2.1 Lab grown Arctica islandica
Arctica islandica bivalves were cultured inside the lab of the Royal Netherlands Institute for Sea Research (NIOZ, Texel, the Netherlands). Specimens used for this study were grown under four different, constant, and monitored temperature regimes: 1.1 ± 0.2°C, 3.2 ± 0.4°C, 15 ± 0.3°C and 18 ± 0.3°C (see Table 1 ). Details on the culturing setup are provided inAppendix I and Witbaard et al. (1998). Aragonite from cleaned and driedArctica islandica shells was sampled using a hand-held Dremel 3000 rotary drill at low speed equipped with a tungsten-carbide drill bit (see S1 ). Gathering enough aragonite for reliable ∆47 analyses for each temperature treatment (>2 mg; Müller et al., 2017; Fernandez et al., 2017) typically required combining material from multiple (3‒5) specimens grown under the same temperature conditions. To test potential inter-specimen differences, results were tracked per individual specimen for the 1.1 ± 0.2°C and 18 ± 0.3°C treatments (see Table 1 ).