Joseph A. Resing

Basin-scale transport of hydrothermal dissolved metals across the South Pacific Ocean.

Hydrothermal venting along mid-ocean ridges exerts an important control on the chemical composition of sea water by serving as a major source or sink for a number of trace elements in the ocean. Of these, iron has received considerable attention because of its role as an essential and often limiting nutrient for primary production in regions of the ocean that are of critical importance for the global carbon cycle. It has been thought that most of the dissolved iron discharged by hydrothermal vents is lost from solution close to ridge-axis sources and is thus of limited importance for ocean biogeochemistry. This long-standing view is challenged by recent studies which suggest that stabilization of hydrothermal dissolved iron may facilitate its long-range oceanic transport. Such transport has been subsequently inferred from spatially limited oceanographic observations. Here we report data from the US GEOTRACES Eastern Pacific Zonal Transect (EPZT) that demonstrate lateral transport of hydrothermal dissolved iron, manganese, and aluminium from the southern East Pacific Rise (SEPR) several thousand kilometres westward across the South Pacific Ocean. Dissolved iron exhibits nearly conservative (that is, no loss from solution during transport and mixing) behaviour in this hydrothermal plume, implying a greater longevity in the deep ocean than previously assumed. Based on our observations, we estimate a global hydrothermal dissolved iron input of three to four gigamoles per year to the ocean interior, which is more than fourfold higher than previous estimates. Complementary simulations with a global-scale ocean biogeochemical model suggest that the observed transport of hydrothermal dissolved iron requires some means of physicochemical stabilization and indicate that hydrothermally derived iron sustains a large fraction of Southern Ocean export production.

Aerosol iron and aluminum solubility in the northwest Pacific Ocean: Results from the 2002 IOC cruise

Dust aerosol samples were collected across the western North Pacific Ocean during May–June 2002. Samples were analyzed for soluble aerosol Fe(II), Fe(II) + Fe(III), and Al as well as major cations and anions. The aerosol samples were leached using a 10 second exposure to either filtered surface seawater or ultrapure deionized water yielding a measure of the “instantaneous” soluble fraction. A variety of analytical methods were employed, including 57Fe isotope dilution high-resolution ICP-MS, energy dispersive X-ray fluorescence, graphite furnace AAS, ion chromatography, and the FeLume chemiluminescent technique. Fe was found to be more soluble in ultrapure deionized water leaches, especially during periods of higher dust concentrations. Fe solubility averaged 9 ± 8% in ultrapure water leaches and 6 ± 5% in seawater leaches. Significant correlations were found between both soluble aerosol FeT and soluble Fe(II) concentrations and aerosol acidity; however, the percentages of soluble aerosol FeT and Fe(II) did not correlate with aerosol acidity We also did not observe significant correlations between total and soluble aerosol Fe concentrations and the concentrations of either particulate Fe or dissolved Fe in surface waters.

Long-term eruptive activity at a submarine arc volcano

Three-quarters of the Earths volcanic activity is submarine, located mostly along the mid-ocean ridges, with the remainder along intraoceanic arcs and hotspots at depths varying from greater than 4,000 m to near the sea surface. Most observations and sampling of submarine eruptions have been indirect, made from surface vessels or made after the fact. We describe here direct observations and sampling of an eruption at a submarine arc volcano named NW Rota-1, located 60 km northwest of the island of Rota (Commonwealth of the Northern Mariana Islands). We observed a pulsating plume permeated with droplets of molten sulphur disgorging volcanic ash and lapilli from a 15-m diameter pit in March 2004 and again in October 2005 near the summit of the volcano at a water depth of 555 m (depth in 2004). A turbid layer found on the flanks of the volcano (in 2004) at depths from 700 m to more than 1,400 m was probably formed by mass-wasting events related to the eruption. Long-term eruptive activity has produced an unusual chemical environment and a very unstable benthic habitat exploited by only a few mobile decapod species. Such conditions are perhaps distinctive of active arc and hotspot volcanoes.

