Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters, North East Atlantic

The study comprises a data set of CTD, optical properties—K 0(PAR), c p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K 0(PAR), beam attenuation c p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K 0(PAR) was governed by Chl a, shown by a high (r 2 = 0.64) Chl a–K 0(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient $$ K_{0}^{*} \left( {\text{PAR}} \right) $$ of 0.056 (m2 mg−1 Chl a) and a Chl a specific beam attenuation ( $$ c_{\text{p}}^{*} $$ ) of 0.27 (m2 mg−1 Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m−3. Spring bloom Chl a are about 10 mg Chl a m−3 and estimations showed that shelf K 0(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.