Natural and unnatural oil slicks in the Gulf of Mexico

Abstract

When wind speeds are 2–10 m s −1 , reflective contrasts in the ocean surface make oil slicks visible to synthetic aperture radar (SAR) under all sky conditions. Neural network analysis of satellite SAR images quantified the magnitude and distribution of surface oil in the Gulf of Mexico from persistent, natural seeps and from the Deepwater Horizon (DWH) discharge. This analysis identified 914 natural oil seep zones across the entire Gulf of Mexico in pre‐2010 data. Their ∼0.1 µm slicks covered an aggregated average of 775 km 2 . Assuming an average volume of 77.5 m 3 over an 8–24 h lifespan per oil slick, the floating oil indicates a surface flux of 2.5–9.4 × 10 4 m 3 yr −1 . Oil from natural slicks was regionally concentrated: 68%, 25%, 7%, and <1% of the total was observed in the NW, SW, NE, and SE Gulf, respectively. This reflects differences in basin history and hydrocarbon generation. SAR images from 2010 showed that the 87 day DWH discharge produced a surface‐oil footprint fundamentally different from background seepage, with an average ocean area of 11,200 km 2 (SD 5028) and a volume of 22,600 m 3 (SD 5411). Peak magnitudes of oil were detected during equivalent, ∼14 day intervals around 23 May and 18 June, when wind speeds remained <5 m s −1 . Over this interval, aggregated volume of floating oil decreased by 21%; area covered increased by 49% ( p < 0.1), potentially altering its ecological impact. The most likely causes were increased applications of dispersant and surface burning operations.

Responses of Microbial Communities to Hydrocarbon Exposures

“…Chemical dispersants emulsify oil and break up surface slicks, generating dispersant-stabilized oil micro-droplets that dissolve into surface waters, effectively increasing the volume of water polluted with discharged oil (MacDonald et al, 2015). By breaking up surface slicks, dispersant utilization can reduce the amount of thick oil stranded along shorelines and increase the oil-seawater interfacial area.…”

Exploring the Ecology of Deep-Sea Hydrothermal Vents in a Metacommunity Framework

“…Vertical larval transport in the buoyant seep bubble plumes may also enhance dispersal. Worldwide estimates of the number of seeps have been revised upwards to the tens of thousands, largely due to the ability to detect seepage with bubble plumes (Skarke et al, 2014) and oil slicks (MacDonald et al, 2015). Individual seeps are often clustered at the scale of kms (e.g., Sahling et al, 2008), likely enhancing the probability of seep detection by settling larvae.…”

Isotopic composition of sinking particles: Oil effects, recovery and baselines in the Gulf of Mexico, 2010–2015

“…That equilibria are reached at different speeds for differing processes is not surprising. For example, in terms of floating surface oil, the recovery period was weeks following the spill (MacDonald et al, 2015). Regarding the presence of drilling muds in sinking material, the recovery time was in months (Yan et al, 2016).…”