Sedimentary nitrogen isotope (as δ¹⁵N) records from the Southern Ocean provide critical constraints on surface nutrient consumption in the past and the role of Southern Ocean biophysical changes in setting atmospheric pCO₂. We present a field assessment of how surface nitrate consumption is reflected in δ¹⁵N values of total nitrogen and diatom‐bound nitrogen pools of particles and sediments across the Southern Ocean along 170°W during late austral summer. Mixed layer nitrate δ¹⁵N values increase northwards associated with greater nitrate drawdown. Particles and sediments are expected to follow this trend. Contrary to expectations, surface ocean particle total nitrogen and diatom‐bound δ¹⁵N values decreased northward during the late summer, likely due to recycling of nitrogen and the assimilation of regenerated ammonium, as well as nitrate. The relationship between δ¹⁵N values of the total nitrogen and diatom‐bound pools remains relatively constant across this Southern Ocean transect, suggesting that the isotopic composition of these two surface ocean nitrogen pools are largely set by the δ¹⁵N value(s) of the assimilated nutrient(s). Surface sediment δ¹⁵N values do increase away from the region of maximum biogenic silica deposition, suggesting that the recycled nitrogen isotopic signal observed in late summer particles may not significantly impact the sedimentary record. However, the enrichment in δ¹⁵N values of the diatom‐bound pool is greater than what is expected from progressive utilization of the surface nitrate alone and not yet explained.

中文翻译：

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硅藻键合古土壤的测试：将营养素-氮的同位素组成追踪到南部海洋颗粒和沉积物中

沉积氮同位素（如δ ¹⁵从南冰洋N）的记录提供关于过去表面营养物消耗和南部海洋生物物理变化中设置的大气中的作用的关键约束p CO ₂。我们提出的硝酸盐表面消耗是如何反映在δ场评估^15个晚南半球夏季期间总氮和沿170°W颗粒和沉渣横跨南大洋的硅藻-结合氮池的N个值。混合硝酸盐δ层¹⁵的N值增加向北以更大的硝酸盐缩编相关联。预计颗粒和沉积物将遵循这一趋势。与预期相反，表面海洋粒子总氮和硅藻结合的δ ¹⁵在夏末，N值向北下降，这可能是由于氮的循环利用和再生铵以及硝酸盐的同化所致。δ之间的关系^15个的总氮和硅藻绑定池遗体跨越此南冰洋断面相对恒定的N个值，这表明这两个表面海洋氮气池的同位素组成在很大程度上由δ设定¹⁵的N值（S）被吸收的营养物。表面沉积物δ ^15个N个值都从最大生物来源二氧化硅沉积的区域中增加了，这表明在晚夏颗粒中观察到的再循环氮的同位素信号可以不显著影响沉积记录。然而，在δ富集¹⁵硅藻结合池的N值大于单独利用表面硝酸盐的逐步利用所期望的值，尚未解释。