Stable and radiocarbon isotopic composition of dissolved organic matter in the Gulf of Mexico

Abstract

Dissolved organic carbon (DOC) is of primary importance to marine ecosystems and the global carbon cycle. Stable carbon (δ13C) and radiocarbon (Δ14C) isotopic measurements are powerful tools for evaluating DOC sources and cycling. However, the isotopic signature of DOC in the Gulf of Mexico (GOM) remains almost completely unknown. Here we present the first DOC Δ14C and δ13C depth profiles from the GOM. Our results suggest the Mississippi River exports large amounts of DOC with an anthropogenic “bomb” Δ14C signature. Riverine DOC is removed and recycled offshore, and some marine production of DOC is observed in the river plume. Offshore profiles show that DOC has higher Δ14C than its Caribbean feed waters, indicative of a modern deep DOC source in the GOM basin. Finally, high DOC with negative δ13C and Δ14C values were observed near the Macondo Wellhead, suggesting a transformation of Deepwater Horizon hydrocarbons into a persistent population of DOC.

Hydrocarbon degradation and response of seafloor sediment bacterial community in the northern Gulf of Mexico to light Louisiana sweet crude oil

“…This depletion can be attributed to the combined effects of dissolution and biodegradation [12,13]. In fact, microbially sourced radiocarbon-depleted organic molecular species were observed in the water column 4 years after the spill event, potentially accounting for a large proportion of "missing" spilled hydrocarbon [14].…”

Temporal Variability of Polycyclic Aromatic Hydrocarbons in Deep-Sea Cephalopods of the Northern Gulf of Mexico

“…Of all the species studied, H. corona is the only one that lives in the mesopelagic zone and does not migrate to the surface to feed ( Supplementary Table S1). Oil-residues have been observed in the water column years after the spill (Walker et al, 2017), probably from resuspension of contaminated sediments (Romero et al, 2017;Diercks et al, 2018). It is possible that the dietary intake for H. corona was affected like the other species studied (Figure 3), but with an extended period of exposure to oilresidues persistent at depth.…”

“…Oil residues from the DWHOS have persisted in the deep-pelagic habitat of the GoM longer than anticipated. For example, 4-6 years after the DWHOS as found in the water column and in deep-pelagic fishes (Walker et al, 2017;Chanton et al, 2018;Romero et al, 2018). The potential consequences of the DWHOS on deep-pelagic invertebrates are yet to be determined, as exposure to oil-derived toxic compounds has not been previously studied in invertebrates from the pelagic domain of the GoM.…”

UV Photochemical Oxidation and Extraction of Marine Dissolved Organic Carbon at UC Irvine: Status, Surprises, and Methodological Recommendations

“…One split (2-800 μgC) is graphitized via sealed-tube Zn reduction (Xu et al 2007;Walker and Xu 2019) for accelerator mass spectrometry radiocarbon (AMS 14 C) measurements. The other split is cryogenically transferred to 3 mm diameter, 5.5 cm length, Pyrex tubes for δ 13 C analysis with a Gas Bench II and Finnigan Delta Plus IRMS (Walker et al 2017). Consensus values for isotopic standards are either known (e.g.…”