Description: Summary Meteor Cruise M81/1 was dedicated to the investigation of the distribution of dissolved and particulate trace metals and their isotopic compositions (TEIs) in the full water column of the tropical Atlantic Ocean and their driving factors including main external inputs and internal cycling and ocean circulation. The research program is embedded in the international GEOTRACES program (e.g. Henderson et al., 2007), which this cruise was an official part of and thus corresponds to GEOTRACES cruise GA11. This cruise was completely dedicated to the trace metal clean and contamination-free sampling of waters and particulates for subsequent analyses of the TEIs in the home laboratories of the national and international participants. Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was realized by using a dedicated and coated trace metal clean rosette equipped with Teflon-coated GO-FLO bottles operated via a polyester coated cable from a mobile winch that was thankfully made available by the U.S. partners of the GEOTRACES program for this cruise. The particulate samples were also collected under trace metal clean conditions using established in-situ pump systems. The cruise track led the cruise southward from the Canary Islands to 11°S and then continued northwestward along the northern margin of South America until it reached Port of Spain, Trinidad & Tobago. The track crossed areas of major external inputs including exchange with the volcanic Canary Islands, the Saharan dust plume, as well as the plume of the Amazon outflow. In terms of internal cycling the equatorial high biological productivity band, as well as increased productivity associated with the Amazon Plume were covered. All major water masses contributing the Atlantic Meridional Overturning Circulation, as well as the distinct narrow equatorial surface and subsurface east-west current bands were sampled. A total of 17 deep stations were sampled for the different dissolved TEIs, which were in most cases accompanied by particulate sampling. In addition, surface waters were continuously sampled under trace metal clean conditions using a towed fish.

Description: Oceanic and atmospheric circulation patterns varied considerably during the Tertiary and Quaternary and influenced the geochemical cycles of elements in seawater. We report the first resolution lead and neodymium isotopic record of such changes at a high time resolution in two depths profiles from a hydrogenous FeMn crust. The crust, Va13-2, is located in the central Pacific (146°W, 9°25′N, 4830 m) and has previously been dated by 230Th and 10Be. The first profile was drilled with a sample time resolution of ∼3 kyr and allows evaluation of short-term changes to lead and neodymium sources to central Pacific seawater over the last 400 kyr (marine δ18O stages 2 to 11). Longer-term changes were monitored at lower time resolution in a second profile to an age of 10 Ma. Short-term variations in lead and neodymium isotope ratios are resolved in the high resolution profile (0 to 400 kyr). Superimposed on the short-term variations is a secular decrease in Full-size image (〈1 K) ratios beginning at ∼130 kyr in marine δ18O stage 5, implying a change in the lead sources to the central Pacific. Lead and neodymium isotopic compositions indicate an increased influence from Central American eolian sources to Pacific seawater at this time. Lead isotopes are found to be statistically more variable during interglacial than glacial periods. These observations are supported by the greater eolian dust fluxes found in sediment cores from the equatorial Pacific during interglacial stages. The most important paleoceanographic event of the last 10 Ma to affect Pacific seawater was the closure of the Panama gateway. Changes in lead and neodymium isotopes in Val3-2 during the last 10 Ma occurred along with gradual closure of the Panama straits. However, these changes did not occur in tandem: while neodymium isotope ratios increase between 10 and 8 Ma, lead isotope ratios remain constant. In contrast, the period 7 to 1 Ma is marked by a secular increase in lead isotope ratios but nearly constant neodymium. These changes are consistent with a source of radiogenic lead and neodymium conveyed by the Circumpolar Current into the Pacific, rather than by the Panama gateway, and involve 20 to 40% Southern Component Water (SCW) input of lead and neodymium. Modelling of lead and neodymium isotopic mixing between the different water masses involved in generating Pacific deep waters lead us to the following conclusions: (1) Small variations in the strength and composition of North Atlantic Deep Water (NADW) have a relatively minor effect on the amounts of lead and neodymium from SCW contributing to the Pacific and (2) an enhanced SCW flow with an open isthmus of Panama, as suggested by General Circulation Models (GCM), requires a corresponding reduction in NADW Pb and Nd contributions to SCW. The general agreement between the isotopic compositions of surface layers of Mn nodules, integrated over such long time intervals, and those of present-day bottom waters at their respective locations show that the present-day ocean circulation pattern has dominated through the Pleistocene. Our study of Mn crust Va13-2 shows that shorter-term changes in lead and neodymium isotope ratios can be resolved, provided that such crusts are sampled at an appropriate time resolution.

