The vertical flux of marine snow particles significantly reduces atmospheric carbon dioxide concentration. In the mesopelagic zone, a large proportion of the organic carbon carried by sinking particles dissipates thereby escaping long term sequestration. Particle associated prokaryotes are largely responsible for such organic carbon loss. However, links between this important ecosystem flux and ecological processes such as community development of prokaryotes on different particle fractions (sinking vs. non-sinking) are yet virtually unknown. This prevents accurate predictions of mesopelagic organic carbon loss in response to changing ocean dynamics. Using combined measurements of prokaryotic heterotrophic production rates and species richness in the North Atlantic, we reveal that carbon loss rates and associated microbial richness are drastically different with particle fractions. Our results demonstrate a strong negative correlation between prokaryotic carbon losses and species richness. Such a trend may be related to prokaryotes detaching from fast-sinking particles constantly enriching non-sinking associated communities in the mesopelagic zone. Existing global scale data suggest this negative correlation is a widespread feature of mesopelagic microbes.

海洋雪粒的垂直通量显着降低了大气中的二氧化碳浓度。在中远洋带，下沉颗粒携带的大部分有机碳消散，从而逃脱了长期封存。颗粒相关的原核生物是造成这种有机碳损失的主要原因。然而，这种重要的生态系统通量与生态过程之间的联系，例如原核生物在不同颗粒部分（下沉与非下沉）上的群落发展，实际上仍是未知的。这阻止了准确预测中层有机碳损失以响应不断变化的海洋动力学。利用对北大西洋原核生物异养生产率和物种丰富度的综合测量，我们发现碳损失率和相关的微生物丰富度与颗粒分数截然不同。我们的结果表明原核生物碳损失与物种丰富度之间存在很强的负相关性。这种趋势可能与从快速下沉的粒子分离的原核生物不断丰富中远洋带中的非下沉相关群落有关。现有的全球规模数据表明，这种负相关是中层微生物的普遍特征。