Marine ferromanganese crusts and nodules host high concentrations of many economically interesting metals such as platinum (Pt), with Pt concentrations in the range of 44 to 3207 ppb in 182 analyzed samples from various locations in the global ocean. Different mechanisms have been proposed to explain this strong enrichment in the MnFe oxide phases compared to seawater, including reduction of seawater Pt(II) to Pt(0) or oxidation to Pt(IV) and surface adsorption on the Fe-oxyhydroxide or Mn-oxide phases. To shed more light on the process of Pt enrichment in nodules and crusts, we applied a multi-method approach including bulk analyses, statistics (correlations and Q-mode factor analyses), sequential leaching, sorption experiments, and XANES and EXAFS measurements. Our analyses lend new support to the heterogeneous oxidation/sorption mechanism advanced by Maeno et al. (2016) to explain the initial Pt(II) enrichment on FeMn crusts, with Pt oxidation only taking place on the Mn-oxide phase but not on the Fe-oxyhydroxide phase of crusts. Nodules show lower concentrations and a lesser association of Pt with the Mn phase as the latter is partly of diagenetic origin while the origin of Pt is hydrogenetic. Our results also indicate that sorption of Pt-(aq)(2+) to FeO(OH) is possible if Pt((aq))(2+)exists under conditions typical of nodule and crust growth in the oceans. Platinum concentrations are consistently highest in phosphatized FeMn crusts where they appear to be related to the occurrence of a 10 A manganate, so they are likely to be the best exploration target for Pt globally in marine FeMn crusts. However, further work is needed to understand the geochemical reactions that dominate mass transfer of Pt under conditions under which crusts are phosphatized and to identify the exact mineral type which hosts the Pt enrichment. The complex Pt geochemistry in marine FeMn crusts and nodules due to the different phase associations and enrichment processes on the different carrier phases make a straightforward interpretation of Pt data in specific samples difficult. Our findings suggest that only spatially resolved, species-specific methods available via synchrotron-based X-ray and modern electron-probe micro-analyzers (in development) could provide the combination of spatial resolution and species-specificity to determine which of several proposed mechanisms are actually responsible for Pt enrichment in FeMn crusts.

Cobalt-rich ferromanganese crusts from the seafloor are gaining significance due to the presence of a variety of major, minor, and trace metals that are of strategic importance for sustained demands of the industry in future. This chapter describes the occurrence and nature, mineralogy, formation and growth, chemical composition as well as their inter-relationships. The chapter further looks at total and regional metal potentials and proposes a resource assessment model for ferromanganese crust deposits and their economic considerations.

Seafloor Massive Sulfides (SMS) are increasingly accepted as important marine raw material resources for the future, in particular because of their polymetallic character. Many industrial nations are researching not only on the scientific importance of these deposits but also on their economic value. Regarding the current state of the international exploration, mainly two-dimensional surface-close observations are accessible, whereas only some core data and measurements are publicly available to date. In fact, there are few successful drilling campaigns containing information about the size and shape, which also give information on the structure and content of modern massive sulfide ore bodies in their third dimension. Regarding the mechanical properties of SMS samples, only few data are available. Geotechnical data of these deposits are important in order to develop an efficient mining technology for exploitation. In this research, 12 SMS samples from two different locations were investigated. Based on the mineralogical characterization of the studied samples the geotechnical properties were preliminary correlated with the mineralogical results. The comparative study indicates how far the geotechnical data are controlled by mineral type and composition, including the porosity. A regression relation between compressive strength and the porosity based on the mineralogy shows a distinct relation between these parameters. Therefore, the geomechanical and mineralogical features have a strong importance for deep-sea mining applications and this should be kept in mind considering the hyperbaric effects on the rock cutting.

Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.

