The twilight zone remineralization (TZR) consumes over 70% of organic carbon exported from the sunlit ocean, significantly affecting oceanic carbon sequestration and atmospheric CO concentration. Despite the well-established importance, the quantification of TZR remains challenging, as reflected by conspicuous methodological discrepancy and the unsolved imbalance between carbon supply from the upper layer and demand at depth. Here we combined three independent approaches, including biogeochemical profiling floats (BGC-float) observation, reduction of the tetrazolium salt by the cellular electron transport system ( INT), and the synthesis of prokaryotic respiration (PR) determined by radiolabeled leucine incorporation and zooplankton respiration (ZR) empirically estimated from the biomass (PR + ZR), to investigate the TZR in the South China Sea basin. Our results show that the BGC-float and PR + ZR approaches gave more consistent results, with the respective values of 5.1 ± 0.5 and 6.4 ± 3.0 mol C m yr. However, INT approach yielded a TZR nearly an order of magnitude higher at 30.0 ± 6.1 mol C m yr. To further reconcile methodological discrepancies, we estimated the possible range of carbon supply by integrating comprehensive carbon sources, including sinking particles, dissolved organic carbon input, lateral transport, dark carbon fixation, and active carbon transport by zooplankton migration. After considering multiple carbon sources, we successfully balanced the carbon demand as indicated by BGC-float and PR + ZR approaches. Our intercomparison exercise suggests a potential overestimation of TZR by the INT approach, and also highlights the importance of integrating multiple carbon sources in closing the twilight zone carbon budget.

中文翻译：

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制约南海盆地暮色带再矿化：多方法对比的见解


暮光区再矿化（TZR）消耗了阳光照射海洋输出的有机碳的 70% 以上，显着影响海洋碳固存和大气 CO 浓度。尽管 TZR 的重要性已得到证实，但 TZR 的量化仍然具有挑战性，这反映在明显的方法论差异以及上层碳供应与深层需求之间尚未解决的不平衡问题上。在这里，我们结合了三种独立的方法，包括生物地球化学分析浮子（BGC-float）观察、通过细胞电子传递系统（INT）还原四唑盐以及通过放射性标记亮氨酸掺入和浮游动物呼吸测定的原核呼吸（PR）的合成（ZR）根据生物量（PR + ZR）经验估计，以调查南海盆地的TZR。我们的结果表明，BGC-float 和 PR + ZR 方法给出了更一致的结果，分别为 5.1 ± 0.5 和 6.4 ± 3.0 mol C m yr。然而，INT 方法产生的 TZR 几乎高出一个数量级，为 30.0 ± 6.1 mol C m yr。为了进一步协调方法上的差异，我们通过整合综合碳源来估计碳供应的可能范围，包括沉降颗粒、溶解有机碳输入、横向运输、暗碳固定和浮游动物迁移的活性碳运输。在考虑多种碳源后，我们成功平衡了 BGC-float 和 PR + ZR 方法所表明的碳需求。我们的比较工作表明，INT 方法可能高估了 TZR，并且还强调了整合多种碳源在关闭暮色区碳预算中的重要性。