Arctic phytoplankton bloom regimes are associated with distinct dissolved carbohydrate signatures and transparent exopolymer particle (TEP) formation

Abstract. Phytoplankton are major producers of marine dissolved organic matter (DOM), including carbohydrates that fuel microbial carbon cycling or contribute to the biological carbon pump through exopolymer particle aggregation. In the Arctic Ocean, climate-driven changes are expected to restructure phytoplankton communities, yet the consequences for the molecular composition of DOM and its fate within microbial and aggregation pathways remain unclear. Here, we examined potential linkages between phytoplankton community composition (18S-rRNA), dissolved organic carbon (DOC), dissolved combined carbohydrates (DCCHO) and transparent exopolymer particles (TEP) in the Fram Strait and the Kara Sea. An advanced spring bloom dominated by the haptophyte Phaeocystis pouchetii coincided with a DOM pool enriched in neutral and acidic carbohydrates and elevated TEP concentrations. In contrast, ice-edge diatom blooms dominated by Thalassiosira spp. were characterized by glucose-enriched DOM signatures and low TEP formation. Our findings indicate an association between specific phytoplankton taxa and exopolymeric carbohydrate composition, suggesting that shifts in phytoplankton biodiversity may alter carbon processing pathways.