NADW Photodegradation FTICR-MS@en

Duplicate, filtered samples of North Atlantic Deep Water (NADW) were irradiated for 28 days in a solar simulator. Duplicate dark controls were placed alongside the irradiated samples. After 28 days, samples were extensively photo-degraded based upon colored dissolved organic matter (CDOM) photo-bleaching (> 95%). Samples were solid phase extracted using PPL resin to isolate, concentrate and desalt the dissolved organic matter (DOM) in the samples. Ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) enabled 3024 molecular formulas to be identified in the dark control. Photo-degradation decreased molecular diversity, with 2402 formulas assigned post-irradiation. Molecular formulas were classified based upon their photo-lability as 1) photo-resistant; 2) photo-labile; and, 3) photo-produced. Photo-resistant DOM made up 73% of all formulas and was dominated by highly unsaturated molecular signatures consistent with carboxylic-rich alicyclic molecules, suggesting that these apparently bio-refractory compounds may also survive multiple passages through sunlit surface waters and thus accumulate for timeframes exceeding ocean ventilation. Photo-labile DOM was enriched in low molecular weight formulas, aromatic molecular formulas, and sulfur and phosphorous containing formulas. Compounds containing both sulfur and nitrogen were particularly photo-labile and may represent an underappreciated component of the photo-reactive CDOM pool. Photo-produced DOM was enriched in higher molecular weight formulas, as well as aliphatic and peptide formulas. Molecular formulas are indexed by their photo-lability classification in the supplementary information.对北大西洋深层水（North Atlantic Deep Water, NADW）的平行重复过滤样品在太阳模拟器中进行了为期28天的辐照处理，辐照样品旁同步设置平行黑暗对照样品。经过28天处理后，依据有色溶解有机物（colored dissolved organic matter, CDOM）的光漂白程度（>95%）判断，所有样品均已发生显著光降解。采用PPL树脂对样品进行固相萃取，以分离、浓缩并脱除其中溶解有机物（dissolved organic matter, DOM）中的盐分。利用超高分辨率电喷雾电离傅里叶变换离子回旋共振质谱（Ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, FTICR-MS），在黑暗对照样品中鉴定出3024个分子分子式。光降解作用降低了分子多样性，辐照后仅鉴定出2402个分子式。根据光不稳定性将分子分子式划分为三类：1）抗光降解型；2）易光降解型；3）光生成型。抗光降解型DOM占总分子式的73%，其分子特征以高度不饱和结构为主，与富羧酸脂环族分子特征一致，这表明这类看似生物难降解的化合物或可在多次经过光照表层水体后保持稳定，并在远超海洋换气的时间尺度下持续积累。易光降解型DOM则富集有低分子量分子式、芳香族分子式以及含硫、含磷的分子式；同时含有硫和氮的化合物尤其易发生光降解，这可能代表了光反应性CDOM库中一个此前未被充分重视的组成部分。光生成型DOM则富集有高分子量分子式以及脂肪族和肽类分子式。所有分子分子式的光不稳定性分类信息已收录于补充材料中。