Kemp Caldera

Kemp Caldera[lower-alpha 1] and Kemp Seamount are two submarine volcanoes south of the South Sandwich Islands. The seamount rises to a depth of 80 metres (260 ft) below sea level, the caldera has a diameter of 8.3 by 6.5 kilometres (5.2 mi × 4.0 mi) and reaches a depth of 1,600 metres (5,200 ft). The caldera contains several hydrothermal vents, including white smokers and diffuse venting areas, which are settled by chemolithotrophic ecological communities.

Kemp Caldera
Summit depth80
Location
Coordinates59°42′S 28°15′W[1]
History
Discovery date2009
First visit2009

Geography and geomorphology

Kemp Caldera lies at the southern end of the South Sandwich Islands, between the Scotia Sea to the north and the Weddell Sea to the south[1] and about 50 kilometres (31 mi) westsouthwest of Thule Island.[3] The caldera was discovered in 2009 during bathymetric mapping[4] by the RRS James Clark Ross and sampled on the same occasion.[5] Further sampling efforts took place in 2010 and 2011.[6] Another caldera, Adventure Caldera, lies east of Kemp Seamount;[7] together with several other seamounts they form the Vysokaya Bank.[8] The Nelson Seamount lies farther south.[9]

The volcano consists of two submarine edifices, the Kemp Caldera proper to the west and Kemp Seamount to the east.[1] The latter rises to a depth of 80 metres (260 ft) below sea level.[10] The caldera is elongated in east-west direction and has dimensions of 8.3 by 6.5 kilometres (5.2 mi × 4.0 mi). The caldera floor lies at 1,600 metres (5,200 ft) depth, 700 metres (2,300 ft) below the margin of the caldera, and contains a resurgent cone 1 kilometre (0.62 mi) wide and 250 metres (820 ft) high. Numerous volcanic cones and volcanic craters dot its rims, presumably from post-caldera volcanism. Deposits left by mass failures such as slide blocks and debris flow chutes occur both in and outside of the caldera.[4] Basaltic rocks, sediments,[11] sulfur and volcanic ash cover the seafloor.[3]

Geology

Volcanic activity in Antarctica and the Southern Ocean has been known since the 19th century. Volcanoes are found both on the mainland (Antarctic Peninsula, Marie Byrd Land, Victoria Land) and the outlying islands (e.g South Sandwich Islands, South Shetland Islands) and feature earthquakes, eruptions and fumarole systems. Hydrothermal vents occur at the Australian-Antarctic Ridge and the East Scotia Ridge.[12]

Subduction of the South American Plate beneath the Sandwich Plate occurs at a rate of 7–7.9 centimetres per year (2.8–3.1 in/year) and is responsible for volcanism in the South Sandwich Arc.[13] The South Sandwich Arc contains the eleven volcanic South Sandwich Islands and submarine volcanoes such as Protector Shoal in the north and Kemp Seamount/Kemp Caldera in the south. Hydrothermal vents are found at Quest Caldera and Adventure Crater.[12]

Geochemistry and activity

Kemp Caldera has erupted low-potassium[10] tholeiite and basaltic andesite,[3] and the geochemistry of volcanic rocks at Kemp Seamount is consistent with a volcanic arc magma.[14] Kemp Seamount has not had its summit torn down by icebergs, implying that it is young.[10] The fresh appearance of the submarine volcanic features at Kemp Caldera, including the lack of sediments filling the caldera, indicate that it was recently active.[4] The caldera has a volume of about 9–12 cubic kilometres (2.2–2.9 cu mi) and may have been excavated during the course of multiple eruptions.[15]

Hydrothermal vents occur at the foot and on the flanks of the resurgent cone[4] and include white smokers. Hydrothermal vents form both diffuse venting areas[16] and discrete chimneys, and have deposited anhydrite and sulfur.[11] Liquid sulfur has been observed.[17] Temperatures of 103–202 °C (217–396 °F) have been measured at the white smokers.[18] Water temperatures at Kemp Caldera reach 1 °C (34 °F) while sediments are warmed by volcanic activity to 5 °C (41 °F).[19]

Biology
Images of a limpet found at Kemp Caldera

Bacterial mats,[11] clams[19] and limpets settle on the hydrothermal vents,[16] which feature chemosynthetic communities.[20] Sponges grow on the periphery of the vent areas.[2] There are "dead zones", accumulations of animal carcasses, which have also been found at other submarine hydrothermal systems on Earth.[18] Most of the bacteria belong to the class gammaproteobacteria.[21]

Numerous marine animals have been identified at sites of venting, such as actinostolid anemones, the barnacle Neolepas scotiaensis, vesicomyid clams such as Archivesica puertodeseadoi, Lepetodrilus concentricus clams, cocculinid limpets, pycnogonids of the genus Sericosura and the starfish Paulasterias tyleri. Away from hydrothermal vents alcyonaceans, brisingids, cnidarians, holothuroids, ophiuroids[lower-alpha 2], polychaetes[lower-alpha 3][23] and shrimp[lower-alpha 4] live on and in the seafloor.[24] The bivalve species Spinaxinus caldarium and Parathyasira dearborni were first identified at Kemp Caldera,[6] as were two "bone-eating worm" species, Osedax crouchi and Osedax rogersi.[22]

Vesicomyid clam communities occur on the hydrothermal vents.[26] Whale falls have been found and feature their own biological communities; in total about nine different biological communities have been identified in Kemp Caldera,[23] and the occurrence of a limpet on both hydrothermal vents and whale falls has been used as evidence that whale falls may be a stepping stone for species to propagate to submarine hydrothermal vents.[27]

Kemp Caldera lies within the South Georgia and the South Sandwich Islands Marine Protected Area. Longline fishery is restricted and bottom trawling outright prohibited;[12] As of 2019 further legislation protecting the environment from mining and hydrocarbon exploration was in the works.[28]

Notes
  1. Also known as McIntosh Caldera[2]
  2. Such as Amphioplus sp., Ophiura antarctica and Ophiura irrorata[5]
  3. Including siboglinids[6] such as the "bone-eating worms" Osedax[22]
  4. Such as Eualus amandae[24] which was first discovered at Kemp Caldera and the East Scotia Ridge[25]

References
  1. Linse et al. 2019, p. 4.
  2. IRVD, p. 1.
  3. Cole et al. 2014, p. 23.
  4. Linse et al. 2019, p. 6.
  5. Boschen, Tyler & Copley 2013, p. 28.
  6. Oliver & Rodrigues 2017, p. 267.
  7. Bohrmann 2019, Fig 1.
  8. Leat et al. 2013, p. 70.
  9. Leat et al. 2004, p. 19.
  10. Leat et al. 2004, p. 23.
  11. Linse et al. 2019, p. 7.
  12. Linse et al. 2019, p. 2.
  13. Barry et al. 2006, p. 224.
  14. Barry et al. 2006, p. 235.
  15. Leat et al. 2013, p. 74.
  16. Linse et al. 2019, p. 9.
  17. Bohrmann 2019, p. 1.
  18. Linse et al. 2019, p. 18.
  19. Bohrmann 2019, p. 2.
  20. Linse et al. 2019, p. 22.
  21. Linse et al. 2019, p. 16.
  22. Amon et al. 2014, p. 405.
  23. Linse et al. 2019, pp. 7-9.
  24. Linse, Bohrmann & Sigwart 2019, p. 2937.
  25. Nye, Copley & Linse 2013, p. 145.
  26. Chen & Linse 2020, p. 355.
  27. Chen & Linse 2020, p. 354.
  28. Linse et al. 2019, p. 3.

Sources
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