During the first leg of R/V Meteor cruise M44 in February 1999, geoscientific studies in two areas in the Sea of Marmara were carried out. The studies mainly focused on cool fluid and gas (mainly methane) emanations in the deepest zones of the Sea of Marmara along the northern strand of the North Anatolian Fault Zone, which were particularly expected because of the availability of fault zones as a preferential pathway for fluid migration. Fluids and gases both within the pore water and the benthic water were investigated through long cores and water samples to reveal their relationship with the solid substance of the sediments. In order to determine the coring, water sampling and video stations, bathymetric charts of the study areas A and B were obtained by using the HYDROSWEEP mapping system. The first multibeam bathymetric maps at 1:50.000 scale of the Sea of Marmara revealed E-W-trending strike-slip faults cutting the basins and the ridges, adding new insights to previous studies which reported ridges and basins bounded by NE-SW-trending strike-slip faults and E-W-trending normal faults.

A strong increase in the global demand for metallic raw materials, coupled with rising market prices, has heightened interest in marine seabed mineral deposits and the feasibility of their extraction for many marine scientists, engineers, and mining companies. This interest focuses not only on base and precious metals but also on strategically important elements needed for high‐technology applications, such as cobalt, nickel, molybdenum, titanium, gallium, selenium, telurium, indium, and the rare earth elements.A symposium and workshop on deep‐sea minerals and mining was convened at the Rheinisch‐Westfälische Technische Hochschule (RWTH) Aachen, in Germany. More than 100 scientists from 16 countries assembled to discuss the opportunities and challenges of interdisciplinary research concerning deep‐ocean mineral resources. Two days of plenary talks presented by invited experts representing diverse disciplines were followed by a 1‐day workshop to discuss the current knowledge; to develop research strategies that address emerging exploration and recovery techniques; and to assess economic, legal, and ecological issues inherent in deep‐sea mining.

Little is known about the role of island arcs as hydrothermal sources to the ocean when compared to the extensive research that has been carried out on hydrothermal systems at spreading ridges, although increasingly more work is being done on intraoceanic arcs. Here, we present fluid geochemistry data from the Kick'em Jenny (KeJ) submarine volcano of the Lesser Antilles island arc. Discharge of diffuse hydrothermal fluid was discovered on the southwestern flanks of the volcano. Hydrothermal input into the water column was recognized from CH4 and trace-metal anomalies in water-column profiles in a depth range of 500-700 m. Samples collected directly on the seafloor also showed evidence for hydrothermal emissions where Mg and Cl were depleted in the fluids compared to ambient seawater, while CH4 and several trace metals were enriched. The chemical composition of these samples, including 0 and H isotope data, suggests that the fluids are a mixture between a condensed vapor phase derived from a phase-separated hydrothermal fluid, which was conductively cooled in the sub-surface, and seawater. Increased dissolved organic carbon (DOC) concentrations of the fluids also indicate interaction with the sediment layer through which the fluids percolated. Although the volcanic crater could not be sampled directly due to safety concerns, delta(3) He and some trace-metal values in seawater samples indicate fluid input containing a mantle component, probably from a hot, focused-flow source in the crater region around 200-300 m depth. (c) 2007 Elsevier B.V. All rights reserved.

Three sediment cores taken from the Central Sea of Marmara were sedimentologically and geochemically investigated. All the cores show a continuous sedimentation record. According to isotopic age-dating measurements, two of the cores cover an age range of more than 20,000 years. Since the Sea of Marmara was an isolated lacustrine system during the last glacial maximum (about 20 ka BP), the two cores should include the transition from lacustrine to marine environmental conditions. The third core has a very high sedimentation rate (70 cm/ka), and therefore does not reach the transitional section. In two cores, however, a very calcite-rich layer (Unit C) was observed. Carbon-isotope investigations show that this calcite is not of diagenetic or biogenic origin but may represent a direct inorganic precipitate out of a deepwater layer. In order to prove this hypothesis, we used a geochemical model based on thermodynamic calculations. This model shows that the calcite precipitation can only be explained by mixing of anoxic deep lacustrine water with oxic marine Mediterranean water. The necessary aqueous conditions are also obtained. The model presented thus provides an important contribution to the evolution of the Sea of Marmara during the transition from lacustrine to marine conditions. The thickness of the Unit C layer indicates that this environmental change lasted approximately 1.5 ka.

