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Iron and manganese concentrations were measured in seawater from the upper water column (≤350 m water depth) in the subantarctic region to the south and west of Tasmania, Australia, during January 1995. Dissolved and total-dissolvable Fe and dissolved Mn were determined in samples from four stations along 140°E ranging from polar to subtropical waters, and from one station over the continental slope off north-west Tasmania. Dissolved Fe concentration were generally low ( 2 nM) observed in shallower waters over the continental slope. Vertical concentration profiles suggest biological removal of dissolved Fe from the photic zone at the deep-ocean stations, except in the subantarctic front. The higher mixed-layer concentrations of Fe and Mn observed over the continental slope and in the deep ocean at 40°S are thought to reflect inputs from the continental shelves or atmospheric deposition. Water-column Fe and Mn profiles from 45°S, 50°S and 53°S show no evidence for significant inputs of these metals via atmospheric deposition or upwelling of metal-rich deep waters, although there was evidence of shelf-derived particulate Fe at 45°S. The low concentrations of dissolved Fe measured at 45°S, 50°S and 53°S indicate that iron deficiency could limit summertime primary production in these high-nitrate lowchlorophyll waters.

Subtidal springs in and around the submarine limestone cavern of Grotta Azzurra, at Capo Palinuro, Italy, discharge fluids which are warm ( 10%). Excess Si, alkalinity, Ca2+, Sr2+ and Mn relative to seawater are likely derived from the groundwater component or dissolution/hydrothermal alteration of the host rocks. Magnesium has been removed from the seawater component in exchange for Ca2+, due to dolomitisation of the limestone and/or hydrothermal alteration reactions. Saturation-state calculations suggest that the vented fluids are near saturation with respect to calcite and supersaturated with respect to dolomite. This and the presence of dolomite in the host rocks and cave-floor sediments suggest that “mixing-zone” dolomitisation of the limestones is occurring, perhaps kinetically assisted by elevated temperature and/or bacterial mediation in the reducing subseafloor zone. One possible “end-member” condition is considered for the thermal fluid — zero-Mg — which suggests an end-member temperature of 50.5°C and a fluid composition derived from ∼ 38% seawater and ∼ 62% groundwater. The heat source for the circulating fluids is uncertain, but may involve warm underlying igneous rocks or heating via the geothermal gradient. A continuous in-situ record of vent-fluid temperature, salinity, pH and O2 concentration collected within the cavern is consistent with our interpretation of the fluid origin, and suggests that tidal forcing affects circulation and venting of the warm fluids.

Results are presented from a geochemical survey of active submarine warm springs off the island of Vulcano, an active island-arc volcanic centre in the Aeolian Archipelago, Italy. Water samples were collected from submarine ‘fumaroles’ which discharge hot (~ 50–100 °C), acidic, gas-rich, low-chlorinity fluids into the shallow embayment of Porto di Levante, adding dissolved Si, K, Li, Rb, Fe, Mn, NH3 and H2S into surrounding seawater. These fluids are interpreted as a mixture of seawater and low-salinity groundwater which has undergone high-temperature (> 100 °C) hydrothermal alteration, followed by mixing with cool seawater in the sub-seafloor and during venting. The fluid compositions also suggest the chemical ‘overprint’ of reactions resulting from the input of significant amounts of the volcanic gases CO2, SO2 and H2S at this site, specifically, the attack of igneous silicate phases by dissolved CO2, and the hydrolysis and oxidation of SO2 and H2S to SO42−, H+ and elemental sulphur. These overprinting reactions have been proposed for other gas-rich submarine hydrothermal fluids collected from shallow island-arc and hotspot volcanoes, and may be typical of such settings. Several water samples were also collected from a site where warm (

Dissolved cobalt (dCo), iron (dFe) and aluminum (dAl) were determined in water column samples along a meridional transect (?31°N to 24°N) south of Bermuda in June 2008. A general north-to-south increase in surface concentrations of dFe (0.3–1.6 nM) and dAl (14–42 nM) was observed, suggesting that aerosol deposition is a significant source of dFe and dAl, whereas no clear trend was observed for near-surface dCo concentrations. Shipboard aerosol samples indicate fractional solubility values of 8–100% for aerosol Co, which are significantly higher than corresponding estimates of the solubility of aerosol Fe (0.44–45%). Hydrographic observations and analysis of time series rain samples from Bermuda indicate that wet deposition accounts for most (>80%) of the total aeolian flux of Co, and hence a significant proportion of the atmospheric input of dCo to our study region. Our aerosol data imply that the atmospheric input of dCo to the Sargasso Sea is modest, although this flux may be more significant in late summer. The water column dCo profiles reveal a vertical distribution that predominantly reflects ‘nutrient-type’ behavior, versus scavenged-type behavior for dAl, and a hybrid of nutrient- and scavenged-type behavior for dFe. Mesoscale eddies also appear to impact on the vertical distribution of dCo. The effects of biological removal of dCo from the upper water column were apparent as pronounced sub-surface minima (21 ± 4 pM dCo), coincident with maxima in Prochlorococcus abundance. These observations imply that Prochlorococcus plays a major role in removing dCo from the euphotic zone, and that the availability of dCo may regulate Prochlorococcus growth in the Sargasso Sea.

