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Bowie Seamount, or SG̱áan ḴínghlasAlso written "Sg̱áan Ḵínghlas". ("Supernatural One Looking Outward") in the Haida language, is a large submarine volcano in the northeastern Pacific Ocean, located west of Haida Gwaii, British Columbia, Canada. The seamount is also known as Bowie Bank. The English name for the feature is after William Bowie of the United States Coast and Geodetic Survey.
The volcano has a flat-topped summit rising about above the seabed, to below sea level. The seamount lies at the southern end of a long underwater volcanic mountain range called the Pratt-Welker or Kodiak-Bowie Seamount chain, stretching from the Aleutian Trench in the north almost to Haida Gwaii in the south.
Bowie Seamount lies on the Pacific Plate, a large segment of the Earth's surface which moves in a northwestern direction under the Pacific Ocean. It is adjacent to two other submarine volcanoes; Hodgkins Seamount on its northern flank and Graham Seamount on its eastern flank.
With a height of at least and rising to within only of the sea surface, Bowie Seamount is the shallowest submarine volcano on the British Columbia Coast, as well as in Canadian waters, and one of the shallowest submarine volcanoes in the northeast Pacific Ocean. Most seamounts are found hundreds to thousands of metres below sea level, and are therefore considered to be within the deep sea. If Bowie Seamount were on land it would be about higher than Whistler Mountain in southwestern British Columbia and lower than Mount Robson, the highest mountain in the Canadian Rockies.
Bowie Seamount is about long and wide. Its flat-topped summit is made of weakly consolidated tephra and consists of two terraces. The lowest terrace is about below sea level while the highest is about below sea level, but contains steep-sided secondary summits that rise to within below sea level. From a physical perspective, the effective size of the submarine volcano is considerably large. The effects of other submarine volcanoes along the Pacific Northwest, including Cobb Seamount off the coast of Washington, affect the composition and abundance of plankton up to away from the seamount summit due to the upwelling of nutrients from deeper waters. Because of its similar size, Bowie Seamount most likely has a similar effect on its adjacent waters.
Close to Bowie's submerged summit, former coastlines cut by wave actions and beach deposits show that the submarine volcano would once have stood above sea level, as either a single volcanic island or as a small cluster of shoals that would have been volcanically active. Sea levels during the last glacial period, when Bowie Seamount was formed, were at least lower than they are today. It would have had a land area similar to, if not larger than, Midway Atoll in the central Pacific Ocean.
The volcanic rocks which make up some of the seamounts in the Kodiak-Bowie Seamount chain are unusual in that they have an acid-neutralizing chemical substance like typical ocean-island basalts but a low percentage of strontium as found at mid-ocean ridge basalts. However, the strontium-bearing volcanic rocks comprising Bowie Seamount also contain lead. Therefore, the magma mixtures that formed Bowie Seamount seem to have originated from varying degrees of partial melting of a depleted source in the Earth's mantle and basalts which had distinctly high lead isotopic ratios. Estimates during geological studies indicate that the abundance of the depleted-source component ranges from 60 to 80 percent of the erupted material.
Some aspects of the origin of the Kodiak-Bowie Seamount chain remain uncertain. The volcanic rocks found at the Tuzo Wilson Seamounts south of Bowie are fresh glassy of recent age, as would be expected if these seamounts are located above or close to a mantle plume south of Haida Gwaii. However, the origin of Bowie Seamount is less certain because even though the seafloor which Bowie lies on formed 16 million years ago during the late Miocene period, Bowie's summit shows evidence of recent volcanic activity. If Bowie Seamount formed above a mantle plume at the site presently occupied by the Tuzo Wilson Seamounts, it has been displaced from its magma source by about at a rate of about per year. The geologic history of Bowie Seamount is consistent with its flat-topped eroded summit, but the source for Bowie's recent volcanic activity remains uncertain. Still others, such as Dickens Seamount and Pratt Seamount further north of Bowie Seamount, fall a little to the side of the chain's expected trend. Another hypothesized origin of some or all seamounts in the Kodiak-Bowie Seamount chain is that they formed on top of the Explorer Ridge, a divergent plate tectonics boundary west of Vancouver Island, and have been displaced from it by seafloor spreading.
Although some of the seamounts in the Kodiak-Bowie Seamount chain appear to follow the expected age progression for a mantle plume trail, others, such as Denson Seamount, are older than that hypothesis would suggest. As a result, the Kodiak-Bowie Seamount chain has also been proposed by geoscientists to be a mix of ridge and mantle plume volcanism.
The Marine Protected Area measures about long and wide, totaling an area of . The Bowie Seamount Marine Protected Area also includes Peirce Seamount (also called Davidson Seamount) and Hodgkins Seamount. Previous to this designation, beginning in 1997, Bowie Seamount was a Haida marine protected area.
In August 1969, Canadian Forces Maritime Command divers made more dives during scientific studies by the Fisheries Research Board of Canada. They found very dense shoals of Sebastes floating over Bowie's flat-topped summit and a variety of bottom life. A number of monochrome photographs were taken and a few were collected, but no species record was created for other types of oceanic life around Bowie Seamount.
In November 1996, an issue of National Geographic magazine included an article titled "Realm of the Seamount", describing dives made at Bowie Seamount by two explorers named Bill Curtsinger and Eric Hiner. They explored the slopes of Bowie Seamount using scuba diving equipment down to . Their photographs featured one of Bowie's rugged peaks thickly covered with seaweeds and colourful sea bottom invertebrates. Shoals of young rockfish were seen on Bowie's steep flanks.
Scientist Bill Austin of Khoyatan Marine Lab in the Northeast Pacific examined a video made during the National Geographic dives to identify the benthic flora and fauna of Bowie Seamount. From the video, Austin recognized some of the most noticeable invertebrates and noted that a few species generally occurring in the intertidal zone and in shallow subtidal environments were found deeper than might normally be expected, and were bigger than normal.
A team of five divers, led by photographer/videographer Neil McDaniel, visited the seamount August 3–5, 2003 and conducted a biological and photographic survey of the summit down to depths of about . A total of 18 taxa of algae, 83 taxa of conspicuous invertebrates and 12 taxa of fishes were documented, approximately 180 underwater still photographs were taken and approximately 90 minutes of digital video were recorded. Of particular note were the dense schools of rockfish hovering over the summit and numerous curious prowfish.
Haida have long recognized seamount as a special place. Gidansda Guujaaw, former President of the Council of the Haida Nation, has said: "SG̱aan Ḵinghlas represents a shift in recognizing the need for respect and care for the Earth. This is a very significant turning point in reversing the trends that have been leading to the depletion of life in the sea."
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