Radiogenic isotope compositions (Sr, Nd, Pb, Hf, and Os) of sediment‐hosted seafloor ferromanganese crusts and sediments incrusted with ferromanganese oxyhydroxides from the Lesser Antilles island arc were measured to distinguish between hydrogenous (seawater‐derived) and hydrothermal metal sources. The ages of the precipitates range between recent (last few thousand years) and a few 100 kyr as deduced from 10 Be and Co concentrations. Evidence from the presence of bladed todorokite and nontronite, together with the major element and REE composition, suggests that a significant proportion of these sediment‐hosted precipitates formed at relatively low temperatures from a mixture of seawater and hydrothermal fluids associated with island arc volcanism. The radiogenic isotope compositions of all metals mentioned above, except Pb, show large differences in hydrothermal versus hydrogenous contributions over space and time. In contrast to precipitates of high‐temperature fluids which mainly scavenge their REE contents from seawater the crusts of this study show 143 Nd/ 144 Nd of up to 0.512817 (ɛNd = +3.5). This is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of ∼0.51209 (ɛNd = −10.7). These crusts also show high 176 Hf/ 177 Hf (up to 0.283102), low 87 Sr/ 86 Sr (up to 0.7069), and low 187 Os/ 188 Os (up to 0.16) compared with local seawater, as expected from hydrothermal, island‐arc‐derived metal contributions. In contrast, the Pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources. It is suggested that Pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of Pb from the rocks or sediments. External sources such as Saharan dust, particulate inputs from the Orinoco River, or even incongruent release of Pb isotopes from the island arc rock‐derived particles must have contributed to the observed Pb isotope variability. Our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater.

Hydrothermal sulfides were recovered from the 16 degrees 50'S triple junction area in the North Fiji Basin, at a water depth of ca. 1900 m. The chimney samples can be divided into three groups based on their major metal contents: 1) type 1 (Fe-Cu-rich), 2) type 2 (Fe-Cu-rich with minor Zn), and 3) type 3 (Zn-rich) chimneys. Type 1 chimneys are mainly composed of chalcopyrite and pyrite, and are enriched in elements commonly precipitated under high temperature conditions (> 300 degrees C), such as Cu, Co, Mo, and Se. Type 3 chimneys consist dominantly of sphalerite and marcasite with traces of pyrite and chalcopyrite, and are enriched in elements commonly associated with relatively low temperatures (150 to 250 degrees C), such as Zn, Cd, Pb, As, and Ga. Type 2 chimneys have a mineralogy similar to that of type I chimneys although their trace metal contents range between those of type 1 and type 3 samples. Type 2 chimneys appear to be the products of low-temperature replacement, which might be related to formation of type 3 chimneys, of type 1 chimneys.The trace element composition of basaltic rocks indicates that magma generation in the triple junction area was influenced by two different sources: N-MORB and E-MORB. Sulfur and lead isotope patterns of the hydrothermal chimneys show distinct differences between the type 1 and type 3 chimneys. The type 1 sulfides (delta S-34 = 2.8 +/- 1.2 parts per thousand; Pb-206/Pb-204= 18.082 to 18.132; Pb-207/Pb-204 = 15.440 to 15.481; Pb-208/Pb-204 = 37.764 to 37.916) are depleted in S-34 and have lower Pb isotope ratios compared to types 2 and 3 chimneys (delta S-34 = 4.1 +/- 0.9 parts per thousand; Pb-206/Pb-104 = 18.122 to 18.193; Pb-207/Pb-204 = 15.475 to 15.554; Pb-208/Pb-204 = 37.882 to 38.150). The higher delta S-34 values for types 2 and 3 sulfides than type 1 sulfides can be explained by mixing of hydrothermal fluids with ambient seawater. The more radiogenic Pb isotope composition of types 2 and 3 chimneys compared to type 1 chimneys suggest that the formation of types 2 and 3 chimneys were possibly related to E-MORB volcanism that shows higher Pb isotope composition than N-MORB rocks. However, ferromanganese crust samples have radiogenic Pb isotope compositions that are identical to those of E-MORB. Therefore, input of hydrogenous Pb is also a possible source for radiogenic Pb isotopes in the types 2 and 3 chimneys. (c) 2006 Elsevier B.V. All rights reserved.