Dissolved CO2, δ13C, He, and 3He4He were determined in warm (

[1] The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2 sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a “winter reserve” of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (∼0.1 nM) that limit phytoplankton growth in the austral summer (December–February). Here we report new iron data for the Ross Sea polynya during austral summer 2005–2006 (27 December–22 January) and the following austral spring 2006 (16 November–3 December). The summer 2005–2006 data show generally low dFe concentrations in polynya surface waters (0.10 ± 0.05 nM in upper 40 m, n = 175), consistent with previous observations. Surprisingly, our spring 2006 data reveal similar low surface dFe concentrations in the polynya (0.06 ± 0.04 nM in upper 40 m, n = 69), in association with relatively high rates of primary production (∼170–260 mmol C m−2 d−1). These results indicate that the winter reserve dFe may be consumed relatively early in the growing season, such that polynya surface waters can become “iron limited” as early as November; i.e., the seasonal depletion of dFe is not necessarily gradual. Satellite observations reveal significant biomass accumulation in the polynya during summer 2006–2007, implying significant sources of “new” dFe to surface waters during this period. Possible sources of this new dFe include episodic vertical exchange, lateral advection, aerosol input, and reductive dissolution of particulate iron.

DSRV Alvin dives in the Northern Mariana island arc recovered warm hydrothermal fluids from the summit areas of seamounts Kasuga 2 and Kasuga 3, as well as hydrothermal deposits of elemental sulfur, Fe- and Mn-oxides, and nontronite. The composition of a gas-rich ∼ 39°C vent fluid sampled from Kasuga 2 Seamount is unusual compared to other submarine hydrothermal fluids in that it is enriched by 27% in Mg 2+ and 17% in SO 4 2− , and depleted by 64% in Ca 2+ , relative to ambient seawater. The elevated concentrations of dissolved CO 2 (calculated from pH and A T ), HCO 3 − and SO 4 2+ , and near absence of H 2 S, suggest that the unusual composition of this sample may result from the sub-seafloor addition of volcanic CO 2 and SO 2 to a seawater-derived hydrothermal fluid, resulting in: (1) ‘chemical weathering’ reactions, whereby igneous minerals or alteration phases are attacked by CO 2 , adding Mg 2+ and other cations, Si, and HCO 3 − into solution; and (2) hydrolysis of SO 2 to SO 4 2− and S(0), adding excess SO 4 2− with a light δ 34 S signature to the fluid and causing deposition of elemental sulfur at the seafloor vents. Saturation-state calculations suggest that the concentrations of Si and Ca 2+ in the fluid may be controlled at saturation with amorphous silica and dolomite respectively. The origin of the 9.3°C fluid collected from Kasuga 3 is difficult to determine because it is compositionally close to ambient seawater and shows possible evidence of both high- and low-temperature seawater-rock reaction. Banded and interlayered deposits of nontronite and Fe- and Mn-oxides were recovered from the Kasuga 3 summit, with oxygen-isotope geothermometry suggesting a formation temperature of ∼ 22°C for the nontronite.

[1] Paytan et al. (2009) argue that the atmospheric deposition of aerosols lead to copper concentrations that are potentially toxic to marine phytoplankton in a large area of tropical and subtropical North Atlantic Ocean. A key assumption in their model is that all marine aerosols (mineral dust and anthropogenic particles) have a high (40%) fractional solubility of copper. Our data show that the fractional solubility of copper for Saharan dust over the Sargasso Sea and Bermuda is significantly lower (1–7%). In contrast, anthropogenic aerosols with non-Saharan sources have significantly higher values (10–100%). Hence, the potential Cu toxicity in the tropical and subtropical North Atlantic should be re-estimated, given the low fractional solubility of Cu in the Saharan dust that dominates aerosol deposition to this region.

