EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-4192 Arctic phytoplankton bloom regimes are associated with distinct dissolved carbohydrate signatures and transparent exopolymer particle (TEP) formation Hirschmann Sophia https://orcid.org/0009-0005-4838-8299 1 von Jackowski Anabel https://orcid.org/0000-0001-6204-5341 1 2 Pontiller Benjamin 1 Metfies Katja 3 Povazhnyi Vasily 4 Neuhaus Stefan 3 Nöthig Eva-Maria https://orcid.org/0000-0002-7527-7827 3 Engel Anja https://orcid.org/0000-0002-1042-1955 1 Marine Biogeochemistry, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany Stockholm University, Stockholm, Sweden Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany Arctic and Antarctic Research Institute, St. Petersburg, Russia 17 07 2026 2026 1 41 Copyright: © 2026 Sophia Hirschmann et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4192/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-4192/egusphere-2026-4192.pdf

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 <em>Phaeocystis pouchetii</em> coincided with a DOM pool enriched in neutral and acidic carbohydrates and elevated TEP concentrations. In contrast, ice-edge diatom blooms dominated by <em>Thalassiosira </em>spp<em>.</em> 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.