Permafrost degradation in the catchment of major Siberian rivers, combined with higher precipitation in a warming climate, could increase the flux of terrestrially derived dissolved organic matter (tDOM) into the Arctic Ocean (AO). Each year, ∼ 7.9 Tg of dissolved organic carbon (DOC) is discharged into the AO via the three largest rivers that flow into the Laptev Sea (LS) and East Siberian Sea (ESS). A significant proportion of this tDOM-rich river water undergoes at least one freeze–melt cycle in the land-fast ice that forms along the coast of the Laptev and East Siberian seas in winter. To better understand how growth and melting of land-fast ice affect dissolved organic matter (DOM) dynamics in the LS and ESS, we determined DOC concentrations and the optical properties of coloured dissolved organic matter (CDOM) in sea ice, river water and seawater. The data set, covering different seasons over a 9-year period (2010–2019), was complemented by oceanographic measurements (T, S) and determination of the oxygen isotope composition of the seawater.Although removal of tDOM cannot be ruled out, our study suggests that conservative mixing of high-tDOM river water and sea-ice meltwater with low-tDOM seawater is the major factor controlling the surface distribution of tDOM in the LS and ESS. A case study based on data from winter 2012 and spring 2014 reveals that the mixing of about 273 km³ of low-tDOM land-fast-ice meltwater (containing ∼ 0.3 Tg DOC) with more than 200 km³ of high-tDOM Lena River water discharged during the spring freshet (∼ 2.8 Tg DOC yr⁻¹) plays a dominant role in this respect. The mixing of the two low-salinity surface water masses is possible because the meltwater and the river water of the spring freshet flow into the southeastern LS at the same time every year (May–July). In addition, budget calculations indicate that in the course of the growth of land-fast ice in the southeastern LS, ∼ 1.2 Tg DOC yr⁻¹ (± 0.54 Tg) can be expelled from the growing ice in winter, together with brines. These DOC-rich brines can then be transported across the shelves into the Arctic halocline and the Transpolar Drift Current flowing from the Siberian Shelf towards Greenland.The study of dissolved organic matter dynamics in the AO is important not only to decipher the Arctic carbon cycle but also because CDOM regulates physical processes such as radiative forcing in the upper ocean, which has important effects on sea surface temperature, water column stratification, biological productivity and UV penetration.

中文翻译：

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陆上冰冻融循环对拉普捷夫和东西伯利亚海（西伯利亚北极）溶解有机物分布的影响

西伯利亚主要河流集水区的永久冻土退化，加上气候变暖导致降水增加，可能会增加陆源溶解有机物 (tDOM) 流入北冰洋 (AO) 的通量。每年，～ 7.9 Tg 的溶解有机碳 (DOC) 通过流入拉普捷夫海 (LS) 和东西伯利亚海 (ESS) 的三大河流排放到 AO 中。这种富含 tDOM 的河水中有很大一部分在冬季沿拉普捷夫和东西伯利亚海沿岸形成的陆上冰中至少经历了一次冻融循环。为了更好地了解陆上快速冰的生长和融化如何影响 LS 和 ESS 中的溶解有机物 (DOM) 动态，我们确定了海冰、河水和海水中的 DOC 浓度和有色溶解有机物 (CDOM) 的光学特性. 该数据集涵盖了 9 年期间（2010-2019 年）的不同季节，并辅以海洋测量（T , S) 和海水中氧同位素组成的测定。虽然不能排除 tDOM 的去除，但我们的研究表明，高 tDOM 河水和海冰融水与低 tDOM 海水的保守混合是控制表面的主要因素LS 和 ESS 中 tDOM 的分布。一项基于 2012 年冬季和 2014 年春季数据的案例研究表明，约 273 公里³的低 tDOM 陆地快速冰融水（含有约 0.3 Tg DOC）与 200 多公里³的高 tDOM 勒拿河混合春季新鲜时排放的水 ( ∼  2.8 Tg DOC yr ^-1)在这方面起着主导作用。由于融水和春季淡水河水每年在同一时间（5-7 月）流入 LS 东南部，因此两种低盐度地表水团有可能混合。此外，预算计算表明，在 LS 东南部陆上快冰生长过程中， ∼  1.2 Tg DOC yr ^-1 ( ± 0.54 Tg) 可以与盐水一起从冬季生长的冰中排出。然后这些富含 DOC 的盐水可以穿过大陆架运输到北极盐环层和从西伯利亚大陆架流向格陵兰的跨极漂移流。 AO 中溶解有机物质动力学的研究不仅对解读北极碳循环很重要，而且还因为 CDOM 调节上层海洋的辐射强迫等物理过程，这对海面温度、水柱分层、生物生产力和紫外线穿透具有重要影响。