Figure 1.
Maps of the position and geophysical setting of the ESR vents.
(A) The Scotia Sea showing the ESR in relation to the Scotia Plate (SCO), South Sandwich Plate (SAN), South American Plate (SAM), the Antarctic Plate (ANT), the Antarctic Peninsula (AP), and the South Sandwich Trench (SST). Oceanographic features shown include the Polar Front (PF), the Sub-Antarctic Front (SAF), and the southern Antarctic Circumpolar Current Front (SACCF). The sites E2 and E9 are indicated by red arrows. (B) Ship-based swath bathymetry of the vent sites at E2 showing the axial summit graben. The black circle indicates the sites of main venting. (C and D) ROV-based 3-D swath bathymetry of E2 (C) and high-resolution swath bathymetry of the major steep-sided fissure that runs north–south through the centre of the site, between longitude 30° 19.10′W and 30° 19.15′W (D). Dog's Head vent site is indicated. White arrows indicate vent sites not mentioned in text. (E) Ship-based swath bathymetry of the vent sites at E9 showing the axial fissures and the collapsed crater called the Devil's Punchbowl. The black spot indicates the sites of main venting. (F) ROV-based 3-D swath bathymetry of the vent sites at E9. The vent sites Ivory Tower, Car Wash, and Black and White are indicated. Other vent sites are indicated by white arrows.
Figure 2.
Photographs of vents and associated biological communities.
(A) Active black smoker chimneys at E2 (Dive 128, 2,602 m depth). (B) Vent flange at E2 with trapped high-temperature reflective hydrothermal fluid (Dive 129, 2,621 m depth). (C) Microbial mat covering rock surfaces on vent periphery at E2 (Dive 134, 2,604 m depth). (D) Active vent chimney at E9 supporting the new species of the anomuran crab Kiwa. (Dive 144, 2,396 m depth). (E) Dense mass of the anomuran crab Kiwa n. sp. at E9 with the stalked barnacle cf. Vulcanolepas attached to nearby chimney (Dive 138, 2,397 m depth). Scale bars: 10 cm for foreground.
Table 1.
Chemical composition of the vent fluid end-member at E2 and E9 vent fields.
Figure 3.
Photographs of the ESR vent fauna.
(A) Actinostolid sea anemones surrounded by cf. Vulcanolepas on a chimney with diffuse hydrothermal venting at E9 (Dive 138, 2,396 m depth). (B) Dense field of actinostolid sea anemones along with peltospiroid gastropods (Dive 140, 2,394 m depth). (C) Anemone field at E9 with juvenile Kiwa n. sp. interspersed (Dive 139, 2,398 m depth). (D) Undescribed peltospiroid gastropod at E2 surrounding single Kiwa n. sp. and partially covered by Lepetodrilus n. sp. The pycnogonid cf. Sericosura is at the bottom right of the image (Dive 132, 2,608 m depth). (E) An undescribed seven-arm sea star predatory on the stalked barnacles cf. Vulcanolepas at E9 (Dive 139, 2,402 m depth). (F) Unidentified octopus at E9 (Dive 144, 2,394 m depth). Scale bars: 10 cm for foreground.
Figure 4.
Collage of frame grabs of high-definition video to show fauna dispersion on the E9 vent site Ivory Tower.
The vertical chimneys are covered with the anomuran Kiwa n. sp., and the area between the chimneys is occupied primarily by an undescribed peltospiroid gastropod (Dive 142, 2,398 m depth, ROV heading 090°). Scale bar: 1 m for foreground. Collage created by L. M.
Table 2.
Dominant fauna at East Scotia Ridge vents E2 and E9.
Figure 5.
Selection of the multivariate regression tree for the global datasets of vent species.
The datasets are species data from Bachraty et al. [8] (red/filled circles/solid line) and the same dataset with Southern Ocean vent sites added (blue/open circles/dashed line). Top panel: Frequency plot of the optimal tree size for 1,000 multiple cross-validations. The most common optimal tree size was five or seven provinces for the Bachraty et al. [8] dataset and 11 provinces for the combined dataset. Bottom panel: The cross-validated relative error indicates that predictive power is similar for a wide range of tree sizes. Vertical bars indicate ± one standard error, and the horizontal lines indicate one standard error above the minimum cross-validated relative error.
Figure 6.
Results of geographically constrained clustering using multivariate regression trees.
An 11-province model based on the combined dataset was the most frequent optimal model when using multiple cross-validations. Vent provinces are resolved comprising the Mid-Atlantic Ridge, the ESR, the northern, central, and southern East Pacific Rise, a further province located south of the Easter Microplate, four provinces in the western Pacific, and a further Indian Ocean province.