Deepwater Horizon Oil in Gulf of Mexico Waters after 2 Years: Transformation into the Dissolved Organic Matter Pool

Abstract

Recent work has shown the presence of anomalous dissolved organic matter (DOM), with high optical yields, in deep waters 15 months after the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico (GOM). Here, we continue to use the fluorescence excitation-emission matrix (EEM) technique coupled with parallel factor analysis (PARAFAC) modeling, measurements of bulk organic carbon, dissolved inorganic carbon (DIC), oil indices, and other optical properties to examine the chemical evolution and transformation of oil components derived from the DWH in the water column of the GOM. Seawater samples were collected from the GOM during July 2012, 2 years after the oil spill. This study shows that, while dissolved organic carbon (DOC) values have decreased since just after the DWH spill, they remain higher at some stations than typical deep-water values for the GOM. Moreover, we continue to observe fluorescent DOM components in deep waters, similar to those of degraded oil observed in lab and field experiments, which suggest that oil-related fluorescence signatures, as part of the DOM pool, have persisted for 2 years in the deep waters. This supports the notion that some oil-derived chromophoric dissolved organic matter (CDOM) components could still be identified in deep waters after 2 years of degradation, which is further supported by the lower DIC and partial pressure of carbon dioxide (pCO2) associated with greater amounts of these oil-derived components in deep waters, assuming microbial activity on DOM in the current water masses is only the controlling factor of DIC and pCO2 concentrations.

Linking optical and molecular signatures of dissolved organic matter in the Mediterranean Sea

“…These compounds were negatively correlated with peak M*, fluorescence ratios A/T, C/T and M/T and BIX and positively with peak T*, a 254* and HIX. These findings are in agreement with the fact that some polyphenols fluoresce in an area relatively close to the protein-like substances region 58, 71 . Furthermore, it was suggested that hydrocarbons are detected in the peak T* region 27 .…”

Characterization of hydraulic fracturing flowback water in Colorado: Implications for water treatment

“…Investigations into crude oil in the Gulf of Mexico have also associated fluorescence signatures similar to those in Fig. 3 with the presence of hydrocarbons (Bianchi et al, 2014). These observations suggest that waters impacted by hydrocarbons (e.g., flowback, produced water, and crude oil in ocean) may have a similar fluorescence signature characterized by blue-shifted intensity (predominantly less than 400 nm).…”

Impact of Photooxidation and Biodegradation on the Fate of Oil Spilled During the Deepwater Horizon Incident: Advanced Stages of Weathering

“…The general absorbance features in this range of wavelengths of the sand patty-derived DOM were reminiscent of other reports of DOM emanating from the weathering of the Deepwater Horizon oil. 53 Most notably, the quantitative increase in aromatic DOM constituents formed as a result of natural weathering processes seems to be a generalizing feature of oil decomposition. 24 An assessment of the aerobic biodegradability of sand patty-derived DOM was examined by comparing the rate of oxygen consumption in sediment samples amended with dark or irradiated DOM, whole sand patty material or only endogenous organic matter.…”