The contribution of zooplankton to methane supersaturation in the oxygenated upper waters of the central Baltic Sea
The contribution of zooplankton to methane supersaturation in the oxygenated upper waters of the central Baltic Sea
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DOI：
10.1002/lno.10640
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发表时间：
2018-01
影响因子：
4.5
通讯作者：
O. Schmale;Janine Wäge;V. Mohrholz;N. Wasmund;U. Gräwe;G. Rehder;M. Labrenz;N. Loick‐Wilde
中科院分区：
文献类型：
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作者：
O. Schmale;Janine Wäge;V. Mohrholz;N. Wasmund;U. Gräwe;G. Rehder;M. Labrenz;N. Loick‐Wilde
我们报告了夏季在波罗的海中部哥特兰盆地上层水柱中观察到的甲烷富集。在盆地东部，温跃层以下的甲烷浓度在15 nM ~ 77 nM之间变化，而在盆地西部，没有检测到甲烷富集。甲烷的稳定碳同位素比值（δ13C‐CH4为- 67.6‰）表明甲烷来源于CO2还原，克隆序列与产甲烷古菌科（Methanomicrobiaceae）聚集在一起。以相关深度获得的长角田葵为主的菌群片段进行孵育实验，结果表明菌群浓度与产甲烷率呈正相关。我们的研究结果，结合先前的文献结果，表明东部盆地的甲烷富集可能是由鞭毛动物褐皮龙和桡足动物长角龙之间的饮食-消费关系维持的。然而，我们的质量平衡表明，维持甲烷富集需要110 pmol L−1 d−1的局部甲烷产量，而我们从孵化实验中估计的每只成虫0.3 pmol CH4 d−1（约1 pmol L−1 d−1）的产量太低，无法仅通过浮游动物相关的甲烷生产来维持甲烷富集。这些计算还表明，甲烷在温跃层以下被消耗，而不是被输送到海洋上层，这表明需要在95 pmol L−1 d−1范围内的混合层中的其他来源来维持观测到的甲烷海气通量。
We report on methane enrichments that were observed during summer in the upper water column of the Gotland Basin, central Baltic Sea. In the eastern part of the basin, methane concentrations just below the thermocline varied between 15 nM and 77 nM, in contrast to the western part where no methane enrichments could be detected. Stable carbon isotope ratios of methane (δ13C‐CH4 of −67.6‰) indicated its in situ biogenic origin from CO2 reduction, which was supported by clonal sequences that clustered with Methanomicrobiaceae, a family of methanogenic Archaea. Incubation experiments with a Temora longicornis dominated seston fraction obtained from the relevant depth showed a positive correlation between seston concentration and methane production rates. Our results, in combination with previous literature outcomes, suggest that the methane enrichment in the eastern basin might be sustained by a diet‐consumer relationship between the dinoflagellate Dinophysis norvegica and the copepod T. longicornis. However, our mass balance indicates that a local methane production of 110 pmol L−1 d−1 was needed to maintain the methane enrichment, and that the estimated production rate from our incubation experiments of 0.3 pmol CH4 d−1 per adult T. longicornis (about 1 pmol L−1 d−1) was too low to maintain the methane enrichment by zooplankton associated methane production only. These calculations also showed that methane was consumed below the thermocline and not transported into the upper‐ocean, suggesting that other sources in the mixed layer in the range of 95 pmol L−1 d−1 are needed to maintain the observed methane air–sea flux.