234Th scavenging and its relationship to acid polysaccharide abundance in the Gulf of Mexico
234Th scavenging and its relationship to acid polysaccharide abundance in the Gulf of Mexico
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DOI：
10.1016/s0304-4203(02)00012-9
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发表时间：
2002-05
期刊：
影响因子：
3
通讯作者：
Laodong Guo;C. Hung;P. Santschi;I. Walsh
中科院分区：
文献类型：
--
作者：
Laodong Guo;C. Hung;P. Santschi;I. Walsh
在墨西哥湾沿着样带采集了不同粒径的颗粒物234 Th和酸性多糖（APS），以研究APS含量在控制海洋234 Th清除程度和速率中的作用，并首次探讨Th清除与颗粒物生化组成之间的关系。溶解和particulate 234 Th浓度的海洋学一致的垂直剖面观察到，与一个可接受的234 Th赤字相对于238 U在上层水柱和底栖云状层，但达到长期平衡between 234 Th和238 U在中间沃茨。在总颗粒234 Th库（>0.5 μm）中，10-53 μm的颗粒占234 Th的比例最大（37-57%），其次是>53 μm的颗粒（13-36%），1-10 μm的颗粒（10-21%），0.5-1 μm的颗粒（8-17%）。用多箱模型计算的234 Th在粒度分级颗粒中的停留时间，如预期的那样，一致地短于总颗粒234 Th的停留时间，在较小的颗粒级（0.5-10 μm）和>53 μm的大颗粒中观察到最短的停留时间（在沿海站<0.5天，在深水站<1-5天）。这些结果表明，亚微米和微米级颗粒是Th清除的最重要的媒介，较小颗粒（<10 μm）上的234 Th可以非常迅速地凝聚成10-53 μm的颗粒，时间尺度<1天。234 Th/POC与OC归一化的总APS含量之间呈正相关，表明海水中的表面活性物质外聚纤维状APS是最有效的Th（IV）清除有机化合物。最重要的是，粒径在1-10 μ m和>53 μm的颗粒的停留时间与糖醛酸（URA，总APS的一部分）浓度显著负相关，表明APS含量不仅控制234 Th吸附的速率和量，而且控制颗粒的凝聚速率。因此，海洋颗粒物的生化组成需要考虑在改进的Th（IV）清除模型。
Size-fractionated particulate234Th and acid polysaccharides (APS) were collected from stations along a transect in the Gulf of Mexico, in order to examine the role of APS content in controlling the extent and rates of234Th scavenging in the ocean and to explore, for the first time, the relationship between Th scavenging and biochemical composition of particulate matter. Oceanographically consistent vertical profiles of dissolved and particulate234Th concentrations were observed, with a considerable234Th deficit relative to238U in the upper water column and in benthic nepheloid layers, but reaching secular equilibria between234Th and238U in intermediate waters. Within the total particulate234Th pool (>0.5 μm), the 10–53 μm fraction had the largest share of234Th (37–57%), followed by the >53 μm (13–36%), the 1–10 μm (10–21%), and the 0.5–1 μm (8–17%) fractions, resulting in a decrease of POC/234Th ratios with increasing particle size. Residence times of234Th in size-fractionated particles, calculated with a serial multi-box model, were, as expected, consistently shorter than those for total particulate234Th, with the shortest residence times (<0.5 day at coastal stations and <1–5 days at deep stations) observed in the smaller particulate fractions (0.5–10 μm), and the large particles >53 μm. These results suggest that submicron and micron-sized particles are the most important intermediary in the Th scavenging and that234Th on smaller particles (<10 μm) can coagulate into the 10–53 μm particles very rapidly, within a time scale of <1 day. A positive correlation between234Th/POC and OC-normalized total APS content was observed, suggesting that exopolymeric fibrillar APS, the surface active substances in seawater, are the most effective organic compounds for Th(IV) scavenging. Most importantly, residence times of particles in the size ranges of 1–10 and the >53 μm were also significantly and inversely correlated with uronic acid (URA, a fraction of total APS) concentrations, indicating that the APS content controls not only rates and amounts of234Th sorption, but also rates of coagulation of particles. Thus, the biochemical composition of marine particles needs to be considered in improved Th(IV) scavenging models.