Particulate absorption spectra (350-750 nm) collected in the Amundsen and Nansen basins of the Arctic Ocean in July/August 2024.

This data sets contains spectra of the light absorption coefficients of particles (ap(λ), m-1), detritus (ad(λ), m-1) and phytoplankton pigments (aph(λ), m-1) from samples collected during the Arctic Ocean 2024 cruise (AO2024, Dodd et al., 2024), on board of the research icebreaker r/v Kronprins Haakon, between 19 July - 12 August 2024. Its main goals were to collect a transect of physical, chemical, and biological observations of the ocean and sea ice across the western Amundsen and Nansen basins of the Arctic Ocean, Water samples were collected at three depths, at the surface, at the Deep Chlorophyll-a Maximum (DCM) and 50 m, at the main coupled physical and biological stations. The depth at which the DCM was located was determined from chlorophyll-a fluorescence profile measured by the standard fluorometer attached to the ship’s CTD rosette. On secondary stations samples were collected at standard horizons, 10, 25, and 50 m. Collected water samples were filtered onboard using Whatman filters (GF/F, 25 mm). Filters with the retained material were stored in liquid nitrogen or in deep-freeze conditions until the measurements. Measurements were performed in the land based laboratory in the Institute of Oceanology Polish Academy of Sciences, Sopot, Poland, using a Perkin-Elmer Lambda 650 spectrophotometer equipped with an integrating sphere with a diameter of 15 cm. The spectra of light absorption coefficients were measured in the spectral range of 350-750 nm according to the methodology described by Tassan and Ferrari (1995, 2002) and Woźniak et al. (2011). Transmission and reflectance (T-R) measurements were performed for filters with suspended particles and again after bleaching with 2% sodium hypochlorite NaClO2 (Meler et al., 2020). To account for the optical path extension of light on the filter with suspension in relation to the same suspension in water, the beta factor correction was applied according to formulae developed by Stramski et al. (2015). This allowed to determine the spectra of the light absorption coefficient by all particles, ap(λ), as well as the absorption by bleached and mineral particles, (detritus - both organic and mineral), ad(λ). The light absorption coefficients by phytoplankton pigments aph(λ) were then calculated as the difference between ap(λ) and ad(λ).
Dodd, P. A., Wold, A., Ahmed, F., Darecki, M., Duncan, R., Fossan, K., Goraguer, L., Granskog, M., Itkin, P., Kern, Y., Koenig, Z., Kohlbach, D., Kovacs, K., Kowalczuk, P., Christensen, J., Leu, E., Lydersen, C., Muilwijk, M., Nowak, B., . . . Helgerud, T. L. S. Arctic Ocean 2024 cruise report: 19 July - 12 August 2024 (cruise ID: 2024007009). https://hdl.handle.net/11250/3145717, 2024
Meler, J., Woźniak, S.B., and Stoń-Egiert, J.: Comparison of methods for indirectly estimating the phytoplankton population size structure and their preliminary modifications adapted to the specific conditions of the Baltic Sea, J. Mar. Sys, 212, 103446, https://doi.org/10.1016/j.jmarsys.2020.103446, 2020.
Stramski, D., Reynolds R.I., Kaczmarek, S., Uitz, J., and Zheng, G.: Correction of pathlength amplification in the filter-pad technique for measurements of particulate absorption coefficient in the visible spectral region. Applied Optics 54(22):6763-6782, https://doi.org/10.1364/AO.54.006763, 2015.
Tassan, S., Ferrari, G.M., 1995. An alternative approach to absorption measurements of aquatic particles retained on filters. Limnol. Oceanogr. 40(8), 1358–1368.
Tassan, S., Ferrari, G.M., 2002. A sensitivity analysis of the ’transmittance-reflectance’ method for measuring light absorption by aquatic particles. J. Plankton Res. 24(8), 757–774. https://doi.org/10.1093/plankt/24.8.757
Woźniak, S.B., Meler, J., Lednicka, B., Zdun, A., and Stoń-Egiert, J.: Inherent optical properties of suspended particulate matter in the southern Baltic Sea. Oceanologia 53(3):691-729, https://doi.org/10.5697/oc.53-3.691, 2011.