We examined biogenic silica production and elementary composition (biogenic Si, particulate organic carbon and particulate organic nitrogen) of Rhizaria and diatoms in the upper 200 m along a transect in the Southwest Pacific sector of the Southern Ocean during austral summer (January–February 2019). From incubations using the ³²Si radioisotope, silicic acid uptake rates were measured at 15 stations distributed in the Polar Front Zone, the Southern Antarctic Circumpolar Current and the Ross Sea Gyre. Rhizaria cells are heavily silicified (up to 7.6 nmol Si cell⁻¹), displaying higher biogenic Si content than similar size specimens found in other areas of the global ocean, suggesting a higher degree of silicification of these organisms in the silicic acid rich Southern Ocean. Despite their high biogenic Si and carbon content, the Si/C molar ratio (average of 0.05 ± 0.03) is quite low compared to that of diatoms and relatively constant regardless of the environmental conditions. The direct measurements of Rhizaria's biogenic Si production (0.8–36.8 μmol Si m⁻² d⁻¹) are of the same order of magnitude than previous indirect estimations, confirming the importance of the Southern Ocean for the global Rhizaria silica production. However, diatoms largely dominated the biogenic Si standing stock and production of the euphotic layer, with low rhizarians' abundances and biogenic Si production (no more than 1%). In this manuscript, we discuss the Antarctic paradox of Rhizaria, that is, the potential high accumulation rates of biogenic Si due to Rhizaria in siliceous sediments despite their low production rates in surface waters.

中文翻译：

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小根瘤菌和硅藻在南大洋远洋二氧化硅生产中的作用

我们在南方夏季（2019 年 1 月至 2 月）沿南大洋西南太平洋部分的一个横断面研究了根茎和硅藻的生物二氧化硅产量和元素组成（生物硅、颗粒有机碳和颗粒有机氮） . 通过使用³² Si 放射性同位素的孵化，在分布在极地锋区、南南极环极流和罗斯海环流的 15 个站点测量了硅酸吸收率。Rhizaria 细胞高度硅化（高达 7.6 nmol Si 细胞^-1)，显示出比在全球海洋其他区域发现的类似大小的标本更高的生物硅含量，表明这些生物在富含硅酸的南大洋中具有更高的硅化程度。尽管它们的生物硅和碳含量很高，但与硅藻相比，Si/C 摩尔比（平均 0.05 ± 0.03）非常低，并且无论环境条件如何都相对恒定。有孔虫界的生物硅生产的直接测量（0.8-36.8  μ摩尔的Si米^-2  d ^-1) 与之前的间接估计具有相同的数量级，证实了南大洋对全球根茎二氧化硅生产的重要性。然而，硅藻在很大程度上主导了富光层的生物硅存量和生产，而根瘤菌的丰度和生物硅产量较低（不超过 1%）。在这份手稿中，我们讨论了根茎的南极悖论，即尽管根茎在地表水中的生产率低，但由于根茎在硅质沉积物中的潜在高生物硅积累率。