He isotope, U/Th isotope, Calcium carbonate, biogenic opal, rare earth element concentrations, and grain size distribution measured on core-top sediments during SONNE cruise SO202 (INOPEX)

Eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient-low chlorophyll status of the Subarctic North Pacific. We map the spatial distribution of dust input using three different geochemical tracers of eolian dust, 4He, 232Th and rare earth elements, in combination with grain size distribution data, from a set of core-top sediments covering the entire Subarctic North Pacific. Using the suite of geochemical proxies to fingerprint different lithogenic components, we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash, ice-rafted debris, riverine and hemipelagic input. While the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust, lithogenic components other than eolian dust play a more crucial role along the arcs. In sites dominated by dust, eolian dust input appears to be characterized by a nearly uniform grain size mode at ~4 µm. Applying the 230Th-normalization technique, our proxies yield a consistent pattern of uniform dust fluxes of 1-2 g/m**2/yr across the Subarctic North Pacific. Elevated eolian dust fluxes of 2-4 g/m**2/yr characterize the westernmost region off Japan and the southern Kurile Islands south of 45° N and west of 165° E along the main pathway of the westerly winds. The core-top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the Subarctic North Pacific. The dust flux pattern compares well with state-of-the-art dust model predictions in the western and central Subarctic North Pacific, but we find that dust fluxes are higher than modeled fluxes by 0.5-1 g/m**2/yr in the northwest, northeast and eastern Subarctic North Pacific. Our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust-induced iron fertilization of past changes in biological productivity in the Subarctic North Pacific.

Dissolved seawater neodymium isotopes, radium isotopes and rare earth element concentrations measured in coastal waters around Oahu and at HOT-ALOHA

Dissolved seawater neodymium isotopes, radium isotopes and rare earth element concentrations measured in coastal waters around Oahu and at HOT-ALOHA. Data from R/V Kilo Moana cruise KM1107 supplement by data from Kilo Moana cruises KM1215 (Hoe-Dylan V), KM1219 (Hoe-Dylan IX), KM1309 (Hoe-Phor I) and KM1316 (Hoe-Phor II).

Rare earth element concentrations and geochemistry of carbonate minerals from the Logatchev Hydrothermal Field and the Gakkel Ridge

The ultramafic-hosted Logatchev Hydrothermal Field (LHF) at 15°N on the Mid-Atlantic Ridge and the Arctic Gakkel Ridge (GR) feature carbonate precipitates (aragonite, calcite, and dolomite) in voids and fractures within different types of host rocks. We present chemical and Sr isotopic compositions of these different carbonates to examine the conditions that led to their formation. Our data reveal that different processes have led to the precipitation of carbonates in the various settings. Seawater-like 87Sr/86Sr ratios for aragonite in serpentinites (0.70909 to 0.70917) from the LHF are similar to those of aragonite from the GR (0.70912 to 0.70917) and indicate aragonite precipitation from seawater at ambient conditions at both sites. Aragonite veins in sulfide breccias from LHF also have seawater-like Sr isotope compositions (0.70909 to 0.70915), however, their rare earth element (REE) patterns show a clear positive europium (Eu) anomaly indicative of a small (< 1%) hydrothermal contribution. In contrast to aragonite, dolomite from the LHF has precipitated at much higher temperatures (~100 °C), and yet its 87Sr/86Sr ratios (0.70896 to 0.70907) are only slightly lower than those of aragonite. Even higher temperatures are calculated for the precipitation of deformed calcite veins in serpentine-talc fault schists form north of the LHF. These calcites show unradiogenic 87Sr/86Sr ratios (0.70460 to 0.70499) indicative of precipitation from evolved hydrothermal fluids. A simple mixing model based on Sr mass balance and enthalpy conservation indicates strongly variable conditions of fluid mixing and heat transfers involved in carbonate formation. Dolomite precipitated from a mixture of 97% seawater and 3% hydrothermal fluid that should have had a temperature of approximately 14 °C assuming that no heat was transferred. The much higher apparent precipitation temperatures based on oxygen isotopes (~ 100 °C) may be indicative of conductive heating, probably of seawater prior to mixing. The hydrothermal calcite in the fault schist has precipitated from a mixture of 67% hydrothermal fluid and 33% seawater, which should have had an isenthalpic mixing temperature of ~ 250 °C. The significantly lower temperatures calculated from oxygen isotopes are likely due to conductive cooling of hydrothermal fluid discharging along faults. Rare earth element patterns corroborate the results of the mixing model, since the hydrothermal calcite, which formed from waters with the greatest hydrothermal contribution, has REE patterns that closely resemble those of vent fluids from the LHF. Our results demonstrate, for the first time, that (1) precipitation from pure seawater, (2) conductive heating of seawater, and (3) conductive cooling of hydrothermal fluids in the sub-seafloor all can lead to carbonate precipitation within a single ultramafic-hosted hydrothermal system.

Major element compositions, minerals and trace elements at DSDP Leg 67 Holes

Mineralogical (microprobe) and geochemical (X-ray fluorescence, neutron activation analyses) data are given for 18 samples of volcanic rocks from the Guatemala Trench area (Deep Sea Drilling Project Leg 67). Typical fresh oceanic tholeiites occur in the trench itself (Hole 500) and in its immediate vicinity on the Cocos Plate (Site 495). Several samples (often reworked) of "spilitic" oceanic tholeiites are also described from the Trench: their mineralogy (greenschist facies association - actinolite + plagioclase + chlorite) and geochemistry (alteration, sometimes linked to manganese and zinc mineralization) are shown to result from high-temperature (300°-475°C) hydrothermal sea water-basalt interactions. The samples studied are depleted in light rare-earth elements (LREE), with the exception of the slightly LREE-enriched basalts from Hole 500. The occurrence of such different oceanic tholeiites in the same area is problematic. Volcanic rocks from the Guatemala continental slope (Hole 494A) are described as greenschist facies metabasites (actinolite + epidote + chlorite + plagioclase + calcite + quartz), mineralogically different from the spilites exposed on the Costa Rica coastal range (Nicoya Peninsula). Their primary magmatic affinity is uncertain: clinopyroxene and plagioclase compositions, together with titanium and other hygromagmaphile element contents, support an "active margin" affinity. The LREE-depleted patterns encountered in the present case, however, are not frequently found in orogenic samples but are typical of many oceanic tholeiites.