Submarine venting of liquid carbon dioxide on a Mariana Arc volcano

Although CO2 is generally the most abundant dissolved gas found in submarine hydrothermal fluids, it is rarely found in the form of CO2 liquid. Here we report the discovery of an unusual CO2-rich hydrothermal system at 1600-m depth near the summit of NW Eifuku, a small submarine volcano in the northern Mariana Arc. The site, named Champagne, was found to be discharging two distinct fluids from the same vent field: a 103°C gas-rich hydrothermal fluid and cold (<4°C) droplets composed mainly of liquid CO2. The hot vent fluid contained up to 2.7 moles/kg CO2, the highest ever reported for submarine hydrothermal fluids. The liquid droplets were composed of ∼98% CO2, ∼1% H2S, with only trace amounts of CH4 and H2. Surveys of the overlying water column plumes indicated that the vent fluid and buoyant CO2 droplets ascended <200 m before dispersing into the ocean. Submarine venting of liquid CO2 has been previously observed at only one other locality, in the Okinawa Trough back-arc basin (Sakai et al., 1990a), a geologic setting much different from NW Eifuku, which is a young arc volcano. The discovery of such a high CO2 flux at the Champagne site, estimated to be about 0.1% of the global MOR carbon flux, suggests that submarine arc volcanoes may play a larger role in oceanic carbon cycling than previously realized. The Champagne field may also prove to be a valuable natural laboratory for studying the effects of high CO2 concentrations on marine ecosystems.

High-resolution surveys along the hot spot–affected Galápagos Spreading Center: 1. Distribution of hydrothermal activity

The spatial density of hydrothermal activity along most mid-ocean ridges is a robust linear function of spreading rate (or magmatic budget), but extreme crustal properties may alter this relationship. In 2005–2006 we tested the effect of thickened crust on hydrothermal activity using high-resolution mapping of plumes overlying the hot spot–affected Galapagos Spreading Center from 95° to 89°42′W (∼560 km of ridge crest). Plume mapping discovered only two active, high-temperature vent fields, subsequently confirmed by camera tows, though strong plume evidence indicated minor venting from at least six other locations. Total plume incidence (ph), the fraction of ridge crest overlain by significant plumes, was 0.11 ± 0.014, about half that expected for a non–hot spot mid-ocean ridge with a similar magmatic budget. Plume distributions on the Galapagos Spreading Center were uncorrelated with abrupt variations in the depth of the along-axis melt lens, so these variations are apparently not controlled by hydrothermal cooling differences. We also found no statistical difference (for a significance level of 0.05) in plume incidence between where the seismically imaged melt lens is shallow (2 ± 0.56 km, ph = 0.108 ± 0.045) and where it is deep (3.4 ± 0.7 km, ph = 0.121 ± 0.015). The Galapagos Spreading Center thus joins mid-ocean ridges near the Iceland (Reykjanes Ridge), St. Paul-Amsterdam (South East Indian Ridge), and Ascension (Mid-Atlantic Ridge) hot spots as locations of anomalously scarce high-temperature venting. This scarcity implies that convective cooling along hot spot–affected ridge sections occurs primarily by undetected diffuse flow or is permanently or episodically reduced compared to normal mid-ocean ridges.

The water-column chemical signature after the 1998 eruption of Axial Volcano

The eruption of Axial Volcano in January 1998 produced extensive plumes in the overlying water column with large anomalies in Fe, Mn, pH, light attenuation, and temperature. A strong correlation between total iron and light attenuation (dc) suggests a low abundance of particulate sulfur (PS) in the plumes. Because total carbon dioxide (ΣCO2) samples were not collected, high-precision pH measurements were used to estimate maximum CO2 anomalies (ΔCO2) which, when compared to the other physical and chemical data, suggest that the fluids being vented 3 weeks after eruption were formed by the interaction between an intruded dike and a mixture of interstitial seawater and mature hydrothermal fluids.

Chemical plumes from low‐temperature hydrothermal venting on the eastern flank of the Juan de Fuca Ridge

We report evidence for chemical anomalies in the water column from low-temperature ridge-flank hydrothermal venting. During cruises in 1992 and 1994, samples were taken from the water column for trace metals, nutrients, dissolved gases, and particles near each of three basaltic outcrops overlying 3.5 m. y. old crust on the eastern flank of the Juan de Fuca Ridge in Cascadia Basin. The water column above one of these outcrops, Baby Bare, which rises about 70 m above a flat turbidite plain, was the most thoroughly sampled. Thermal, chemical (Mn, Fe, δ(3He)%, CH4, and O2), and particulate anomalies in the water column confirm the existence of (1) early diagenesis of organic matter in seafloor sediment which produces a flux of dissolved metals and nutrients to bottom seawater, (2) hydrothermal emissions which are both focused (spring-like) and diffuse, and (3) resuspension of sediment by turbulent flow of tidal currents about a topographical high. On the basis of data from the water column and thermal and chemical pore water data from 46 piston and gravity sediment cores near and on Baby Bare (FlankFlux 90 and 92), we constrain the composition of seawater in basement and thus the composition of spring-like water. Given this composition, no measurable dissolved silica or phosphate hydrothermal anomalies are expected in the water column.

