This study examined particulate organic carbon (POC) and its isotopic composition (δ13CPOC) in the Cosmonaut and Cooperation Seas in the Antarctica during the summer of 2019. Our results show that the spatial variation of POC concentration in summer surface water generally mirrors that of δ13CPOC, with higher POC and δ13CPOC values in the Cosmonaut Sea compared to the Cooperation Sea. The δ13CPOC values in both seas were positively correlated with the proportion of Chl-a in smaller particles (< 20 μm). However, the relationship with the proportion of biogenic POC in smaller particles (< 20 μm) differed between the two seas. This discrepancy is attributed to differences in the dominant phytoplankton species. In the Cosmonaut Sea, smaller phytoplankton (nano- and pico-phytoplankton) were dominated by Phaeocystis antarctica, whereas in the Cooperation Sea, they were dominated by pennate diatoms. The δ13CPOC in deep waters of both seas increased with depth, reflecting the effects of organic remineralization. The carbon isotope fractionation factors during remineralization, estimated using Rayleigh model, were 1.5 ± 0.2‰ and 1.6 ± 0.2‰ in the Cosmonaut Sea and the Cooperation Sea, respectively. These small isotope effects indicate that the isotope signals of organic matter exported from the upper layer are well preserved in the deep ocean. Additionally, anomalously high δ13CPOC values were observed in the bottom water outside the Cape Darnley polynya in the Cooperation Sea, reflecting the input of ice algae-derived organic matter from the shelf during AABW formation. A simple isotopic mass balance estimate suggests that 6–19% of the POC in the AABW of the Cooperation Sea is contributed by ice algae. Our study highlights the complexity of factors affecting δ13CPOC in the Southern Ocean, emphasizing the importance of phytoplankton community composition.

中文翻译：

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夏季宇航员海和合作海颗粒有机物的稳定碳同位素组成


这项研究检查了 2019 年夏季南极洲宇航员海和合作海中的颗粒有机碳 （POC） 及其同位素组成 （δ13CPOC）。结果表明，夏季表层水中 POC 浓度的空间变化通常与 δ13CPOC 相同，与合作海相比，宇航员海的 POC 和 δ13CPOC 值更高。两个海域的 δ13CPOC 值与较小颗粒 （< 20 μm） 中 Chl-a 的比例呈正相关。然而，与较小颗粒 （< 20 μm） 中生物成因 POC 比例的关系在两个海域之间有所不同。这种差异归因于主要浮游植物物种的差异。在宇航员海，较小的浮游植物（纳米和微微浮游植物）以南极浮游植物为主，而在合作海，它们以羽状硅藻为主。两海深水区的 δ13CPOC 随深度的增加而增加，反映了有机再矿化的影响。使用 Rayleigh 模型估计的再矿化过程中的碳同位素分馏因子在宇航员海和合作海分别为 1.5 ± 0.2‰ 和 1.6 ± 0.2‰。这些小的同位素效应表明，从上层输出的有机物的同位素信号在深海中保存完好。此外，在合作海的达恩利角冰间湖外的底层水中观察到异常高的 δ13CPOC 值，这反映了在 AABW 形成过程中冰藻衍生的有机物从大陆架输入。一个简单的同位素质量平衡估计表明，合作海 AABW 中 6-19% 的 POC 是由冰藻贡献的。 我们的研究强调了影响南大洋 δ13CPOC 的因素的复杂性，强调了浮游植物群落组成的重要性。