Dissolved organic matter in the Lena River Delta Region, Siberia, Russia

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation.

受气候变化影响，北极地区陆地与海洋环境间的连通性正发生改变，这既影响了淡水收支，也干扰了向海洋的碳输入。本研究对勒拿河三角洲区域内溶解有机物（dissolved organic matter, DOM）的光学特性进行了表征，并评估了DOM在淡水-海洋梯度下的变化行为。通过平行因子分析（Parallel Factor Analysis, PARAFAC）共识别出6种荧光组分：4种类腐殖质组分、1种海洋类腐殖质组分以及1种类蛋白组分，其中外源类腐殖质信号占绝对主导地位。有色溶解有机物（Colored DOM, CDOM）与溶解有机碳（dissolved organic carbon, DOC）呈现高度相关，二者的分布特征与水文条件密切相关。勒拿河低盐度水体中DOM浓度及腐殖化程度更高，随着向盐度更高的拉普捷夫海陆架水体过渡，其数值逐渐降低。研究结果表明，DOM混合过程对水柱垂直结构存在不同响应，这反映了该区域的水文动力特征。DOM的混合过程呈现出两条明显的变化曲线：在密度跃层以上的表层水体中，DOM浓度随盐度升高出现更为显著的下降，这暗示了DOM的移除过程；而在底层水体中，DOM浓度随盐度升高的下降幅度相对平缓。本研究提出，DOM的移除主要发生在表层水体，其驱动机制大概率为光降解与絮凝作用。