Microbial degradation of dissolved organic matter (DOM) contributes to the formation and preservation of oxygen minimum zones (OMZs) in the ocean, but information on the spatial distribution and molecular composition of DOM in OMZ regions is scarce. We quantified molecular components of DOM that is, dissolved amino acids (DAA) and dissolved combined carbohydrates (DCCHO), in the upwelling region off Peru. We found the highest concentrations of DCCHO in fully oxygenated surface waters steeply declining at shallow depth. The highest DAA concentrations were observed close to the surface also, but attenuation of DAA concentration over depth was less pronounced. Compositional changes of DCCHO were strongest within more oxygenated waters. Compositional changes of DAA were also evident under suboxic conditions (<5 µmol O₂ kg⁻¹) and indicated bacterial peptide degradation. Moreover, specific free amino acids (alanine and threonine) were enhanced within suboxic waters, pointing to a potential production of dissolved organic nitrogen under suboxic conditions. Our results therewith suggest that deoxygenation supports a spatial decoupling of DCCHO and DAA production and degradation dynamics and give new insights to carbon and nitrogen cycling in the OMZ off Peru.

中文翻译：

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秘鲁上涌系统中溶解的有机物：细菌活动和水团特征的印记

溶解有机物 (DOM) 的微生物降解有助于海洋中最低氧区 (OMZ) 的形成和保存，但关于 OMZ 区域中 DOM 的空间分布和分子组成的信息很少。我们在秘鲁附近的上升流区域量化了 DOM 的分子成分，即溶解氨基酸 (DAA) 和溶解结合碳水化合物 (DCCHO)。我们发现完全氧化的地表水中 DCCHO 的最高浓度在浅层急剧下降。在靠近表面的地方也观察到最高的 DAA 浓度，但 DAA 浓度随深度的衰减不太明显。DCCHO 的成分变化在含氧量较高的水中最强。在低氧条件下（<5 µmol O ₂kg ^-1 ) 和指示细菌肽降解。此外，特定的游离氨基酸（丙氨酸和苏氨酸）在低氧水中增强，表明在低氧条件下可能会产生溶解的有机氮。我们的结果表明，脱氧支持 DCCHO 和 DAA 生产和降解动力学的空间解耦，并为秘鲁附近的 OMZ 中的碳和氮循环提供了新的见解。