Antarctica Arctic Arctic rapid warming Laohugou glacier POPs TXRF X-ray absorption fine structure spectroscopy X-ray absorption near edge spectroscopy X-ray absorption spectroscopy X-ray fluorescence X-ray fluorescence spectroscopy XANES XANES and LCF XAS spectroscopy atmospheric mineral dust bacteria compositional data analysis contaminants cryoconite cryosphere cryospheric sciences droplets dust environment evaporation global warming hiatus global warming slowdown ice ice core ice cores