Fig 1.
Sites of sediment collection for time series (green), high PAH (yellow), and RPO analysis (red).
Table 1.
Sites examined in this study, measurements performed, location and date.
Fig 2.
Bulk radiocarbon signatures of time series and high PAH sediment from DWH affected sites and natural seep GC600.
A) GIP07 and replicate cores from mega seep site GC600, B) GIP17, C) GIP16, D) GIP24, E) high PAH sites reported by Mason et al. [23] sampled in 2015 and Site BP444 revisited in 2017. Bulk Δ14C values of sediment in A-D exhibit recovery back to baseline values, while the high PAH sites in E indicate that not all sites had returned to baseline-like values.
Fig 3.
A) Crude Oil, Seep site GC600 and Control site GB480, B) GIP17, crude oil and control site, C) BP444, crude oil and control site, D) GIP07, crude oil and control site. Vertical “tic” marks designate temperature boundaries of isotopic sample collections.
Fig 4.
Percent CO2 evolved from low (300°C), medium (300–500°C) and high (>500°C) temperature.
Table 2.
Comparison of bulk measured isotopic values vs RPO weighted average bulk values.
A paired t-test indicated no difference for Δ14C values, p = 0.259, t = 1.103, while bulk measured Δ 13C values were significantly enriched relative to the RPO weighted average (p = 0.002, t = 4.158).
Table 3.
Percent of CO2 evolved at low, medium, and high temperatures.
Fig 5.
CO2 thermograph and isotopic composition of evolved CO2.
Temperature interval of CO2 fractions indicated by horizontal bars. A) Control site GB480: Δ14C, B) Control site GB480 δ13C, C) Seep site GC600 Δ14C, D) Seep site GC600 δ13C.
Table 4.
Summary of ramped pyrolysis/oxidation (RPO) results.
Fig 6.
CO2 thermograph and isotopic composition of evolved CO2 for site GIP 17.
Temperature interval of CO2 fractions indicated by horizontal bars. A) GIP17 2010 Δ14C, B) GIP17 2010 δ13C, C) GIP17 2011 Δ14C, D) GIP17 2011 δ13C, E) GIP17 2015 Δ14C, F) GIP17 2015 δ13C.
Fig 7.
CO2 thermograph and isotopic composition of evolved CO2 for site GIP07.
Temperature interval of CO2 fractions indicated by horizontal bars. A) GIP07 2010 Δ14C, B) GIP07 2010 δ13C, C) GIP07 2011 Δ14C, D) GIP07 2011 δ13C, E) GIP07 2014 Δ14C, F) GIP07 2014 δ13C.
Fig 8.
CO2 thermograph and isotopic composition of evolved CO2 for high PAH site BP444.
Temperature interval of CO2 fractions indicated by horizontal bars. A) 0-1cm Δ14C, B) 0-1cm δ13C, C) 1-2cm Δ14C, D) 1-2cm δ13C, E) 3-4cm Δ14C, and F) 3-4cm δ13C.
Fig 9.
Plot of RPO averaged Δ14C and δ13C from each site.
Darker shades are more contaminated, shifting towards lighter shades of the recovered time points. Dash) Overall regression (y = 92.295x + 1824.9, r = 0.9187, n = 11, p < 0.0001), time series sediments: Red) GIP17 (y = 100.06x + 2021.5, r = 0.9217, n = 3, p = 0.0783), Blue) GIP07 (y = 184.68x + 4072.6, r = .9999, n = 3, p < 0.001), Aqua) depth trend from BP444 (y = 257.42x + 5431.4, r = 0.9843, n = 3, p = 0.0157).
Table 5.
Estimated percent petrocarbon from RPO analyzed sediments using a 14C mass balance with 2 endmembers, petrocarbon at -1000‰ and background at -200‰.
Table 6.
Sensitivity test for 2 end member model estimating percent carbon sources.