The aim of this study was to investigate the light transfer through sea ice with a focus on bio-optical substances both in fast ice and in the drift ice zones in the northern Baltic Sea. The measurements included snow and ice structure, spectral irradiance and photosynthetically active radiation below the sea ice. We also measured the concentrations of the three main bio-optical substances which are chlorophyll-a, suspended particulate matter, and coloured dissolved organic matter (CDOM). These bio-optical substances were determined for melted ice samples and for the underlying sea water. The present study provides the first spectral light transfer data set for drift ice in the Baltic Sea. We found high CDOM absorption values typical to the Baltic Sea waters also within sea ice. Our results showed that the transmittance through bare ice was lower for the coastal fast ice than for the drift ice sites. Bio-optical substances, in particular CDOM, modified the spectral distribution of light penetrating through the ice cover. Differences in crystal structure and the amount of gas inclusions in the ice caused variation in the light transfer. Snow cover on ice was found to be the dominant factor influencing the light field under ice, confirming previous studies. In conclusion, snow cover dominated the amount of light under the ice, but did not modify its spectral composition. CDOM in the ice absorbs strongly in the short wavelengths. As pure water absorbs most in the long wavelengths, the light transfer through ice was highest in the green (549–585 nm).

这项研究的目的是研究通过海冰的光传输，重点是波罗的海北部快速冰和流冰区中的生物光学物质。测量包括海冰下的冰雪结构，光谱辐照度和光合有效辐射。我们还测量了三种主要生物光学物质即叶绿素a的浓度，悬浮颗粒物和有色溶解有机物（CDOM）。确定了这些生物光学物质用于融化的冰样品和下层海水。本研究为波罗的海的流冰提供了第一个光谱光传输数据集。我们发现，在海冰中，波罗的海水域的典型CDOM吸收值也很高。我们的结果表明，沿海快冰的裸露冰透射率比流冰场低。生物光学物质，特别是CDOM，改变了穿过冰盖的光的光谱分布。冰中晶体结构和气体中夹杂物数量的差异导致了光传输的变化。冰上的积雪被发现是影响冰下光场的主要因素，证实了先前的研究。总之，积雪主导了冰下的光量，但没有改变其光谱组成。冰中的CDOM在短波长下会强烈吸收。由于纯水在长波长中吸收最多，因此在绿色中，通过冰的光传输最高（549-585 nm）。