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To advance national and state renewable energy goals, the Bureau of Ocean Energy Management (BOEM), USGS, and the State of California are considering the implications and potential impacts of wind energy development miles offshore of Morro Bay in southern California.

A group of smiling men and women wearing lifejackets pose on the bow of a ship at sea with a bridge far off in the distance.
The USGS California Deepwater Investigations and Groundtruthing, or Cal DIG I, science crew aboard research vessel Bold Horizon on San Francisco Bay.

BOEM, along with USGS researchers from the Pacific Coastal and Marine Science Center (PCMSC) and partners, identified a study area west of Morro Bay where high winds could be harnessed for renewable energy. The final report of a three-part analysis compiled by USGS titled California Deepwater Investigations and Groundtruthing (Cal DIG) I was published in April 2022.  

Cal DIG I comprises three reports: A biological analysis of seafloor video data collected in the study area (published June 2021); an analysis and report on geologic properties and related hazards (published November 2021); and an analysis and characterization of seafloor habitats (published April 2022). The reports are based on data collected from a series of research cruises that took place from 2016 to 2019; some of these cruises were conducted in conjunction with the EXpanding Pacific Research and Exploration of Submerged Systems project. 

The Morro Bay study area, located three miles offshore at depths of 500 to 1,200 meters, is considered an area of high wind resource and is adjacent to waters used for commercial and recreational fishing, tourism, oil and gas extraction, multiple defense installations, and major shipping routes. Additionally, the study area is directly offshore from a decommissioned nuclear power plant with a developed electric grid connection, meaning that much of the infrastructure needed to transmit wind-driven energy is already in place.  

Two men stand on the deck of a ship, and one is giving hand signals while they retrieve a large instrument from the ocean.
Retrieving the MBARI (Monterey Bay Aquarium Research Institute) MiniROV from the Pacific Ocean offshore of California, on research vessel (R/V) Bold Horizon.

BOEM is the lead agency responsible for planning and leasing in the U.S. Exclusive Economic Zone, which extends 200 miles from the U.S. shoreline. BOEM funded Cal DIG I to assess baseline conditions of, and the potential effects on, the study area’s seafloor environment. 

First, the researchers used multibeam echosounders to map the depth and induration, or rockiness, of the seafloor with sonar. Seismic reflection data were collected to determine sediment thickness and the presence of tectonic faults. The team also collected sediment cores and examined the layers of sediment stretching back into geologic time, piecing together a seismic history of the area.  

Then they used remote-operated submersible vehicles equipped with video cameras to identify and characterize biotic communities on the seafloor. “The two most important variables for determining the assemblages of organisms you’re going to find down there with the ROV are substrate type and depth,” said Guy Cochrane, PCMSC Research Geophysicist and lead author of the latest report. “Either it’s rough, rocky substrate; flat, hard substrate; or soft, sediment substrate.” 

Finally, these data were used to create a numerical classification model—combining data on depth, induration, and associated biotic communities—that could be extrapolated from the existing video footage across the entire 8,424-square-kilometer study area. 

“For the numerical classification, I look at a small subset of the video footage aligned with the derivatives of our multibeam data. Then I can use the statistics of this ‘known’ section of seafloor to classify the unknown areas where there’s no video,” Cochrane said. “The remaining video footage can then be used to fine-tune the accuracy of the classification. Our target is 80 percent accuracy or higher.” 

As the Cal DIG I reports note, there is a critical need for seismic fault mapping, seafloor mapping, understanding of sediment dynamics, and site-characterization information to evaluate the structural integrity of proposed energy projects and the environmental impacts to seafloor habitats. In order to make environmentally sound decisions about managing energy activities and developing mitigation measures, the potential direct, indirect and cumulative impacts of offshore development on the human, coastal, and marine environments must be evaluated.

Critters on the bottom of the ocean, a sea star, skate, and rockfish.
A small juvenile skate (left) and a large rockfish (right) hang out on the murky, silty seafloor with sea stars, offshore of Morro Bay, California. Water depth: 856 m (2808 ft).
Anemones attached to a rocky outcrop on the seafloor.
These “pom-pom” anemones (Liponema sp.) have attached to the rock where the currents likely are favorable, supplying them with small floating particles of food. Water depth: 1041 m (3415 ft).

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