Particulate (POM) and dissolved (DOM) organic matter in the ocean are important players in the earth’s biogeochemical cycle and in constant dynamic change. However, they are often treated as distinct entities, separated operationally by size (0.7µm). We studied the dynamics of DOM and POM in an Arctic fjord between September 2020 and August 2021. Surface water was filtered through a GF/F filter (0.7 µm), while another part was unfiltered, and then rotated for 36h. Samples for dissolved and particulate organic carbon concentrations (DOC, POC), DOM composition, extracellular polymeric substances (EPS) and flow cytometry were taken before and after the incubation. From April to September, POC concentrations increased in both, filtered and unfiltered treatments by a factor of 0.04 - 1.5, while the lability of DOM decreased. Contrary to the measurements in the field, POC concentrations in the filtered water before the incubation were highest in the winter months and decreased in both treatments by 0.1 - 0.6, while the DOM composition indicated a transformation of recalcitrant to labile DOM. In both scenarios, EPS and bacterial activity increased. We confirm that during productive phases, POM can be replenished by the DOM pool through aggregation. However, POM dissolution, DOM transformation and increased bacterial activity during winter suggest that organic matter could be altered by bacteria into more labile material when new production is limited. This challenges common understandings of microbial degradation of DOM and presents a so far unexplored aspect of the carbon cycle.

Primary Presenter: Yasemin Bodur, UiT - the Arctic University of Norway (yasemin.bodur@uit.no)

Authors:

Yasemin Bodur, UiT - the Arctic University of Norway/Arctic and Marine Biology  (yasemin.bodur@uit.no)

Maria Digernes, Norwegian University of Science and Technology/Department of Chemistry  (maria.g.digernes@ntnu.no)

Martí Amargant-Arumí, UiT - the Arctic University of Norway/Arctic and Marine Biology  (marti.a.arumi@uit.no)

Jeffrey Hawkes, Uppsala University/Department of Chemistry  (jeffrey.hawkes@kemi.uu.se)

Ulrike Dietrich, UiT - the Arctic University of Norway/Arctic and Marine Biology  (ulrike.dietrich@uit.no)

Tobias Kielland, Norwegian University of Science and Technology/Department of Chemistry  (tobias.kielland@ntnu.no)

Stephen Koehler, Norwegian University of Science and Technology/Department of Chemistry  (stephen.g.kohler@ntnu.no)

Oliver Müller, University of Bergen/Marine Microbiology  (oliver.mueller@uib.no)

Marit Reigstad, UiT - the Arctic University of Norway/Arctic and Marine Biology  (marit.reigstad@uit.no)

Maria Paulsen, Uppsala University/Department of Chemistry  (marialundpaulsen@gmail.com)