It is generally anticipated that particulate organic carbon (POC) for most part is degraded by attached microorganisms during the descent of “marine snow” aggregates toward the deep sea. There is, however, increasing evidence that fresh aggregates can reach great depth and sustain relatively high biological activity in the deep sea. Using a novel high-pressure setup, we tested the hypothesis that increasing levels of hydrostatic pressure inhibit POC degradation in aggregates rapidly sinking to the ocean interior. Respiration activity, a proxy for POC degradation, was measured directly and continuously at up to 100 MPa (corresponding to 10 km water depth) in a rotating pressure tank that keeps the aggregates in a sinking mode. Model diatom-bacteria aggregates, cultures of the aggregate-forming diatom Skeletonema marinoi, and seawater microbial communities devoid of diatoms showed incomplete and complete inhibition of respiration activity when exposed to pressure levels of 10–50 and 60–100 MPa, respectively. This implies reduced POC degradation and hence enhanced POC export to hadal trenches through fast-sinking, pressure-exposed aggregates. Notably, continuous respiration measurements at ≥50 MPa revealed curved instead of linear oxygen time series whenever S. marinoi was present, which was not captured by discrete respiration measurements. These curvatures correspond to alternating phases of high and low respiration activity likely connected to pressure effects on unidentified metabolic processes in S. marinoi.

中文翻译：

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高静水压力下“海洋雪”的呼吸作用：来自旋转压力罐中连续氧气测量的见解

人们普遍预计，在“海洋雪”聚集体向深海下降期间，颗粒有机碳 (POC) 大部分会被附着的微生物降解。然而，越来越多的证据表明，新鲜的聚集体可以到达很深的地方，并在深海中维持相对较高的生物活动。我们使用一种新的高压设置，测试了以下假设：增加静水压力水平会抑制快速沉入海洋内部的聚集体中的 POC 降解。呼吸活动是 POC 降解的代表，在使聚集体保持下沉模式的旋转压力罐中，在高达 100 MPa（对应于 10 公里水深）的压力下直接连续测量。模型硅藻聚集体，形成聚集体的硅藻Skeletonema marinoi 的培养和没有硅藻的海水微生物群落分别在 10-50 和 60-100 MPa 的压力水平下显示出对呼吸活动的不完全和完全抑制。这意味着 POC 降解减少，因此通过快速下沉、暴露在压力下的骨料增强了 POC 向海沟的出口。值得注意的是，每当S. marinoi存在时，≥ 50 MPa 的连续呼吸测量显示曲线而不是线性氧时间序列，这不是由离散呼吸测量捕获的。这些曲率对应于高低呼吸活动的交替阶段，这可能与对海参中不明代谢过程的压力影响有关。