Climate warming is accelerating the release of voluminous organic carbon from thawing permafrost into the Arctic Ocean via riverine transport. However, the seasonal variations in riverine dissolved organic carbon (DOC) exports in Arctic river basins with different areal extents of permafrost and how changes in water temperature (T_w) impact seasonal DOC exports are not fully understood. In this study, the concentrations, ages and seasonality of riverine DOC in the estuaries of six major Arctic rivers (Ob, Yenisei, Lena, Kolyma, Yukon and Mackenzie) were analysed using Arctic Great Rivers Observatory (ArcticGRO) datasets from 2003 to 2019. The results showed that DOC concentrations generally increased with the increases in the streamflow, but always dropped to the minimum with the oldest Δ¹⁴C-DOC ages (as old as 1650 years BP) in the freezing period (November–April), when the streamflow originates predominantly from groundwater. During the flood pulse period (May or June), a rapid increase in riverine DOC concentration with younger organic carbon (Δ¹⁴C values from −61 to 152‰) was observed, likely associated with snowmelt-dominated runoff regimes (lower δ¹⁸O-H₂O of approximately −20.4 ± 1.6‰). During the ice-free period (June–September), DOC concentrations decreased due to the enhanced dilution of streamflow from precipitation. In the Lena and Kolyma River basins with large areal extents of continuous permafrost, over 70% of DOC flux exported during the ice-free period originated from DOC sources from ∼410 years and ∼230 years BP to the present, respectively; this suggests that greater permafrost extents restrict the release of older DOC into rivers. However, riverine DOC exports likely respond positively to changes in T_w during the ice-free period. In addition, such a positive response is likely to be enhanced in basins with larger percentages of sporadic permafrost, thicker active layers, more precipitation and less soil organic carbon. Ultimately, under a warming climate, riverine DOC exports are expected to rise with increasing river water temperatures.

气候变暖正在加速通过河流运输从解冻的永久冻土中释放大量有机碳到北冰洋。然而，具有不同永久冻土面积的北极河流域河流溶解有机碳 ( DOC ) 出口的季节性变化以及水温 (Tw) 变化如何影响季节性 DOC出口_尚不完全清楚。在这项研究中，使用北极大河流观测站 (ArcticGRO) 数据集从 2003 年到 2019 年分析了六大北极河流（Ob、Yenisei、Lena、Kolyma、Yukon 和 Mackenzie）河口中河流DOC的浓度、年龄和季节性。结果表明，DOC浓度通常随着径流的增加而增加，但在冰冻期（11 月至 4 月），当径流主要来自地下水时，随着Δ ¹⁴ C-DOC年龄最早（早至 1650 年），浓度总是下降到最小值. 在洪水脉冲期（5 月或 6 月），观察到河流DOC浓度快速增加，有机碳较年轻（Δ ¹⁴ C值从 -61 到 152‰），可能与融雪为主的径流状态（较低的δ ¹⁸ O-H ₂ O约为 -20.4 ± 1.6‰)。在无冰期（6 月至 9 月），DOC由于降水对径流的稀释作用增强，浓度下降。在大面积连续多年冻土的勒拿河流域和科雷马河流域，无冰期输出的DOC通量的 70%以上分别来自 BP ～ 410 年和～230 年的DOC源；这表明更大的永久冻土范围限制了较旧的DOC释放到河流中。然而，河流DOC出口可能对T _w的变化做出积极反应在无冰期。此外，在零星多年冻土比例较大、活动层较厚、降水较多和土壤有机碳较少的盆地，这种积极响应可能会增强。最终，在气候变暖的情况下，预计河流DOC出口将随着河流水温的升高而增加。