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 (Ωa) and calcite (Ωc) 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 Ωa in the upper 50 m in the fjord in winter was 1.59–1.74 and in summer 1.65–2.66. The lowest Ωa (1.5) was close to the reported critical threshold for aragonite-forming organisms such as the pteropod Limacina helicina. In summer 2013, Ωa, pHT 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 Ωa 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 Ωa by the same amount as the biological effect increased Ωa. The seasonal increase in temperature only played a minor role on the increase of Ωa. 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.