Upwelling and downwelling spectral (320–920 nm) distributions and photosynthetic active radiation (PAR) intensities were measured below a first-year land-fast sea ice in a western Greenland fjord with and without a snow cover. Time-series of surface upwelling PAR, downwelling PAR, and under-ice PAR were also obtained. Spectral distributions of upwelling and downwelling irradiances were similar except for reduced intensities in the UV, the red, and NIR parts of the spectrum when the ice was snow-covered. Upwelling PAR amounted to about 10% of downwelling intensities, giving 5.1 µmol photons m^-2 s^-1 at the bottom of the ice with a snow cover and 8.2 µmol photons m^-2 s^-1 without. PAR partitioning analyses showed that the upwelling was related to scattering by suspended particles in the water column. A snow melt increased under-ice daily maximum downwelling PAR from 50 to 180 µmol photons m^-2 s^-1 and overall under-ice PAR of 55 and 198 µmol photons m^-2 s^-1 with 10% upwelling. It is concluded that upwelling PAR below sea ice might be an important factor regarding sea ice algae photophysiology and performance with a 10% higher PAR; specifically when PAR > E_k the light saturation point of the sea ice algae.

中文翻译：

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海冰下的上升流辐照度——PAR 强度和光谱分布

在有和没有积雪的格陵兰西部峡湾的第一年陆地快速海冰下测量了上升和下降光谱（320-920 nm）分布和光合有效辐射（PAR）强度。还获得了地表上升流 PAR、下降流 PAR 和冰下 PAR 的时间序列。上升流和下降流辐照度的光谱分布相似，除了当冰被雪覆盖时光谱的紫外线、红色和 NIR 部分的强度降低。上升流 PAR 约为下降流强度的 10%，在有积雪的冰底提供 5.1 µmol 光子 m ^-2 s ^-1和 8.2 µmol 光子 m ^-2 s ^-1没有。PAR 分配分析表明，上升流与水体中悬浮颗粒的散射有关。雪融化使冰下每日最大下流 PAR 从 50 增加到 180 µmol 光子 m ^-2 s ^-1和 55 和 198 µmol 光子 m ^-2 s ^{-1 的}整体冰下 PAR，上升流为 10%。得出的结论是，海冰以下上升流 PAR 可能是海冰藻光生理学和性能的重要因素，PAR 高 10%；特别是当 PAR > E _k时海冰藻的光饱和点。