Recent retreat of major outlet glaciers on Novaya Zemlya, Russian Arctic, influenced by fjord geometry and sea-ice conditions

Substantial ice loss has occurred in the Russian High Arctic during the past decade, predominantly on Novaya Zemlya, yet the region has been studied relatively little. Consequently, the factors forcing mass loss and the relative contribution of ice dynamics versus surface melt are poorly understood. Here we evaluate the influence of atmospheric/oceanic forcing and variations in fjord width on the behaviour of 38 glaciers on the northern ice cap, Novaya Zemlya. We compare retreat rates on land- versus marine-terminating outlets and on the Kara versus Barents Sea coasts. Between 1992 and 2010, 90% of the study glaciers retreated and retreat rates were an order of magnitude higher for marine-terminating outlets (52.1 m a–1) than for land-terminating glaciers (4.8 m a–1). We identify a post-2000 acceleration in marine-terminating glacier retreat, which corresponded closely to changes in sea-ice concentrations. Retreat rates were higher on the Barents Sea coast, which we partly attribute to lower sea-ice concentrations, but varied dramatically between individual glaciers. We use empirical data to categorize changes in along-flow fjord width, and demonstrate a significant relationship between fjord width variability and retreat rate. Results suggest that variations in fjord width exert a major influence on glacier retreat

Dynamic changes in outlet glaciers in northern Greenland from 1948 to 2015

The Greenland Ice Sheet (GrIS) is losing mass in response to recent climatic and oceanic warming. Since the mid-1990s, tidewater outlet glaciers across the ice sheet have thinned, retreated, and accelerated, but recent changes in northern Greenland have been comparatively understudied. Consequently, the dynamic response (i.e. changes in surface elevation and velocity) of these outlet glaciers to changes at their termini, particularly calving from floating ice tongues, is poorly constrained. Here we use satellite imagery and historical maps to produce an unprecedented 68-year record of terminus change across 18 major outlet glaciers and combine this with previously published surface elevation and velocity datasets. Overall, recent (1995–2015) retreat rates were higher than at any time in the previous 47 years (since 1948). Despite increased retreat rates from the 1990s, there was distinct variability in dynamic glacier behaviour depending on whether the terminus was grounded or floating. Grounded glaciers accelerated and thinned in response to retreat over the last 2 decades, while most glaciers terminating in ice tongues appeared dynamically insensitive to recent ice tongue retreat and/or total collapse. We also identify glacier geometry (e.g. fjord width, basal topography, and ice tongue confinement) as an important influence on the dynamic adjustment of glaciers to changes at their termini. Recent grounded outlet glacier retreat and ice tongue loss across northern Greenland suggest that the region is undergoing rapid change and could soon contribute substantially to sea level rise via the loss of grounded ice

Distribution and seasonal evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

Supraglacial lakes (SGLs) enhance surface melting and can flex and fracture ice shelves when they grow and subsequently drain, potentially leading to ice shelf disintegration. However, the seasonal evolution of SGLs and their influence on ice shelf stability in East Antarctica remains poorly understood, despite some potentially vulnerable ice shelves having high densities of SGLs. Using optical satellite imagery, air temperature data from climate reanalysis products and surface melt predicted by a regional climate model, we present the first long-term record (2000–2020) of seasonal SGL evolution on Shackleton Ice Shelf, which is Antarctica's northernmost remaining ice shelf and buttresses Denman Glacier, a major outlet of the East Antarctic Ice Sheet. In a typical melt season, we find hundreds of SGLs with a mean area of 0.02 km2, a mean depth of 0.96 m and a mean total meltwater volume of 7.45×106 m3. At their most extensive, SGLs cover a cumulative area of 50.7 km2 and are clustered near to the grounding line, where densities approach 0.27 km2 km−2. Here, SGL development is linked to an albedo-lowering feedback associated with katabatic winds, together with the presence of blue ice and exposed rock. Although below-average seasonal (December–January–February, DJF) temperatures are associated with below-average peaks in total SGL area and volume, warmer seasonal temperatures do not necessarily result in higher SGL areas and volumes. Rather, peaks in total SGL area and volume show a much closer correspondence with short-lived high-magnitude snowmelt events. We therefore suggest seasonal lake evolution on this ice shelf is instead more sensitive to snowmelt intensity associated with katabatic-wind-driven melting. Our analysis provides important constraints on the boundary conditions of supraglacial hydrology models and numerical simulations of ice shelf stability

