Temporal variability in Coal Oil Point Marine Hydrocarbon Seep Field emissions, 1940-present: Driving Factors and Global Implications

Abstract:

The Coal Oil Point (COP) seep field, is one of the strongest natural marine hydrocarbon seep fields and is located in near-shore, shallow waters of the northern Santa Barbara Channel, Southern California. Accessibility have arguably made it the best-studied seep field in the world. Seep field observations include five sonar / seep location surveys spanning seven decades, continuous atmospheric total hydrocarbon concentration measurements spanning three decades, six years of beach tar accumulation data, as well as detailed studies of seabed and atmospheric emissions and their composition, and oil emissions assessments. Order of magnitude or larger variations on a vast range of times scales both episodic and non-episodic are observed. Key factors on seasonal and shorter time scales are storms, tides, hydrostatic pressure and oiliness. On longer time scales (multi-year to multi-decadal) processes that can affect migration drive temporal and spatial variability, from shallow reservoir depletion/recharge to migration pathways deposition and formation, seismicity, and earth tides. Long-term data, such as available for the COP seep field are critical to accurate assessment of annualized emissions and their ecosystem and atmospheric implications.

The fate of the gaseous emissions depends on the water column/atmosphere partitioning, which depends on seabed depth, bubble size, bubble plume intensity, oiliness, and water column transport. The fate and impacts of the emitted oil depend on the sea-surface/water column/seabed and beach partitioning, which in turn depends on transport from winds, currents, and waves and weathering.