Description: © The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS Biology 10 (2012): e1001234, doi:10.1371/journal.pbio.1001234.

Description: Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised.

Description: The ChEsSo research programme was funded by a NERC Consortium Grant (NE/DO1249X/1) and supported by the Census of Marine Life and the Sloan Foundation, and the Total Foundation for Biodiversity (Abyss 2100)(SVTH) all of which are gratefully acknowledged. We also acknowledge NSF grant ANT-0739675 (CG and TS), NERC PhD studentships NE/D01429X/1(LH, LM, CNR), NE/H524922/1(JH) and NE/F010664/1 (WDKR), a Cusanuswerk doctoral fellowship, and a Lesley & Charles Hilton-Brown Scholarship, University of St. Andrews (PHBS).

Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 139 (2014): 47-71, doi:10.1016/j.gca.2014.04.024.

Description: The East Scotia Ridge is an active back-arc spreading centre located to the west of the South Sandwich island arc in the Southern Ocean. Initial exploration of the ridge by deep-tow surveys provided the first evidence for hydrothermal activity in a back-arc setting outside of the western Pacific, and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments E2 and E9. Here we report the chemical and isotopic composition of high- and low-temperature vent fluids, and the mineralogy of associated high-temperature chimney material, for two sites at E2 (Dog’s Head and Sepia), and four sites at E9 (Black & White, Ivory Tower, Pagoda and Launch Pad). The chemistry of the fluids is highly variable between the ridge segments. Fluid temperatures were ∼350 °C at all vent sites except Black & White, which was significantly hotter (383 °C). End-member chloride concentrations in E2 fluids (532–536 mM) were close to background seawater (540 mM), whereas Cl in E9 fluids was much lower (98–220 mM) indicating that these fluids are affected by phase separation. Concentrations of the alkali elements (Na, Li, K and Cs) and the alkaline earth elements (Ca, Sr and Ba) co-vary with Cl, due to charge balance constraints. Similarly, concentrations of Mn and Zn are highest in the high Cl fluids but, by contrast, Fe/Cl ratios are higher in E9 fluids (3.8–8.1 × 10−3) than they are in E2 fluids (1.5–2.4 × 10−3) and fluids with lowest Cl have highest Cu. Although both ridge segments are magmatically inflated, there is no compelling evidence for input of magmatic gases to the vent fluids. Fluid δD values range from 0.2‰ to 1.5‰, pH values (3.02–3.42) are not especially low, and F concentrations (34.6–54.4 μM) are lower than bottom seawater (62.8 μM). The uppermost sections of conjugate chimney material from E2, and from Ivory Tower and Pagoda at E9, typically exhibit inner zones of massive chalcopyrite enclosed within an outer zone of disseminated sulphide, principally sphalerite and pyrite, in an anhydrite matrix. By contrast, the innermost part of the chimneys that currently vent fluids with lowest Cl (Black & White and Launch Pad), is dominated by anhydrite. By defining and assessing the controls on the chemical composition of these vent fluids, and associated mineralisation, this study provides new information for evaluating the significance of hydrothermal processes at back-arc basins for ocean chemistry and the formation of seafloor mineral deposits.

Description: This work was funded by the Natural Environment Research Council consortium grant NE/D01249X/1. C.R.G. acknowledges further support from the National Science Foundation’s Office of Polar Programs grant ANT-0739675. N.R.B. acknowledges funding from the National Sciences and Engineering Research Council of Canada, Ontario Ministry of Research and Innovation, and the Academic Development Fund at Western University.

Description: To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. "Dentoglobigerina" venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (〉 355 mm diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of "D." venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of "D." venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of "D." venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that "D." venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for "D." venezuelana. Our size fraction data advocate the absence of photosymbionts in "D." venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that d18O and d13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the "sample hungry" palaeoceanographic records.