Biogeochemical and absorption properties of different size fractions of suspended matter in the western Spitsbergen fjords (Svalbard Archipelago) in the summer

In the summers of 2022 and 2023, the variability of biogeochemical properties and light absorption of suspended particulate matter (SPM) was investigated in three western Spitsbergen fjords: Hornsund, Kongsfjorden, and Isfjorden. Analyses included SPM and its organic (POM) and inorganic (PIM) fractions, chlorophyll a (Tchla), and light absorption coefficients of total particles (ap(λ)), phytoplankton (aph(λ)), and detritus (ad(λ)). Measurements were conducted on unfractionated seawater and on size-fractionated samples obtained by cascade filtration, allowing the assessment of four particle classes: pico- (0.2–2 µm), ultra- (2–5 µm), nano- (5–20 µm), and micro-particles (20–200 µm). The obtained results revealed clear differences in particle size contributions in the fjord waters. Ultra-particles dominated the total concentrations, contributing 39 %–56 % of SPM, POM, PIM, and Tchla. Pico-particles also had large contribution: 16 %–29 %, and micro- and nano-particles accounted for 12 %–17 %. The average POM/SPM ratio was 33 %, indicating the dominance of inorganic matter. However, organic contributions varied with size of particles: micro- and pico-particles contained more organic material (45 % and 43 %), while nano- and ultra-particles had lower proportions (38 % and 26 %). Ultra-particles also played a leading role in light absorption at 443 nm, contributing 44 %–62 % to ap(443), ad(443), and aph(443). Pico-, nano-, and micro-particles contributed 24 %–28 %, 10 %–19 %, and 4 %–9 %, respectively. Considerable variability in absorption properties was observed across size classes. Since variability ranges often overlap for different size classes, this may prevent unambiguous identification of particle size class based on light absorption spectra.