Seen in flakes & drops: local heterogeneity of marine snow, biogeochemistry, and plankton in Svalbard's glacial bays

Abstract. Glacier retreat is one of the most spectacular effects of climate warming in the Svalbard Archipelago, and is having a substantial impact on physical, biogeochemical and ecological processes in marine ecosystems. Here we propose that marine snow acts as a direct agent linking water chemistry, mineral particles, and primary and secondary producers. Marine snow plays a key role in carbon export and also carries knowledge about the biophysical state of the pelagic ecosystems. We propose that structuring of marine snow, assessed via high-resolution imaging by the Underwater Vision Profiler (UVP6), may serve as an informative currency for inter-regional, inter-seasonal and fine-scale system comparisons. In this study, we investigated small-scale variability in nutrients, carbon, plankton and marine snow in fjord waters proximal to glaciers in Hornsund, Rechercherfjorden and Isfjorden. We observed strong seasonal differences in biogeochemical properties, shifts in plankton composition (protists and zooplankton) and marine snow morphology between late summers (2022, 2023) and spring 2023. Fine-scale observations show various interplays between marine snow populations with hydrography, turbidity, biogeochemistry, and composition of plankton communities. Alongside expected relations between marine snow composition and morphology with for example temperature and macronutrients, we also identified other potentially important correlations, including with manganese, iron, and total alkalinity. Given the high spatiotemporal variability in physical, biogeochemical conditions and associated particles and plankton, we conclude that seasons and local heterogeneity are the strongest drivers. These results provide new interdisciplinary insight into coupled physical-biogeochemical-ecological processes and improve our understanding of land-ocean interaction on marine production and carbon burial near glaciers at varying states of recession.