of the completeness and preservation of palaeoclimate signals recorded by ice‐marginal moraines

Glaciers fluctuate in response to climate change and record these changes by building sedimentary landforms, including moraines. Therefore, glacial landscapes are a potentially valuable archive of terrestrial palaeoclimate change. Typically, a cooling climate causes glaciers to expand and a warming climate causes glaciers to shrink. However, the glacier response time and the influence of mountainous topography on glacier dynamics complicates this behaviour, such that moraines are not always a straightforward indicator of glacier change in response to climate change. We used a glacial landscape evolution model to simulate the response of a hypothetical mountain glacier to simple changes in climate and the resulting formation and preservation of moraines. These results show that the rate of climate change relative to the glacier response time determines the geometry, number, and position of moraines. Glaciers can build distinct moraines in the absence of climate change. The distance from the maximum ice extent may not represent the chronological order of moraine formation. Moraines can be preserved after being overrun and eroded by subsequent glaciations, but moraine sequences may also contain gaps that are unidentifiable in the field

Late Holocene glaciers in western Scotland?

In this paper we use a numerical glacier-climate model, a detailed photogrammetric survey and lichenometry to reconstruct small palaeoglaciers on Ben Nevis and surrounding mountains in western Scotland. These glaciers would have been sustained under a climate where the mean annual air temperature was –1.0°C to –2.0°C compared to present-day values either with or without a decrease in precipitation amount of 10–30%. Historical meteorological data show that these air temperatures were reached on Ben Nevis in the latter part of the 19th century. Although we have no data on the age of these small glaciers, palaeoclimate reconstructions suggest that such conditions almost certainly existed several times during the Holocene in Scotland; the last time being the Little Ice Age of the 16th to 19th Centuries. We argue from this that small Scottish glaciers may have been able to develop in high sheltered cirques at many times during the Holocene and that the glacial history of Scotland therefore requires revision

Lowest observed surface and weld losses in fused silica fibres for gravitational wave detectors

High purity fused silica has become the cornerstone choice for use in the final monolithic stage of the mirror suspensions in the gravitational wave observatories Advanced LIGO (aLIGO) and Advanced Virgo (AdV). The ultra-low thermal noise contributed by these suspensions is one of the key improvements that permitted the Nobel prize winning first direct measurement of gravitational waves in 2015. This paper outlines the first in situ study undertaken to analyse the thermal noise of the final monolithic stage of the aLIGO Hanford detector mirror suspensions. We analysed short operational periods of this detector, when high excitation of the transverse 'violin' modes of the silica suspension fibres occurred. This allowed detailed measurements of the Q-factor of violin modes up to order 8 of individual fibres on separate masses. We demonstrate the highest silica fibre violin mode Q-factors yet measured of up to 2 × 109. From finite element modelling, the dominant surface and weld losses have been calculated to be a factor of 3 to 4 better than previously accepted, and as a result, we demonstrate that the level of noise in the aLIGO final stage silica suspensions is around 30%–40% better than previously estimated between frequencies of 10–500 Hz. This leads to an increase in the estimated event rate by a factor of 2 for aLIGO, if suspension thermal noise became the main limitation to the sensitivity of the detector

Heterogeneous water storage and thermal regime of supraglacial ponds on debris-covered glaciers

The water storage and energy transfer roles of supraglacial ponds are poorly constrained, yet they are thought to be important components of debris-covered glacier ablation budgets. We used an unmanned surface vessel (USV) to collect sonar depth measurements for 24 ponds to derive the first empirical relationship between their area and volume applicable to the size distribution of ponds commonly encountered on debris-covered glaciers. Additionally, we instrumented nine ponds with thermistors and three with pressure transducers, characterising their thermal regime and capturing three pond drainage events. The deepest and most irregularly-shaped ponds were those associated with ice cliffs, which were connected to the surface or englacial hydrology network (maximum depth = 45.6 m), whereas hydrologically-isolated ponds without ice cliffs were both more circular and shallower (maximum depth = 9.9 m). The englacial drainage of three ponds had the potential to melt ~100 ± 20 × 103 kg to ~470 ± 90 × 103 kg of glacier ice owing to the large volumes of stored water. Our observations of seasonal pond growth and drainage with their associated calculations of stored thermal energy have implications for glacier ice flow, the progressive enlargement and sudden collapse of englacial conduits, and the location of glacier ablation hot-spots where ponds and ice cliffs interact. Additionally, the evolutionary trajectory of these ponds controls large proglacial lake formation in deglaciating environments

Non-ideality of quantum operations with the electron spin of a 31P donor in a Si crystal due to interaction with a nuclear spin system

We examine a 31P donor electron spin in a Si crystal to be used for the purposes of quantum computation. The interaction with an uncontrolled system of 29Si nuclear spins influences the electron spin dynamics appreciably. The hyperfine field at the 29Si nuclei positions is non-collinear with the external magnetic field. Quantum operations with the electron wave function, i.e. using magnetic field pulses or electrical gates, change the orientation of hyperfine field and disturb the nuclear spin system. This disturbance produces a deviation of the electron spin qubit from an ideal state, at a short time scale in comparison with the nuclear spin diffusion time. For H_ext=9 T, the estimated error rate is comparable to the threshold value required by the quantum error correction algorithms. The rate is lower at higher external magnetic fields.Comment: 11 pages, 2 figure

Provenance and transport of supraglacial debris revealed by variations in debris geochemistry on Khumbu Glacier, Nepal Himalaya

The origin of supraglacial debris covers is often conceptualised as the formation of a surface lag by melt-out of englacial debris from slow-moving ice, where complexity arises from feedback between debris thickness and sub-debris ice melt. Here, we examine the origin of a debris cover from the perspective of debris provenance and changing tributary supply in a high-elevation compound valley glacier. Geochemical analysis of 11 major elements in 21 debris samples from six tributaries of Khumbu Glacier (Nepal) shows unambiguous statistical differentiation of debris sources reflecting lithological differences between tributary catchments. Twenty-four samples from transects across the ablation area are partitioned according to their source areas using the FR2000 sediment unmixing model. We estimate the age of ice at each transect using a higher order ice flow model. The results show greater proportions of debris from lateral tributaries in downglacier locations that have experienced longer flowline histories. More recently, ice from the Main Himalayan Divide (Western Cwm) has become relatively more important. This suggests a change in the state of the lower glacier's structure depending on the relative ice discharges of lateral and divide sources. Ice flux from lower elevation tributaries was more important probably prior to a weakening of the Indian Summer Monsoon at around 1420 CE. The lower elevation tributaries lie within the range of late Holocene equilibrium line altitude variation and therefore respond most sensitively to climatic drivers of the glacier's flow structure. Negative glacier mass balance since around 1900 CE caused tributary glaciers to detach and high-elevation catchments to re-establish as the dominant ice source to Khumbu Glacier

A beryllium-10 chronology of late-glacial moraines in the upper Rakaia valley, Southern Alps, New Zealand supports Southern- Hemisphere warming during the Younger Dryas

Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination