| Davidson Seamount | |
|---|---|
 Bathymetric map of Davidson Seamount. | |
  | |
| Summit depth | 4,101 ft (1,250 m)[2] |
| Height | 7,480 ft (2,280 m)[2] |
| Location | |
| Coordinates | 35°43′N122°43′W / 35.717°N 122.717°W /35.717; -122.717[1] |
| Country | California, United States |
| Geology | |
| Type | Seamount (underwater volcano) |
| Age of rock | 9–15 million years[3] |
| Last eruption | ~9.8 million years ago[2] |
| History | |
| Discovery date | 1933[4] |
Davidson Seamount is aseamount (underwater volcano) located off thecoast of Central California, 80 mi (129 km) southwest ofMonterey and 75 mi (121 km) west ofSan Simeon. At 26 mi (42 km) long and 8 mi (13 km) wide, it is one of the largest known seamounts in the world.[4] From base to crest, the seamount is 7,480 ft (2,280 m) tall, yet its summit is still 4,101 ft (1,250 m) below the sea surface. The seamount is biologically diverse, with 237 species and 27 types ofdeep-sea coral having been identified.[2]
Discovered during the mapping ofCalifornia's coast in 1933, Davidson Seamount is named after geographerGeorge Davidson of theUnited States Coast and Geodetic Survey. Studied only sparsely for decades,NOAA expeditions to the seamount in 2002 and 2006 cast light upon its unique deep-sea coral ecosystem. Davidson Seamount is populated by a dense population of large, ancient corals, some over 100 years old. The data gathered during the studies led to the Davidson Seamount being added to theMonterey Bay National Marine Sanctuary in 2008.
Aseamount is anunderwater volcano; Davidson rises 7,480 ft (2,280 m) above the surrounding ocean floor. Although there are over 30,000 seamounts in thePacific Ocean alone, only about 0.1% of them have been explored.[4] The aqueous environment of the seamount means that it behaves differently from volcanoes on land. Its surface is mostlyblocky lava flows, with somepillow lava, more typical of a seamount, prevailing at its deeper flanks. The summit is composed of layeredvolcanic ash andpyroclastic material. These rocks indicate mildly explosive eruptions of gas-rich lava near the summit. The base is likely buried in a deep layers of muds.[3]
At 26 mi (42 km) long and 8 mi (13 km) wide, Davidson Seamount would dominate the landscape similar toMount Shasta. Put in perspective, the size of the seamount is enough to fillMonterey Bay from theSanta Cruz boardwalk to Monterey's Fishermen's Wharf.[5]
Davidson Seamount is part of a group of seamounts off the continental margin, includingGuide,Pioneer,Gumdrop, andRodriguez seamounts, all located roughly between 37.5° and 34.0°latitude. This group is morphologically unique, yet very similar to one another. All 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 ancientspreading center which has since been replaced in its role by theSan Andreas Fault system.[3] They are unique in this origin, as they are formed from the remnants of an oldocean-ridge spreading center.[6] A series of "knobs" are aligned with the ridges; however the distinctive summitcrater, 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.[3]
Analysis ofargon–argon dating 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.[3]
Studies have indicated that a seamount functions as an "oasis of life," with a higher species count and morebiodiversity than the surrounding seafloor.[4] Although previous analysis has stressed the exceptionalism of the seamount habitat, recent biological analysis, much of it centered on Davidson Seamount, has indicated that this does not necessarily translate into a higherendemic percentage.[7][8][9] However, itis believed that they provide a refuge for rare species that have difficulty surviving elsewhere.[8]
There are reasons that seamounts are biologically important. They 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 ecologicalfood web. Scientists have found that seamounts often provide a habitat forendemic species that are not found anywhere else.[4]
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[update] scientists have observed and recorded 168 species ofmegafauna on the seamount. Of these, about 7% of the species at Davidson areendemic, meaning they live only at Davidson. 71% of the species can be confidently classified ascosmopolitan (widespread), and sufficient 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. Thirteen species have been identified in other areas, but never in other seamounts.[8]
The seamount is populated by a large variety ofdeep-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, largesponge field,crabs,deep-sea fish,basket stars, and a number of rarebenthic species, some of which have yet to be studied properly or even named.[2] 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.[6]
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 andtrawling typically does not occur below a depth of 1,500 ft (457 m), and waste disposal and discharge occurs much closer to shore.[5]
In comparisons drawn to the nearbyMonterey 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.[8]
The ecology on Davidson Seamount is dominated by an extensive "forest" of ancientdeep-sea coral andsponges, some of which are over 100 years old. Although these species also grow elsewhere, they are generally sparsely distributed and far smaller and younger than the coral growth on Davidson. Conversely,sea cucumbers, which are very common on the walls ofMonterey Canyon, are all but absent on Davidson, an example of the polarity between Davidson and Monterey Bay.[7]
Researchers speculate that Davidson Seamount is an ideal habitat for deep-sea corals and sponges because it has favorable bottom rock (barelava rock), a steady food supply (supplied by a water current favoring the seamount; seethe section above), and has not been disturbed by strong bottom currents than often bother other seafloor areas.[7]
Craig McClain, one of the scientists studying the seamount, toldPhysOrg:
"The large groves of corals and sponges are unique to seamounts. The crests of seamounts are particularly good because they provide flat rocky surfaces that don't accumulate much sediment. This is partly due to the fact that seamounts are so far offshore. In contrast when you look at the seafloor in Monterey Canyon, it's mucky. That makes it tough for filter feeders, especially sponges. Any flat surface in the canyon collects mud. This makes it tough for corals to settle anywhere except on near-vertical surfaces. Just staying attached to these surfaces can be a challenge in itself."[7]
Research also suggests that seamounts such as Davidson Seamount may be ecologically valuable to rare species that use them asbreeding grounds. The seamounts are likely to be a source oflarvae that maintains the population of the species in nearby, sub-optimal areas, known as "sinks." Sinks are low-lying areas in which species can live, but do so very poorly; if they are not replenished by nearby population centers, such as at Davidson, they could disappear from the area entirely.DNA studies may in the future help scientists prove seamounts are indeed sources of larvae for their surrounding seafloor.[7]
Davidson Seamount was initially discovered and mapped in 1933.[4] Davidson Seamount was the first underwater volcano to be classified as "seamount" by theUnited States Board of Geographic Names, in 1938, and was named in honor of theUnited States Coast and Geodetic Survey scientistGeorge Davidson, one of the key figures in the survey of America's west coast.[2]
Because of its great depth, for a long time Davidson Seamount had been preceded only by a sparse few investigations. Davidson is interesting tovolcanologists because of its unique geology, and tobiologists for its unique ecology. In 2002 the NOAA sponsored the first modern in-depth study of the seamount. The team included scientists, educators, and resource managers, with the goal of documenting species, taking geologic samples, and describing the ocean environment.[10] The expedition documented many rare, previously undiscovered species that exist nowhere else, not even on nearby seamounts,[4] including ancient coral gardens that are vulnerable to human activity.[11]
Recent expeditions to Davidson have focused on its ecology, and specifically on the variety ofdeep-sea corals, some over 100 years old, that live on its banks. These large colonies are extremely fragile to human interaction. 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.[4]
In 2006, another exploration, a collaboration of the Monterey Bay National Marine Sanctuary, theMonterey Bay Aquarium Research Institute (MBARI), andMoss Landing Marine Laboratories was undertaken, mainly to test a model that had been developed to predict the availability of coral and to advance the understanding of the seamount's deep-sea coral.[11] The NOAA outlined a set of 4 goals for the expedition:[12]
Scientific data on thewater currents and food availability of the seamount was collected, as was information on theage andgrowth patterns of the corals themselves. TheBritish Broadcasting Corporation (BBC) filmed the cruise for their series,Planet Earth.[11] A total of 70 hours of observations and 102 deep-sea animal and rock specimens were collected during the cruise.[12] The expedition, which lasted from January 26 through February 4, made use if the MBARI'sresearch vesselWestern Flyer and theROVTiburon.[13]
Following the information learned from the 2002 and 2006 expeditions, there was public support for the making of Davidson Seamount into amarine sanctuary.[13] 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 aNational Marine Sanctuary under the National Marine Sanctuaries Act, and if so whether to make it its own sanctuary, or incorporate it into the nearbyMonterey Bay National Marine Sanctuary. The group decided that the seamount was eligible for sanctuary designation, and the majority of the group recommended its incorporation into the nearby Monterey Bay sanctuary.[4]
The Monterey Bay advisory group concurred with the findings, and submitted its approval to theNOAA, with whom the final decision rested.[4] In a press release dated November 20, 2008, the NOAA finalized its approval of the plans, and expandedMonterey Bay National Marine Sanctuary by a total of 775 sq mi (2,007 km2) to include Davidson Seamount in its protected area.[14] After a management plan was created, Davidson Seamount was incorporated into Monterey Bay in 2009, 7 years after it was originally proposed.[2]
In July 2017, under the direction ofExecutive Order 13795 from PresidentDonald Trump, the U.S. Department of Commerce began re-evaluating the status of theMonterey Bay National Marine Sanctuary, which includes the Davidson Seamount. The move was opposed by many environmentalists and residents.[15]
| International | |
|---|---|
| National | |
| Other | |