Inter- and intra-beach thermal variation for Green Turtle nests on Ascension Island, South Atlantic

Nest temperatures for green turtles (Chelonia mydas) nesting on Ascension Island, South Atlantic (7°57\u27S 14°22\u27W), were examined. Temperature probes were placed into nests on two beaches, Long Beach (26 nests) and North East Bay (8 nests). Within these beaches there was relatively little thermal variation (SD of nest temperature was 0.32°C for Long Beach and 0.30°C for North East Bay). To examine inter-beach thermal variation temperature probes were buried at 55 cm on 12 beaches. Inter-beach thermal variation was large and was related to the beach albedo with the darkest beach (albedo, 016) being 4.2°C warmer than the lightest coloured beach (albedo, 0.73)

Inter- and intra-beach thermal variation for Green Turtle nests on Ascension Island, South Atlantic

Nest temperatures for green turtles (Chelonia mydas) nesting on Ascension Island, South Atlantic (7°57\u27S 14°22\u27W), were examined. Temperature probes were placed into nests on two beaches, Long Beach (26 nests) and North East Bay (8 nests). Within these beaches there was relatively little thermal variation (SD of nest temperature was 0.32°C for Long Beach and 0.30°C for North East Bay). To examine inter-beach thermal variation temperature probes were buried at 55 cm on 12 beaches. Inter-beach thermal variation was large and was related to the beach albedo with the darkest beach (albedo, 016) being 4.2°C warmer than the lightest coloured beach (albedo, 0.73)

Bounds from Primordial Black Holes with a Near Critical Collapse Initial Mass Function

Recent numerical evidence suggests that a mass spectrum of primordial black holes (PBHs) is produced as a consequence of near critical gravitational collapse. Assuming that these holes formed from the initial density perturbations seeded by inflation, we calculate model independent upper bounds on the mass variance at the reheating temperature by requiring the mass density not exceed the critical density and the photon emission not exceed current diffuse gamma-ray measurements. We then translate these results into bounds on the spectral index n by utilizing the COBE data to normalize the mass variance at large scales, assuming a constant power law, then scaling this result to the reheating temperature. We find that our bounds on n differ substantially (\delta n > 0.05) from those calculated using initial mass functions derived under the assumption that the black hole mass is proportional to the horizon mass at the collapse epoch. We also find a change in the shape of the diffuse gamma-ray spectrum which results from the Hawking radiation. Finally, we study the impact of a nonzero cosmological constant and find that the bounds on n are strengthened considerably if the universe is indeed vacuum-energy dominated today.Comment: 24 pages, REVTeX, 5 figures; minor typos fixed, two refs added, version to be published in PR

Primordial Black Hole Evaporation and Spontaneous Dimensional Reduction

Several different approaches to quantum gravity suggest the effective dimension of spacetime reduces from four to two near the Planck scale. In light of such evidence, this letter re-examines the thermodynamics of primordial black holes (PBHs) in specific lower-dimensional gravitational models. Unlike in four dimensions, \done-D black holes radiate with power P \sim \Mbh^2, while it is known no $(2+1)-$D (BTZ) black holes can exist in a non-anti-deSitter universe. This has important relevance to the PBH population size and distribution, and consequently on cosmological evolution scenarios. The number of PBHs that have evaporated to present day is estimated, assuming they account for all dark matter. Entropy conservation during dimensional transition imposes additional constraints. If the cosmological constant is non-negative, no black holes can exist in the $(2+1)$-dimensional epoch, and consequently a $(1+1)$-dimensional black hole will evolve to become a new type of remnant. Although these results are conjectural and likely model-dependent, they open new questions about the viability of PBHs as dark matter candidates.Comment: 20 pp, 1 figure; title changed and discussion significantly expanded; to appear in Phys. Lett.

