DataSheet_1_Export of particulate organic carbon (POC) in the eddy region of the tropical northwest Pacific.docx

We examined particulate organic carbon (POC) export using 238U–234Th disequilibrium in the tropical northwest Pacific Ocean, where numerous eddies are present. We obtained data from an anticyclonic eddy in 2019 and from both anticyclonic and cyclonic eddies in 2020. In 2019, excess 234Th and higher POC concentrations were observed in the upper 100 m layer inside the anticyclonic eddy compared with the outer area of the eddy (the reference site). We speculate that the peculiar feature of excess 234Th in the surface layer was caused by horizontal transport of POC into the eddy and consequent POC degradation and release of particulate 234Th to a dissolved form. However, in 2020, lower POC concentrations with 234Th deficiency were observed in both cyclonic and anticyclonic eddies relative to the reference site. In both years, POC export was lower in the cores of the anticyclonic and cyclonic eddies relative to the reference site. We propose that severe nutrient depletion in the upper 150 m layer hindered nutrient supply by vertical water movement in the eddies. Despite the low POC export at 100 m depth, POC export at 500 m depth was comparable to values observed at 500 m depth at Station Papa in the more productive northeastern Pacific region. Our results imply that POC export into the deep ocean interior in this region may not be as low as expected from the low primary productivity in the euphotic zone.

本研究探讨了热带西北太平洋海洋中颗粒有机碳（POC）的输出，该区域存在众多涡旋。我们收集了2019年反气旋涡旋以及2020年反气旋和气旋涡旋的数据。2019年，与涡旋外围区域（参照点）相比，在反气旋涡旋内部100米水层内观察到234Th过剩及较高的POC浓度。我们推测，表层234Th过剩的奇特特征是由POC水平输运进入涡旋及其随后的POC降解和颗粒234Th向溶解形式的释放所导致。然而，2020年，与参照点相比，在气旋和反气旋涡旋中均观察到POC浓度降低且234Th含量不足。在两年中，与参照点相比，反气旋和气旋涡旋的核心区域POC输出均较低，这可能是由于上层150米层中营养物质的严重耗竭阻碍了涡旋中垂直水流的营养物质供应。尽管在100米深度处的POC输出较低，但在500米深度处的POC输出与在生产力更丰富的东北太平洋区域帕帕站500米深度处的观测值相当。我们的研究结果表明，该区域深层海洋内部的POC输出可能并不像从表观光层低初级生产力所预期的那样低。