Bioturbation and particle transport in Carolina slope sediments: A radiochemical approach
Bioturbation and particle transport in Carolina slope sediments: A radiochemical approach
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DOI：
10.1357/002224099321618245
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发表时间：
1999-03-01
影响因子：
0.5
通讯作者：
Blair, NE
中科院分区：
文献类型：
--
作者：
Fornes, WL;DeMaster, DJ;Blair, NE
原位示踪剂实验研究了卡罗莱纳州两个大陆边缘地点（水深 = 850 m）的短期沉积物混合过程，其特征在于不同的有机碳通量、Th-234 混合系数 (D-b) 和底栖组合。分别用 Pb-210、Sn-113 和 Th-228 标记的浮游植物、斜坡沉积物和沙子大小的玻璃珠通过潜水器放置在两个现场地点（开普菲尔附近的地点 I 和哈特拉斯角附近的地点 m）的沉积物-水界面处。示踪剂放置后 0 天、1.5 天和 90 天对实验样地进行取样，以检查短期垂直运输。这两个站点最初都以非局部混合为主。两个位点向表面混合层底部的传输速度比基于 Th-234 的 D-b 值预测的要快； 1.5 天后，在地点 I 的沉积物-水界面下方 5 厘米和地点 III 的沉积物-水界面下方 12 厘米处观察到标记的颗粒。 90 天后，站点 m 的脉冲示踪曲线主要表现出扩散分布，很可能是由于大量随机、非局部混合事件造成的。通过 90 天的粒子标记实验确定的 D-b 值与从附近位置自然发生的 Th-234 剖面（类似于 100 天的时间尺度）获得的 D-b 值相当。脉冲示踪剂混合系数与稳态自然示踪剂混合系数之间的一致性表明，每月时间尺度上生物扰动的扩散模拟是一种现实且有用的方法。两个位点的示踪剂分布均表现出一定程度的颗粒选择性混合，但较不稳定的含碳颗粒的优先传输仅发生 30% 的时间。因此，海洋沉积物中年龄相关的混合程度的变化可能取决于动物群落和有机碳通量等因素。
In situ tracer experiments investigated short-term sediment mixing processes at two Carolina continental margin sites (water depth = 850 m) characterized by different organic C fluxes, Th-234 mixing coefficients (D-b) and benthic assemblages. Phytoplankton, slope sediment, and sand-sized glass beads tagged with Pb-210, Sn-113, and Th-228, respectively, were placed via submersible at the sediment-water interface at both field sites (Site I off Cape Fear, and Site m off Cape Hatteras). Experimental plots were sampled at 0, 1.5 days, and 90 days after tracer emplacement to examine short-term, vertical transport. Both sites are initially dominated by nonlocal mixing. Transport to the bottom of the surface mixed layer at both sites occurs more rapidly than Th-234-based D-b values predict; after 1.5 days, tagged particles were observed 5 cm below the sediment-water interface at Site I and 12 cm below at Site III. Impulse tracer profiles after 90 days at Site m exhibit primarily diffusive distributions, most likely due to a large number of random, nonlocal mixing events. The D-b values determined from 90-day particle tagging experiments are comparable to those obtained from naturally occurring Th-234 profiles (similar to 100-day time scales) from nearby locations. The agreement between impulse tracer mixing coefficients and steady-state natural tracer mixing coefficients suggests that the diffusive analogue for bioturbation on monthly time scales is a realistic and useful approach. Tracer profiles from both sites exhibit some degree of particle selective mixing, but the preferential transport of the more labile carbon containing particles only occurred 30% of the time. Consequently, variations in the extent to which age-dependent mixing occurs in marine sediments may depend on factors such as faunal assemblage and organic carbon flux.