The eastern tropical South Pacific (ETSP) represents one of the most productive areas in the ocean that is characterised by a pronounced oxygen minimum zone (OMZ). Particulate organic matter (POM) that sinks out of the euphotic zone is supplied to the anoxic sediments and utilised by microbial communities, and the degradation of POM is associated with the production and reworking of dissolved organic matter (DOM). The release of DOM to the overlying waters may, therefore, represent an important organic matter escape mechanism from remineralisation within sediments but has received little attention in OMZ regions so far. Here, we combine measurements of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) with DOM optical properties in the form of chromophoric (CDOM) and fluorescent (FDOM) DOM from pore waters and near-bottom waters of the ETSP off Peru. We evaluate diffusion-driven fluxes and net in situ fluxes of DOC and DON to investigate processes affecting DOM cycling at the sediment–water interface along a transect at 12^∘ S. To our knowledge, these are the first data for sediment release of DON and pore water CDOM and FDOM for the ETSP off Peru. Pore water DOC accumulated with increasing sediment depth, suggesting an imbalance between DOM production and remineralisation within sediments. High DON accumulation resulted in very low pore water DOC ∕ DON ratios (≤1) which could be caused by an “uncoupling” in DOC and DON remineralisation. Diffusion-driven fluxes of DOC and DON exhibited high spatial variability and ranged from 0.2±0.1 to 2.5±1.3 $\mathrm{mmol}{\mathrm{m}}^{-\mathrm{2}}{\mathrm{d}}^{-\mathrm{1}}$ and from $-\mathrm{0.04}\pm \mathrm{0.02}$ to 3.3±1.7 $\mathrm{mmol}{\mathrm{m}}^{-\mathrm{2}}{\mathrm{d}}^{-\mathrm{1}}$, respectively. Generally low net in situ DOC and DON fluxes, as well as a steepening of spectral inclination (S) of CDOM and an increase in humic-like DOM at the sediment–water interface over time, indicated active microbial DOM utilisation. The latter may potentially be stimulated by the presence of nitrate (${\mathrm{NO}}_{\mathrm{3}}^{-}$) and nitrite (${\mathrm{NO}}_{\mathrm{2}}^{-}$) in the water column. The microbial DOC utilisation rates, estimated in our study, are potentially sufficient to support denitrification rates of 0.2–1.4 $\mathrm{mmol}{\mathrm{m}}^{-\mathrm{2}}{\mathrm{d}}^{-\mathrm{1}}$, suggesting that the sediment release of DOM may on occasion contribute to nitrogen loss processes in the ETSP off Peru.

中文翻译：

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沉积物将溶解的有机物释放到秘鲁附近的氧气最小区域

东部热带南太平洋（ETSP）代表了海洋中生产力最高的地区之一，其特征在于明显的最小氧气区（OMZ）。下沉到富营养区的颗粒有机物（POM）被提供给缺氧沉积物，并被微生物群落利用，并且POM的降解与溶解性有机物（DOM）的产生和再加工有关。因此，DOM向上层水体的释放可能代表了沉积物中再矿化过程中重要的有机物逸出机制，但迄今为止在OMZ地区鲜为人知。这里，我们将来自秘鲁ETSP孔隙水和近底部水的发色（CDOM）和荧光（FDOM）DOM形式的DOM光学性质与溶解有机碳（DOC）和溶解有机氮（DON）的测量结果结合起来。我们评估了DOC和DON的扩散驱动通量和净原位通量，以研究影响DOM在沿12点样线在沉积物-水界面处循环的过程。^∘S  .据我们所知，这是秘鲁外海ETSP的DON和孔隙水CDOM和FDOM沉积物释放的第一个数据。孔隙水DOC随着沉积物深度的增加而积累，这表明DOM产生与沉积物内的再矿化之间存在失衡。DON的大量积累导致孔隙水DOC ∕  DON比非常低 （ ≤1），这可能是由于DOC和DON再矿化中的“解耦”所致。DOC和DON的扩散驱动通量表现出高空间变异性，范围从0.2±0.1到2.5±1.3 $\mathrm{毫摩尔}{\mathrm{米}}^{--\mathrm{2}}{\mathrm{d}}^{--\mathrm{1个}}$ 和从 $--\mathrm{0.04}\pm \mathrm{0.02}$到3.3±1.7 $\mathrm{毫摩尔}{\mathrm{米}}^{--\mathrm{2}}{\mathrm{d}}^{--\mathrm{1个}}$， 分别。通常，随着时间的流逝，原位DOC和DON的净净通量较低，并且沉积物-水界面的CDOM光谱倾斜度（S）陡峭，腐殖质类DOM增加，这表明微生物DOM的利用非常活跃。硝酸盐的存在可能会刺激后者（${\mathrm{没有}}_{\mathrm{3}}^{--}$）和亚硝酸盐（${\mathrm{没有}}_{\mathrm{2}}^{--}$）在水栏中。我们研究中估计的微生物DOC利用率可能足以支持0.2-1.4的反硝化率 $\mathrm{毫摩尔}{\mathrm{米}}^{--\mathrm{2}}{\mathrm{d}}^{--\mathrm{1个}}$，这表明DOM的沉积物释放有时可能导致秘鲁ETSP的氮损失过程。