Table of Contents

• Dataset Description
  • Methods & Sampling
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

SPE-DOM = Solid-Phase Extracted Dissolved Organic Matter 
FT-ICR MS = Fourier transform ion cyclotron resonance mass spectrometry

For full details on irradiation experiments, please see Related Dataset page https://www.bco-dmo.org/dataset/938807.

The irradiation experiment described here was a separate experiment to couple with FT-ICR-MS analysis. Because a pH electrode was found to contaminate samples for mass spectrometry, no pH control was used in this experiment (sample pH ~ 4.5). Additionally, the sample volume was doubled compared to other experiments to minimize volume changes when subsampling. The absorbed photon dose was also decreased due to the larger volume, so that a 46 h time point was equivalent to ~20 h exposure in the previous irradiation experiments described in the Photodeg/pH dependence document mentioned above. At time points of 2, 4, 6, 22, and 46 h, 0.2 mL was sampled from the reactor and was added to 0.8 mL of methanol until analysis by ultrahigh resolution mass spectrometry (for full details please related FT-ICR-MS dataset https://www.bco-dmo.org/dataset/938847) using negative ion mode electrospray ionization (ESI). Only CHO formula assignments are described here because they were most abundant using negative ESI mode in the Sargassum SPE-DOM analyzed previously (Powers et al., 2019). 

NSF Award Abstract:

Chromophoric dissolved organic matter (CDOM), the sunlight absorbing components in filtered water, is important in the study of marine and freshwater ecosystems as it can be used to trace the mixing of surface waters, as a proxy for carbon cycles, and other biogeochemical processes. Although its importance in ocean studies has been firmly established over the last several decades, sources and structural composition of CDOM within the oceans remains unclear and continues to be a subject of debate. Sargassum, a brown alga, is widely distributed in temperate and subtropical marine waters and may be important source of CDOM to the Sargasso Sea and Gulf of Mexico where Sargassum is abundant. This project will investigate the contribution of macro brown algae-derived compounds to the marine CDOM pool. Results from this study will have implications for the marine carbon cycle and satellite remote sensing of ocean color to assess mixing of surface water masses and biogeochemical processes. The project will provide educational opportunities for a postdoctoral scholar, summertime undergraduate internships (through a local NSF-sponsored Research Experiences for Undergraduates (REU) program), and workshop and research opportunities for local high schools students.

Sources of marine CDOM remain debatable and a comprehensive understanding of its origins, distribution and fate have been difficult. Marine CDOM, and in particular the "humic-like" component, have been suggested to originate from terrestrial sources, primarily lignins. However, recent evidence indicates that the exudation of phlorotannins produced by macro brown algae may contribute significantly to the marine CDOM pool. Phlorotannins, a class of polyphenols that are only found in, and continuously exuded by macro brown algae such as Sargassum, strongly absorb ultraviolet light and may have been underestimated in their contribution to the marine CDOM pool within certain geographic locales. Upon partial oxidation, light absorption by these specific compounds extends into longer wavelengths in the visible creating an absorption spectrum similar to that of lignin. These phlorotannins and their transformation products absorb light that might explain in part the "humic-like" signatures observed in open ocean environments. This study aims to characterize the optical properties and molecular composition of Sargassum-derived CDOM including its aerobic oxidation and photochemical behavior, as well as quantify Sargassum-derived CDOM to better estimate its possible contribution to the CDOM pool in the Sargasso Sea and Gulf of Mexico.