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The study, conducted in an area slated for the development of a wind farm offshore of Central California, mapped more than 5,000 pockmarks at depths ranging from 500 to 1,500 meters. Researchers used an array of tools, including high-resolution seafloor maps, video footage, sediment cores, and subsurface images, to investigate these curious formations.

Contrary to the prevalent belief that many pockmarks are created and maintained by methane seepage, the collected data revealed no significant signs of methane gas. Instead, the team found that the pockmarks contain alternating layers of fine sediments and sandy deposits. The sandy layers, identified as turbidites, are the result of large sediment flows that periodically scour the pockmark centers. 

These turbid sediment flows not only carve out the pockmarks but also cause them to shift positions, sometimes over distances of tens of kilometers. This phenomenon has been occurring intermittently over the past 280,000 years, continuously reshaping the seafloor.

Interestingly, the study found that the pockmarks are not randomly scattered but are distributed in a regular, equally spaced pattern. This regular spacing further supports the hypothesis that the pockmarks are maintained by periodic sediment flows rather than by random methane fluxes.

The findings have significant implications for the proposed wind farm project. Understanding the provenance of these pockmarks allows development to proceed with a clearer picture of the seafloor's stability and history, minimizing potential risks to infrastructure.

Read a related press release from MBARI.

Read the study, Pockmarks Offshore Big Sur, California Provide Evidence for Recurrent, Regional, and Unconfined Sediment Gravity Flows, in the Journal of Geophysical Research: Earth Surface.

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