Ballast, sinking velocity, and apparent diffusivity within marine snow and zooplankton fecal pellets: Implications for substrate turnover by attached bacteria
Ballast, sinking velocity, and apparent diffusivity within marine snow and zooplankton fecal pellets: Implications for substrate turnover by attached bacteria
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DOI：
10.4319/lo.2008.53.5.1878
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发表时间：
2008-09
影响因子：
4.5
通讯作者：
H. Ploug;M. Iversen;G. Fischer
中科院分区：
文献类型：
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作者：
H. Ploug;M. Iversen;G. Fischer
我们分析了特定尺寸的干质量，下沉速度和表观扩散率在现场采样的海洋雪，实验室制造的聚集体形成的硅藻或颗石藻，和小型和大型浮游动物粪便颗粒与自然变化的内容压载材料。使用微传感器直接测量聚集体和大（毫米长）粪便颗粒内的表观扩散率。在毛里塔尼亚布兰克角沿海涌升流中收集的大型粪便颗粒显示出最高的体积比干质量和下沉速度，因为蛋白石、碳酸盐和成岩物质（主要是撒哈拉粉尘）含量高，它们共同构成了干质量的约80%。这些大粪便颗粒中的平均固体物质密度为1.7 g cm-3，而其过量密度为0.25 ± 0.07 g cm-3。所有聚集体和粪便颗粒来源的体积比干质量范围为3.8至960 µg mm-3，平均下沉速度范围为51至732 m d-1。粪便颗粒和浮游植物来源的聚集体的孔隙率分别>0.43和>0.96。大粪粒和聚集体内的气体的表观扩散系数的平均值分别是在海水中的自由扩散系数的0.74和0.95倍。压载物增加下沉速度，因此，也潜在的O2通量沉降聚集体和粪便颗粒。因此，压载矿物限制聚集体在水柱中的停留时间，通过增加下沉速度，但表观扩散率和潜在的氧气供应聚集体内是高的，从而大部分不稳定的有机碳可以在沉积过程中呼吸。
We analyzed size‐specific dry mass, sinking velocity, and apparent diffusivity in field‐sampled marine snow, laboratory‐made aggregates formed by diatoms or coccolithophorids, and small and large zooplankton fecal pellets with naturally varying content of ballast materials. Apparent diffusivity was measured directly inside aggregates and large (millimeter‐long) fecal pellets using microsensors. Large fecal pellets, collected in the coastal upwelling off Cape Blanc, Mauritania, showed the highest volume‐specific dry mass and sinking velocities because of a high content of opal, carbonate, and lithogenic material (mostly Saharan dust), which together comprised ~80% of the dry mass. The average solid matter density within these large fecal pellets was 1.7 g cm‐3, whereas their excess density was 0.25 ± 0.07 g cm‐3. Volume‐specific dry mass of all sources of aggregates and fecal pellets ranged from 3.8 to 960 µg mm‐3, and average sinking velocities varied between 51 and 732 m d‐1. Porosity was >0.43 and >0.96 within fecal pellets and phytoplankton‐derived aggregates, respectively. Averaged values of apparent diffusivity of gases within large fecal pellets and aggregates were 0.74 and 0.95 times that of the free diffusion coefficient in sea water, respectively. Ballast increases sinking velocity and, thus, also potential O2 fluxes to sedimenting aggregates and fecal pellets. Hence, ballast minerals limit the residence time of aggregates in the water column by increasing sinking velocity, but apparent diffusivity and potential oxygen supply within aggregates are high, whereby a large fraction of labile organic carbon can be respired during sedimentation.