Hydrothermal fluids were sampled from Pele's Vents on the summit of Loihi Seamount, an intraplate, hotspot volcano, on four occasions from February 1987 to September 1990. The warm (≤ 31°C) vent solutions are enriched in dissolved Si, CO 2 , H 2 S, alkalinity, K + , Li + , Rb + , Ca 2+ , Sr 2+ , Ba 2+ , Fe 2+ , Mn 2+ , NH 4 + , and possibly Ni 2+ , and depleted in SO 4 2− , O 2 , Mg 2+ , 87 Sr 86 Sr , NO 3 − , and sometimes Cl − and Na + (calculated), relative to ambient seawater. Dissolved Si correlates linearly with sample temperature, suggesting that the solutions sampled from numerous vents in the ~ 20 m diameter field have a common source and that Si can be used as a conservative tracer for mixing of the vent fluids with ambient seawater. There are general similarities of the vent waters with ridge-axis warm springs on the Galapagos Rift and Axial Seamount, but also striking differences: very high total dissolved CO 2 (> 200 mmol/kg), high alkalinity (> 8 meq/kg) and dissolved Fe 2+ (almost 1 mmol/kg), and relatively low pH (~ 4.2–4.4 estimated, in situ, sws) and dissolved H 2 S (several μmol/kg). The Mg 2+ and SO 4 2− data are inconsistent with the “Galapagos model” proposed for the warm springs at 86°W, Galapagos Rift, whereby the warm fluids result from sub-seafloor mixing of a high-temperature (~ 350°C) hydrothermal endmember with essentially unaltered seawater. The variable Cl − depletions in the vent fluids, however, suggest that the warm vent fluids do contain a high-temperature (> 200°C) component. The fluid history can be qualitatively described by a modified “Galapagos model” which includes the overprint of reactions resulting from the addition of juvenile CO 2 and SO 2 to the circulating fluids; the CO 2 attacks the basalt releasing metal cations, HCO 3 − and possibly Si into solution, and the SO 2 is hydrolyzed to SO 4 2− . These juvenile inputs likely reflect the shallow, hotspot setting of this hydrothermal system. A simple quantitative fluidhistory model is considered and shown to be consistent with mass-balance constraints and saturationstate calculations, which suggest that the Si concentration of the fluids may be controlled by amorphous silica saturation at ~ 31°C. Observed temporal variations in fluid composition between expeditions—specifically, in Cl − , A T , C T , Na + (calculated), Mg 2+ , Ca 2+ , Sr 2+ , 87 Sr 86 Sr , Fe 2+ , Mn 2+ and perhaps NH 4 + , relative to Si—are, excepting Mg 2+ , 87 Sr 86 Sr , and Mn 2+ , consistent with the effects of variable phase segregation at the proposed high-temperature endmember.

Hydrothermal plumes associated with nearshore lava flows from Kilauea Volcano, Hawaii were studied on five occasions during 1989–1990 to address the current lack of data on direct lava-seawater interactions. The following enrichments were found in the sea-surface hydrothermal plumes above the active underwater lava flows: H2, 15,000x ambient seawater concentrations; Mn, 250x; and Si, 20x. Water temperatures reached 46°C. Lower concentrations and temperatures were observed in the plumes with increasing distance from shore, with H2, Si, and Mn concentrations linearly related to seawater temperature. Unlike deep sea spreading center hydrothermal plumes, no CH4 enrichment was observed. The elevated H2 is likely to be from water-rock reactions, rather than from the release of magmatic gas. The plume mass/heat ratios presented here suggest that submarine flood basalts, although aerially large, should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust.

To examine the chemical alteration of seawater by submarine lava, seawater was sampled at a depth of 21 m east of Kupapau Point, Hawaii, after contact with molten lava from Kilauea Volcano. The warm, mildly acid (pH ∼6.5 at 27°C) hydrothermal solutions are highly enriched in dissolved Si (>40×) and Mn (>400×) relative to ambient seawater. Chloride shows a slight but discernable enrichment in the most altered samples, probably due to boiling and partial phase segregation (steam loss) during heating. Assuming Cl behaves conservatively, Ca and Mg are on the order of 1% depleted in the altered solutions, which we attribute to anhydrite precipitation and secondary silicate formation during the water-rock exchange. Dissolved iron is not enriched in the solutions, although examination of filtered particles suggests that some Fe is mobilized from the basalt. These distinctive chemical changes are consistent with a brief, moderate temperature (

In an effort to identify back-arc seafloor hydrothermal activity in the North Fiji Basin (NFB), five hydrocasts were made along the NFB spreading center between 15°S and 17°S during January 1987. Near-bottom anomalies in total dissolvable manganese (TDM) and methane were approximately five times background over the NFB triple junction. At four stations over the northwest portion of the spreading center, a mid-depth TDM anomaly of 2–5.5 nmol kg−1 was observed between 2 and 2.5 km depth; it has no associated anomaly in methane and extends along-axis at least 140 km north of the triple junction. A recently discovered, active ydrothermal system on the NFB triple junction is a likely source for these water column anomalies. A single hydrocast made over a small basin northwest of Viti Levu showed elevated near-bottom methane and TDM (approximately twice and four times background, respectively) of either hydrothermal or sedimentary origin.

