Application of visual stratigraphy from line-scan images to constrain chronology and melt features of a firn core from coastal Antarctica

Abstract

Establishing an accurate chronology is crucial for interpretation of ice core-based climatic records. While high snow accumulation rates characterise coastal Antarctica, thus enabling recovery of highly resolved climatic records, summertime melting at such low-elevation sites offers challenges in establishing a reliable chronological framework through traditional approaches using the seasonality of stable water isotope and ionic proxy records. Here, we assess visual stratigraphy (VS) obtained from line-scan images as a proxy for annual layer counting in firn section (top 50 m) of the IND-36/B9 ice core (dated 1919–2016 CE) from the Djupranen Ice Rise in central Dronning Maud Land, East Antarctica. We also used these images to obtain melt history for the site and found that traditional thickness-based quantification of melt proportion results in significant overestimations. Since density has dominant control on VS profile over the firn section, we first used circulant single-spectrum analysis to remove the secular trend and then we extracted the seasonal VS signals attributed to dust and sea-salt inclusions. We find that melt layers do not significantly alter the VS records if masked during pre-processing. The age–depth model based on the reconstructed VS profile revealed an excellent match with identified time-markers within an uncertainty of ±2 years.

Investigating the spatial representativeness of Antarctic ice cores: A comparison of ice core and radar-derived surface mass balance

“…We quantify the density-related error by calculating the standard deviation error between the ice core raw measured densities and the exponential fit of the densities, at each site. We note that this calculated density error matches that of the ice core density measurement errors where reported (Hubbard et al, 2013;Pratap et al, 2022;Dey et al, 2023). We then evaluate the impact of this density error on the calculation of the ice core SMB.…”

“…The mean SMB for each time interval contained between successive pairs of IRHs at the ice core location (where the density profile is known) is obtained by dividing the difference between the deepest and the shallowest CM IRH of successive IRHs by the time interval contained between the pairs of dated IRHs. We note that we use the updated Dey et al (2023) chronology for the Djupranen ice core.…”

“…We would like to highlight that the ages of the IRHs over the Lokkeryggen and Hammarryggen ice rises have been updated from those provided in Cavitte et al (2022), which were based on preliminary chronologies (Wauthy et al, submitted). In addition, note that for the Djupranen site, we use the IRH twtts as given in the Pratap et al (2022) and the recent chronology update published by Dey et al (2023), while based on comparison of mass balance estimates though different approaches (Goel et al, 2022), we highlight that it is suspected that the age chronology of the Kupol Moskovskij ice core might be in error. 2011,2009,2006,2003,2002,2000,1998 2.2 98 KC(4) Goel et al (2017b, a) 3.…”

Visual Stratigraphy-Based Age Scale Developed for the Shallow Mount Siple Firn Core, Antarctica

“…Visual stratigraphy reveals cyclicity in the grey-scale of polar ice cores. Line scan images can be used to detect and highlight annual layers [7]. There are different factors that could cause the cyclicity in the grey-scale: melt layers, precipitation grain size [8] or dust content [9].…”

Spatial variability and post-depositional diffusion of stable isotopes in high accumulation regions of East Antarctica

“…Therefore, temporal resolution in low accumulation ice core isotope records from inland Antarctica varies typically from multi-year to multi-decadal scales (e.g., Petit et al, 1982;Ekaykin et al, 2002). Compared to these, isotope records from high-accumulation coastal sites of Antarctica have been shown to achieve seasonal to annual resolution (e.g., Küttel et al, 2012;Goursaud et al, 2019;Ejaz et al, 2021;Dey et al, 2022). Further, the coastal areas of Antarctica are also shown to have different moisture sources than inland as cyclonic activity and the presence of sea ice play a crucial role.…”