ALBERT

Description: Increasingly more data have indicated that the 40Ar/39Ar crushing technique provides a very useful approach to determine the mineralization ages of hydrothermal ore deposits. In this study novel gas mixing lines are proposed based on the data of two quartz samples by 40Ar/39Ar crushing. Electron microprobe analyses indicate that the quartz grains contain K-rich silicate microlites. Both quartzs by crushing yield two mixing lines with ages corresponding respectively to those of K-feldspar or sericite (post-mineralization fluids) and muscovite samples (ore-forming fluids). This is the first report that both ages of secondary and primary fluid inclusions (SFIs and PFIs) are confirmed correspondingly by those of the K-rich minerals. This study strongly indicates that the 40Ar/39Ar crushing technique is very useful to determine the ages of geofluid activities. The newly proposed gas mixing patterns are shown on the inverse and normal isochron diagrams, indicating: (1) the mixtures are in different proportions of the PFIs and SFIs in different crushing steps; (2) the gas mixing lines yield PFI ages with low initial 40Ar/36Ar ratios; (3) an intermediate age between PFI and SFI ages cannot be obtained because the progressive crushing technique never release gas mixtures with a constant PFI/SFI proportion for each step. The gas mixing lines are thus interpreted to yield significant geological ages. The mixing patterns will help us better understand the 40Ar/39Ar dating results and be used for references to other isotopic mixing isochron systems.

Description: A novel acidophilic member of the phylum Actinobacteria was isolated from an acidic stream draining an abandoned copper mine in north Wales. The isolate (PY-F3) was demonstrated to be a heterotroph that catalyzed the oxidation of ferrous iron (but not of sulfur or hydrogen) under aerobic conditions, and the reduction of ferric iron under micro-aerobic and anaerobic conditions. PY-F3 formed long entangled filaments of cells (〉50 μm long) during active growth phases, though these degenerated into smaller fragments and single cells in late stationary phase. Although isolate PY-F3 was not observed to grow below pH 2.0 and 10 °C, harvested biomass was found to oxidize ferrous iron at relatively fast rates at pH 1.5 and 5 °C. Phylogenetic analysis, based on comparisons of 16S rRNA gene sequences, showed that isolate PY-F3 has 91–93% gene similarity to those of the four classified genera and species of acidophilic Actinobacteria, and therefore is a representative of a novel genus. The binomial Acidithrix ferrooxidans is proposed for this new species, with PY-F3 as the designated type strain (=DSM 28176T, =JCM 19728T).

Description: Stable isotopes (15,14N, 18,16O) of dissolved inorganic nitrogen (N) were measured in sediment porewaters and benthic flux chambers across the Peruvian oxygen minimum zone (OMZ) from 74 to 1000 m water depth. Sediments at all locations were net consumers of bottom water NO3−. In waters shallower than 400 m, this sink was largely attributed to dissimilatory nitrate reduction to ammonium (DNRA) by filamentous nitrate-storing bacteria (Marithioploca and Beggiatoa) and to denitrification by foraminifera. The apparent N isotope effect of benthic NO3− loss (15εapp) was 7.4 ± 0.7‰ at microbial mat sites and 2.5 ± 0.9‰ at the lower fringe of the OMZ (400 m) where foraminifera were abundant. The OMZ sediments were a source of 15N-enriched NO2− (28.9 to 65.5‰) and NH4+ (19.4–20.5‰) to the bottom water. Model simulations generally support a previous hypothesis attributing the 15NH4+ enrichment to a coupling between DNRA and anammox (termed DAX) using biologically-stored NO3− from Marithioploca and NH4+ from the porewater. The model predicts that 40% of NO3− that is actively transported into the sediment by Marithioploca is reduced to N2 by this pathway. DAX enhances N2 fluxes by a factor of 2–3 and accounts for 70% of fixed N loss to N2. Moreover, because most of the ambient porewater NH4+ is generated by DNRA, up to two-thirds of biologically-transported NO3− could end up being lost to N2. This challenges the premise that Marithioploca-dominated sediments tend to conserve fixed N. By limiting the flux of 15NH4+ back to the ocean, DAX also tends to decrease benthic N fractionation. Tracking the fate of NH4+ once it leaves the sediment is critical for understanding how the benthos contributes to N isotope signals in the water column.

