Concentration and isotopic composition of bromine and chlorine in Antarctic sea ice

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Vallelonga, P, de Gois, JS, Borges, DLG, Costas-Rodriguez, M, Gkinis, V, Lannuzel, D, Spolaor, A, Vanhaecke, F
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2021
• Subjects: Earth Sciences; Physical geography and environmental geoscience; Glaciology; Antarctic; Austral; Southern Ocean; Antarc*; Sea ice
• Online Access: https://doi.org/10.1016/j.gca.2020.10.020; http://ecite.utas.edu.au/141570

This work presents the first investigation of Br and Cl isotopic partitioning in Southern Ocean sea ice. The sea ice samples characterized were collected during the Australian-led Sea Ice Physics and Ecosystem eXperiment-2 (SIPEX-2) marine voyage in austral spring of 2012 (26 Sept 10 Nov), within the area bounded by 115125E and 6266 o S off the East Antarctic coast. Bromine concentrations ranged from 710 20 μg L -1 to 31440 570 μg L -1 and chlorine concentrations ranged from 218 12 mg L -1 to 7945 351 mg L -1 . Bromine and chlorine concentrations were positively correlated with a slope of 0.0038 (r=0.996, p<0.001), consistent with the seawater Br/Cl ratio of 0.0035. Bromine isotopic compositions (denoted δ 81 Br with respect to SMOB isotopic reference) varied from -0.64 to 0.10 with a mean of -0.16 and standard deviation of 0.04. Chlorine isotopic compositions (denoted δ 37 Cl with respect to SMOC isotopic reference) varied from -1.10 to 0.43 with a mean of -0.26 and standard deviation of 0.10. Despite their strong concentration correlation, there was a much less consistent relation between Br and Cl isotopic compositions (r=0.74, p<0.01) and great variability within individual sea ice cores. The samples showing the largest degree of fractionation in their Br and Cl isotopic compositions were found deepest in the sea ice samples. Multiple parameters may influence isotopic fractionation processes in sea ice including ice texture, age, salt content, and algal biomass content (represented by Chlorophyll-a concentrations); although no single factor was found to consistently correlate with the bromine or chlorine isotopic signature. We consider the possibility of isotopic fractionation resulting from brine rejection and desalinization processes.