27 Sep 2023
 | 27 Sep 2023

Review article: Melt-Affected Ice Cores for (Sub-)Polar Research in a Warming World

Dorothea Elisabeth Moser, Elizabeth R. Thomas, Christoph Nehrbass-Ahles, Anja Eichler, and Eric Wolff

Abstract. Melting polar and alpine ice sheets in response to global warming pose ecological and societal risks but will also hamper our ability to reconstruct past climate and atmospheric composition across the globe. Since coastal low-elevation ice caps are crucial environmental archives but changing rapidly, the (sub-)polar research community is increasingly faced with melt-affected ice cores common in alpine settings. Here, we review the characteristics and effects of near-surface melting on ice-core records focussing on a (sub-)polar readership and make recommendations for melt-prone study regions. This review covers (1) melt layer formation; (2) identification and quantification of melt; (3) structural characteristics of melt features; effects of melting on (4) records of chemical impurities, i.e. major ions, trace elements, black carbon, and organic species, (5) stable water isotopic signatures, and (6) gas record; (7) applications of melt layers as environmental proxies.

Melting occurs during positive surface energy balance events, which are shaped by global to local meteorological forcing, regional orography, glacier surface conditions and subsurface characteristics. Meltwater flow ranges from homogeneous wetting to spatially heterogeneous preferential flow paths and is determined by temperature, thermal conductivity and stratigraphy of the snowpack. Melt layers and lenses are the most common consequent features in ice cores and are usually recorded manually or using line-scanning. Chemical ice-core proxy records of water-soluble species are generally less preserved than insoluble particles such as black carbon or mineral dust due to their strong elution behaviour during percolation. However, a high solubility in ice as observed for ions like F, Cl, NH4+, or ultra-trace elements can counteract the high mobility of these species due to a burial in the ice interior. Stable water isotope records like δ18O are often preserved but appear smoothed if significant amounts of meltwater were involved. Melt-affected ice cores are further faced with questions about the permeability of the firn column for gas movement, and gas concentrations can be increased through dissolution and in-situ production. Noble gas ratios can be useful tools to identify melt-affected profile sections in deep ice. Despite challenges for ice-core climate reconstruction based on chemical records, melt layers are a proxy of warm temperatures above freezing, which is most sensitive in the dry snow and percolation zone.

Bringing together insights from snow physics, firn hydrology and ice-core proxy research, we aim to foster a more comprehensive understanding of ice cores as climate and environmental archives, provide a reference on how to approach melt-affected records, and raise awareness of the limitations and potential of melt layers in ice cores.

Dorothea Elisabeth Moser et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1939', Anonymous Referee #1, 29 Oct 2023
  • RC2: 'RC2 comment', Veijo Pohjola, 22 Nov 2023

Dorothea Elisabeth Moser et al.

Dorothea Elisabeth Moser et al.


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Short summary
Increasing temperatures worldwide lead to more melting of glaciers and ice caps, even in the polar regions. This is why ice core scientists need to prepare for analysing records affected by melting and refreezing. In this paper, we present a summary of how near-surface melt forms, what structural imprints it leaves in snow, how various signatures used for ice-core climate reconstruction are altered, and how we can still extract valuable insights from melt-affected ice cores.