Abstract:

Mesocosm experiments was conducted in May 2019 as part of ADDOMEx-2 program funded through the Gulf of Mexico Research Initiative (GoMRI). Marine oil snow samples were collected during the mesocosm experiments and subjected to solid-state 13C nuclear magnetic resonance (NMR) spectroscopic analysis before and after dichloromethane extraction. The data contained in this dataset represents the raw chemical shift and intensity data obtained directly from the instrument. There are eight samples and sixteen NMR spectra results included in this dataset.

Suggested Citation:

Chen, Hongmei and Patrick Hatcher. 2020. Molecular level characterization of oil and aggregate oxidation products: LTOPOS, a Long Term Oil and Particle Oxidation Study, Nuclear magnetic resonance (NMR) data. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/5ZC7V4G9

Purpose:

With the higher resolution of sampling time points, the goal is to examine the molecular level dynamic changes in sinking aggregate organic matter (OM), sinking aggregates OM impacted by oil, and sinking aggregates OM impacted by oil and dispersant mixtures.

Data Parameters and Units:

Data file naming convention includes the mesocosm experiment number (M7), treatment (control, dilute chemically enhanced water accommodated fraction of oil = DCEWAF), time since start (in days), marine oil snow (MOS), and processing state (before or after dichloromethane[DCM] extraction). For example, “M7_DCEWAF_Day1_MOS_Before_DCM.xls” is the NMR result for particles (i.e., MOS) produced in the seawater that was mixed with diluted chemically enhanced water accommodated fraction of oil, at time Day 1, from May 2019 Mesocosm 7 experiment. And the NMR result for the insoluble part of this MOS particle sample after DCM extraction was named as “M7_DCEWAF_Day1_MOS_After_DCM.xls” accordingly. Spectral Intensity (Int.) = the spectral response (arbitrary units) at the given chemical shift Chemical Shift = parts per million (ppm).

Methods:

Marine snow from control samples and marine oil snow (MOS) from dilute chemically enhanced water accommodated fraction of oil (DCEWAF) samples were freeze-dried prior to analysis. After initial 13C NMR analysis on the whole particle (“Before DCM”), samples were extracted with dichloromethane (DCM) solvent to remove oil-associated components (Reference 1). DCM-insoluble particles were isolated, freeze-dried, saved for 13C NMR analysis, and named as “After DCM” samples. Solid-state 13C NMR analyses were carried out on a Bruker Advance II NMR spectrometer with 1H resonating at 400 MHz and 13C resonating at 100 MHz fitted with a 4mm H-X solid-state MAS probe head. Each sample (~50 mg) was packed into a zirconium rotor and sealed with a Kel-F cap for measurement. Samples were spun at the magic angle (54.7O) at a frequency of 14 KHz. NMR spectra were collected by applying a composite-pulse multiple cross-polarization (multi-CP) pulse sequence previously developed to be quantitative (References 1 & 2). Each sample spectrum was acquired for 20,000 scans, with a recycle delay of 1 s. The relative contributions (%) of total spectral signal) from major carbon moieties present in each sample were obtained by integrating the spectral signal over chemical shift regions corresponding to those major carbon moieties: methylenic C (CHx): 0-45 ppm, αC in peptides: 45-60 ppm, alkyl-O carbon (HCOH): 60-95 ppm, anomeric C (O-C-O): 95-110 ppm, aromatic C (C=C): 110-145 ppm, aromatic-O-carbon (C=C-O): 145-165 ppm, Amide/Carboxyl C (C=O): 165-215 ppm. The sum of all integrals together was set to equal 100%. The seawater used in the Test of Coastal water with coastal microbial concentrate (TeCOAST) mesocosm studies was collected ~0.5 km offshore south of Galveston (Texas) on May 7, 2019, from the Gulf of Mexico. Water was settled in large tanks to remove large particles and debris before collection. A plankton concentrate was collected nearby in Galveston Bay using a mesh size of 63 µm plankton net; 2 L of this “concentrate” was added to all mesocosm treatments, immediately prior to the start of the experiment to make a final volume of 102 L per mesocosm. The control tank was filled with the seawater directly from the storage tank of filtered seawater plus the added plankton concentrate. This seawater was also used to fill recirculating glass flumes (References 3, 4, & 5) to make water accommodated fraction (WAF) and a chemically enhanced water accommodated fraction of oil (CEWAF). A PTFE stopcock 10 cm off the bottom of the tank was used for sampling. The oil used was Macondo “surrogate” oil from the Marlin Platform Dorado and the dispersant used was Corexit. The WAF mixture was prepared by mixing 25 mL oil with ~130 L seawater in a stirring baffled recirculating borosilicate glass tanks of 170 L capacity (43 × 88 × 44 cm) and allowed to equilibrate over 24 hours. After that, only the aqueous phase at the bottom layer (no surface slick: the WAF fraction) was removed and added to the mesocosm tanks. CEWAF was made by adding dispersant to the oil at a ratio of oil‐to‐dispersant of 20:1. The DCEWAF was prepared by diluting the CEWAF with seawater.

Instruments:

Avance II 400 MHz nuclear magnetic resonance spectroscope.

Provenance and Historical References:

[1] Hatcher, P. G., Obeid, W., Wozniak, A. S., Xu, C., Zhang, S., Santschi, P. H., & Quigg, A. (2018). Identifying oil/marine snow associations in mesocosm simulations of the Deepwater Horizon oil spill event using solid-state 13 C NMR spectroscopy. Marine Pollution Bulletin, 126, 159–165. doi:10.1016/j.marpolbul.2017.11.004 [2] Johnson, R. L., & Schmidt-Rohr, K. (2014). Quantitative solid-state 13C NMR with signal enhancement by multiple cross polarization. Journal of Magnetic Resonance, 239, 44–49. doi:10.1016/j.jmr.2013.11.009 [3] Wozniak, A. S., Prem, P. M., Obeid, W., Waggoner, D. C., Quigg, A., Xu, C., Santschi, P.H., Schwehr, K.A. & Hatcher, P. G. (2019). Rapid Degradation of Oil in Mesocosm Simulations of Marine Oil Snow Events. Environmental Science & Technology, 53(7), 3441–3450. doi:10.1021/acs.est.8b06532 [4] Knap, A. H., Burns, K. A., Dawson, R., Ehrhardt, M., & Palmork, K. H. (1986). Dissolved/dispersed hydrocarbons, tarballs and the surface microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December 1984. Marine Pollution Bulletin, 17(7), 313–319. doi:10.1016/0025-326x(86)90217-1 [5] Wade, T. L., Morales-McDevitt, M., Bera, G., Shi, D., Sweet, S., Wang, B., Gold-Bouchot, G., Quigg., A. & Knap, A. H. (2017). A method for the production of large volumes of WAF and CEWAF for dosing mesocosms to understand marine oil snow formation. Heliyon, 3(10), e00419. doi:10.1016/j.heliyon.2017.e00419

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