Abstract The biological carbon pump is a critical component for uptake of carbon by the oceans. Most of this is mediated by gravitational sinking of particles and it is generally assumed that there is a positive relationship between sinking velocities and sizes of particles. Due to the difficulties inherent in measuring the sinking velocity of untouched and undamaged particles, the majority of studies have been based on artificial solid particles or laboratory generated marine snow formed from homogenous material, e.g. phytoplankton cultures. Here, we present results from a newly developed optical method that measures sizes and sinking velocities of undisturbed in situ aggregates in the mesopelagic zone. The measurements were done at depths between 90 and 530 m throughout day and night. In total we measured 55 image sequences of aggregate sizes and sinking velocities, resulting in measurements of 1060 individual aggregates. Only 10 sequences showed significant correlations between aggregate size and sinking velocity. Furthermore, only 8 of the 10 significant correlations between size and settling were positive. Despite similar optical appearance, similar sized aggregates had different sinking velocities, suggesting that aggregates formed in situ are heterogeneous with different compositions, structure and densities. This complicates estimates of sinking velocity from aggregate size only and one has to be careful when estimating downward particle flux based on in situ size-distribution and abundance of aggregates and theoretical relationships between size and sinking velocity. Hence, this study forces the conclusion that estimates of downward particle flux which use particle size distributions must also include information about aggregate composition, compactness and density from in situ optics or direct particle and aggregate sampling.

中文翻译：

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毕竟大小并不重要：没有证据表明海洋雪的大小下沉关系

摘要 生物碳泵是海洋吸收碳的关键部件。其中大部分是由粒子的重力下沉介导的，并且通常假设下沉速度与粒子大小之间存在正相关关系。由于测量未接触和未损坏颗粒的下沉速度所固有的困难，大多数研究都是基于人造固体颗粒或实验室生成的由同质材料形成的海洋雪，例如浮游植物培养物。在这里，我们展示了一种新开发的光学方法的结果，该方法可以测量中层海带中未受干扰的原位聚集体的大小和下沉速度。测量是在白天和黑夜 90 到 530 m 的深度进行的。我们总共测量了 55 个聚集体大小和下沉速度的图像序列，从而测量了 1060 个个体聚集体。只有 10 个序列显示了聚集体大小和下沉速度之间的显着相关性。此外，尺寸和沉降之间的 10 个显着相关性中只有 8 个是正相关的。尽管具有相似的光学外观，但相似尺寸的聚集体具有不同的下沉速度，这表明原位形成的聚集体具有不同的组成、结构和密度，是不均匀的。这使得仅根据骨料尺寸估计下沉速度变得复杂，并且在根据原位尺寸分布和骨料丰度以及尺寸和下沉速度之间的理论关系估计向下的粒子通量时必须小心。因此，