Dominique Birot

A new chemical analyzer for in situ measurement of nitrate and total sulfide over hydrothermal vent biological communities

A new submersible chemical analyzer, ALCHIMIST (AnaLyseur CHIMique In SiTu), based on colorimetric detection and flow injection analysis (FIA), was adapted to allow in situ measurements of nitrate+nitrite (N+N) and total dissolved sulfide (∑S) in the deep sea hydrothermal environment. Before in situ trials, the influence of hydrostatic pressure and temperature on the analytical responses was examined under simulated conditions (1–300×105 Pa, 5–25°C). First trials were performed during dives of the Remotely Operated Vehicle (ROV), VICTOR 6000, over the Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge). ALCHIMIST, installed on the ROV, enabled simultaneous N+N and ∑S calibration and measurements at 1650 m depth, at a rate of 22 analyses per hour. At depth, the precision of the in situ ∑S and N+N measurements is estimated to be, respectively, 1.1% and 0.8%. The detection limit is 0.8 μM for ∑S and 0.5 μM for N+N. At a vent site of the Lucky Strike area, ALCHIMIST enabled to resolve, at the decimeter scale, the chemical gradients which characterize the patchy distribution of hydrothermal fauna. Additionally, temperature–concentration relationships offered further information on the processes controlling the chemistry of the habitats. Like former in situ analyzers used in this field, this new instrument should be valuable to characterize the physico-chemical characteristics of vent fauna environment.

A flow injection-fluorometric method for the determination of ammonium in fresh and saline waters with a view to in situ analyses.

A version of the orthophthaldialdehyde-fluorescence ammonium determination for flow injection analysis (FIA) is presented here, with a view to its use for in situ, low-power consumption systems. Thus, the reaction temperature was limited to 30 degrees C and FIA was used in stop-flow mode (3 min stop). The calibration is linear up to 50 mumol l-1, but concentrations up to 100 mumol l-1 can be measured. Repeatability is around 1% in the range of 0.5-4 mumol l-1 and the detection limit is about 0.03 mumol l-1. Over the salinity range of 5-35 (seawater practical salinity scale) the salt effect is almost negligible (within +/- 2%); and below salinity of 5 it increases to a maximum of -9% in fresh water compared to seawater. Hydrogen carbonate, dissolved oxygen and turbidity (either suspended sediments or phytoplankton cells) have almost no adverse effect in a wide range of concentrations, covering most natural water conditions. Relative interference of primary amines is negligible and mercury (a common sample preservative) does not depress the signal up to 20 mg l-1 Hg II. Sulfide, that may be present in areas with anoxic waters, depresses the signal only slightly and linearly (-9% at 100 mumol l-1 S2-). The method appears to be convenient for the determination of ammonium in most coastal, estuarine and fresh waters. Sample throughput is 9 h-1. The performance of the method can be improved, either by increasing the reaction time (low throughput) or, if enough energy is available, by increasing the reaction temperature (non-stop-flow mode, high throughput). Combining FIA and fluorometry appears to be interesting for in situ determination (submersible devices) of dissolved compounds in environments with variable salinity and turbidity (especially coastal and estuarine waters).

Determination of rare earth elements and other trace elements (Y, Mn, Co, Cr) in seawater using Tm addition and Mg(OH)2 co-precipitation

This paper reports on a novel procedure for determining trace element abundances (REE and Y, Cr, Mn, Co) in seawater by inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The procedure uses a combination of pre-concentration using co-precipitation onto magnesium hydroxides and addition of thulium spike. The validity of the method was assessed onto 25 ml volumes of certified reference materials (NASS- and CASS-4) and in house seawater standard. Procedural blanks were determined by applying the same procedure to aliquots of seawater previously depleted in trace elements by successive Mg(OH)(2) co-precipitations, yielding estimated contributions to the studied samples better than 1.1% for all elements, with the exception of Cr (<3.3%) and Co (up to 8%). The reproducibility of the method over the six month duration of the study was smaller than 11% RSD for all the studied elements. Results obtained for NASS-5 and CASS-4 agree well with published working values for trace elements.

Characterization and reduction of interferences in flow-injection analysis for the in situ determination of nitrate and nitrite in sea water

Abstract The aim of this work is to improve the precision and the sensitivity of nitrite and nitrate determination by flow-injection analysis (FIA) for an in situ utilization. Two kinds of signal treatment are proposed in order to eliminate the refractive index provoked by the heterogeneous flow in FIA and the errors induced by temperature, salinity and pressure variations. The concentration range of this method is 0–100 μ M NO − 3 -N with a detection limit (3 σ b ) of 0.45 μ M NO − 3 -N ( A t = 0.151 C NO3 + 0.072, n = 40, r 2 = 0.997). The relative standard deviation is 5% for nitrate solutions containing 0.5 μ M NO − 3 -N. The sampling rate is about 45 h −1 .

A submersible flow-injection analyser for the in-situ determination of nitrite and nitrate in coastal waters

An flow-injection system is described for the in-situ determination of nutrient concentrations in rivers and ocean waters. In estuarine and coastal waters, significant interferences may be caused by temperature and salinity variations. Therefore, we used a dual wavelength detector to measure simultaneously the reference and sample signals. The device has been used to measure spatial and temporal variations of nitrite and nitrate concentrations in coastal waters exhibiting strong salinity variations (Bay of Brest and Iroise Sea, France). Our original detection system coupled with flow-injection analysis (FIA) allows high-frequency measurements (40 samples per hour), very good precision (1%) and a low detection limit (0.45 μM NO3). The device can work up to a depth of 300 m, within a temperature range of 2 to 35 °C, and with salinities varying from 0 to 35. The dynamic range (0–150 μM NO3) can be adapted to the expected concentrations of the study area by using flow cells with various path lengths. Intercalibration with samples collected by conventional means and analysed with a spectrophotometric reference method at the laboratory showed a good agreement between both methods (1.3%).

Laboratory adaptation of the methylene blue method to flow injection analysis: towards in situ sulfide analysis in hydrothermal seawater

This preliminary study presents the laboratory adaptation of the methylene blue method for the analysis of sulfide in hydrothermal seawater to flow injection analysis (FIA) before its integration on an in situ analyser. The manifold used after optimisation enables us to work on a 0–450 µmol l–1 sulfide range with a detection limit between 0.1 and 0.4 µmol l–1 and a relative standard deviation < 1%. The following steps will be the adaptation of the manifold on the in situ analyser and field tests.

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

During the scientific expedition GAZCOGNE2 at the Bay of Biscay nine gas seeps were sampled for the first time and their flux was measured using an in situ pressure-preservation sampler (PEGAZ, ©IFREMER). Overall, three sites were investigated to determine the nature and the origin of the gases bubbling at the seafloor and forming acoustic plumes into the water column, as this was the question raised from the first geologic study of the area. This has guided our study and accordingly corresponds to the main purpose of the present article. Thus, the molecular and isotopic (δD and δ13C) analyses revealed that the gas seeps were primarily composed of methane. Both methane and ethane are of microbial origin, and the former has been generated by microbial reduction of carbon dioxide. Heavier hydrocarbons accounted for less than 0.06% mol of the total amount. Despite the microbial origin of methane, the samples exhibit subtle differences with respect to the values, which varied between −72.7 and −66.1 . It has been suggested that such a discrepancy was predominantly governed by the occurrence of anaerobic methane oxidation. The PEGAZ sampler also enabled us to estimate the local gas fluxes from the sampled streams. The resulting values are extremely heterogeneous between seeps, ranging from 35 to 368 mLn·min−1. Assuming a steady discharge, the mean calculated methane emission for the nine seeps is of 38 kmol·yr−1. Considering the extent of the seep area, this very local estimate suggests that the Aquitaine Shelf is a very appropriate place to study methane discharge and its fate on continental shelves.

In-situ pH measurement: A continuous flow analysis method for seawater pH determination using a ion sensitive field effect transistor (ISFET)

With the aim of adapting ISFET sensors to in-situ seawater pH monitoring, a continuous flow method was set up in the laboratory. The system used consists of a peristaltic pump, a two position valve and a measurement cell including the ISFET detector and a renewable junction reference electrode. The calibration and measurement procedure was achieved by alternating buffers and sample flowing over the detector. This enables the authors to eliminate inherent ISFET drift. The method was tested on acidified seawater samples of pH 8.00 to 7.38. Results obtained, with a resolution of 0.06 pH, are in good agreement with pH-metric measurements (using a glass electrode). This method could be utilized in an autonomous underwater system.<<ETX>>

Evaluation of flow injection analysis based method for in situ chemical measurements

This work constitutes a preliminary study for the development of a submersible chemical analyser based on FIA. A method based on a reverse FIA manifold and differential dual wavelength absorbtiometry is proposed in order to eliminate the refractive index interference and to achieve the sensitivity and accuracy needed for nitrate analysis in coastal seawater. Characterization of the effects of variations in simulated environmental conditions (salinity, temperature, pressure) on the measurements confirms the interest of this approach.<<ETX>>

Optical fiber spectrofluorimetry for in-situ algae discriminations

Nowadays it becomes more and more necessary to identify suspended matter in oceans in order to increase knowledge about primary productivity as well as the transfer of contaminants or to discriminate toxic phytoplanctonic species. It has been demonstrated for many years that fluorescence can be a well suited method to obtain specific signatures of organic matter in the sea. The paper presented here describes an interesting design of instrumentation based on optical fiber use and multiwavelength analysis which will offer wide possibilities for in situ monitoring of algae. Combining the flexibility of optical fibers and video as data carrier, results show great promise for new oceanographic equipment. In addition to technical descriptions, responses of some different grown species like dinoflagelates or diatoms families will be presented and discussed.