Production line part of the key point incubations in part 1 (dissolved organic matter release) of the microcosm experiment, Gulf of Finland, Baltic Sea

The data were collected from an experiment using phytoplankton cultures (Apocalathium malmogiense and Rhodomonas marina). The aim of the experiment was to study carbon cycling among phytoplankton and bacteria, and the effects on the dissolved organic matter (DOM) pool. The experiment was conducted at Tvärminne Zoological Station, Hanko, Finland with non-axenic unialgal phytoplankton cultures and bacteria originating from the Baltic Sea. The experiment was conducted between Dec. 2017 and Apr. 2018. The experiment consisted of two parts, the DOM release experiment (part 1) and the DOM consumption experiment (part 2). Separate triplicate batch cultures of both phytoplankton species were grown for each experiment. In the DOM release experiment the cultures were grown for over 4 months and three day-long incubations (key point incubations, KPI's) were initiated on three occasions; the first KPI at early exponential growth phase and the second and third KPI's when the phytoplankton had grown more abundant. During each KPI and aliquot of the culture was inoculated with freshly collected sea water bacteria, and bacterial community composition was measured. This aliquot was then divided into two further aliquots; one was incubated with radioisotopes for productivity (primary and bacterial production) and 14C-flow analyses (production line) and one filtered through 0.8 µm for analysis of DOM optical properties. During the KPI's measurements were taken at 0, 4, 8 and 12 h. Nutrient concentrations (measured from non-filtered and 0.8 µm filtered samples) and concentration of dissolved organic carbon were measured only at 0 and 12 h. Concentrations of particulate organic carbon and nitrogen and chlorophyll a were measured only once for each KPI at the beginning of the incubation. In the DOM consumption experiments the cultures were grown to high abundance, after which the phytoplankton and most of the bacteria were filtered out. The filtrate was then inoculated with freshly collected sea water bacteria, after which it was incubated for 7 days. Bacterial abundance, production, respiration, and community composition, and concentration and optical properties of DOM were measured daily. The experimental design is explained in figure 1 of the associated publication.

This data table contains measurements taken during the production line, i.e. all the measurements involving radioisotopes. It is structured based on two light and one dark measurements of primary production. Primary production measurements themselves are given in https://doi.pangaea.de/10.1594/PANGAEA.937723. From each of these subsamples (2 light and 1 dark) the following variables were measured: 14C-DOM production from 14C-NaHCO3, bacterial incorporation of 14C originating from 14C-NaHCO3, 3H-thymidine incorporation rate, and 3H-thymidine based bacterial production (calculated from thymidine incorporation rate). Raw reads from the scintillation counting are not given, only the calculated production rates calculated as explained in the methods of the associated publication. This data table is explained in figure 2 of the associated publication.