北极孔斯峡湾表层沉积物中溶解有机质的来源与转化历史

在北极地区孔斯峡湾采集28个表层沉积物样品,测定了其中水溶性有机质(也称溶解有机质,DOM)的分子量分布、紫外/可见吸收光谱和三维荧光光谱特征,并利用平行因子分析(PARAFAC)模型对DOM的荧光组分和来源进行了解析。结果表明:孔斯峡湾表层沉积物中有色溶解有机质(CDOM)及其中的荧光溶解有机质(FDOM)含量均从内湾向外湾方向呈逐渐累积的趋势,但CDOM中的FDOM所占比例逐渐减小,与DOM趋于老龄化密切相关。沉积作用减弱以及长期的光化学降解和微生物降解作用对此起主要贡献,并导致腐殖质和小分子组分在沉积物DOM中所占的比例呈逐渐递增的趋势。沉积物DOM包含陆源类腐殖质、自生源类腐殖质和类蛋白等三个荧光组分,但是其组成比例空间差异很大。吸收光谱斜率比(S_R)随自生源所占百分比增加而减小,随DOM腐殖质组分中陆源与自生源的比值增加而增加;腐殖化指数(HIX)随类腐殖质与类蛋白质比值和水深的增加而增加,生物源指数(BIX)随自生源比例增加而增加。峡湾沉积物DOM的组成和来源存在着高度的空间差异,在冰川湾区由水体颗粒有机质(POM)的近期转化和迁移而来,而在峡湾中央及口门附近以较老的腐殖质为优势,主要源于水体DOM长期迁移和转化。研究表明,FDOM/CDOM,S_R,HIX和BIX等构成的CDOM光谱指纹信息可以作为揭露沉积物溶解有机质来源及迁移转化历史的工具,对探索海洋与冰川相互作用影响下的峡湾环境演变有着重要意义。

Retrieving the origin and transformation history of dissolved organic matter in the surface sediment from an Arctic fjord

Twenty eight surface sediment samples were collected from the Kongsfjorden (Svalbard) in Arctic Area. We measured the molecular weight distribution, UV-Visible absorbance spectrum and three-dimensional fluorescence spectrum of water soluble organic matter (also named dissolved organic matter, DOM) in the sediment. Moreover, the fluorescence components and sources of DOM were resolved by using parallel factor analysis (PARAFAC). It was showed that the contents of chromatophoric DOM (CDOM) and fluorescent DOM (FDOM) had a tendency to accumulate gradually from the head to the mouth in this arctic fjord. But the ratio of FDOM to CDOM decreased gradually, which is closely related to the aging process of sediment DOM. It is mainly due to the long-term photodegradation and biodegradation, and the weakening sedimentation, which also contributes to the accumulation of humic substances and small molecules. FDOM in the sediment comprised three fluorescent components including terrestrial humic-like material, autochthonous humic-like and protein-like material. The spectral slope ratio (S_R) decreased with the increase of the percentage of autochthonous DOM while it increased with the increase of the ratio of terrestrial DOM to autochthonous DOM. The humification index (HIX) increased with the increase of humic-like to protein-like ratio and water depth while the biological origin index (BIX) increased with the autochthonous percentage increasing. Large spatial variability of the composition and sources of sedimentary organic matter was found in this fjord. In the glacial bay area, sediment DOM mainly came from the newly transport and transformation of particulate organic matter (POM) in the water column; in the center and mouth of the fjord, sediment DOM was dominated by old humic substances, which originate from the long-term of transport and transformation of DOM in the water column. The spectral fingerprint of CDOM acts as a proxy for revealing the origins and transformation history of dissolved organic matter in the sediment. It is significant for exploring the evolution of fjord environment under the interaction of ocean and glacier.