Hornsund is undergoing rapid environmental transformations, driven by ongoing atlantification of the Arctic. This study examines how foraminiferal assemblages have responded to these changes over the past two decades, providing an exceptional opportunity to link modern ecosystem dynamics with processes recorded in the sedimentary archive. The primary objective of this study aims is to establish diagnostic faunal and isotopic features of atlantification that can be applied in the interpretation of palaeoceanographic records. Results reveal clear indicators of atlantification, including the increasing dominance of boreoarctic and Atlantic Water (AW)-affiliated taxa (Adercotryma glomeratum Brady, Astrononion hamadaense Asano, Nonionellina labradorica Dawson, Recurvoides turbinatus Brady), prevalence of opportunistic species (Cassidulina reniformis Nørvang, Cribroelphidium clavatum Cushman), rising species richness and a greater abundance of agglutinated taxa, particularly in the inner fjord. Spatial distribution patterns reflect progressive AW penetration towards the fjord head, with outer and central fjord stations exhibiting high diversity and evenness, and inner glacial-proximal areas showing increased agglutinated foraminifera dominance. Stable-isotope analyses of selected foraminiferal tests demonstrate increasing δ18O, consistent with higher salinity, and decreasing δ13C, indicative of enhanced primary productivity and terrestrial organic matter input. These changes, occurring within just 22 years, reveal the high sensitivity of benthic foraminifera to environmental change in the Arctic and confirm their value as proxies for reconstructing both contemporary and palaeoceanographic changes in high time resolution.
