Differentiating bubble-free layers from melt layers in ice cores using noble gases

• Published in: Journal of Glaciology
• Main Authors: Orsi, Anais, Kawamura, Kenji, Fegyveresi, John, Headly, Melissa, Alley, Richard, Severinghaus, Jeffrey
• Other Authors: Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), University of California (UC)-University of California (UC), National Institute of Polar Research Tokyo (NiPR), Graduate University for Advanced Studies Hayama (SOKENDAI), Pennsylvania State University (Penn State), Penn State System
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: ice and climate; ice core; meltwater chemistry; polar firn; surface melt; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; Greenland; Journal of Glaciology
• Online Access: https://hal.science/hal-01806136; https://hal.science/hal-01806136/document; https://hal.science/hal-01806136/file/div-class-title-differentiating-bubble-free-layers-from-melt-layers-in-ice-cores-using-noble-gases-div.pdf; https://doi.org/10.3189/2015JoG14J237

International audience Melt layers are clear indicators of extreme summer warmth on polar ice caps. The visual identification of refrozen meltwater as clear bubble-free layers cannot be used to study some past warm periods, because, in deeper ice, bubbles are lost to clathrate formation. We present here a reliable method to detect melt events, based on the analysis of Kr/Ar and Xe/Ar ratios in ice cores, and apply it to the detection of melt in clathrate ice from the Eemian at NEEM, Greenland. Additionally, melt layers in ice cores can compromise the integrity of the gas record by dissolving soluble gases, or by altering gas transport in the firn, which affects the gas chronology. We find that the easily visible 1 mm thick bubble-free layers in the WAIS Divide ice core do not contain sufficient melt to alter the gas composition in the core, and do not cause artifacts or discontinuities in the gas chronology. The presence of these layers during winter, and the absence of anomalies in soluble gases, suggests that these layers can be formed by processes other than refreezing of meltwater. Consequently, the absence of bubbles in thin crusts is not in itself proof of a melt event