Tropical and subtropical rivers deliver large quantities of terrestrial organic carbon (OC_terr) to the ocean, acting as a crucial part of the global carbon cycle, but little is known about the timescale and efficiency of its transport to and in the adjacent coastal sea. Here we examined source-specific biomarker (fatty acids, FAs) contents and isotope compositions in surface sediments in an alongshore transect southwestward from the Pearl River mouth. The C₂₈₊₃₀, rather than other long-chain saturated FAs, were found to be the most representative for OC_terr, and a plant wax mean age of 3060 ± 90 yr (resulting from protracted storage) was estimated in the Pearl River watershed from the ¹⁴C age of C₂₈₊₃₀ FA in a river mouth sample. A compilation of plant wax mean ages in global (sub)tropical river systems including this study suggests that regional differences in climate and morphology may have a limited impact on plant wax mean ages in (sub)tropical regions. A four-source mixing model based on bulk OC and biomarker isotope compositions demonstrated that surface sediments in the Pearl River-derived mudbelt consist of 0.15–0.36 wt.% marine OC, 0.03–0.13 wt.% riverine primary production-derived OC, 0.18–0.49 wt.% soil OC, and 0.07–0.16 wt.% fossil OC. The mean burial efficiency of fossil and soil OC is ∼85% and 49%, respectively, indicating the refractory nature of fossil OC but a significant loss of soil OC due to remineralization during transport in the marine environment before final burial. Over longer timescales, the OC_terr loss experienced during transport may, thus, to some extent reduces the capacity of terrestrial ecosystems (particularly soils) as CO₂ sinks.

热带和亚热带河流向海洋输送了大量陆地有机碳（OC _terr），是全球碳循环的重要组成部分，但对其往来及在邻近沿海海域的运输的时程和效率知之甚少。在这里，我们检查了珠江口西南偏南沿海近岸断面的表层沉积物中特定于源的生物标志物（脂肪酸，FAs）的含量和同位素组成。发现C _{28 + 30}而不是其他长链饱和FAs最能代表OC _terr，据估计珠江流域的植物蜡平均年龄为3060±90年（由于长期储存）从¹⁴的C C年龄_{28 + 30}FA在河口样品中。包括本研究在内的全球（亚）热带河流系统中植物蜡平均年龄的汇编表明，气候和形态的区域差异可能对（亚）热带地区植物蜡平均年龄产生有限的影响。基于散装OC和生物标志物同位素组成的四源混合模型表明，珠江源性泥质带的表层沉积物包括0.15–0.36 wt。％的海洋OC，0.03-0.13 wt。％的河流初级生产来源的OC，0.18 –0.49 wt。％的土壤OC和0.07–0.16 wt。％的化石OC。化石和土壤OC的平均掩埋效率分别为〜85％和49％，这表明化石OC的耐火性质，但由于在最终掩埋之前在海洋环境中运输过程中的再矿化作用，土壤OC的大量损失。在更长的时间范围内，OC因此，运输过程中遇到的_水土流失可能在一定程度上降低了随着CO _2的下沉而导致的陆地生态系统（特别是土壤）的能力。