Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes

The influence of subglacial water on the dynamics of ice flow has been the object of increasing interest in the past decade. In this study we focus on large-scale, long-term changes in surface elevation over Northeast Greenland and the corresponding changes in subglacial water routeways. Our results show that over timescales ranging from decades to millennia the area may experience redistribution of and fluctuation in subglacial water outflux under the main glacier outlets. The fluctuations in subglacial water routing occur even in the absence of external forcing. Based on these results we conclude that changes in the subglacial water routeways are an intrinsic part of the drainage basin dynamics, where the subglacial system is likely always in a transient state. The results also imply that fluctuations at the margins observed at present might originate from changes several hundred kilometres upstream. Since surface elevation changes may propagate upstream over timescales much longer than the observational period, the cause of the fluctuations may not be present in current observational records

Glaciological characteristics in the Dome Fuji region and new assessment for 1.5 Ma old ice

The retrieval of a continuous Antarctic ice-core record dating back 1.5 Ma is a key objective in palaeo-climatologyin order to understand why the frequency of ice ages changed from 40 ka to 100 ka approximately 1 Ma ago. Here,we investigate the probability that the Dome Fuji region in East Antarctica contains ice more than 1.5 Ma old.We use a new radar dataset acquired in the Antarctic seasons 2014/15 and 2016/17 to improve the ice thickness map. Compared to previous maps of the region, the new dataset shows a more complex landscape with networks of valleys and mountain plateaus. We use the new dataset as input in a thermokinematic model that incorporates uncertainties in geothermal heat flux values in order to improve the predictions of potential ice-core sites. Our results indicate several areas of interest, especially the region immediately south of Dome Fuji station appears to be a good candidate site. An initial assessment of basal conditions revealed the existence of several wet-based areas and further radar data analysis shows overall high continuity of layer stratigraphy in the region. Thus, if a new drill operation were to take place in this area, extending the age-depth information from the Dome Fuji ice core to a new ice-core drill site is a viable option

Age-Depth Stratigraphy of Pine Island Glacier Inferred from Airborne Radar and Ice-Core Chronology

Understanding the contribution of the West Antarctic Ice Sheet (WAIS) to past and future sea level has been a major scientific priority over the last three decades. In recent years, observed thinning and ice‐flow acceleration of the marine‐based Pine Island Glacier has highlighted that understanding dynamic changes is critical to predicting the long‐term stability of the WAIS. However, relatively little is known about the evolution of the catchment during the Holocene. Internal Reflecting Horizons (IRHs) provide a cumulative record of accumulation, basal melt and ice dynamics that, if dated, can be used to constrain ice‐flow models. Here, we use airborne radars to trace four spatially‐extensive IRHs deposited in the late Quaternary across the Pine Island Glacier catchment. We use the WAIS Divide ice‐core chronology to assign ages to three IRHs: 4.72 ± 0.28, 6.94 ± 0.31, and 16.50 ± 0.79 ka. We use a 1‐D model, constrained by observational and modelled accumulation rates, to produce an independent validation of our ice‐core‐derived ages and provide an age estimate for our shallowest IRH (2.31‐2.92 ka). We find that our upper three IRHs correspond to three large peaks in sulphate concentrations in the WAIS Divide ice‐core record and hypothesise that the origin of these spatially‐extensive IRHs is from past volcanic activity. The clear correspondence between our IRHs and the ones previously identified over the Weddell Sea Sector, altogether representing ∼20% of the WAIS, indicates that a unique set of stratigraphic markers spanning the Holocene exists over a large part of West Antarctica

Quantum Communication between N partners and Bell's inequalities

We consider a family of quantum communication protocols involving $N$ partners. We demonstrate the existence of a link between the security of these protocols against individual attacks by the eavesdropper, and the violation of some Bell's inequalities, generalizing the link that was noticed some years ago for two-partners quantum cryptography. The arguments are independent of the local hidden variable debate.Comment: 4 pages, 2 figure

HE0107-5240, A Chemically Ancient Star.I. A Detailed Abundance Analysis

We report a detailed abundance analysis for HE0107-5240, a halo giant with [Fe/H]_NLTE=-5.3. This star was discovered in the course of follow-up medium-resolution spectroscopy of extremely metal-poor candidates selected from the digitized Hamburg/ESO objective-prism survey. On the basis of high-resolution VLT/UVES spectra, we derive abundances for 8 elements (C, N, Na, Mg, Ca, Ti, Fe, and Ni), and upper limits for another 12 elements. A plane-parallel LTE model atmosphere has been specifically tailored for the chemical composition of {\he}. Scenarios for the origin of the abundance pattern observed in the star are discussed. We argue that HE0107-5240 is most likely not a post-AGB star, and that the extremely low abundances of the iron-peak, and other elements, are not due to selective dust depletion. The abundance pattern of HE0107-5240 can be explained by pre-enrichment from a zero-metallicity type-II supernova of 20-25M_Sun, plus either self-enrichment with C and N, or production of these elements in the AGB phase of a formerly more massive companion, which is now a white dwarf. However, significant radial velocity variations have not been detected within the 52 days covered by our moderate-and high-resolution spectra. Alternatively, the abundance pattern can be explained by enrichment of the gas cloud from which HE0107-5240 formed by a 25M_Sun first-generation star exploding as a subluminous SNII, as proposed by Umeda & Nomoto (2003). We discuss consequences of the existence of HE0107-5240 for low-mass star formation in extremely metal-poor environments, and for currently ongoing and future searches for the most metal-poor stars in the Galaxy.Comment: 60 pages, 16 figures. Accepted for publication in Ap

Excitations in the Halo Nucleus He-6 Following The Li-7(gamma,p)He-6 Reaction

A broad excited state was observed in 6-He with energy E_x = 5 +/- 1 MeV and width Gamma = 3 +/- 1 MeV, following the reaction Li-7(gamma,p)He-6. The state is consistent with a number of broad resonances predicted by recent cluster model calculations. The well-established reaction mechanism, combined with a simple and transparent analysis procedure confers considerable validity to this observation.Comment: 3 pages of LaTeX, 3 figures in PostScript, approved for publication in Phys. Rev. C, August, 200

Single parity check-coded 16QAM over spatial superchannels in multicore fiber transmission

We experimentally investigate single-parity check (SPC) coded spatial superchannels based on polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16QAM) for multicore fiber transmission systems, using a 7-core fiber. We investigate SPC over 1, 2, 4, 5 or 7 cores in a back-to-back configuration and compare the sensitivity to uncoded PM-16QAM, showing that at symbol rates of 20 Gbaud and at a bit-error-rate (BER) of 10(-3), the SPC superchannels exhibit sensitivity improvements of 2.7 dB, 2.0 dB, 1.7 dB, 1.3 dB, and 1.1 dB, respectively. We perform both single channel and wavelength division multiplexed (WDM) transmission experiments with 22 GHz channel spacing and 20 Gbaud channel symbol rate for SPC over 1, 3 and 7 cores and compare the results to PM-16QAM with the same spacing and symbol rate. We show that in WDM signals, SPC over hl1 core can achieve more than double the transmission distance compared to PM-16QAM at the cost of 0.91 bit/s/Hz/core in spectral efficiency (SE). When sharing the parity-bit over 7 cores, the loss in SE becomes only 0.13 bit/s/Hz/core while the increase in transmission reach over PM-16QAM is 44 %. (C) 2015 Optical Society of Americ