A molecular perspective on the ageing of marine dissolved organic matter

[摘要] Dissolved organic matter (DOM) was extracted by solid-phase extraction (SPE)from 137 water samples from different climate zones and different depthsalong an eastern Atlantic Ocean transect. The extracts were analyzed withFourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) withelectrospray ionization (ESI). Δ¹⁴C analyses were performed onsubsamples of the SPE-DOM. In addition, the amount of dissolved organiccarbon was determined for all water and SPE-DOM samples as well as the yieldof amino sugars for selected samples. Linear correlations were observedbetween the magnitudes of 43 % of the FT-ICR mass peaks and the extractΔ¹⁴C values. Decreasing SPE-DOM Δ¹⁴C values wentalong with a shift in the molecular composition to higher average masses(m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used tomodel the SPE-DOM Δ¹⁴C distribution for all 137 samples. Basedon single mass peaks, a degradation index (I_DEG) was developed tocompare the degradation state of marine SPE-DOM samples analyzed with FT-ICRMS. A correlation between Δ¹⁴C, I_DEG, DOC values and aminosugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends ofbulk DOM. DOM weighted normalized mass peak magnitudes were used to compareaged and recent SPE-DOM on a semi-quantitative molecular basis. The magnitude comparison showed a continuum of different degradationrates for the detected compounds. A high proportion of the compounds shouldpersist, possibly modified by partial degradation, in the course of thermohalinecirculation. Prokaryotic (bacterial) production, transformation andaccumulation of this very stable DOM occur primarily in the upperocean. This DOM is an important contribution to very old DOM, showing thatproduction and degradation are dynamic processes.

[学科分类] 地球化学与岩石