We report empirical estimates of the fractional solubility of aerosol iron over the Sargasso Sea during periods characterized by high concentrations of Saharan dust (summer 2003) and by low concentrations of aerosols in North American/maritime North Atlantic air masses (spring 2004 and early summer 2004). We observed a strong inverse relationship between the operational solubility of aerosol iron (defined using a flow-through deionized-water leaching protocol) and the total concentration of aerosol iron, whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low. This relationship is consistent with source-dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model, wherein bulk aerosols represent a conservative mixture of two air mass end-members that carry different aerosol types: “Saharan air,” which contains a relatively high loading of aerosol iron (27.8 nmol Fe m−3) that has a low fractional solubility (0.44%), and “North American air,” which contains a relatively low concentration of aerosol iron (0.5 nmol Fe m−3) that has a high fractional solubility (19%). Historical data for aerosols collected on Bermuda indicate that the low iron loadings associated with North American air masses are typically accompanied by elevated V/Al, Fe/Al, and V/Mn mass ratios in the bulk aerosol, relative to Saharan dust, which are indicative of anthropogenic fuel-combustion products. The identification of similar compositional trends in our Sargasso Sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with North American air masses reflects the presence of anthropogenic combustion products, which contain iron that is readily soluble relative to iron in Saharan soil dust. We thus propose that the source-dependent composition of aerosol particles (specifically, the relative proportion of anthropogenic combustion products) is a primary determinant for the fractional solubility of aerosol iron over the Sargasso Sea. This hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean.

[1] We report iron measurements for water column and aerosol samples collected in the Sargasso Sea during July-August 2003 (summer 2003) and April-May 2004 (spring 2004). Our data reveal a large seasonal change in the dissolved iron (dFe) concentration of surface waters in the Bermuda Atlantic Time-series Study region, from ∼1–2 nM in summer 2003, when aerosol iron concentrations were high (mean 10 nmol m−3), to ∼0.1–0.2 nM in spring 2004, when aerosol iron concentrations were low (mean 0.64 nmol m−3). During summer 2003, we observed an increase of ∼0.6 nM in surface water dFe concentrations over 13 days, presumably due to eolian iron input; an estimate of total iron deposition over this same period suggests an effective solubility of 3–30% for aerosol iron. Our summer 2003 water column profiles show potentially growth-limiting dFe concentrations (0.02–0.19 nM) coinciding with a deep chlorophyll maximum at 100–150 m depth, where phytoplankton biomass is typically dominated by Prochlorococcus during late summer.

A shipboard-deployable, flow-injection (FI) based instrument for monitoring iron(II) in surface marine waters is described. It incorporates a miniature, low-power photon-counting head for measuring the light emitted from the iron(II)-catalyzed chemiluminescence (CL) luminol reaction. System control, signal acquisition, and data processing are performed in a graphical programming environment. The limit of detection for iron(II) is in the range 8-12 pmol L(-1) (based on 3 s of the blank), and the precision over the range 8-1000 pmol L(-1) varies between 0.9 and 7.6% (n = 4). Results from a day-night deployment during a north-to-south transect of the Atlantic Ocean and a daytime transect in the Sub-Antarctic Front are presented together with ancillary temperature, salinity, and irradiance data. The generic nature of the components used to assemble the instrument make the technology readily transferable to other laboratories and the modular construction makes it easy to adapt the system for use with other CL chemistries.

An adsorptive bubble technique, using two organic precipitating reagents, is applied to separate cobalt, copper, nickel, and manganese from the leach liquors of sulfated deep-sea ferromanganese nodules. Recoveries of the four metal values are studied as a function of pH for each system. The organic precipitating reagents studied are salicylaldoxime and sodium diethyldithiocarbamate.

Stratigraphic information concerning the retreat of the Antarctic ice sheet from the continental shelf after the Last Glacial Maximum is reviewed and compared with new results from a shelf valley off Mac. Robertson Land, East Antarctica. Radiocarbon dates and detailed lithostratigraphic logs indicate that the onset of open-marine conditions over shallow shelfbanks «200 m water depth) was achieved prior to 7000 yr BP and over deep (~l 000 m) middle to oliter shelf valleys, open-marine conditions were achieved prior to 5400 yr BP. Radiocarbon dating of bulk-organic carbon in some diatom oozes by the AMS method demonstrates problems of contamination. Jurassic pollen, spores and organic matter have been eroded and incorporated into Holocene diatom ooze, causing anomalously old 14C dates (e.g. one surface age of7084 ± 86 yr BP was determined). This problem may arise at other locations around East Antarctica where older strata outcrop on the seafloor.