Mean spectral diffuse attenuation coefficients from 320 to 917 nm from high spectrally resolved radiometric underwater light transmission profiles obtained by an undulating platform towed behind the ship

• Main Authors: Bracher, Astrid, Dinter, Tilman, von Appen, Wilken-Jon
• Format: Dataset
• Language: English
• Published: PANGAEA 2022
• Subjects: AC3; ANT-XXXIII/4; Arctic Amplification; Atlantic Ocean transect; CTD-TRIAXUS; DATE/TIME; DEPTH; water; diffuse attenuation coefficient; downward at 320 nm; downward at 323 nm; downward at 326 nm; downward at 329 nm; downward at 332 nm; downward at 335 nm; downward at 338 nm; downward at 341 nm; downward at 344 nm; downward at 347 nm; downward at 350 nm; downward at 353 nm; downward at 356 nm; downward at 359 nm; downward at 362 nm; downward at 365 nm; downward at 368 nm; downward at 371 nm; downward at 374 nm; downward at 377 nm; Arctic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.939927; https://doi.org/10.1594/PANGAEA.939927

Radiometric data was collected on Polarstern expedition PS113, crossing the Atlantic from the Patagonian Shelf to the English Channel with an irradiance sensors (RAMSES ACC-2-VIS, TriOS GmbH, Germany) covering the wavelength region from 320 nm to 917 nm with a spectral sampling of 3.3. nm, resolution of 10 nm, and accuracy of 0.3 nm. The sensor was mounted on an undulating platform (Triaxus, extended version, MacArtney, Denmark) towed behind the research vessel at a speed of 8 knots for several transects along the cruise track and measured the underwater downwelling irradiance Ed(z, λ). Vertical movement of the Triaxus was 1 m/s. The depth was determined with a Seabird CTD mounted to the Triaxus and the inclination in all directions was recorded by the Triaxus hardware (details in von Appen et al. 2020). Measurements were taken with automatically adjusted integration times between 4 ms and 8 s. Data of a light profile was only processed if the euphotic depth was reached and values of the downwelling irradiance at 15 m depth and a wavelength of 400 nm were greater than 150 mW m−2 nm−1. Radiometric data from 6 transects (on 19, 21, 22, 24, 25, and 27 May 2018) between 2 and 48 hours duration were identified useful for determining Kd(λ). Generally, profile measurements were only valid if the instrument's inclination in either dimension was < 14°. Another RAMSES ACC-2-VIS sensor mounted on top of the ship recorded the incident downwelling irradiance above the surface Ed(λ, 0 + ), to correct for incident sunlight variations. Mean Kd was calculated from Ed(z, λ) profiles mostly over the depth interval 7 to 30 m, some 7 to 60 m. Details on measurement procedure and determination of Kd can be found in Bracher et al. (2020a, 2020b).