Program     Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future       Poster Spatial variability of turnover rates of polyamines and dissolved free amino acids in the ocean P-M5-05 Qian Liu* , Second Institute of Oceanography SOA Xue-Wei Xu, Second Institute of Oceanography SOA Ye Lu, Shanghai Jiaotong University Jun Xu, Shanghai Jiaotong University Chun-Sheng Wang, Second Institute of Oceanography SOA Presenter Email: liuqian@sio.org.cn Polyamines are a group of aliphatic organic nitrogen compounds that are dissolved in seawaters and potentially contribute to bacterial nitrogen production. Previous studies have shown that turnover of polyamines in nearshore waters was rapid, similar to that of dissolved free amino acids (DFAA). Bacterial uptake of polyamines could contribute to over 10% of bacterial nitrogen demand, suggesting a significant role of polyamines in nitrogen cycle. In this study, we measured the turnover of polyamines and two DFAA (arginine and glutamic acid) using radioisotope tracing method in the water column of continental shelf and open ocean at the northern South China Sea (SCS) where dissolved organic nitrogen is suggested to be the predominant nitrogen source. Results showed that polyamines were actively utilized through the water column, while DFAA were mostly recycled within euphotic zone. This suggests that the biogeochemical pathways of these two groups of DON are different in northern SCS, possibly due to differences in their sources and sinks. It was estimated that polyamines may contribute up to ~5% of bacterial nitrogen demand at this region.

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