Colored Dissolved Oragnic Matter - CDOM absorption spectra (250-700 nm) collected in the Woodfjorden (Spitsbergen) in August 2024

This data sets contains spectra of the light absorption coefficients by Colored Dissolved Organic Matter – CDOM, aCDOM(), m-1. Samples were collected on during the AREX-2024 cruise on r/v Oceania, in the leg dedicated to a Horizon Europe SeaQuester project in the Woodfjorden, Northern Spitsbergen, between 20-26 August 2024. Water samples were discrete depths, in most cases, at the surface, at the Deep Chlorophyll-a Maximum (DCM) and below it. The depth at which the DCM was located was determined from chlorophyll-a fluorescence profile measured by the standard fluorometer attached to the CTD rosette. Collected water samples were gravity filtered directly from Niskin bottles, through the 02. m flow-through filter (Opticap XL4 Durapore) into μm into acid washed amber glass 200‐ml amber glass sample bottles. The filter cartridge was kept in 10% HCL solution between sampling stations and was rinsed with ultrapure MilliQ and sample water before collecting CDOM samples. All CDOM samples were stored at +4 °C in dark onboard research vessels until land‐based laboratory spectroscopic analysis. Measurements were performed in the land based laboratory in the Institute of Oceanology Polish Academy of Sciences, Sopot, Poland, using a double beam Perkin-Elmer Lambda 650 spectrophotometer with a 10‐cm quartz cells in the spectral range of 250-700 nm. Fresh ultrapure water was used as the reference for all measurements. The absorption coefficient aCDOM(λ) was calculated using the following equation:
aCDOM() = 2.303*(A(l)/L), (1),
where: A(λ) is the absorbance, L is the optical path length in meters, and the factor 2.303 is the natural logarithm of 10.
A nonlinear least squares fitting method using a Trust‐Region algorithm implemented in Matlab R2020 was applied (Kowalczuk et al., 2006; Stedmon et al., 2000) to calculate CDOM absorption spectrum slope coefficient, S, in the spectral range 350–600 nm using the following equation:
aCDOM() = aCDOM(λ0) * e−S(λ0−λ) + K; (2)
where: λ0 is 350 nm and K is a background constant that allows for any baseline shift caused by residual scattering by fine size particle fractions, micro‐air bubbles or colloidal material present in the sample, refractive index differences between sample and the reference, or attenuation not due to CDOM. Three parameters aCDOM(350), S, and K were estimated simultaneously via nonlinear regression using equation (2).
Kowalczuk, P., Stedmon, C. A., & Markager, S. (2006). Modelling absorption by CDOM in the Baltic Sea from season, salinity and chlorophyll. Marine Chemistry, 101, 1–11.
Stedmon, C. A., Markager, S., & Kaas, H. (2000). Optical properties and signatures of chromophoric dissolved organic matter (CDOM) in Danish coastal waters. Estuarine, Coastal and Shelf Science, 51, 267–278.