Carbonate content and stable isotopic composition of aerosol carbon in the Canadian High Arctic

Abstract. The carbon cycle in the Arctic atmosphere is important in understanding abrupt climate changes occurring in this region. Two-years of measurements (summer 2016–spring 2018) of carbonaceous aerosols at the High Arctic station Alert, Canada, showed that in addition to organic carbon (OC) and elemental carbon (EC), carbonate carbon (CC) was episodically but not negligibly present. The relative abundances of CC in total carbon (TC) ranged from 0–65 % with an average of approximately 11 % over the entire period. Also there was a strong correlation of CC with aerosol Ca²⁺ which is associated mostly with soil dust and to a lesser extent sea salt aerosol. Based on this and the analysis of air mass back trajectories (AMBT), we infer two possible sources of CC in the Arctic total suspended particles (TSP). The major one is the erosion and resuspension of limestone sediments, particularly in the semi-desert areas of the northern Canadian Arctic. Another potential more minor source of CC is from marine aerosol sources including calcified marine phytoplankton shells (coccoliths) introduced into the atmosphere via sea-to air emission.

The CC content significantly influenced the stable carbon isotopic composition (δ¹³C) of TC. The higher the CC content, the higher the δ¹³C values, which is consistent with the strong ¹³C enrichment in carbonates. Therefore, carbonates in Arctic TSP must be taken into account not only in isotopic studies using δ¹³C analyses but also when assessing the impact of carbonaceous aerosols on the Arctic climate.