Davidson Seamount

Davidson Seamount is a seamount (underwater volcano) located off the coast of Central California, 80 mi (129 km) southwest of Monterey and 75 mi (121 km) west of San Simeon. Being 26 mi (42 km) long and 8 mi (13 km) wide, it is one of the largest seamounts in U.S. waters, and also the largest in the East Pacific. From base to crest, the seamount is 7,480 feet tall, yet its summit is still 4,101 feet below the sea surface. The seamount is biologically divese, with 237 seperate species and 27 types of deep-sea coral having been identified.

Geology

Structure

A seamount such as Davidson is an underwater volcano; this one rises over 3,280 ft (1,000 m) above the surrounding ocean floor. Although there are over 30,000 seamounts in the Pacific Ocean alone, only about 0.1% of them have been explored. The aqueous environment of the seamount means that it behaves differently from volcanoes on land. The surface of Davidson Seamount is composed mostly of blocky lava flows, although some pillow lava, which is the typical lava type of a seamount, prevails at the deeper flank. The summit is composed of layered deposits of volcanic ash and pyroclastic material. These rocks indicate mildly explosive eruptions of gas-rich lava near the summit of the volcano. The base of Davidson is probably buried in a deep layer of muds.

At 26 mi (42 km) long and 8 mi (13 km) wide, Davidson Seamount is impressively large. If it were on land, it would dominate the landscape in a way similar to how Mount Shasta dominates the horizon of northern California. Put in perspective, the size of the seamount is enough to fill Monterey Bay from the Santa Cruz boardwalk to Monterey's Fishermen's Wharf.

Davidson Seamount is part of a group of seamounts off the continental margin, including Guide, Pioneer, Gumdrop, and Rodriguez seamounts, all located roughly between 37.5° and 34.0° degrees of latitude. This group of seamounts is morphologically unique, and very similar to one another. All of the seamounts in the group are complex northeast-southwest trending structures, consisting of parallel ridges separated by sediment-filled troughs. The ridges constructed run parallel to an ancient spreading center which has since been replaced in its role by the San Andreas Fault system. They are unique in thi origin, as they are formed from the remnants of an old ocean-ridge spreading center. A series of "knobs" are aligned with the ridges; however the distinctive summit crater, evident in many oceanic volcanoes, is absent. This lack of a collapse crater suggests that magma was never stored in a chamber within the structure, as with most other volcanoes.

Age

Analysis of ar-ar studies indicate that Davidson formed between 9 and 15 million years ago, 5 to 12 million years after the formation of the overlaying oceanic crust.

Ecology

Benthoctopus sp. and a clam at 1,461 m (4,793 ft) depth near the summit of Davidson Seamount.

Studes have indicated that a seamount functions as an "oasis of life," with a higher species count and more biodiversity then the surrounding seafloor. Seamounts rise high in the water column, creating complex current patterns that support life on, around, and above the seamount. The surface of the seamount also provides a substrate upon which organisms can attach themselves and grow. This in turn supports the species that feed on them, in turn supporting the whole ecological food web. Scientists have found that seamounts often provide a habitat for endemic species that don't live anywhere else.

Davidson Seamount is among the best biologically described seamounts worldwide. Six major expeditions to the volcano have yielded over 60,000 species observations. As of 2009 scientists have observed and recorded 168 species of megafauna on the seamount. Of these, about 7% of the species at Davidson are edemetic, meaning they live only at Davidson. 71% of the species can be confidently classified as "cosmopolitan" (widespread), and sufficent data exists for 22% of the observed species to strongly suggest that their range is not limited to seamounts. The remaining 7% have only been seen in video footage. Interestingly, 13 species have been identified in other areas, but never in other seamounts. accessdate=December 3, 2009}}</ref>

The seamount is populated by a large variety of deep-sea corals, most of which in turn provide a habitat for other species. It has in the past been called "An Oasis in the Deep", hosting a vast coral forest, large sponge field, crabs, deep-sea fish, basket stars, and a number of rare benthic species, some of which have yet to be studied properly or even named. These are all cold-water species, as the temperature even at the top of the seamount is just above freezing—around 2 °C (36 °F), as compared to 14 °C (57 °F) at the ocean's surface.

Despite its size, the top of Davidson Seamount remains over 4,500 ft (1,372 m) below the ocean's surface. This great depth means that the habitats that the seamount supports have not been significantly disturbed by human activity; anchoring and trawling typically doesn't occur below a depth of 1,500 ft (457 m), and waste disposal and discharge occurs much closer to shore.

In comparisons drawn to the nearby Monterey Bay National Marine Sanctuary, the two were shown to be very different biologically. Species that are rare in Monterey Bay are common on Davidson, and vice versa.

History

Exploration

George Davidson, for whom the seamount was named.

Davidson Seamount was initially mapped in 1933, and is named for George Davidson, an big figure in the early charting and mapping of the West Coast of the United States. Davidson Seamount was the first underwater volcano to be classified as "seamount" by the United States Board of Geographic Names, in 1938, and was named in honor of the United States Coast and Geodetic Survey scientist George Davidson, one of the key figures in the survey of America's west coast.

Recent expeditions to Davidson have focused on its ecology, and specifically on the variety of deep-sea coral that live among its banks, some being over 100 years of age. These large colonies are extremely fragile to human interaction. A 2002 expedition documented many species of rare, as-of-yet undiscovered species that exist nowhere else, not even on nearby seamounts. Davidson's proximity to scientific research institutions has helped its exploration, as multiple dives, mappings, and studies have made it one of the better-studied seamounts in the world. The 2002 exploration was followed by another one in 2006.

As a Marine Sanctuary

Diagram illustrating the orientation of the 3 marine sanctuaries of Central California: Cordell Bank, Gulf of the Farallones, and Monterey Bay. Davidson Seamount, part of the Monterey Bay sanctuary, is indicated at bottom-left.

A key group of research scientists, fishermen, officials, educators, and marine biologists was formed in 2006 to discuss whether or not to make Davidson Seamount a National Marine Sanctuary under the National Marine Sanctuaries Act, and if so whether to make it its own sanctuary, or incorporate it into the nearby Monterey Bay National Marine Sanctuary. The group decided that the seamount was in accordance with the standards for seamount, and the majority of the group recommended its incorporation into the nearby Monterey Bay sanctuary.

The Monterey Bay advisory group concurred with the findings, and submitted its approval to the NOAA, with whom the final decision rested. In a press release dated November 20, 2008, the NOAA finalized its approval of the plans, and expanded Monterey Bay by a total of 775 sq mi (2,007 km²) to include Davidson Seamount in its protected area.

Davidson Seamount is not directly connected to the main sanctuary; it is instead located in its own section, not directly connected to the main body.

External links

• Deep-sea coral research at Davidson (2006)
• SIMoN images
• SIMon Ecological overview