Geoscience Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093, United States.
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, United States.
Environ Sci Technol. 2024 Aug 20;58(33):14709-14717. doi: 10.1021/acs.est.4c03372. Epub 2024 Aug 5.
The use of ultrafiltration to isolate high molecular weight dissolved organic matter (HMWDOM) from seawater is a fundamental tool in the environmental organic chemist's toolbox. Yet, important characteristics of HMWDOM relevant to its origin and cycling, such as its molecular weight distribution, remain poorly defined. We used diffusion-ordered NMR spectroscopy coupled with mixed-mode chromatography to separate and characterize two major components of marine HMWDOM: acylpolysaccharides (APS) and high molecular weight humic substances (HS). The molecular weights (MWs) of APS and HS both fell within distinct, narrow envelopes; 2.0-16 kDa for APS and 0.9-6.5 kDa for HS. In water samples from the North Pacific Ocean the average MW of both components decreased with depth through the mesopelagic. However, the minimum MW of APS was >2 kDa, well above the molecular weight cutoff of the ultrafilter, suggesting APS removal processes below 2 kDa are highly efficient. The MW distribution of APS shows only small variations with depth, while the MW distribution of HS narrowed due to removal of HMW components. Despite the narrowing of the MW distribution, the concentration of HS did not decrease with depth between 15 and 915 m. This suggests that HMW HS produced in surface waters was either degraded into lower MW compounds without significant remineralization, or that HMW HS was remineralized but replaced by an additional source of HS in the mesopelagic ocean. Based on these results, we propose potential pathways for the production and removal of these major components of HMWDOM.
利用超滤从海水中分离高分子量溶解有机物（HMWDOM）是环境有机化学家工具包中的基本工具。然而，与 HMWDOM 的起源和循环相关的重要特征，如其分子量分布，仍然定义不明确。我们使用扩散排序 NMR 光谱学结合混合模式色谱法来分离和表征海洋 HMWDOM 的两个主要成分：酰基多糖（APS）和高分子量腐殖质（HS）。APS 和 HS 的分子量（MW）都落在明显的狭窄范围内；APS 的 MW 为 2.0-16 kDa，HS 的 MW 为 0.9-6.5 kDa。在北太平洋的水样中，这两种成分的平均 MW 都随着中层水的深度而降低。然而，APS 的最小 MW 大于 2 kDa，远高于超滤的分子量截止值，这表明 2 kDa 以下的 APS 去除过程效率很高。APS 的 MW 分布随深度变化很小，而 HS 的 MW 分布因去除 HMW 成分而变窄。尽管 MW 分布变窄，但 HS 的浓度在 15 至 915 米之间并未随深度降低而降低。这表明在表层水中产生的 HMW HS 要么在没有明显矿化的情况下降解为低 MW 化合物，要么 HMW HS 被矿化，但在中层海洋中被 HS 的另一个来源所取代。基于这些结果，我们提出了这些 HMWDOM 主要成分的产生和去除的潜在途径。
