Area 2

core area 2 map&text

Area Two is located off the California Central Coast between the Channel Islands and Monterey Bay National Marine Sanctuaries. Within its boundaries are an upthrust block, a mile deep sea canyon, and seamount. The Santa Lucia Bank uptrust block rises to within 400 meters of the ocean surface 30 to 40 miles offshore from the north face of the Arguello Canyon to offshore Morro Bay. This area lies within the Oceanographic and Meteorological transition zone of the Oregonian and Californian Providences at the complex meeting place of south and north moving major warm and cold ocean currents. Topography within the boundary — the Rodriquez Seamount, the Arguello Canyon, Santa Lucia Bank and the Santa Lucia Escarpment — and adjacent topography to its south area outside the boundary line — the Southern California Bite and the Channel Islands — enhances a meeting place of these major ocean currents that guides and funnels the West Coast’s only persistent upwelling that rise between Points Arguello and Sal.

upwelling currents

This unique oceanographic combination of the mile deep canyon, through which California’s and also the West Coast’s only persistent upwelling flows, the Santa Lucia Bank uptrust block, and the Rodriguez Seamount create the ideal conditions for an internationally and nationally significant diverse density of marine life. Whales and birds come from as far as Hawaii to feed during the fall at the Santa Lucia Bank. The density and diversity of life is equivalent to the former abundant life of Georges Bank, offshore between Cape Cod, Massachusetts and Cable Sable Island, Nova Scotia.

 

Area Two’s complex topography is the result of the meeting place of three major tectonic plates.

The Farallon Plate, moving eastward was subducting beneath the North American Plate. As the Pacific Plate moved northwest, the subduction eventually ceased in our area. Remnants of the Farallon Plate, microplates, were captured by the Pacific Plate beneath the North American Plate; continental margins of the North American Plate became part of the Pacific Plate. That is, all land and sea floor west of the San Andreas Fault that was part of the North American Plate, became part of the Pacific Plate. The microplates ride the Pacific plate. (Neogene Deformation History of Western North America and Volcanism in Coastal California)

As the Pacific Plate continued its northwest migration subducting under Alaska, it rotated the Arguello Microplate, also known as the Transverse block, forming the Southern California Bite. It is bordered on its eastern side by the Transverse Range, on the west side by the Channel Islands with the Ventura-Santa Barbara Basin in the middle, and to its north, the Arguello Canyon. The rotation ended with the capture of Baja that now presses against this block causing folding and uplift.

The Monterey Microplate from the Farallon Plate, beneath western Santa Barbara County and San Luis Obispo County, is bordered on the east by the San Andreas Fault, on the west by the Santa Lucia Bank and the Santa Lucia Escarpment and on the south boundary by the Arguello Microplate. This boundary’s exact location is within the Arguello Canyon. The Monterey Microplate is deformed with a subsistence slant from the coastline to the Santa Lucia Bank. The Santa Lucia Bank is tilted with the uptrust on its eastern most side. Running nearshore is the Hosgri Fault, another huge crack in this microplate.FIG 4.3

FIG 4.1Geomorphology of Eastern Santa Cruz Island Field Guide; Chapter 4, page 31

The Rodriguez Seamount, a volcanic geological formation, is about 90 miles offshore in the southern area of the opening of the Arguello Canyon. Whether the submerging of the seamount was caused by internal volcanic collapse, a victim of tectonic forces or a combination of both is a research project. Its topography is complex with many volcanic cones, one of which is among the largest found along the California coast. Being located on the Arguello Canyon’s south face with the San Miguel Gap to its south, and located in a meeting place of cold and warm currents, the Rodriguez Seamount hosts a complex marine habitat. The sandy beach remnants, for example, have been colonized by a large number of sea cucumbers. Other seamounts have few if any sea cucumbers. There has yet to be a comparison of marine life between the walls of the Arguello Canyon and the Rodriguez Seamount.

What has been found is significant. “Amazingly, biological communities varied significantly even in similar habitats at similar water depths on different parts of Rodriguez Seamount. The seamount’s megafauna consist of a vast array of sponges, including large, brilliant-yellow barrel sponges, many types of coral—including large gorgonians and huge golden coral seafans —abundant brittlestars, crinoids, clams, seastars, polychaete worms, crabs, tunicates, sea urchins, sea cucumbers, octopi, and many more. The giant sponges housed communities of other organisms. New species were found, and some species were rediscovered after not being observed for decades.”

Geologists and Biologists Endeavor to Understand Seamount Environments Off California, Jim Hein Dec. 2003 / Jan. 2004

seamount-1seamount-2

http://www.mbari.org/data/mapping/Santa Barbara Basin/rodriguez.htm

Benthic communities of world-wide significance thrive in the area. The high diversity and density of benthic populations resemble the North Sea and the Georges Bank, which have been two of the most productive regions in the world. The meiofaunal community is among the highest density reported worldwide. The macroinfauna diversities and abundances are much larger than those north or south along the coast of California. The abundance of benthic populations appears related to the area’s unique combination of characteristics the transition zone, the geology of the area, composition of the sea floor, complex currents, and the upwelling itself.

The Santa Lucia Bank area is frequently visited year round by cetaceans (whales, porpoises, dolphins). During the Fall season, at least 13 species of cetaceans have been observed, including simultaneous feeding bouts among humpback, Baird’s, fin, blue, and sperm whales and smaller species.

Numerous fish species are harvested commercially. Among harvested species are sablefish, dover sole, shortspine, longspine, and rex sole. Flora and fauna of the area are associated with two distinct oceanographic and climatic provinces. The habitat is the southern boundary of the range for many northern species, and the northern boundary for southern species.

Ecosystem-based Research

Further research is needed to study the number of bird and fish species found at the Santa Lucia Bank during different seasons. Large numbers of birds have been observed by fishermen during feeding periods. Density maps of seabird populations illustrate the richness of the area. Eastward of the Santa Lucia Bank are a number of unanalyzed spawning areas for fish.

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