Louis Justine, Pedrotti Maria Luiza, Gazeau Frédéric, Guieu Cécile
Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, UPMC University Paris 06, INSU-CNRS, Villefranche-sur-mer, France.
PLoS One. 2017 Feb 17;12(2):e0171980. doi: 10.1371/journal.pone.0171980. eCollection 2017.
The evolution of organic carbon export to the deep ocean, under anthropogenic forcing such as ocean warming and acidification, needs to be investigated in order to evaluate potential positive or negative feedbacks on atmospheric CO2 concentrations, and therefore on climate. As such, modifications of aggregation processes driven by transparent exopolymer particles (TEP) formation have the potential to affect carbon export. The objectives of this study were to experimentally assess the dynamics of organic matter, after the simulation of a Saharan dust deposition event, through the measurement over one week of TEP abundance and size, and to evaluate the effects of ocean acidification on TEP formation and carbon export following a dust deposition event. Three experiments were performed in the laboratory using 300 L tanks filled with filtered seawater collected in the Mediterranean Sea, during two 'no bloom' periods (spring at the start of the stratification period and autumn at the end of this stratification period) and during the winter bloom period. For each experiment, one of the two tanks was acidified to reach pH conditions slightly below values projected for 2100 (~ 7.6-7.8). In both tanks, a dust deposition event of 10 g m-2 was simulated at the surface. Our results suggest that Saharan dust deposition triggered the abiotic formation of TEP, leading to the formation of organic-mineral aggregates. The amount of particulate organic carbon (POC) exported was proportional to the flux of lithogenic particles to the sediment traps. Depending on the season, the POC flux following artificial dust deposition ranged between 38 and 90 mg m-2 over six experimental days. Such variability is likely linked to the seasonal differences in the quality and quantity of TEP-precursors initially present in seawater. Finally, these export fluxes were not significantly different at the completion of the three experiments between the two pH conditions.
为了评估对大气二氧化碳浓度进而对气候可能产生的正负反馈，需要研究在海洋变暖和酸化等人为强迫作用下，有机碳向深海输出的演变情况。因此，由透明胞外聚合物颗粒（TEP）形成所驱动的聚集过程的改变，有可能影响碳输出。本研究的目的是，在模拟撒哈拉沙尘沉降事件后，通过对TEP丰度和大小进行为期一周的测量，实验性地评估有机物的动态变化，并评估沙尘沉降事件后海洋酸化对TEP形成和碳输出的影响。在实验室中，使用300升水箱进行了三项实验，水箱中装有在地中海采集的经过过滤的海水，实验分别在两个“无藻华”时期（分层期开始时的春季和分层期末尾的秋季）以及冬季藻华期进行。对于每项实验，两个水箱中的一个被酸化，使其pH值略低于预计的2100年的值（约7.6 - 7.8）。在两个水箱中，均在水面模拟了10 g m-2的沙尘沉降事件。我们的结果表明，撒哈拉沙尘沉降引发了TEP的非生物形成，导致有机-矿物聚集体的形成。输出的颗粒有机碳（POC）量与成岩颗粒向沉积物捕集器的通量成正比。根据季节不同，人工沙尘沉降后的POC通量在六个实验日期间介于38至90 mg m-2之间。这种变异性可能与海水中最初存在的TEP前体的质量和数量的季节性差异有关。最后，在三项实验结束时，两种pH条件下的这些输出通量没有显著差异。
