Dissolved organic matter of the spring bloom in the Labrador Sea; chracterized using optical properties and parallel factor analysis

The dynamics of dissolved organic matter (DOM) during the decline of annual spring phytoplankton bloom in the Labrador Sea in May/June 2022 were investigated using fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC). Samples from two short term bioassays aimed to investigate phytoplankton production of DOM under varying temperature and nutrient conditions. Three series of biodegradation assays were used to investigate the microbial transformations of DOM over a six-month time period. Fluorescence data from both experiments of a five component PARAFAC model was validated and used alongside dissolved organic carbon and total dissolved nitrogen data to gain insight into the DOM dynamics. The PARAFAC model was compared to other models using the OpenFluor database and found that all components had been found in previous studies. Of the five components C1, C4, and C5 have been associated with more refractory DOM while C2 and C3 have been linked to freshly produced, more labile DOM and microbial activity. For the bioassay experiments, there were no distinctive trends in temperature or nutrient conditions that could be used to indicate how changing climate conditions may affect DOM production by phytoplankton. Biodegradation data had slight trends between the series for C1 and C2 but no overall trends across components. The lack of trends in both experiments was largely attributed to the bloom composition being dominated by Phaeocystis spp. which primarily releases polysaccharides which are unable to fluoresce. This data provides a basis into future DOM analysis during the spring bloom in this region and highlights a need of additional analysis techniques for phaeocystis blooms.