Evidence of sea ice source in aerosol sulfate loading and size distribution in the Canadian High Arctic from isotopic analysis

Abstract

The influence of frost flowers and seawater brine on ion chemistry in snow, snowpack, ice cores, and aerosols is detected when a lower sulfate to sodium ratio than in seawater is present in polar regions. This evidence can be masked when large amounts of non-sea-salt sulfate are present from other sources such as biogenic and anthropogenic sulfate. Frost flower δ 34 S values were measured for the first time in frost flower sulfates and did not differ significantly from the sea salt δ 34 S values of +21‰. A method using stable isotopes is introduced to determine the limit of contributions from sea salt and sea ice sources (including frost flowers and brine) on sulfate concentrations in aerosol samples from Alert, Canada. Knowledge of the range of values of δ 34 S nss and the SO 4 /Na ratio found in sea ice sources (i.e., frost flowers) is used to quantitatively constrain the contributions from frost flowers and sea salt in the Arctic aerosol mass during the onset of winter in 2007 and 2008, allowing for quantification of non-sea-salt sulfate amounts during times when frost flowers are present. Frost flower and/or brine influence was found predominantly in the coarse-mode aerosols (>0.95 μm). This method to determine the contributions from sea salt and sea ice sources can be carried over to future studies with snow and ice cores.

A Factor and Trends Analysis of Multidecadal Lower Tropospheric Observations of Arctic Aerosol Composition, Black Carbon, Ozone, and Mercury at Alert, Canada

“…Based on chemical-transport-model simulations, Huang and Jaeglé (2017) suggested that wind-driven resuspension of sea salt deposited on surface snow was the dominant source of wintertime sea salt at Alert, more important than frost flowers. A minor role for frost flowers was supported by the sulfur isotope analysis of Seguin et al (2014), although it had been suggested otherwise (Xu et al, 2016). Xie et al (1999) suggested sea spray transported from the North Atlantic Ocean and Bering Sea as the explanation for the higher sea salt aerosol concentrations at Alert.…”

Processes Controlling the Composition and Abundance of Arctic Aerosol

“…Two inter‐related mechanisms of primary aerosol formation from snow and ice‐covered areas have been hypothesized to explain observations of Arctic sea salt aerosol. First, the wind‐driven generation of aerosol from frost flowers formed at ice surfaces could explain ambient sea salt seasonality and composition (e.g., Seguin et al, ; L. Xu et al, ). Frost flowers are formed on rapidly freezing sea water and brine can be drawn into frost flowers during freezing, resulting in enhanced ion concentrations (Douglas et al, ).…”

Sea Ice Versus Storms: What Controls Sea Salt in Arctic Ice Cores?

“…A chemical fingerprint of SISS is fractionation of the sea salt sulfate (ssSO 4 2− ) to Na + ratio relative to the seawater value, which results from the precipitation of mirabilite (Na 2 SO 4 • 10H 2 O) within or on top of sea ice (Rankin et al, ; Wagenbach et al, ). In the present‐day Arctic anthropogenic sulfate pollution masks other sulfate contributions (Goto‐Azuma & Koerner, ) meaning that the relative proportions of SISS and OOSS in aerosol or snow cannot be estimated using either the ssSO 4 2− to Na + ratio (Jourdain et al, ) or the sulfur stable isotopic ratio (δ 34 S) of samples (Seguin et al, ). The dominant control on Na variability in Arctic ice cores is unclear. Which is more important—changing sea ice extent or storminess?…”

“…A chemical fingerprint of SISS is fractionation of the sea salt sulfate (ssSO 4 2À ) to Na + ratio relative to the seawater value, which results from the precipitation of mirabilite (Na 2 SO 4 • 10H 2 O) within or on top of sea ice (Rankin et al, 2002;Wagenbach et al, 1998 SISS and OOSS in aerosol or snow cannot be estimated using either the ssSO 4 2À to Na + ratio (Jourdain et al, 2008) or the sulfur stable isotopic ratio (δ 34 S) of samples (Seguin et al, 2014). 2.…”