from 厦门大学碳循环研究组 http://mel.xmu.edu.cn/group/ocg/supervisefile.asp?id=149

颗粒有机碳(POC)从真光层向深海的输送是海洋生物泵的主要驱动力之一，而生物泵的强度和效率在某种程度上调控着大气CO₂的浓度。因此，理解调控海洋生物泵强度和效率的主要机制对评估全球气候变化影响下海洋碳埋藏的作用显得十分重要。传统观点认为初级生产力POC输出通量的主控因素。随后的观点认为，浮游生物群落是调控POC输出的主控因素，其中大型浮游生物尤其是硅藻对POC输出通量的贡献比例远大于其对初级生产力的贡献。而最近的观点认为微微型浮游生物的聚集作用是颗粒物沉降的直接和间接控制机制。因此，对调控POC通量的机制目前尚未有统一认识。

在CHOICE-C航次的支持下，我实验室蔡平河老师在初级生产力、POC输出及浮游生物群落结构迥异的南海北部开展了POC输出通量及其主控机制的研究。研究结果显示，南海北部POC的输出通量存在显著的时空差异，其主控机制也存在显著的空间差异。对南海北部近岸区域，POC的输出通量主要受大型浮游植物尤其是硅藻的控制。南海北部陆架区，POC输出通量则主要受控于POC的储量。对南海北部海盆区，POC输出通量的调控机制较为复杂，小型浮游植物主导浮游植物群落结构，并可能影响POC输出通量。

该研究展示了南海北部POC输出通量调控机制的空间差异，表明了POC输出通量调控机制的复杂性。该成果已于2015年3月27日发表于国际顶级期刊《Journal of Geophysical Research: Oceans》。

Cai, P.H., D.C. Zhao, L. Wang, B.Q. Huang, and M.H. Dai, 2015. Role of particle stock and phytoplankton community structure in regulating particulate organic carbon export in a large marginal sea. Journal of Geophysical Research: Oceans, 120, 2063-2095, doi:10.1002/2014JC010432.

In this study, we utilize ²³⁴Th/²³⁸U disequilibrium to determine particulate organic carbon (POC) export from the euphotic zone in the South China Sea. Depth profiles of ²³⁴Th, total chlorophyll, pigments, and POC were collected during four cruises from August 2009 to May 2011, covering an entire seasonal cycle of spring, summer, autumn, and winter. The extensive data set that was acquired allows for an evaluation of the seasonal variability of upper ocean POC export and its controls in a large marginal sea. The results show that ²³⁴Th fluxes from the euphotic zone fall in the range of 528-1550, 340-2694, and 302-2647 dpm m^-2d^-1 for the coastal, shelf, and basin regimes, respectively. In these regimes, POC/²³⁴Th ratios at the base of the euphotic zone fall in the range of 5.7–58.2, 4.6–44.0, and 2.5–15.5 mmol dpm^-1, respectively. Accordingly, for the coastal, shelf, and basin regimes, the mean POC export fluxes from the euphotic zone are 24.3, 18.3, and 6.3 mmolC m^-2 d^-1, respectively. Seasonal variations in POC export flux are remarkable in the study area, and POC export peaks were generally observed in autumn. We use a simple linear regression (LLS) method to examine the correlation of POC export versus POC stock and versus plankton community structure. We found a strong correlation (R²=0.73, p<0 .005) between poc export flux and the fraction of diatom in the coastal area, indicating that poc export flux in this province is driven by large phytoplankton, in particular, diatoms. in the shelf area, a relatively strong correlation (r²=0.54, p<0 .0001) was noted for poc export flux and poc stock in the euphotic zone. this indicates that poc export flux in the south china sea shelf is primarily controlled by poc stock. in contrast, in the south china sea basin, we identified a weak but intriguing correlation (r²=0.26, p<0 .0001) between poc export flux and the fraction of haptophytes and prasinophytes that are typically <5 lm in size. this suggests that mechanisms controlling poc export flux in the south china sea basin are complicated. however, small phytoplankton may play a significant role in controlling poc export flux since they dominate the phytoplankton community structure in this region.

Full text Link: http://onlinelibrary.wiley.com/doi/10.1002/2014JC010432/abstract#footer-article-info