Description: Editorial

Description: Transient tracer data (CFC-12 and SF6) from three oceanographic field campaigns to the Mauritanian Upwelling area conducted during winter, spring and summer from 2005 to 2007 is presented. The transient tracers are used to constrain a possible solution to the transient time distribution (TTD) along 18°N and to quantify the mean ages in vertical sections perpendicular to the coast. We found that an Inverse Gaussian distribution where the ratio of the moments δ and Γ equals 1.2 is a possible solution (δ/Γ=1.2) of the TTD. The transient tracers further show considerable under-saturation in the mixed layer during the winter and spring cruises that can only be maintained by mixing or upwelling by tracer-poor water from below the mixed layer. We use dissipation data from microstructure measurements and the tracer depth distribution to quantify the flux of tracers to the mixed layer by vertical diffusivity and wind data from the ship to quantify the air-sea flux. We then use the magnitude of the under-saturation in the mixed layer to estimate the advective upwelling velocity which is the balance the first two processes, in a steady state assumption. We find that the upwelling velocities range from less than 1 to 5.6×10-5ms-1 (〈0.8-4.8md-1), with generally higher values close to the coast, but with comparable upwelling velocities during spring and winter. During the summer cruise the transient tracers were close to equilibrium with the atmosphere, suggesting no upwelling. We have shown the use of CFC-12 and SF6 transient tracer data for calculating upwelling velocity, and found an overall uncertainty of roughly ±50%.

Description: In this chapter the role of the ocean on climate and climate change is discussed in terms of the properties of oceans and in terms of the tools available to oceanographers. The details of the Atlantic Meridional Overturning Circulation (AMOC) are described with special reference to motivation, driving mechanisms, heat transport and the ocean's uptake of carbon and the ventilation of the deep ocean. The past changes of the AMOC and the Atlantic climate are also discussed. The chapter ends with a discussion of three questions: • Why should the AMOC change as a result of climate change? • Can we detect changes in the AMOC? • Is the AMOC already changing as a result of climate change?

Description: Diapycnal diffusivity estimates from two Tracer Release Experiments (TREs) and microstructure measurements in the oxycline and core of the oxygen minimum zone (OMZ) in the eastern tropical North Atlantic are compared. For the first time, two TREs within the same area at different depths were realized: the Guinea Upwelling Tracer Release Experiment (GUTRE) initiated in 2008 in the oxycline at approximately 320 m depth, and the Oxygen Supply Tracer Release Experiment (OSTRE) initiated in 2012 in the core of the OMZ at approximately 410 m depth. The mean diapycnal diffusivity Dz was found to be insignificantly smaller in the OMZ core with (1.06 ± 0.24) × 10− 5 m2 s− 1 compared to (1.11 ± 0.22) × 10− 5 m2 s− 1 90 m shallower in the oxycline. Unexpectedly, GUTRE tracer was detected during two of the OSTRE surveys which showed that the estimated diapycnal diffusivity from GUTRE over a time period of seven years was within the uncertainty of the previous estimates over a time period of three years. The results are consistent with the Dz estimates from microstructure measurements and demonstrate that Dz does not vary significantly vertically in the OMZ within the depth range of 200–600 m and does not change with time. The presence of a seamount chain in the vicinity of the GUTRE injection region did not cause enhanced Dz compared to the smoother bottom topography of the OSTRE injection region, although the analysis of vertical shear spectra from ship ADCP data showed elevated internal wave energy level in the seamount vicinity. However, the two tracer patches covered increasingly overlapping areas with time and thus spatially integrated increasingly similar fields of local diffusivity, as well as the difference in local stratification counteracted the influence of roughness on Dz. For both experiments no significant vertical displacements of the tracer were observed, thus diapycnal upwelling within the ETNA OMZ is below the uncertainty level of 5 m yr− 1.

