Intense but variable autotrophic activity in a rapidly flushed shallow-water hydrothermal plume (Kueishantao Islet, Taiwan).

Shallow-water hydrothermal plumes concomitantly host both photosynthetic and chemoautotrophic organisms in a single biotope. Yet, rate measurements to quantify the contributions of different autotrophic activity types are scarce. Herein, we measured the light and dark dissolved inorganic carbon (DIC) uptake rates in the plume water of the Kueishantao hydrothermal field using the 13 C-labeling approach. Seventy percent of the plume-water samples had chemoautotrophy as the dominant mode of carbon fixation, with the dark DIC uptake rates (up to 18.6 mg C/m3 /h) within the range of the primary production in productive inner-shelf waters. When considered alongside the geochemical and microbiological observations, the rate data reveal the distribution of different trophic activities in the hydrothermal plume. The autotrophic activity at the initial phase of plume dispersal is low. This is explained by the short response time the chemoautotrophs have to the stimulation from vent-fluid discharge, and the harmful effects of hydrothermal substances on phytoplankton. As plume dispersal and mixing continue, chemoautotrophic activities begin to rise and peak in waters that have low-to-moderate Si(OH)4 content. Toward the plume margin, chemoautotrophy declines to background levels, whereas photosynthesis by phytoplankton regains importance. Our results also provide preliminary indication to the loci of enhanced heterotrophy in the plume. Results of artificial mixing experiments suggest that previously formed plume water is the primary source of microbial inoculum for new plume water. This self-inoculation mechanism, in combination with the intense DIC uptake, helps to sustain a distinct planktonic autotrophic community in this rapidly flushed hydrothermal plume.

Improved analytical techniques of sulfur isotopic composition in nanomole quantities by MC-ICP-MS.

We propose an improved method for precise sulfur isotopic measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in conjunction with a membrane desolvation nebulization system. The problems of sulfur loss through the membrane desolvation apparatus are carefully quantified and resolved. The method overcomes low intrinsic sulfur transmission through the instrument, which was initially 1% when operating at a desolvation temperature of 160 °C. Sulfur loss through the membrane desolvation apparatus was resolved by doping with sodium. A Na/S ratio of 2 mol mol-1 produced sulfur transmissions with 98% recovery. Samples of 3 nmol (100 ng) sulfur achieved an external precision of ±0.18‰ (2 SD) for δ34S and ±0.10‰ (2 SD) for Δ33S (uppercase delta expresses the extent of mass-independent isotopic fractionation). Measurements made on certified reference materials and in-house standards demonstrate analytical accuracy and reproducibility. We applied the method to examine microbial-induced sulfur transformation in marine sediment pore waters from the sulfate-methane transition zone. The technique is quite versatile, and can be applied to a range of materials, including natural waters and minerals.

Trace metal determination in natural waters by automated solid phase extraction system and ICP-MS: the influence of low level Mg and Ca.

A fully automated high pressure pretreatment system with Nobias Chelate-PA1 resin (PA1) was developed for trace metal determination by ICP-MS in natural waters. By varying the concentrations of Mg and Ca to mimic the concentrations in the eluate obtained by PA1 or iminodiacetate type resins, the overall analytical performance of the system was assessed for the determination of Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Cd, Ag, Pb and REE. Comparing with the low mM level Mg and Ca (both ranging from 1 to 4mM) eluted by iminodiacetate type resins, the eluate obtained by PA1 contains sub-µM level Mg and Ca, which remarkably decrease matrix effect in ICP-MS analysis and significantly improve the analytical performance. With recovery better than 90% for most the trace metals examined, the accuracy was further verified through the analysis of five natural water reference materials with salinity spanning from 0 to 35‰. We have successfully applied the pretreatment system to determine trace metals in the seawater samples collected in the Western Philippine Sea through Taiwan GEOTRACES cruise.

Temporal distributions of anthropogenic Al, Zn and Pb in Hong Kong Porites coral during the last two centuries.

A 182-year long record of trace metal concentrations of aluminum, zinc and lead was reconstructed from a massive Porites coral skeleton from southeastern Hong Kong to evaluate the impacts of anthropogenic activity on the marine environment. Zn/Ca and Pb/Ca ratios fluctuate synchronously from the early 19th century to the present, indicating that the marine environment has been anthropogenically influenced since industrialization. Additionally, land reclamation, mining, and ship building activities are recorded by elevated Al/Ca ratios from 1900 to 1950. The coral record indicates that high levels of Zn, Pb and Al occur coincidentally with local wars, and may have contributed to partial colony mortality. Pb/Ca does not correlate well with hemispheric proxy records after 1950, indicating that coastal corals may be recording local rather than hemispheric contamination. Pb/Ca levels in Hong Kong, Guangdong and Hainan corals imply a continuous supply of Pb-based contamination to southern China not reflected in hemispheric signals.

Direct separation of boron from Na- and Ca-rich matrices by sublimation for stable isotope measurement by MC-ICP-MS.

An improved technique for precise and accurate determination of boron isotopic composition in Na-rich natural waters (groundwater, seawater) and marine biogenic carbonates was developed. This study used a 'micro-sublimation' technique to separate B from natural sample matrices in place of the conventional ion-exchange extraction. By adjusting analyte to appropriate pH, quantitative recovery of boron can be achieved (>98%) and the B procedural blank is limited to <8 pg. An additional mass bias effect in MC-ICP-MS was observed which could not be improved via the standard-sample-standard bracketing or the 'pseudo internal' normalization by Li. Therefore a standard other than NBS SRM 951 was used to monitor plasma condition in order to maintain analytical accuracy. An isotope cross-calibration with results from TIMS shows that the space-charge mass bias on MC-ICP-MS can be successfully corrected using off-line mathematical manipulation. Several reference materials, including the seawater IAPSO and two groundwater standards IAEA-B-2 and IAEA-B-3, were used to validate this approach. We found that the delta(11)B of the reference coral JCp-1 was 24.22+/-0.28 per thousand, corresponding to seawater pH based on the coral delta(11)B-pH function.

Fractionation correction methodology for precise and accurate isotopic analysis of boron by negative thermal ionization mass spectrometry based on BO2(-) ions and using the 18O/16O ratio from ReO4(-) for internal normalization.

A novel approach to obtain a fractionation free (11)B/(10)B isotope ratio based on oxygen isotopes determined in situ from the same filament loading by N-TIMS is described. The method uses only a few nanograms of B to produce BO(2)(-) ions. First, the oxygen isotopes are determined at a lower filament temperature using ReO(4)(-) ions and employing (187)Re/(185)Re for internal normalization. Subsequently, the filament temperature is increased to get sufficient BO(2)(-) ions and predetermined (18)O/(16)O isotopes from the same filament loading is used to correct for boron mass fractionation. The validity of the method has been demonstrated by analyzing a NIST-SRM-951 boron isotopic certified standard, two synthetic B mixtures, and two coral reference materials. An average analytical precision of 0.6 per thousand (n = 6) has been demonstrated. This is an important and crucial step forward in making the application of BO(2)(-) ions by N-TIMS routine in coral, foraminifera, and other samples where only limited amounts of boron are available. This new method does not require any additional effort in loading or in carrying out the mass spectrometric analysis but eliminates the need of assuming a fixed (18)O/(16)O ratio and thus provides higher accuracy for applications in paleo-oceanography, geochemistry, and cosmo-chemistry.