Rate of Iceland Sea acidification from time series measurements

Abstract. The Iceland Sea is one part of the Nordic Seas. Cold Arctic Water prevails there and the deep-water is an important source of North Atlantic Deep Water. We have evaluated time series observations of measured pCO₂ and total CO₂ concentration from discrete seawater samples during 1985–2008 for the surface and 1994–2008 for deep-water, and following changes in response to increasing atmospheric carbon dioxide. The surface pH in winter decreases at a rate of 0.0024 yr⁻¹, which is 50% faster than average yearly rates at two subtropical time series stations, BATS and ESTOC. In the deep-water regime (>1500 m), the rate of pH decline is a quarter of that observed in surface waters. The surface seawater carbonate saturation states (Ω) are about 1.5 for aragonite and 2.5 for calcite, about half of levels found in subtropical surface waters. During 1985–2008, the degree of saturation (Ω) decreased at an average rate of 0.0072 yr⁻¹ for aragonite and 0.012 yr⁻¹ for calcite. The aragonite saturation horizon is currently at 1710 m and shoaling at 4 m yr⁻¹. Based on this rate of shoaling and on the local hypsography, each year another 800 km² of seafloor becomes exposed to waters that have become undersaturated with respect to aragonite.