Accelerated volume loss in glacier ablation zones of NE Greenland, Little Ice Age to present

Mountain glaciers at the periphery of the Greenland ice sheet are a crucial freshwater and sediment source to the North Atlantic and strongly impact Arctic terrestrial, fjord, and coastal biogeochemical cycles. In this study we mapped the extent of 1,848 mountain glaciers in NE Greenland at the Little Ice Age. We determined area and volume changes for the time periods Little Ice Age to 1980s and 1980s to 2014 and equilibrium line altitudes. There was at least 172.76 ± 34.55‐km3 volume lost between 1910 and 1980s, that is, a rate of 2.61 ± 0.52 km3/year. Between 1980s and 2014 the volume lost was 90.55 ± 18.11 km3, that is, a rate of 3.22 ± 0.64 km3/year, implying an increase of ~23% in the rate of ice volume loss. Overall, at least ~7% of mass loss from Greenland mountain glaciers and ice caps has come from the NE sector

Accelerated volume loss in glacier ablation zones of NE Greenland, Little Ice Age to present

Mountain glaciers at the periphery of the Greenland ice sheet are a crucial freshwater and sediment source to the North Atlantic and strongly impact Arctic terrestrial, fjord, and coastal biogeochemical cycles. In this study we mapped the extent of 1,848 mountain glaciers in NE Greenland at the Little Ice Age. We determined area and volume changes for the time periods Little Ice Age to 1980s and 1980s to 2014 and equilibrium line altitudes. There was at least 172.76 ± 34.55‐km3 volume lost between 1910 and 1980s, that is, a rate of 2.61 ± 0.52 km3/year. Between 1980s and 2014 the volume lost was 90.55 ± 18.11 km3, that is, a rate of 3.22 ± 0.64 km3/year, implying an increase of ~23% in the rate of ice volume loss. Overall, at least ~7% of mass loss from Greenland mountain glaciers and ice caps has come from the NE sector

Cyclic Constraints on Conformational Flexibility in γ‑Peptides: Conformation Specific IR and UV Spectroscopy

Single-conformation spectroscopy has been used to study two cyclically constrained and capped γ-peptides: Ac-γ_ACHC-NHBn (hereafter γ_ACHC, Figure 1a), and Ac-γ_ACHC-γ_ACHC-NHBn (γγ_ACHC, Figure 1b), under jet-cooled conditions in the gas phase. The γ-peptide backbone in both molecules contains a cyclohexane ring incorporated across each Cβ-Cγ bond and an ethyl group at each Cα. This substitution pattern was designed to stabilize a (g+, g+) torsion angle sequence across the Cα–Cβ–Cγ segment of each γ-amino acid residue. Resonant two-photon ionization (R2PI), infrared–ultraviolet hole-burning (IR–UV HB), and resonant ion-dip infrared (RIDIR) spectroscopy have been used to probe the single-conformation spectroscopy of these molecules. In both γ_ACHC and γγ_ACHC, all population is funneled into a single conformation. With RIDIR spectra in the NH stretch (3200–3500 cm^–1) and amide I/II regions (1400–1800 cm^–1), in conjunction with theoretical predictions, assignments have been made for the conformations observed in the molecular beam. γ_ACHC forms a single nearest-neighbor C9 hydrogen-bonded ring whereas γγ_ACHC takes up a next-nearest-neighbor C14 hydrogen-bonded structure. The gas-phase C14 conformation represents the beginning of a 2.6₁₄-helix, suggesting that the constraints imposed on the γ-peptide backbone by the ACHC and ethyl groups already impose this preference in the gas-phase di-γ-peptide, in which only a single C14 H-bond is possible, constituting one full turn of the helix. A similar conformational preference was previously documented in crystal structures and NMR analysis of longer γ-peptide oligomers containing the γ_ACHC subunit [Guo, L., et al. Angew. Chem. Int. Ed. 2011, 50, 5843−5846]. In the gas phase, the γ_ACHC-H₂O complex was also observed and spectroscopically interrogated in the molecular beam. Here, the monosolvated γ_ACHC retains the C9 hydrogen bond observed in the bare molecule, with the water acting as a bridge between the C-terminal carbonyl and the π-cloud of the UV chromophore. This is in contrast to the unconstrained γ-peptide-H₂O complex, which incorporates H₂O into both C9 and amide-stacked conformations