Beebe Hydrothermal Vent Field

The Beebe Hydrothermal Vent Field (also known as the Piccard Vent Field) is located just south of Grand Cayman in the Caribbean, on the north side of the Mid-Cayman Spreading Centre in the Cayman Trough. Approximately south of Beebe is the Von Damm Vent Field.

At nearly below sea level, Beebe is the world's deepest known hydrothermal vent site, and one of the few known in the abyssopelagic. The hydrothermal plume nicknamed "Piccard" was detected in 2010, and the Beebe site was confirmed later that year. The combined depth and vent fluid temperature make it a popular site for studying aqueous thermodynamics, high-pressure biology, and geochemistry.

Expedition history

The Beebe vent field was initially detected in October 2009 by CTD, Eh, and optical backscatter anomalies in the water column above the Mid-Cayman Rise aboard the R/V ''Cape Hatteras''. The team deployed HROV ''Nereus'' to conduct surveys which identified a double hydrothermal plume at and deep and subsequently nicknamed it "Piccard". From collected plume samples, the team were able to predict the approximate location of the vent field at a depth of approximately deep, usurping the Ashadze vent field (Mid-Atlantic Ridge, ) as the deepest known hydrothermal field.

In 2010, the ''RRS James Cooks 44th voyage returned to the Mid-Cayman Rise to survey the areas predicted to host hydrothermal sites in 2009. The team deployed the AUV ''Autosub6000'' to map anomalies and RUV ''HyBIS'' to collect video, visually confirming the site named "Beebe" after William Beebe at a depth of .

The vent field was further explored by the NOAAS ''Okeanos Explorer'' in 2011, R/V ''Falkor'' cruise FK008 and R/V ''Yokosuka'' cruise YK13-05 in 2013, and cruises AT18-16 and AT42-22 of the R/V ''Atlantis'' in 2012 and 2020 resepctively.

Geography

The Beebe vent field is in the Caribbean Sea, at the northern end of the Mid-Cayman Rise on the segments closest to the Septentrional-Oriente fault zone.

The Beebe vent field consists of 7 sulfide mounds on the western side of the spreading center, the majority of which are inactive. Central to the field are the main endmember vents, known as Beebe 1 - 5 which branch from the same mound. Surrounding these endmember vents are Hot Chimlet to the north, Beebe Sea to the East, and Beebe Woods to the South. The series of mounds continue to the northeast of the field, where high-temperature hydrothermal activity used to take place, as evidenced by extinct chimneys.

The vent field is in the territorial waters of the Cayman Islands, which is a self-governing British Overseas Territory.

Geology

The Beebe vent field is located in the very near vicinity of the spreading center, which has been described as an ultraslow ridge at a rate of to per year. The area is primarily basalt, with metal-sulfide mounds and talus sourced from hydrothermal activity.

Unlike the Von Damm Vent Field, there is little sediment cover at Beebe.

Chimneys

Beebe vents 1 - 5 form a branching complex consisting of pyrite, pyrrhotite, and other oxidized metal-sulfides. These chimneys emit the hottest fluids of anywhere within the field, up to . Beebe Woods to the south has a similar geological composition, though temperatures are cooled slightly (). These temperatures are hot enough that iron and other metals have not yet precipitated, giving the chimneys a distinctive black-smoker appearance. These metal-sulfide chimneys are conductive of precious and semi-precious mineral precipitation, such as gold, silver, and copper.

Hot Chimlet to the north features venting at a significantly lower temperature (), such that the fluids are clear and devoid of metals. Residing on the slope of the mound, the Hot Chimlet site has a light dusting of sulfide materials likely sourced from the center of the field. Hot Chimlet also does not have the impressive chimney structures as at the center of the field, and requires the use of dive markers to identify quickly. Shrimp Gulley, similarly, is a location within the Beebe Sea which is distinguished by abundant biology. The Gulley reaches temperatures around , with markers also required to find the exact locations of diffuse flow.

Chemistry

As with many basalt-hosted systems, Beebe has endmember fluids that are highly acidic in association with basalt dissolution reactions. Such reactions with basalt can be favorable in forming hydrothermal ore deposits. Concentrations of carbon dioxide and hydrogen sulfide are elevated relative to deep sea water, attributed to origin in the mantle.

The vent field hosts two main areas of black smoker venting, with a fluid at temperatures of over 400 °C and a low salinity of about 2.3 wt% NaCl. Under these conditions, the venting fluids surpass the supercritical threshold of seawater at 407 °C and 298 bar, and is one of few vent sites shown to host sustained supercritical venting. These hot, acidic conditions make precipitation of metal-sulfide chimneys possible, also giving the hottest vents their characteristic black-smoker appearance from high concentrations of dissolved metals.