Thermal conductivity of sand and its effect on the temperature of Loggerhead Sea Turtle (Caretta Caretta) nests

The conductivity of sand at a depth of 30–50 cm was measured at 15 sites on the beach at Captiva Island in south-west Florida which is used by nesting loggerhead turtles (Caretta caretta). The mean daily temperature of the sand was correlated with conductivity at the same depth measured the same day (r=0·611). When day to day variation was removed the correlation between nest temperature and conductivity increased to 0·694. The sand was highly variable in its grain structure. The dominant variability (80·6%) was redescribed by the first two principal components of a Principal Components Analysis (PCA). These two components were influenced mostly by percentages of large (> 1 mm) and small (< 500 μm) grains respectively. Conductivity was strongly correlated with the grain structure of the sand. The first three principal components describing sand grain structure, explained 84·1% of the variation in conductivity. Moisture content of the sand (always < 5%) was not an important factor. Sites dominated by larger grains generally had poorer conductivity and were cooler. Comparisons of eight nests to seven adjacent random sites revealed no strong evidence for directional selection in nest placement relative to sand conductivity. The variance in conductivities recorded at nests was also not significantly different from the variance at random sites

Biochar Reduced Nitrous Oxide and Carbon Dioxide Emissions from Soil with Different Water and Temperature Cycles

Interactions among biochar, respiration, nitrification, and soils can result in biochar increasing, decreasing, or not impacting greenhouse gas (GHG) emissions. This experiment determined the impact of water-filled porosity (WFP) and corn (Zea mays L.) stover biochar on CO2 and N2O emissions in May (spring) and August (summer). The May experiment contained two N rates [0 and 224 kg Ca(NO3)2–N ha–1], whereas the August had three N rates [0, 224 kg Ca(NO3)2–N ha–1, and 224 kg (NH4)2SO4–N ha–1]. The average temperatures in the May and Augusts 2014 experiments were 14 and 24°C, respectively. Biochar reduced CO2–C emissions in the high WFP Ca(NO3)2 treatment in the May and August experiments 15.4 and 16.3 kg ha–1, respectively. Associated with the CO2–C decrease was a 15.7% reduction in the soil solution dissolved organic C. In addition, N2O–N and CO2–C emissions were not correlated in the May Ca(NO3)2 ha–1 treatment, whereas in the August experiment, N2O–N and CO2–C emissions were correlated (r2 = 0.98, P \u3c 0.01). In August, biochar increased the apparent nitrification from 16 to 25 kg NH4–N (ha × d)–1 in the low WFP (NH4)2SO4treatment, and it did not influence the nitrification rate in the high WFP (NH4)2SO4 treatment. In general, N2O–N emissions increased with WFP and N rate and were reduced 21.7% by biochar. The findings suggest that multiple mechanisms contributed to N2O emissions and seasonal differences in soil temperature could result in biochar having a mixed impact on GHG emissions

The UK HeartSpare study: randomised evaluation of voluntary deep-inspiratory breath-hold in women undergoing breast radiotherapy

Purpose: to determine whether voluntary deep-inspiratory breath-hold (v_DIBH) and deep-inspiratory breath-hold with the active breathing coordinator™ (ABC_DIBH) in patients undergoing left breast radiotherapy are comparable in terms of normal-tissue sparing, positional reproducibility and feasibility of delivery.Methods: following surgery for early breast cancer, patients underwent planning-CT scans in v_DIBH and ABC_DIBH. Patients were randomised to receive one technique for fractions 1–7 and the second technique for fractions 8–15 (40?Gy/15 fractions total). Daily electronic portal imaging (EPI) was performed and matched to digitally-reconstructed radiographs. Cone-beam CT (CBCT) images were acquired for 6/15 fractions and matched to planning-CT data. Population systematic (?) and random errors (?) were estimated. Heart, left-anterior-descending coronary artery, and lung doses were calculated. Patient comfort, radiographer satisfaction and scanning/treatment times were recorded. Within-patient comparisons between the two techniques used the paired t-test or Wilcoxon signed-rank test.Results: twenty-three patients were recruited. All completed treatment with both techniques. EPI-derived ? were ?1.8?mm (v_DIBH) and ?2.0?mm (ABC_DIBH) and ? ?2.5?mm (v_DIBH) and ?2.2?mm (ABC_DIBH) (all p non-significant). CBCT-derived ? were ?3.9?mm (v_DIBH) and ?4.9?mm (ABC_DIBH) and ? ??4.1?mm (v_DIBH) and ??3.8?mm (ABC_DIBH). There was no significant difference between techniques in terms of normal-tissue doses (all p non-significant). Patients and radiographers preferred v_DIBH (p?=?0.007, p?=?0.03, respectively). Scanning/treatment setup times were shorter for v_DIBH (p?=?0.02, p?=?0.04, respectively).Conclusions: v_DIBH and ABC_DIBH are comparable in terms of positional reproducibility and normal tissue sparing. v_DIBH is preferred by patients and radiographers, takes less time to deliver, and is cheaper than ABC_DIB