In this study, we present B isotopic data for cold-water corals at high spatial resolution determined by UV femtosecond laser ablation system coupled to a Nu Plasma II MC-ICP-MS. Boron isotope records in biogenic carbonates provide constraints on the evolution of seawater pH and insights into biomineralization processes. We investigated B isotopic ratios in recent cold-water corals (Desmophyllum dianthus) from a field experiment in the Comau Fjord (Chile) to resolve seasonal variations. Corals from the head and the mouth of the fjord and from different water depths were stained with calcein, replaced at the same location or cross-transplanted and observed for a whole year to investigate time-resolved environmental signatures and potential adaptation effects under new environmental conditions. B isotopic ratios were measured at the upper part of the calyx in transverse sections between septa at the skeletal increment. δ11B values range between 23.5 and 27.0‰ and varies with seasonality and location in the fjord. Isotope signature of cross-transplanted corals do not differ significantly from those of local corals showing that the recorded signature is directly influenced by environmental conditions. B isotopic signatures correspond to an internal pH up-regulation for calcification of 0.78 to 1.14 pH units, which is likely controlled by ambient seawater pH and nutrient availability. These results show the potential of in situ techniques to decipher marine archive to reconstruct environmental conditions.