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Photochemical bleaching of oceanic dissolved organic matter and its effect on absorption spectral slope and fluorescence

机译：海洋溶解有机物的光化学漂白及其对吸收光谱斜率和荧光的影响

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摘要

Photobleaching of open-ocean dissolved organic matter (DOM) is typically treated as a removal mechanism; however, photobleaching also encompasses a poorly characterized suite of transformative processes. To examine the qualitative changes to DOM optical properties during photobleaching, 674 m N. Pacific DOM, concentrated and desalted by reverse osmosis with electrodialysis (RO/ED), was subjected to 68 days of continuous irradiation in a UV solar simulator. Approximately 84% of chromophoric and fluorescent DOM (CDOM and FDOM respectively) and 38% of dissolved organic carbon (DOC) were lost during the irradiation. Based on these results the concentration of photochemically refractory DOC in the surface pacific is estimated to be 27 μmol of carbon per liter. In addition, the spectra of the remaining CDOM and FDOM were shifted towards shorter wavelengths, a result which has important implications for the interpretation of fluorescence excitation emission matrix (EEM) spectra because the relative positions of fluorescence maxima are often attributed to differences in FDOM source. Qualitative indices derived from CDOM and FDOM spectra for the irradiated deep DOM sample resembled those for surface waters of the North Pacific Ocean indicating that photobleaching has a significant influence upon the optical properties of DOM in the open ocean.
机译：开放性海洋溶解有机物（DOM）的光漂白通常被视为一种去除机制；然而，光漂白也包含了一系列转化过程的特征。为了检查光漂白过程中DOM光学性质的质变，对674 m N.通过电渗析（RO / ED）进行反渗透浓缩和脱盐的Pacific DOM在UV太阳模拟器中进行了68天连续照射。在照射过程中损失了约84％的发色和荧光DOM（分别为CDOM和FDOM）和38％的溶解有机碳（DOC）。根据这些结果，估计太平洋表面光化学难处理DOC的浓度为每升碳27微摩尔。此外，剩余的CDOM和FDOM的光谱向较短的波长移动，这一结果对于解释荧光激发发射矩阵（EEM）光谱具有重要意义，因为荧光最大值的相对位置通常归因于FDOM光源的差异。 。从CDOM和FDOM光谱得出的深部DOM样品的定性指标与北太平洋地表水的定性指标相似，这表明光漂白对大洋中DOM的光学性质有重要影响。

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