Description: Highlights • “Black Smokers” on slow-spreading ridges can host larger seafloor massive sulfide (SMS) deposits than on fast ridges. • The largest slow-ridge SMS deposits are typically associated with long-lived tectonic fractures ± sustained fluid flow. • Ultramafic-, tectonic-hosted sites exhibit high average Cu (〉 10wt.%) and Au (〉 3ppm) contents in their surface SMS samples. • Hydrothermal plume surveys are consistent with equal abundances of magmatic vs tectonic vent-control along ultraslow ridges. • The first “Black Smokers” on any ultraslow ridges exhibit high Cu ± Au SMS contents at both magmatic and tectonic vent-sites. Abstract Here, we review the relationship between the distribution of modern-day seafloor hydrothermal activity along the global mid-ocean ridge crest and the nature of the mineral deposits being formed at those sites. Since the first discovery of seafloor venting, a sustained body of exploration has now prospected for one form of hydrothermal activity in particular – high temperature “black smoker” venting – along 〉 30% of the global mid-ocean ridge crest. While that still leaves most of that ~ 60,000 km continuous network to be explored, some important trends have already emerged. First, it is now known that submarine venting can occur along all mid-ocean ridges, regardless of spreading rate, and in all ocean basins. Further, to a first approximation, the abundance of currently active venting, as deduced from water column plume signals, can be scaled linearly with seafloor spreading rate (a simple proxy for magmatic heat-flux). What can also be recognized, however, is that there is an “excess” of high temperature venting along slow and ultra-slow spreading ridges when compared to what was originally predicted from seafloor spreading/magmatic heat-budget models. An examination of hydrothermal systems tracked to source on the slow spreading Mid-Atlantic Ridge reveals that no more than half of the sites responsible for the “black smoker” plume signals observed in the overlying water column are associated with magmatic systems comparable to those known from fast-spreading ridges. The other half of all currently known active high-temperature submarine systems on the Mid-Atlantic Ridge are hosted under tectonic control. These systems appear both to be longer-lived than, and to give rise to much larger sulfide deposits than, their magmatic counterparts — presumably as a result of sustained fluid flow. A majority of these tectonic-hosted systems also involve water–rock interaction with ultramafic sources. Importantly, from a mineral resource perspective, this subset of tectonic-hosted vent-sites also represents the only actively-forming seafloor massive sulfide deposits on mid-ocean ridges that exhibit high concentrations of Cu and Au in their surface samples (〉 10 wt.% average Cu content and 〉 3 ppm average Au). Along ultraslow-spreading ridges, first detailed examinations of hydrothermally active sites suggest that sulfide deposit formation at those sites may depart even further from the spreading-rate model than slow-spreading ridges do. Hydrothermal plume distributions along ultraslow ridges follow the same (~ 50:50) distribution of “black smoker” plume signals between magmatic and tectonic settings as the slow spreading MAR. However, the first three “black smoker” sites tracked to source on any ultra-slow ridges have all revealed high temperature vent-sites that host large polymetallic sulfide deposits in both magmatic as well as tectonic settings. Further, deposits in both types of setting have now been revealed to exhibit moderate to high concentrations of Cu and Au, respectively. An important implication is that ultra-slow ridges may represent the strongest mineral resource potential for the global ridge crest, despite being host to the lowest magmatic heat budget.

Description: We present high-resolution records of sedimentary nitrogen (δ15Nbulk) and carbon isotope ratios (δ13Cbulk) from piston core SO201-2-85KL located in the western Bering Sea. The records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr. The δ15Nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization (~62–80%) despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction (mterr). This suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today (~84%). δ15Nbulk increases from Marine Isotope Stage (MIS) 5.4 and culminates during the Last Glacial Maximum, which indicates that nitrate utilization in the Bering Sea was raised during cold intervals (MIS 5.4, 5.2, 4) and almost complete during MIS 3 and 2 (~93–100%). This is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone, thereby increasing the iron-to-nutrient ratio and therefore the nitrate utilization in the mixed surface layer. Large variations in δ15Nbulk were also recorded from 180 to 130 ka BP (MIS 6), indicating a potential link to insolation and sea-level forcing and its related feedbacks. Millennial-scale oscillations were observed in δ15Nbulk and δ13Cbulk that might be related to Greenland interstadials.

Description: Nitric oxide (NO) is a short-lived compound of the marine nitrogen cycle. However, measurements of NO in seawater are analytically challenging and our knowledge about its oceanic distribution is, therefore, rudimentary. NO was measured in the oxygen minimum zone (OMZ) of the eastern tropical South Pacific Ocean (ETSP) off Peru during R/V Meteor cruise M93 in February/March 2013. NO concentrations ranged from close to or below the detection limit (0.5nmolL-1) in the surface layer to 9.5nmolL-1 in the OMZ. NO concentrations increased significantly when oxygen (O2) concentrations dropped below 1-2μmolL-1. We found positive correlations between NO and NO2 - as well as between NO and the abundance of archaeal amoA, a marker gene for archaeal nitrifiers. No trends between NO and nirS and hzo, marker genes for canonical denitrification and anammox, respectively, were found. To this end, we conclude that NO off Peru was mainly produced by archaeal nitrifier-denitrification at low O2 concentrations in the OMZ.