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Halophilic proteins subjected to below about 15% salt in vitro denature through misfolding, aggregation and/or precipitation. Halobacteria, however, have been detected in environments of fluctuating salinity such as coastal salterns and even around fresh water springs in the depths of the Dead Sea. In order to identify the underlying mechanisms of low salt survival, we explored the reactivation capacity of Halobacterium (Hbt) salinarum sub-populations after incubation in low salt media and recovery in physiological salt. Respiratory oxygen consumption was assessed in stressed cells and cell viability was estimated by Live/Dead staining and flow cytometry. In vivo neutron scattering experiments showed that the recovery of Hbt salinarum sub-populations exposed to severe low salt conditions is related to a rapid retrieval of functional molecular dynamics in the proteome. In the hypothesis that the observations on Hbt salinarum have wider relevance, they could be of key ecological significance for the dispersion of extremophiles when environmental fluctuations become severe.

Ice can sculpt extraordinary landscapes, yet the efficacy of, and controls governing, glacial erosion on geological timescales remain poorly understood and contended, particularly across Polar continental shields. Here, we assimilate geophysical data with modelling of the Eurasian Ice Sheet — the third largest Quaternary ice mass that spanned 49°N to 82°N — to decipher its erosional footprint during the entire last ~100 ka glacial cycle. Our results demonstrate extreme spatial and temporal heterogeneity in subglacial erosion, with rates ranging from 0 to 5 mm a−1 and a net volume equating to ~130,000 km3 of bedrock excavated to depths of ~190 m. A hierarchy of environmental controls ostensibly underpins this complex signature: lithology, topography and climate, though it is basal thermodynamics that ultimately regulates erosion, which can be variously protective, pervasive, or, highly selective. Our analysis highlights the remarkable yet fickle nature of glacial erosion — critically modulated by transient ice-sheet dynamics — with its capacity to impart a profound but piecemeal geological legacy across mid- and high latitudes.

We present modelling results of the atmospheric circulation at the cold periods of marine isotope stage 5b (MIS 5b), MIS 4 and the Last Glacial Maximum (LGM), as well as the interglacial. The palaeosimulations are forced by ice-sheet reconstructions consistent with geological evidence and by appropriate insolation and greenhouse gas concentrations. The results suggest that the large-scale atmospheric winter circulation remained largely similar to the interglacial for a significant part of the glacial cycle. The proposed explanation is that the ice sheets were located in areas where their interaction with the mean flow is limited. However, the LGM Laurentide Ice Sheet induces a much larger planetary wave that leads to a zonalisation of the Atlantic jet. In summer, the ice-sheet topography dynamically induces warm temperatures in Alaska and central Asia that inhibits the expansion of the ice sheets into these regions. The warm temperatures may also serve as an explanation for westward propagation of the Eurasian Ice Sheet from MIS 4 to the LGM.

We here reconstruct the paleotopography of Northern Hemisphere ice sheets during the glacial maxima of marine isotope stages (MIS) 5b and 4.We employ a combined approach, blending geologically based reconstruction and numerical modeling, to arrive at probable ice sheet extents and topographies for each of these two time slices. For a physically based 3-D calculation based on geologically derived 2-D constraints, we use the University of Maine Ice Sheet Model (UMISM) to calculate ice sheet thickness and topography. The approach and ice sheet modeling strategy is designed to provide robust data sets of sufficient resolution for atmospheric circulation experiments for these previously elusive time periods. Two tunable parameters, a temperature scaling function applied to a spliced Vostok–GRIP record, and spatial adjustment of the climatic pole position, were employed iteratively to achieve a good fit to geological constraints where such were available. The model credibly reproduces the first-order pattern of size and location of geologically indicated ice sheets during marine isotope stages (MIS) 5b (86.2 kyr model age) and 4 (64 kyr model age). From the interglacial state of two north–south obstacles to atmospheric circulation (Rocky Mountains and Greenland), by MIS 5b the emergence of combined Quebec–central Arctic and Scandinavian–Barents-Kara ice sheets had increased the number of such highland obstacles to four. The number of major ice sheets remained constant through MIS 4, but the merging of the Cordilleran and the proto-Laurentide Ice Sheet produced a single continent-wide North American ice sheet at the LGM.