Surface sediment samples from near-shore shallow water as well as deeper water locations N and NE of the island of Methana were investigated geochemically. Shallow water samples from Thiafi Bay reveal up to 38-fold enrichment of As, associated with elevated contents of Sb, Fe and Zn. Deeper water samples NE of Methana show moderate Mn enrichment accompanied with elevated trace metal concentrations of As and, in some samples, Cd and Cu. In an area, where small mounds of possible hydrothermal origin were observed on the sea floor, fine-grained Fe-rich sediment was sampled with enrichment of typical hydrothermal trace elements As, P and Sb. Element enrichment in the investigated areas off Methana corresponds in terms of absolute concentrations and element suite to comparable hydrothermally influenced sediments from other locations of the Hellenic volcanic arc. The region between Methana peninsula and Aegina Island is not marked by vigorous hydrothermal activity, but localised enrichments of Fe and/or Mn, As, Sb as well as associated trace elements typically found in hydrothermally influenced sediments were identified.

Sulphate concentration profiles with non-constant gradients are reported from porewater samples in continental margin sediments. Recent results on a sediment core from the Ganos Fault in the Sea of Marmara revealed a porewater pattern with two gradients. Comparisons with the respective methane concentrations show the position of a sulphate–methane reaction zone (SMRZ) within the sediment column. Methane emanations from the seafloor as observed at other locations along the deeper Ganos Fault indicate the SMRZ as a transient system. A computer model based on an unsteady process estimates the starting time of the methane rise between 1096 and 907 years before present. Within this time period, one remarkable earthquake occurred in the direct vicinity of our study area in the year 1063 A.D. We suggest this could have opened the pathways for the ascending methane front.

Chromium redox speciation analysis was carried out onboard ship in several water column profiles off the islands of Dominica, St Lucia and Grenada (Lesser Antilles), and at two stations offshore from the Otago Peninsula (New Zealand). The catalytic adsorptive stripping voltammetry with diethylenetriaminepentaacetic acid as complexing reagent and a hanging mercury drop as a working electrode were used. In the samples from the Lesser Antilles, Cr(VI) concentrations ranged around a relatively constant background of 1.5–2.5 nM, except for one higher value of 4.3 nM, whereas Cr(III) was highly variable and reached maximum concentrations of 12 nM. Variable environmental influences, such as hydrothermal activity and atmospheric input, are probable sources for reduced chromium species. In contrast, the Cr(III) contribution was less than 50% of total Cr in subantarctic non-hydrothermal water offshore from the Otago Peninsula and the presence of Cr(III) was restricted to the upper 100 m of the water column. In these depth profiles, Cr (VI) (up to 3.7 nM) was clearly the dominating species.Onboard ship redox speciation was shown to be an effective means to avoid storing artefacts in species determination. We conclude that seafloor hydrothermal activity contributes significantly to the reduced Cr species chemistry of the surrounding seawater.

This article focuses on possible geochemical consequences of potential industrial activities in the deep sea, such as manganese nodule mining, for the heavy metal cycle of the deep sea and possible reactions of the benthic ecosystem. The metal fluxes induced by sediment resuspension are compared with fluvial, atmospheric, and hydrothermal metal fluxes into the ocean. The results of geochemical laboratory experiments and analyses of deep-sea benthic organisms are discussed with respect to their ecological importance in case of a seabed disturbance.A limited short-term increase of heavy metal concentrations in the benthic layer will probably cause only negligible harmful effects on the biota. An essential precondition is that the geochemical milieu remains largely unchanged; especially variations of the redox conditions would result in changes in metal speciation, bioavailability, and toxicity.