Bromine enrichment signal in Svalbard shallow cores reflects changes of seasonal sea ice variability

Description Bromine enrichment (Brenr) has been widely used as a proxy for past sea ice reconstructions. In this study, three firn cores drilled on Holtedahlfonna (Svalbard) were analysed for trace elements. Excluding a single year data, a positive correlation was observed between Brenr and springtime sea ice variability in the potential source region during 2005-2016. Accounting for different sea ice ages, Brenr signal resulted significantly correlated only with first-year sea ice, reinforcing its role as a major contributor to springtime gas-phase bromine emissions. Comparisons between Na and Br concentrations in shallow cores and temporally corresponding values in annual snow pits collected at the same site reveal that elemental reallocation similarly affects both chemicals, resulting in a generally stable Brenr signal over time. Finally, the negative correlation with the δ¹⁸O temperature proxy further supports the capability of Brenr to capture past climate-change-driven sea ice fluctuations. In this database sodium (Na) and bromine (Br) concentrations for the three shallow firn cores and annual snow pits are provided. For additional information contact [e-mail] Acknowledgments This work has been supported by the "Programma di Ricerca in Artico" (PRA; project no. PRA2019-0011, Sentinel), by the Svalbard Science Forum/Research Council of Norway through the Arctic Field Grant call (projects ASIHAD, ISSICOS, and BIOMASS), by the French Polar Institute (IPEV; Institut Polaire Français Paul-Émile Victor) science funding (programmes 399 and 1192), and by the Svalbard Strategic Grant (project C2S3, no. 257636; SnowNet no. 295779 and BC3D no. 283466). The project was also funded by the European Union's Horizon Europe Research and Innovation Programme through the project LIQUIDICE (Grant Number: 101184962) and by the Svalbard Environmental Protection Fund (Svalbards miljøvernfond) through the project Threaten - The Svalbard biogeochemical shift duRing the AnThropocENe (Ref. 22/71). Moreover, this project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 689443 via project iCUPE (Integrative and Comprehensive Understanding on Polar Environments). The University of Perugia's research cluster no. 5, "Climate, Energy, and Mobility" has also partially funded this research. In addition, CryoGrid simulations have been supported by the Nansen Legacy project (Research Council of Norway, Grant 276730) and SIOS-InfraNor (Research Council of Norway, Grant 269927). Finally, this research work was supported by a PNRR-funded (National Recovery and Resilience Plan) PhD scholarship in Polar Sciences at Ca' Foscari University of Venice, within the framework of the European Union - Next Generation EU, Mission 4 Component 1 (CUP H73C23000510006), pursuant to Ministerial Decree No. 118/2023.