Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 151-
Arctic sea ice may play an important role in the biogeochemical cycling of trace metals (TM). However, details of the mechanisms for TM accumulation into sea ice and their release into seawater are still unknown. To gain a better understanding of these mechanisms, an Arctic sea ice core was analyzed to investigate the association between TM concentrations and ice structure. The core was initially planed (~ 2 cm) with acid-cleaned ceramic knifes in a cold tank (-20˚C) located inside a clean room. It was separated via visual inspection of ice structure and photographed. Each section was melted at room temperature in acid cleaned LDPE buckets. The meltwater was separated for salinity, nutrients, δ18O and TM (Fe, Mn, Cd) analysis. TM samples were prepared as unfiltered (Total Dissolvable; TD), filtered (Dissolved; D, ＜0.22 µm; Labile Particulate; LP = TD – D) and acidified (0.05 M HCl, final concentration) before pre-concentration via NOBIAS Chelate PA1 resin and analyzed via GFAAS. To determine ice structure, pictures taken after planing were transformed to black and white to calculate the % micropore area (% Pore). Ice formation influences from snow and seawater were determined via δ18O. Using a combination of picture analysis, % micropore area analysis and δ18O analysis ice structure was determined as Snow Ice (-4.1 to -2.6 ‰), Granular Ice (-1.1 to -0.83 ‰), Mixed Ice (Granular + Columnar; -1.1 ‰) and Columnar Ice (-1.2 ‰). Salinity (1.3-2.1 psu) and nutrients (＜0.1 µmol/L NO2-NO3, ＜0.04 µmol/L PO4) were low indicating brine drainage. TM were heterogeneous and seemed to have a relationship with ice structure. DFe, DMn, and DCd showed higher concentrations in Snow (3.1 nM, 5.5 nM, and 0.11 nM, respectively) and Granular Ice (3.6 ± 0.8 nM, 8.5 ± 3.5 nM, and 0.10 ± 0.06 nM, respectively) when compared to Mixed (1.1 nM, 1.5 nM, and 0.018 nM, respectively) and Columnar Ice (1.3 nM, 1.4 nM, and ＜DL, respectively). LPFe, LPMn and LPCd was detected in Snow (95.4 nM, 0.66 nM, and ＜DL, respectively) and Granular Ice (232.9 ± 172 nM, 0.02 ± 0 nM, and 0.04 ± 0.03 nM, respectively) where LPFe was the only detected metal in Mixed (7.6 nM) and Columnar Ice (2.2 nM). Concentrations in Snow Ice may point to an atmospheric supply where metals in Granular Ice likely entrained due to particle scavenging during frail ice formation in seawater. High concentrations of D metals in Granular Ice can be explained by the chemical transformation of Fe and Mn-oxides. Low metal concentrations in Mixed and Columnar Ice are a result of brine drainage.
