The sea ice cover of the Arctic Ocean has changed dramatically in the last decades, and the resulting consequences for the sea-ice-associated ecosystem remain difficult to assess. Algal aggregates underneath sea ice are of great importance for the ice-associated ecosystem and the pelagic-benthic coupling. However, the frequency and distribution of their occurrence is not well quantified. During the IceArc expedition (ARK-27/3) of RV Polarstern in late summer 2012, we observed different types of algal aggregates floating underneath various ice types in the Central Arctic basins. We investigated the spatial distribution of ice algal aggregates and quantified their biomass, using under-ice image surveys obtained by an upward-looking camera on a remotely operated vehicle. On basin scale, filamentous aggregates of Melosira arctica are more frequently found in the inner part of the Central Arctic pack ice, while rounded aggregates mainly formed by pennate diatoms are found closer to the ice edge, under melting sea ice. On the scale of an ice floe, the distribution of algal aggregates in late summer is mainly regulated by the topography of the ice underside, with aggregates accumulating in dome-shaped structures and at the edges of pressure ridges. The average biomass of the aggregates from our sites and season was 0.1–6.0 mg C m−2. However, depending on the approach used, differences in orders of magnitude for biomass estimates may occur. This highlights the difficulties of upscaling observations and comparing results from surveys conducted using different methods or on different spatial scales.

中文翻译：

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北极中部夏季海冰下藻类聚集体的分布

在过去的几十年里，北冰洋的海冰覆盖面发生了巨大变化，对海冰相关生态系统的影响仍然难以评估。海冰下的藻类聚集体对于冰相关的生态系统和远洋-底栖生物的耦合具有重要意义。然而，它们发生的频率和分布没有得到很好的量化。在 2012 年夏末 RV Polarstern 的 IceArc 探险 (ARK-27/3) 期间，我们观察到不同类型的藻类聚集体漂浮在北极中部盆地的各种冰类型下。我们研究了冰藻聚集体的空间分布并量化了它们的生物量，使用遥控车辆上的向上摄像头获得的冰下图像调查。在流域尺度上，Melosira arctica 的丝状聚集体更常见于北极中部浮冰的内部，而主要由羽状硅藻形成的圆形聚集体则在靠近冰边缘的海冰融化下被发现。在浮冰尺度上，夏末藻类聚集体的分布主要受冰底地形的调节，聚集体聚集在圆顶状结构和压力脊边缘。我们地点和季节的聚集体的平均生物量为 0.1-6.0 mg C m-2。然而，根据所使用的方法，生物量估计值可能会出现数量级的差异。这凸显了提升观测和比较使用不同方法或在不同空间尺度上进行的调查结果的困难。