Late winter-to-summer change in ocean acidification state in Kongsfjorden,with implications for calcifying organisms

Late winter-to-summer changes (April to July) in ocean acidification state, calcium carbonate (CaCO₃) saturation for aragonite (Ω _a) and calcite (Ω _c) and biogeochemical properties were investigated in 2013 and 2014 in Kongsfjorden, Svalbard. We investigated physical (salinity, temperature) and chemical (carbonate system, nutrient) properties in the water column from the glacier front in the fjord to the west Spitsbergen shelf. The average range of Ω _a in the upper 50 m in the fjord in winter was 1.59–1.74 and in summer 1.65–2.66. The lowest Ω _a (1.5) was close to the reported critical threshold for aragonite-forming organisms such as the pteropod Limacina helicina. In summer 2013, Ω _a, pH_T and salinity were generally lower than in 2014 as a result of a larger influence of high-CO₂ water from the coastal current and less Atlantic water. The inner fjord was influenced by glacial water in summer which decreased Ω _a by 0.7. Biological CO₂ consumption based on a winter-to summer decrease in nitrate was larger in 2014 than in 2013, suggesting more primary production in 2014. The influence of freshwater decreased Ω _a by the same amount as the biological effect increased Ω _a. The seasonal increase in temperature only played a minor role on the increase of Ω _a. The biological effect showed more inter-annual variability than the effect of freshwater. Based on this study, we suggest that changes in the inflow of different water masses and freshwater directly influence ocean acidification state, but also indirectly affect the biological drivers of carbonate chemistry in the fjord.