Icy thermometers : quantifying the impact of volcanic heat on glacier elevation

ACKNOWLEDGEMENTS This project was supported by the NERC Global Partnerships Seedcorn grant NE/W003724/1 and the Leverhulme Trust Research Project RPG-2019-093. We thank Kevin A. Reath for support in analysing volcanic thermal anomalies. A.G.P. and M.E.P. were partly supported by the NASA Science Mission Directorate Earth Surface and Interior grant 80NSSC21K0842. J.J. was supported by the NERC Quadrat Doctoral Training Partnership. We express our gratitude to John Smellie and an anonymous reviewer for fruitful feedback which greatly improved the manuscript.Peer reviewedPostprin

Icy thermometers: quantifying the impact of volcanic heat on glacier elevation

We present a continent-wide study of 600 glaciers located on and near 37 ice-clad volcanoes in South America, that demonstrates glacier sensitivity to volcanic heat. We distinguish between ‘volcanic-glaciers’ (≤1 km from volcanic centres; n=74), and ‘proximal glaciers’ (1-15 km; n=526) and calculate their equilibrium line altitudes (ELA). For each ice-clad volcano we compare the ELAs of its volcanic-glaciers to those of its proximal glaciers which shows that the ELAs of the former are higher than the ELAs of the latter. ΔELAmean, defined as the offset between the mean ELA of the volcanic-glaciers and that of the proximal glaciers, is calculated for each ice-clad volcano. ΔELAmean is positive for 92% of the 37 volcanoes, and a quantitative relationship between ΔELAmean and volcanic thermal anomaly is established. Results highlight the impact of volcanic heat on glacier elevation; emphasise the need to exclude glaciers on, or near, volcanoes from glacier-climate investigations; and demonstrate the first-order potential for glaciers as ‘volcanic thermometers’. Volcanic-glacier monitoring could contribute to our understanding of magmatic and thermal activity, with changes in glacier geometries potentially reflecting long-term fluctuations in volcanic heat and unrest

Original paper<br>Low output syndrome following aortic valve replacement. Predictors and prognosis

Introduction: Low output syndrome (LOS) is a dangerous postoperative complication, which significantly worsens the prognosis; it is an essential risk factor of postoperative death. The aim of the study was to analyze the predictors of postoperative low cardiac output syndrome in patients subjected to aortic valve replacement due to aortic stenosis or regurgitation. Material and methods: Three hundred (300) patients with significant isolated aortic valve defect due to either aortic stenosis (n=150) or regurgitation (n=150), who underwent isolated aortic valve replacement were included in the study. Low cardiac output syndrome (LOS) was defined as the need for high dosages of inotropic medication, and/or intra-aortic balloon pumping to sustain adequate hemodynamic status. Results: Postoperative low cardiac output syndrome was developed in 86 patients (28.6%), including 39 patients with aortic stenosis (26.0%) and 47 patients with aortic regurgitation (31.3%). We selected the following independent predictors of postoperative LOS (odds ratio in parentheses): (1) aortic stenosis group – advanced age (4.7), end-systolic (5.5) and end-diastolic intraventricular septum thickness (4.2) before the surgery, LVEF Ł50% (5.4) and insignificant mitral regurgitation (4.1) in the early postoperative period; (2) aortic regurgitation group – obesity (4.8), left ventricular end-systolic (4.5) and end-diastolic diameters (6.4) in the preoperative period and left ventricular end-systolic (4.7) and end-diastolic diameters (6.1), and left ventricular ejection fraction Ł50% (7.2) in the early postoperative period. Conclusions: The patients at high risk for the development of low cardiac output syndrome should be the focus of trials of new techniques of myocardial protection to effectively resuscitate the ischemic myocardium and optimization of preexisting heart failure symptoms

The Protonation States of Oxo-Bridged Mn IV

In nature, the protonation of oxo bridges is a commonly encountered mechanism for fine-tuning chemical properties and reaction pathways. Often, however, the protonation states are difficult to establish experimentally. This is of particular importance in the oxygen evolving complex of Photosystem II, where identification of the bridging oxo protonation states is one of the essential requirements toward unraveling the mechanism. In order to establish a combined experimental and theoretical protocol for the determination of protonation states, we have systematically investigated a series of Mn model complexes by Mn K pre-edge X-ray absorption spectroscopy. An ideal test case for selective bis-μ-oxo-bridge protonation in a Mn-dimer is represented by the system [Mn(IV)(2)(salpn)(2)(μ-OH((n)))(2)]((n+)). Although the three species [Mn(IV)(2)(salpn)(2)(μ-O)(2)], [Mn(IV)(2)(salpn)(2)(μ-O)(μ-OH)](+) and [Mn(IV)(2)(salpn)(2)(μ-OH)(2)](2+) differ only in the protonation of the oxo bridges, they exhibit distinct differences in the pre-edge region while maintaining the same edge energy. The experimental spectra are correlated in detail to theoretical ly calculated spectra. A time-dependent density functional theory approach for calculating the pre-edge spectra of molecules with multiple metal centers is presented, using both high-spin (HS) and broken-symmetry (BS) electronic structure solutions. The most intense pre-edge transitions correspond to an excitation of the Mn-1s core electrons into the unoccupied orbitals of local e(g) character (d(z(2)) and d(xy) based in the chosen coordinate system). The lowest by energy experimental feature is dominated by excitations of 1s-α electrons and the second observed feature is primarily attributed to 1s-β electron excitations. The observed energetic separation is due to spin polarization effects in spin-unrestricted density functional theory and models final state multiplet effects. The effects of spin polarization on the calculated Mn K pre-edge spectra, in both the HS and BS solutions, are discussed in terms of the strength of the antiferromagnetic coupling and associated changes in the covalency of Mn-O bonds. The information presented in this paper is complemented with the X-ray emission spectra of the same compounds published in an accompanying paper. Taken together, the two studies provide the foundation for a better understanding of the X-ray spectroscopic data of the oxygen evolving complex (OEC) in Photosystem II