@article {Brandl2012,
	title = {{Volcanism on the flanks of the East Pacific Rise: Quantitative constraints on mantle heterogeneity and melting processes}},
	journal = {Chemical Geology},
	volume = {298{\textendash}299},
	year = {2012},
	month = {feb},
	pages = {41{\textendash}56},
	abstract = {We present major and trace element and Sr, Nd and triple-spike Pb isotope data for 17 fresh volcanic glasses from Seamount 6, a 10-km diameter seamount located 140~km east of the East Pacific Rise at 12{\textdegree}45'N. Geological and geochronological evidence show that magma compositions evolved from tholeiitic basalts to alkalic basalts and basaltic trachyandesites during the 1{\textendash}2~Ma active lifetime of the seamount. Major and trace element compositions in Seamount 6 lavas vary systematically with isotope ratios; the youngest lavas with the highest incompatible trace element concentrations have the highest La/Yb, Nb/Zr, K2O/TiO2, 87Sr/86Sr, 206Pb/204Pb and the lowest 143Nd/144Nd, MgO and CaO. The range in element concentrations, incompatible element ratios, and isotope compositions in Seamount 6 lavas exceeds that observed in lavas erupted at the adjacent ridge axis, and is comparable to the range in lava compositions reported from all near-ridge seamounts studied to date. The observed range in lava compositions is consistent with mixing between enriched and depleted melts at shallow levels in the crust. The inferred difference in composition between these mixing endmembers cannot be explained by variable degrees of melting of a single source composition, and requires that the upper mantle is extremely heterogeneous on the scale of the melting region beneath a single seamount. We can show that the range in composition of EPR seamount lavas cannot be generated by melting of variably heterogeneous mantle in which enriched and depleted materials contribute equally to melting (source mixing). Instead, the trace element and isotope compositions of seamount lavas can be reproduced by melting models in which more enriched, fertile mantle lithologies are preferentially melted during mantle upwelling. At progressively lower degrees of melting, erupted lavas are thus more enriched in incompatible trace elements, have higher La/Yb, K/Ti, 87Sr/86Sr ratios and lower 143Nd/144Nd. If this is a common process, then mantle-derived magmas are unlikely to inherit the average incompatible trace element and isotope composition of their mantle source, which is likely to be significantly more depleted, nor will they display the full range of compositions present in the mantle melting region. These results have implications for the way in which oceanic basalts can be used to infer the composition of the upper mantle.},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	issn = {0009-2541},
	doi = {10.1016/j.chemgeo.2011.12.015},
	url = {http://dx.doi.org/10.1016/j.chemgeo.2011.12.015},
	author = {Brandl, P A and Beier, C and Regelous, M and Abouchami, W and Haase, K M and Garbe-Schonberg, D and Galer, S J G}
}
@article {Thiel2012,
	title = {{Widespread occurrence of two carbon fixation pathways in tubeworm endosymbionts: lessons from hydrothermal vent associated tubeworms from the Mediterranean Sea}},
	journal = {Frontiers in Microbiology},
	volume = {2},
	year = {2012},
	pages = {423},
	abstract = {Vestimentiferan tubeworms (siboglinid polychetes) of the genus Lamellibrachia are common members of cold seep faunal communities and have also been found at sedimented hydrothermal vent sites in the Pacific. As they lack a digestive system, they are nourished by chemoautotrophic bacterial endosymbionts growing in a specialized tissue called the trophosome. Here we present the results of investigations of tubeworms and endosymbionts from a shallow hydrothermal vent field in the Western Mediterranean Sea. The tubeworms, which are the first reported vent-associated tubeworms outside the Pacific, are identified as Lamellibrachia anaximandri using mitochondrial ribosomal and cytochrome oxidase I (COI) gene sequences. They harbor a single gammaproteobacterial endosymbiont. Carbon isotopic data, as well as the analysis of genes involved in carbon and sulfur metabolism indicate a sulfide-oxidizing chemoautotrophic endosymbiont. The detection of a hydrogenase gene fragment suggests the potential for hydrogen oxidation as alternative energy source. Surprisingly, the endosymbiont harbors genes for two different carbon fixation pathways, the Calvin-Benson-Bassham (CBB) cycle as well as the reductive tricarboxylic acid (rTCA) cycle, as has been reported for the endosymbiont of the vent tubeworm Riftia pachyptila. In addition to RubisCO genes we detected ATP citrate lyase (ACL {\textendash} the key enzyme of the rTCA cycle) type II gene sequences using newly designed primer sets. Comparative investigations with additional tubeworm species (Lamellibrachia luymesi, Lamellibrachia sp. 1, Lamellibrachia sp. 2, Escarpia laminata, Seepiophila jonesi) from multiple cold seep sites in the Gulf of Mexico revealed the presence of acl genes in these species as well. Thus, our study suggests that the presence of two different carbon fixation pathways, the CBB cycle and the rTCA cycle, is not restricted to the Riftia endosymbiont, but rather might be common in vestimentiferan tubeworm endosymbionts, regardless of the habitat.},
	keywords = {ROV Jason (Remotely Operated Vehicle)},
	doi = {10.3389/fmicb.2012.00423},
	author = {Thiel, Vera and Hugler, M and Bl{\"u}mel, M and Baumann, H I and G{\"a}rtner, A and Schmaljohann, R and Strauss, H and Garbe-Schonberg, D and Petersen, S and Cowart, D A and Fisher, C R and Imhoff, J F}
}
@article {Schmidt2011,
	title = {{Fluid elemental and stable isotope composition of the Nibelungen hydrothermal field (8 degrees18{\textquoteright}S, Mid-Atlantic Ridge): Constraints on fluid-rock interaction in heterogeneous lithosphere}},
	journal = {Chemical Geology},
	volume = {280},
	number = {1-2},
	year = {2011},
	pages = {1{\textendash}18},
	abstract = {Depending on the geological setting, the interaction of submarine hydrothermal fluids with the host rock leads to distinct energy and mass transfers between the lithosphere and the hydrosphere. The Nibelungen hydrothermal field is located at 8{\textdegree}18'S, about 9~km off-axis of the Mid-Atlantic Ridge (MAR). At 3000~m water depth, 372~{\textdegree}C hot, acidic fluids emanate directly from the bottom, without visible sulfide chimney formation. Hydrothermal fluids obtained in 2009 are characterized by low H2S concentrations (1.1~mM), a depletion of B (192~$μ$M) relative to seawater, lower Si (13.7~mM) and Li (391~$μ$M) concentrations relative to basaltic-hosted hydrothermal systems and a large positive Eu anomaly, and display a distinct stable isotope signature of hydrogen (∆2HH2O~=~7.6{\textendash}8.7{\textperthousand}) and of oxygen (∆18OH2O~=~2.2{\textendash}2.4{\textperthousand}). The heavy hydrogen isotopic signature of the Nibelungen fluids is a specific feature of ultramafic-hosted hydrothermal systems and is mainly controlled by the formation of OH-bearing alteration minerals like serpentine, brucite, and tremolite during pervasive serpentinization. New isotopic data obtained for the ultramafic-hosted Logatchev I field at 14{\textdegree}45'N, MAR (∆2HH2O~=~3.8{\textendash}4.2{\textperthousand}) display a similar trend, being clearly distinguished from other, mafic-hosted hydrothermal systems at the MAR. The fluid geochemistry at Nibelungen kept stable since the first sampling campaign in 2006 and is evident for a hybrid alteration of mafic and ultramafic rocks in the subseafloor. Whereas the ultramafic-fingerprint parameters Si, Li, B, Eu anomaly and ∆2HH2O distinguish the Nibelungen field from other hydrothermal systems venting in basaltic settings at similar physico-chemical conditions and are related to the interaction with mantle rocks, the relatively high concentrations of trace alkali elements, Pb, and Tl can only be attributed to the alteration of melt-derived gabbroic rocks. The elemental and isotopic composition of the fluid suggest a multi-step alteration sequence: (1) low- to medium-temperature alteration of gabbroic rocks, (2) pervasive serpentinization at moderate to high temperatures, and (3) limited high-temperature interaction with basaltic rocks during final ascent of the fluid. The integrated water/rock ratio for the Nibelungen hydrothermal system is about 0.5. The fluid compositional fingerprint at Nibelungen is similar to the ultramafic-hosted Logatchev I fluids with respect to key parameters. Some compositional differences can be ascribed to different alteration temperatures and other fluid pathways involving a variety of source rocks, higher water/rock ratios, and sulfide precipitation in the sub-seafloor at Logatchev I.},
	keywords = {ROV Jason (Remotely Operated Vehicle)},
	issn = {0009-2541},
	doi = {10.1016/j.chemgeo.2010.07.008},
	url = {http://dx.doi.org/10.1016/j.chemgeo.2010.07.008},
	author = {Schmidt, K and Garbe-Schonberg, D and Koschinsky, A and Strauss, H and Jost, C L and Klevenz, V and Koniger, P}
}