Description: We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

Description: [1] The Terceira Rift formed relatively recently (∼1 Ma ago) by rifting of the old oceanic lithosphere of the Azores Plateau and is currently spreading at a rate of 2–4mm/a. Together with the Mid-Atlantic Ridge, the Terceira Rift forms a triple junction that separates the Eurasian, African, and American Plates. Four volcanic systems (São Miguel, João de Castro, Terceira, Graciosa), three of which are islands, are distinguished along the axis and are separated by deep avolcanic basins similar to other ultraslow spreading centers. The major element, trace element and Sr-Nd-Pb isotope geochemistry of submarine and subaerial lavas display large along-axis variations. Major and trace element modeling suggests melting in the garnet stability field at smaller degrees of partial melting at the easternmost volcanic system (São Miguel) compared to the central and western volcanoes, which appear to be characterized by slightly higher melting degrees in the spinel/garnet transition zone. The degrees of partial melting at the Terceira Rift are slightly lower than at other ultraslow mid-ocean ridge spreading axes (Southwest Indian Ridge, Gakkel Ridge) and occur at greater depths as a result of the melting anomaly beneath the Azores. The combined interaction of a high obliquity, very slow spreading rates, and a thick preexisting lithosphere along the axis probably prevents the formation and eruption of larger amounts of melt along the Terceira Rift. However, the presence of ocean islands requires a relatively stable melting anomaly over relatively long periods of time. The trace element and Sr-Nd-Pb isotopes display individual binary mixing arrays for each volcanic system and thus provide additional evidence for focused magmatism with no (or very limited) melt or source interaction between the volcanic systems. The westernmost mantle sources beneath Graciosa and the most radiogenic lavas from the neighboring Mid-Atlantic Ridge suggest a mantle flow from Graciosa toward the Mid-Atlantic Ridge and hence a flux of mantle material from one spreading axis into the other. The Terceira Rift represents a unique oceanic rift system situated within the thickened, relatively old oceanic lithosphere and thus exhibits both oceanic and continental features.

Description: Understanding oceanic cadmium (Cd) cycling is paramount due to its micronutrient‐like behavior in seawater, which has been inferred from its similarity to phosphate (PO4) cycling. Cadmium concentrations follow a nutrient‐like consumption‐regeneration cycle in the top of the water column and are mainly controlled by water mass mixing and circulation in the deep ocean. However, an additional scavenging mechanism through cadmium sulfide (CdS) precipitates, occurring within sinking biogenic particles in oxygen deficient zones (ODZ), has been proposed. In this study, we report Cd stable isotope and concentration data for seven vertical seawater profiles sampled during GEOTRACES cruise GA08 in the northern Cape and Angola Basins, which feature a significant ODZ along their eastern margins. Outside the ODZ, Cd cycling is similar to that previously reported for the South Atlantic. While water mass mixing largely controls deep ocean Cd isotope signatures, Cd isotope fractionation in surface waters can be modelled as an open system at steady‐state buffered by organic ligand complexation. In the ODZ, stronger Cd depletion relative to PO4 is associated with a shift in δ114Cd towards heavier values, which is indicative of CdS precipitation. Our interpretation is supported by experimental CdS precipitation data and a size‐resolved particle model involving bacterial sulfate reduction as a precursor of CdS. Our estimates of the CdS flux to the seafloor (107 to 109 mol yr‐1) indicate that CdS precipitation is a significant process of Cd removal and constitutes a non‐negligible Cd sink that needs to be better quantified by Cd isotope analyses of marine sediments.

Description: This paper contains the results of an extensive isotopic study of United States Geological Survey GSD-1G and MPI-DING reference glasses. Thirteen different laboratories were involved using high-precision bulk (TIMS, MC-ICP-MS) and microanalytical (LA-MC-ICP-MS, LA-ICP-MS) techniques. Detailed studies were performed to demonstrate the large-scale and small-scale homogeneity of the reference glasses. Together with previously published isotopic data from ten other laboratories, preliminary reference and information values as well as their uncertainties at the 95% confidence level were determined for H, O, Li, B, Si, Ca, Sr, Nd, Hf, Pb, Th and U isotopes using the recommendations of the International Association of Geoanalysts for certification of reference materials. Our results indicate that GSD-1G and the MPI-DING glasses are suitable reference materials for microanalytical and bulk analytical purposes.