Delayed settling of marine snow: Effects of density gradient and particle properties and implications for carbon cycling
Delayed settling of marine snow: Effects of density gradient and particle properties and implications for carbon cycling
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海洋雪的延迟沉降：密度梯度和颗粒特性的影响以及对碳循环的影响
DOI：
10.1016/j.marchem.2015.04.006
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发表时间：
2015
期刊：
影响因子：
3
通讯作者：
C. Arnosti
中科院分区：
文献类型：
--
作者：
J. Prairie;Kai Ziervogel;R. Camassa;R. McLaughlin;B. White;Carolin Dewald;C. Arnosti
海洋积雪通常是碳通量的主要组成部分，也是细菌活动频繁的场所；因此，海洋雪沉降行为的小规模变化可能会影响表层海洋碳输出和再矿化的垂直位置。在这项研究中，我们通过实验研究了滚轮槽中形成的海洋雪聚集体通过急剧的密度梯度沉降时的下沉速度。我们在 3 个不同的实验中观察到 8 到 10 个聚集体，每个聚集体在穿过密度转变时都表现出延迟沉降行为，即沉降速度最小值。延迟沉降行为的特征也与密度分层和聚集体密度和尺寸进行了比较；当密度梯度较陡且骨料密度较小时，骨料沉降速度降低得更多，且持续时间更长。观察到的无量纲参数和骨料沉降之间的关系可以将我们的结果直接应用于现场，从而深入了解可能发生强烈延迟沉降行为的条件。与聚集体所源自的周围水相比，聚集体中的细胞外酶活性（有机物微生物再矿化的第一步）要高出一个数量级以上。将测得的酶活性与延迟沉降行为的观察相结合表明，酶活性的程度以及垂直位置受到聚集体沉降行为的强烈影响：随着分层的增加，密度转变区域内的总酶活性增加了 18 倍。这项研究结合了小规模聚集体沉降和微生物酶活性的直接测量，为确定延迟沉降行为对海洋局部和大规模碳循环的潜在影响提供了机会。
Marine snow aggregates are often a dominant component of carbon flux and are sites of high bacterial activity; thus, small-scale changes in the settling behavior of marine snow can affect the vertical locations of carbon export and remineralization in the surface ocean. In this study, we experimentally investigated the sinking velocities of marine snow aggregates formed in roller tanks as they settled through sharp density gradients. We observed between 8 and 10 aggregates in 3 different experiments, each of which displayed delayed settling behavior — that is, a settling velocity minimum — as they crossed the density transitions. Characteristics of delayed settling behavior were also compared to density stratification and aggregate density and size; aggregate settling velocity decreased more, and for longer periods of time, when density gradients were sharper and when aggregates were less dense. The observed relationships between non-dimensional parameters and aggregate settling allow for direct application of our results to the field, providing insight into the conditions under which strong delayed settling behavior is likely to occur. Activities of extracellular enzymes (the initial step in microbial remineralization of organic matter) were more than an order of magnitude higher in the aggregates compared to the surrounding water from which the aggregates were derived. Coupling measured enzyme activities with observations of delayed settling behavior demonstrates that the extent as well as the vertical location of enzyme activity is strongly affected by aggregate settling behavior: total enzyme activity within the region of the density transition increased by a factor of 18 with increasing stratification. This study, which combines direct measurements of small-scale aggregate settling and microbial enzyme activity, offers an opportunity to determine the potential implications of delayed settling behavior for local and larger-scale carbon cycling in the ocean.
影响因子：
4.5
作者：
H. Ploug;M. Iversen;G. Fischer
通讯作者：
H. Ploug;M. Iversen;G. Fischer