Measurements of iron and manganese at Beebe suggest subsurface temperatures of 452 °C or higher.

Organic compounds

High temperatures acting on seawater can cause diagenesis or pyrolysis of organic compounds, such that they break up into smaller compounds or alter bond configurations. Small quantities of alkanes have been detected, likely derived from hydrothermally-altered compounds of deep seawater. At cooler venting areas, formate and other organic acids have been detected in low concentrations, as high concentrations of carbon dioxide and hydrogen gas may thermodynamically favor abiotic organic acid synthesis.

With abundant iron in the venting plume, there have been many models examining the potential of ligands binding to iron when mixing begins with seawater. These ligands prevent the precipitation of iron in mineral phases, potentially making them bioavailable.

Biology

Beebe has an abundance of shrimp present at venting orifices, particularly those of ''Rimicaris hybisae'', belonging to the family of '' Alvinocarididae'', and are almost completely blind. These shrimp have eyes as juveniles but lose them as they age, developing a light-sensing organ that they can use to detect the infrared glow of hot, venting locations. The shrimp at the Beebe vent field are unique from those found at the Von Damm field in that they are a slightly more brown color due to the high concentrations of iron pumped out by the vents. Observations of shrimp behavior suggests that, when in dense congregations, shrimp ascertain carbohydrates from chemosynthetic bacteria. Though not directly observed, shrimp may predate on other organisms or exhibit cannibalism when more sparsely distributed.

There is also an abundance of deep sea anemones, '' Provannid'' gastropods, and squat lobsters. As with other vent fields, it is possible for deepwater sharks or roaming fishes such as grenadiers to appear around the field.

Microbiology

From a microbial standpoint, there are visible mats of microbial activity at both the Beebe and Von Damm vent systems. Exposed rocks have shown filamentous bacteria and orange sediments around the field, where microorganisms such as '' Beggiatoa'' are suggested to utilize hydrogen sulfide in venting fluids to metabolize chemosynthetically. Some of these microorganisms are present on or within vent crustaceans, being routinely grazed or taking up roles as symbiotic organisms.

At lower-temperature venting locations, ''Sulfurovum'' have been identified as a dominant bacteria whereas '' Methanothermacoccus'' is an abundant archaea. Geochemical calculations suggest that multiple metabolisms other than hydrogen consumption are favorable in these conditions.

Naming

The hydrothermal system was suggested to exist on an American-led oceanographic cruise in 2009 on the R/V ''Cape Hatteras'', with 3 hydrothermal plumes detected in the water column: Piccard, Walsh, and Europa. Beebe was visually confirmed in early 2010 on a British-led expedition with the RRS James Cook, though the Piccard plume could not be found, so the vent field was named Beebe. Americans returned to the vent field in 2011 on the Okeanos Explorer prior to scientific publications from the previous mission, and named the vent field Piccard, therefore creating a second name for the vent field. Th
Interridge Database
lists the vent field as Beebe, though many American journals publish results under the name of Piccard.

The original name for the detected plume, Piccard, comes from Jacques Piccard, a Swiss oceanographer that dove with Don Walsh to the Challenger Deep. The subsequent naming of the field to Beebe is after the American naturalist William Beebe who frequently dove in the Bathysphere prior to powered submersibles.

Human impacts

The Beebe vent field has been explored many times by scientists since 2010, to collect samples and video. Common ecosystem disruptions during hydrothermal expeditions, such as rock collections and artificial illumination, may be particularly detrimental at Beebe where organism photoreceptors may be damaged.

In 2013, cruise YK-13-05 by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) was undertaken to sample and live stream dives of the ''DSV Shinkai 6500''. However, the fiber optical cable was broken during spooling multiple times and was not fully recovered.R/V Yokosuka & DSV Shinkai 6500 Cruise Report YK13-05. ''Japan Agency for Marine-Earth Science and Technology''. 2013. http://www.godac.jamstec.go.jp/catalog/data/doc_catalog/media/YK13-05_all.pdf Uncertainty in cable presence is a potential hazard for human-operated submersibles such as the ''DSV Alvin'', which cannot dive at Beebe due to safety concerns.

Beebe's metal sulfides are rich in gold and other useful industrial elements, which could make deep-sea mining a concern.

External links

The blog of the British expedition from 2010.

Beebe vent site in the Interridge Database

References

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Hydrothermal vents
Caribbean Sea