南中国海陆架区颗粒有机碳的跨陆架输运

Cross-shelf transport of biogenic particualte organic carbon (POC) is a major mechanism that controls the efficiency of the biological pump on the continental shelf. Globally,this process determines the capacity of atmospheric CO2 sequestration by the continental shelf. Cross-shelf transport of POC had been the core of early research programs (such as SEEP and KEEP). Unfortunately, due to the technical and methodological problems, the results of these programs suffered from large biases which led to the inconsistency between the historical observations and recent modeling results . 234Th/238U disequilibrium has been proposed as an ideal proxy for cross-shelf transport of POC. With the advent of the novel methods for determining 234Th in seawater and sediment samples, we feel that now it is time to re-asses the role of the cross-shelf transport of POC in the overall carbon budget on the continental shelf. In this research plan, we propose to quantify the magnitude and the seasonal variability of the cross-shelf flux of POC in the northern South China Sea by using 234Th/238U disequilibrium. We plan to use isotopic composition of carbon (13C) to determine the individual contributions of biogenic POC and terrestrial POC to the overall cross-shelf flux of POC. Finally, we are to evaluate how cross-shelf transport of biogenic POC regulates the efficiency of the biological pump on the continental shelf.

生源颗粒有机碳（POC）的跨陆架输运通量在很大程度上表征了陆架海区生物泵的运作效率，反映了陆架海区对大气CO2的净固碳能力；POC跨陆架输运过程的研究曾一度是海洋学领域的热点，但囿于方法与技术的能力，早期观测计划所得的结果存在着巨大的偏差，导致产生了历史观测结果与近期模型研究之间的矛盾；234Th/238U不平衡法是研究POC跨陆架输运过程的理想方法，近年来，随着234Th分析新技术的问世及发展，早期的方法壁垒已被破除。我们拟择取南中国海北部陆架区为研究对象，采用234Th/238U不平衡法研究跨陆架POC输运通量的空间分布及其季节变化特征，评判生源POC和陆源POC各自对跨陆架POC输运通量的贡献，进而探索跨陆架生源POC输运过程对陆架区生物泵的调控作用。

本研究采用234Th/238U不平衡法研究颗粒有机碳(POC)跨陆架输运，揭示跨陆架输运方式的存在及其输运通量之量值，为更合理的诠释陆架区的碳循环过程提供新的参考及数据支持。2012年夏季对南海北部陆架区的研究发现，跨陆架输运的过程主要发生在地形变化剧烈的陆架-陆坡转换区域，底部沉积物上覆水体~50 m的深度是POC跨陆架输运的主要通道，底部沉积物的沉降-扰动-再悬浮-再沉降是POC跨陆架输运的主要机制。以200米等深线为界，夏季南中国海北部陆架区POC的跨陆架输运通量（Tpoc）为5.53±2.13×108 mol d-1，占水体总输出通量（3.44×109 mol d-1）的~16%，为陆架区初级生产产生的POC的~10%。该比例尽管不大，却远远高于海盆区真光层输出的比例，表明陆架海区更高的生物泵效率，POC的跨陆架输运是可能是南海碳埋藏的重要过程。对西太平洋的研究表明，POC通量与POC储量之间具有良好的正相关关系，POC储量是控制POC输出通量的主要机制，该机制可能是普遍存在的过程。因此，该结果可以为遥感方法估算POC输出通量提供研究基础。

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