Dissolved organic carbon investigations from the Kara Sea

Based on observations during four scientific expeditions to the Kara Sea and the Siberian rivers Ob and Yenisei we determined the discharge, distribution and characteristics of dissolved organic matter (DOM). Surface concentrations of dissolved organic carbon (DOC) ranged from 151 IlM C in the northern Kara Sea to 939 IlM C in the river Ob. The estimated annual mean DOC concentration in the Yenisei (681 IlM C) was slightly higher than in the Ob (640 IlM C). Dissolved organic nitrogen (DON) concentrations typically varied between 5 and 15 IlM N with higher values in the rivers. Freshwater discharge and DOC concentrations experienced pronounced seasonal variations strongly affecting the spatial and temporal distribution of DOM in the Kara Sea. The largely conservative distribution of DOC and DON along the salinity gradient indicated the predominantly refractory character of riverine DOM. This observation was consistent with laboratory experiments, which showed only minor losses due to flocculation processes and bacterial consumption. Optical properties and relatively high C/N ratios (19 to 51) of DO M suggest that a large fraction of river DOM is of terrestrial origin and that phytoplankton contributed little to DOM on the Kara Sea shelf during the sampling periods. Together, the rivers Ob and Yenisei discharge about 8 Tg DOC yr- I into the Kara Sea. Due to the absence of efficient removal mechanisms in these estuaries the majority of riverine DOM appears to pass the estuarine mixing zone and is transported towards the Arctic Ocean.

本研究基于四次对喀拉海及西伯利亚鄂毕河、叶尼塞河的科学考察观测数据，测定了溶解有机物（dissolved organic matter, DOM）的径流量、分布特征与固有特性。
溶解有机碳（dissolved organic carbon, DOC）的表层浓度范围为喀拉海北部的151 μM C至鄂毕河的939 μM C。
叶尼塞河的年平均DOC浓度为681 μM C，略高于鄂毕河的640 μM C。
溶解有机氮（dissolved organic nitrogen, DON）的浓度通常介于5~15 μM N之间，且河流中的DON浓度更高。
淡水径流量与DOC浓度均存在显著的季节变化，这对喀拉海DOM的时空分布产生了强烈影响。
沿盐度梯度，DOC与DON大体呈现保守性分布，这表明河流来源的DOM整体以难降解特性为主。
该观测结果与室内实验结果相符：实验仅观测到因絮凝过程与细菌降解消耗导致的少量DOM损失。
DOM的光学特性与较高的碳氮比（19~51）表明，河流来源的DOM大部分为陆源物质；且在采样时段内，喀拉海陆架区域的浮游植物对DOM的贡献极小。
鄂毕河与叶尼塞河每年向喀拉海输入的DOC总量约为8 Tg DOC yr⁻¹。
由于这些河口区域缺乏高效的DOM去除机制，大部分河流来源的DOM可顺利通过河口混合区，并被输运至北冰洋。