The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles. Whether the origins of inner gorges were fluvial or subglacial has been debated for decades. Here, Jansen et al . present new evidence, in the form of a suite of cosmogenic nuclide exposure ages and a deglaciation map, which suggests a subglacial meltwater origin for inner gorges in northern Sweden.

In a two-stage compression and acceleration system, where each stage compresses a chirped bunch in a magnetic chicane, wakefields affect high-current bunches. The longitudinal wakes affect the macroscopic energy and current profiles of the compressed bunch and cause microbunching at short wavelengths. For macroscopic wavelengths, impedance formulas and tracking simulations show that the wakefields can be dominated by the resistive impedance of coherent edge radiation. For this case, we calculate the minimum initial bunch length that can be compressed without producing an upright tail in phase space and associated current spike. Formulas are also obtained for the jitter in the bunch arrival time downstream of the compressors that results from the bunch-to-bunch variation of current, energy, and chirp. Microbunching may occur at short wavelengths where the longitudinal space-charge wakes dominate or at longer wavelengths dominated by edge radiation. We model this range of wavelengths with frequency-dependent impedance before and after each stage of compression. The growth of current and energy modulations is described by analytic gain formulas that agree with simulations.

After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2–56.9 ka) and 2 (23.2–16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

The pattern and magnitude of deforestation that occurred from 1972 to 2000 in the south central Rift Valley of Ethiopia were analyzed using remote sensing change detection techniques. The results show that natural forest cover declined from 16% in 1972 to 2.8% in 2000. The total natural forest cleared between 1972 and 2000 amounted to 40,324 ha, corresponding to an annual loss of 1440 ha. The total loss was 82% of the 1972 forest cover and the annual loss was equivalent to 0.9% of the national figure. The forest decline in the area involved proximate causal factors as well as causal factors that are more spatially diffuse and are part of the long-term evolution of a region much larger than the study area. In order of importance, the major causes of change were small-scale agriculture, commercial logging, and commercial farms. Two major modes of change were observed: 1) internal, ie openings created by small farm plots, grazing lands, and villages; and 2) external, ie expansion of agriculture from the exterior into the forests. The main consequences of deforestation were habitat destruction and decline of water availability.

A radio frequency system with a fourth-harmonic “Landau” cavity suppresses coupled-bunch instabilities and increases the beam lifetime of the Aladdin electron storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the Landau cavity. Analytical modeling of instability frequencies and growth rates, simulations, and experiments suggest that the observed instabilities result from coupling between dipole and quadrupole Robinson modes.

The areal extents of the Laurentide and Fennoscandian ice sheets during the Last Glacial Maximum (about 20,000 years ago) are well known 1 , but thickness estimates range widely, from high-domed 2 to thin 3 , with large implications for our reconstruction of the climate system regarding, for example, Northern Hemisphere atmospheric circulation and global sea levels. This uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials 4 , a knowledge of which would better constrain reconstructions of ice-sheet thickness. Here we show that, in the absence of direct data, the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen- and thawed-bed conditions. We argue that ribbed moraines were formed by brittle fracture of subglacial sediments, induced by the excessive stress at the boundary between frozen- and thawed-bed conditions resulting from the across-boundary difference in basal ice velocity. Maps of glacial landforms from aerial photographs of Canada and Scandinavia reveal a concentration of ribbed moraines around the ice-sheet retreat centres of Quebec, Keewatin, Newfoundland and west-central Fennoscandia. Together with the evidence from relict landscapes that mark glacial areas with frozen-bed conditions, the distribution of ribbed moraines on both continents suggest that a large area of the Laurentide and Fennoscandian ice sheets was frozen-based—and therefore high-domed and stable—during the Last Glacial Maximum.