A Synthesis Review of Emissions and Fates for the Coal Oil Point Marine Hydrocarbon Seep Field and California Marine Seepage

Abstract

Anthropogenic oil in the ocean is of great concern due to its potential immediate and long-term impacts on the ecosystem, economy, and society, leading to intense societal efforts to mitigate and reduce inputs. Sources of oil in the ocean (in the order of importance) are natural marine seepage, run-off from anthropogenic sources, and oil spills, yet uncertainty and variability in these budgets are large, particularly for natural seepage, which exhibits large spatial and temporal heterogeneity on local to regional scales. When source inputs are comparable, discriminating impacts is complicated, because petroleum is both a bioavailable, chemosynthetic energy source to the marine ecosystem and a potential toxic stressor depending on concentration, composition, and period of time. This synthesis review investigates the phenomena underlying this complexity and identifies knowledge gaps. Its focus is on the Coal Oil Point (COP) seep field, arguably the best-studied example, of strong natural marine hydrocarbon seepage, located in the nearshore, shallow waters of the Northern Santa Barbara Channel, Southern California, where coastal processes complicate oceanography and meteorology. Many of our understandings of seep processes globally are based on insights learned from studies of the oil and gas emissions from the COP seep field. As one of the largest seep fields in the world, its impacts spread far as oil drifts on the sea surface and subsurface, yet much remains unknown of its impacts.

Bubble-mediated transport of benthic microorganisms into the water column: Identification of methanotrophs and implication of seepage intensity on transport efficiency

“…Water column temperature profiles taken over the course of the sampling campaign indicated the buildup of a thermocline over several hours that then collapsed from mixing during the course of the day (data not shown). Throughout the sampling campaign, bottom currents followed the coast, consistent with typical northern Santa Barbara Basin currents, which are driven by the Davidson Current 41 . Water column turbidity changed on a daily basis, resulting in a visibility that ranged from <0.5 m up to 10 m (reported by divers).…”

“…4d). However, as the bubble mediated transport itself is coupled to the volumetric gas flow, we propose that factors influencing this flow, such as hydrostatic pressure 53 (including waves and tides) 41,54 and temperature 55 , likely affect the transportation rate of MOBs though these were beyond the scope of the data collected.…”

“…Even if MOB cell division (about 3 days) 37 within the methane-enriched plume water would further shorten these transportation times, our assessment shows that a relevant part of the water-column MOB stock was likely transported from gas-releasing seep sites further upstream from the COP seep field. Such a scenario is likely since the shallow waters along the southern Californian coast harbor gas-bubble releasing seep sites for at least over 100 km upcurrent 41,67 . These seeps will contribute to a high ambient water column MOB concentration while the waters are transported northwards by the coastal current system [67][68][69] .…”

“…The Coal Oil Point (COP) seep in southern California, USA, extends from the coastline to 3-4 km offshore, with seepage from water depths of a few meters up to 80 m (Fig. 6) 41,78,79 . COP seeps are primarily or entirely supplied by gas, mostly methane (>90%), from the underlying Monterey Formation through faults and fractures in the overlying Sisquoc Formation 78 .…”

Using Time-Series Videos to Quantify Methane Bubbles Flux from Natural Cold Seeps in the South China Sea

“…Methane bubble seep is driven by a pressure difference between the reservoir pressure and the hydrostatic pressure along multiple migration pathways, with higher methane bubble fluxes typically associated with higher permeability pathways [21]. In order to model these complex methane bubble seep systems, an effective seep electrical model was adopted [7,22]. In this model, the electrical circuit components represent methane fluid dynamic processes driven by an oil or gas reservoir [22].…”