Aeolian contamination of Se and Ag in the North Pacific from Asian fossil fuel combustion.

Energy production from fossil fuels, and in particular the burning of coal in China, creates atmospheric contamination that is transported across the remote North Pacific with prevailing westerly winds. In recent years this pollution from within Asia has increased dramatically, as a consequence of vigorous economic growth and corresponding energy consumption. During the fourth Intergovernmental Oceanographic Commission baseline contaminant survey in the western Pacific Ocean from May to June, 2002, surface waters and aerosol samples were measured to investigate whether atmospheric deposition of trace elements to the surface North Pacific was altering trace element biogeochemical cycling. Results show a presumably anthropogenic enrichment of Ag and of Se, which is a known tracer of coal combustion, in the North Pacific atmosphere and surface waters. Additionally, a strong correlation was seen between dissolved Ag and Se concentrations in surface waters. This suggests that Ag should now also be considered a geochemical tracer for coal combustion, and provides further evidence that Ag exhibits a disturbed biogeochemical cycle as the result of atmospheric deposition to the North Pacific.

Evidence for iron and sulfur enrichments in hydrothermal plumes at Axial Volcano following the January–February 1998 eruption

In response to 12 days of seismic activity at Axial Volcano, Juan de Fuca Ridge in January–February 1998, the NSF/NOAA-sponsored Axial Response Team conducted three response cruises in February, August, and August/September to map and sample hydrothermal plumes over the region. Vertical profiles of particulate Fe and S over the eruption site show high concentrations from about 1400 m to the bottom. Chemical and scanning electron microscope analysis of the February plume samples revealed anhydrite, Fe-ferrihydrites, elemental sulfur, and angular glassy basalt shards up to 190 µm in the longest dimension. Many of these shards had halite coatings, which is consistent with subseafloor basalt seawater reactions at temperatures >450°C at 1500 m depth. In August and September cruises the basalt shards were no longer present in the hydrothermal plumes. Instead, the plumes were predominantly composed of Fe-ferrihydrites, elemental sulfur, and sulfur filaments. A unique feature of this data set is the high concentrations of elemental sulfur in the lower 60 m of the water column. The sulfur results are suggestive of a significant enrichment of the bacterial biomass in the water column over the eruption site with time. Within the Axial caldera, approximately 10–20% of the total sulfur is present as sulfur filaments. These post-eruption particle compositional changes have strong similarities to the results from the 1993 CoAxial eruption on the Juan de Fuca Ridge.

Unique event plumes from a 2008 eruption on the Northeast Lau Spreading Center

The creation of ocean crust by lava eruptions is a fundamental Earth process, involving immediate and immense transfers of heat and chemicals from crust to ocean. This transfer creates event plumes (“megaplumes”), massive ellipsoidal eddies with distinctive and consistent chemical signatures. Here we report the discovery of unique event plumes associated with a 2008 eruption on the Northeast Lau Spreading Center. Instead of a large plume hundreds of meters thick, we detected at least eight individual plumes, each ∼50 m thick and apparently only 1–3 km in diameter, yet still rising 200–1000 m above the eruption site. Low and uniform 3He/heat (0.041 × 10−17 mol/J) and dissolved Mn/heat (0.04 nmol/J) ratios in water samples were diagnostic of event plumes. High H2 concentrations (up to 9123 nM) and basalt shards confirmed extensive interactions between molten lava and event plume source fluids. Remote vehicle observations in 2009 mapped a new, small (1.5–5.8 × 106 m3) lava flow. Our results suggest that event plumes are more variable, and thus perhaps more common, than previously recognized. Small event plumes may be preferentially associated with small or sheet-flow eruptions, and massive event plumes with slowly extruding pillow mounds 25–75 m thick. Despite this correlation, and high H2 concentrations, existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes. The creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation.