Climatically driven emissions of hydrocarbons from marine sediments during deglaciation

Abstract

Marine hydrocarbon seepage emits oil and gas, including methane (Ϸ30 Tg of CH4 per year), to the ocean and atmosphere. Sediments from the California margin contain preserved tar, primarily formed through hydrocarbon weathering at the sea surface. We present a record of variation in the abundance of tar in sediments for the past 32,000 years, providing evidence for increases in hydrocarbon emissions before and during Termination IA [16,000 years ago (16 ka) to 14 ka] and again over Termination IB (11-10 ka). Our study provides direct evidence for increased hydrocarbon seepage associated with deglacial warming through tar abundance in marine sediments, independent of previous geochemical proxies. Climate-sensitive gas hydrates may modulate thermogenic hydrocarbon seepage during deglaciation.methane ͉ paleoclimate ͉ Quaternary climate ͉ hydrate ͉ tar

Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments

“…While we cannot rule out a fractionation accompanying degradation of n-alkanes, the pattern is more easily explained by the preferential degradation of terrestrial leaf-wax n-alkanes relative to fossil carbon sources. This phenomenon is potentially related to the inaccessibility of petroleum hydrocarbons associated with tar particles abundant in SBB sediments (Hill et al, 2006). A similar mechanism has been invoked to explain the down-core trend in alkenone 14 C content for the SBB by Mollenhauer and Eglinton (2007).…”

The radiocarbon age of organic carbon in marine surface sediments

“…These may take the form of combustion residues (black carbon), oil spills, organic materials synthesized from petrochemical feedstocks or other inputs (Griffith et al, 2009). Natural sources of fossil carbon emanating from the seafloor may also be significant (e.g., petroleum or methane seeps) (Kvenvolden and Harbaugh, 385 1983;Hill et al, 2006;Pohlman et al, 2009).…”

Geotechnical characterization and strain analyses of sediment in the Mauritania Slide Complex, NW-Africa

“…In contrast, the oldest debris flow unit was emplaced <24 ka BP (the 14 C-age of the underlying hemipelagite), which is known as a period of decreasing sea-level; the maximum sea-level lowstand occurred at about 20 ka BP (Siddall et al, 2003). During periods of sea-level fall/ lowstand such as the Last Glacial Maximum (LGM), hydrostatic pressure decreased, may have exposed gas seeps on the continental shelf or upper continental slope (Luyendyk et al, 2005;Hill et al, 2006). Migration of the free gas through the sediment column may have led to a decrease in sediment strength, which is favored by excess pore pressures.…”