Fig 1.
Locations of 13 sampling sites across the Northern Gulf of Mexico at water depth ranging from 60–1520m. Circles are color-coded representing total organic content (TOC, percent weight of sediments). Schlitzer, R., Ocean Data View, http://odv.awi.de, 2016.
Table 1.
Physical conditions of sediment sites and laboratory incubation conditions.
(CTD: conductivity-temperature-depth device, P: pressure, T: temperature).
Fig 2.
Chromatograms of crude oil biodegradation.
Examples of total ion chromatograms of oil extract (normalized to C30 hopane) from two extremes of biodegradation at different water depths (nC17 = C17 n-alkane, nC18 = C18 n-alkane, Pr = Pristane, Phy = Phytane).
Fig 3.
Depletion of total n-alkane (%) after 18 days of incubation in both water fraction (WAF, triangles) and sediment fraction (SED, circles), the dashed arrow is interpreted as the direction of increasing biodegradation extent: A, All samples: Initial total n-alkanes are represented by squares. Samples are color-coded according to sampling water depths and B, Inhibitory effect of pressure on n-alkane biodegradation at 4°C. Error bars represent one standard deviations from the means.
Table 2.
Comparison in biodegradation of n-alkanes and PAHs between shallow (< 500 m) and deep (> 500 m) sediments.
Fig 4.
Depletion of total PAH (%) of crude oil in sediment fraction (SED, circles) at after 18 days of incubation. The dashed arrow is interpreted as the direction of increasing biodegradation extent. A, All samples: Initial total PAHs are represented by squares. Samples are color-coded according to sampling water depths. Depletion in deep water samples are possibly due to off-gassing effect. B, Distinguishing biodegradation from off-gassing, using different isomer ratios of methylated-PAHs (MF: methyl fluorene m/z 180; MD: methyldibenzothiophene m/z 198; MP: methylphenanthrene m/z 192). Samples are color coded by pressures (MPa). Error bars represent one standard deviations from the means.
Table 3.
Comparison of total n-alkane depletion percent (mean ± one standard deviation) between high in-situ pressure incubation of the three deepest sites and their ambient pressure (0.1Mpa) incubation counterparts.