Shipboard Analysis Research Articles

Automated techniques for real-time shipboard determination of dissolved trace metals in marine surface waters

This review compares methods that are currently employed for shipboard analysis of trace metals in seawater: voltammetric, chemiluminescence and colorimetric methods. Instrumentation and methods are described for collecting surface seawater using pumping, with subsequent on-line analysis by stripping voltammetry. The review is illustrated with data for oceanic and coastal distributions of dissolved copper and nickel, determined using automated stripping voltammetry. Trace-metal levels in estuarine, coastal, and oceanic waters are often quite low. A review is presented of shipboard techniques for determining dissolved trace metals in marine surface waters. These include colorimetric, chemiluminescence, and voltammetric methods. A promising method is cathodic stripping voltammetry, which uses underway pumping as a means of sample collection, thereby obviating the requirement for vessels to stop before the collection of discrete samples. This method has been applied for the real-time determination of nickel in the Atlantic Ocean and copper in the Huelva estuary and the Gulf of Cadiz, Spain.

Determination of cobalt and iron in estuarine and coastal waters using flow injection with chemiluminescence detection

Flow injection with chemiluminescence detection (FI-CL) was used to determine cobalt and iron in estuarine and coastal waters. Cobalt(II) was determined by means of a pyrogallol-hydrogen peroxide-sodium hydroxide reaction in the presence of methanol and the surfactant cetyltrimethylammonium bromide (CTAB). With pyrogallol, the sensitivity was enhanced compared with the traditional reagent, gallic acid. The practical limit of detection in sea-water was 5 pM (3s) and there was good agreement with certified values for the sea-water CRMs NASS-5 (0.16 ± 0.01 nM), CASS-3 (0.60 ± 0.09 nM) and SLEW-2 (0.93 ± 0.13 nM). Results for an Irish Sea sample gave good agreement with data obtained using cathodic stripping voltammetry. Iron(II + III) was determined using a luminol reaction with dissolved oxygen as the oxidant. The practical limit of detection was 40 pM (3s) and results from shipboard analysis of the CRM NASS-4 (1.95 ± 0.14 nM) were in good agreement with the certified value (1.88 ± 0.29 nM). Field evaluation of the instrumentation and analytical methods was achieved through a series of local surveys in the Tamar Estuary (UK), from which environmental data are presented.

Evaluation of a seawater equilibrator for shipboard analysis of dissolved oceanic trace gases

Equilibrators have been used for years to obtain gas phase samples for measurement of the partial pressure of dissolved trace gases in near surface seawater. For air–sea exchange studies these measurements assume (1) complete and instantaneous equilibration and (2) that the water sampled is representative of the water in contact with the atmosphere. We present a simple mathematical model to evaluate the factors that determine the equilibration time constant for any gas of known solubility and to determine the deviation from equilibrium that arises from any vent flow of air into the equilibrator headspace. Both these expressions are functionally dependent on a dimensionless equilibrator coefficient ε. The model predictions were tested using measurements under field conditions utilizing two gases of widely differing solubility, carbon dioxide and carbon monoxide. For both these gases we show that the value of ε for our particular equilibrator is about 0.3–0.4. We also present a depth profile of CO in the top 5 m of the open ocean which demonstrates that seawater sampled through a ship's water inlet at 5 m depth is representative of surface water.

Dissolved iron at subnanomolar levels in the Southern Ocean as determined by ship-board analysis

The biogeochemistry of iron was investigated in remote waters of the Antarctic ocean in the austral summer of 1995/1996. A sensitive flow injection analyser, based on in-line preconcentration and luminol chemiluminescence detection (FIA-CL), was used for underway surface measurements and vertical profiling during a fine scale survey in the Polar Front (PF) in the Atlantic sector of the Southern Ocean. Results indicated a dynamic environment with dissolved iron concentrations ranging from 0.05 to 0.3 nM. Distributions are consistent with chlorophyll a and fCO 2 suggesting a coupling with these parameters. The highest iron concentrations (0.3 nM) were found where chlorophyll a abundance was highest and CO 2 undersaturation the most pronounced. The vertical distribution (upper 500 m) revealed a nutrient type distribution with low subsurface values (0.1 nM) gradually increasing to ∼0.3 nM at depth.

CORTEX, a shipboard XRF-scanner for element analyses in split sediment cores

The CORTEX (Corescanner Texel) is a non-destructive XRF system for the logging of split sediment cores. It is a seaworthy instrument that remains active during heavy weather conditions. The scanner produces reliable counts for K to Sr, highly correlated with concentrations measured with atomic absorption spectrometry (AAS). The option to scan Al, Si, and elements heavier than Sr is in preparation. A core section of 1 m can be scanned at 2-cm intervals within an hour. A maximum resolution of 1 mm can be achieved. At present, each region and sedimentary environment requires separate calibration. In the nearby future the generator settings will be standardized, which may result in the development of a standard calibration procedure. Because of the high resolution of its semi-quantitative records, the CORTEX is a useful tool for detailed time-series analysis, inter-core correlation, and shipboard analysis.

IronEx-I, an in situ iron-enrichment experiment: Experimental design, implementation and results

An in situ iron-enrichment experiment near the Galapagos Islands was performed in October 1993. Here we report the theoretical and practical considerations of creating such a patch of iron-enriched surface water, as well as the strategies employed for the detection of the patch and the biological and chemical signals which developed, in an area dominated by advective processes. Physical and chemical models were used to predict the speciation, solubility, and the final concentration of iron in surface waters injected with acidic iron sulfate. A trial injection off the California coast in which 800 L of a 0.5 M FeSO 4 were introduced into the ship’s wake over a 1.5 km 2 area, was used to test these predictions. Iron concentrations were determined continually onboard during the initial experiment as the ship steamed in transects through the enriched patch. The results indicate excellent spatial agreement with model predictions and final concentrations that were consistent with the chemical model. However, the use of a Cartesian coordinate system during injection resulted in an extremely compressed, heterogeneous patch. Results from this preliminary experiment were then applied towards the development and implementation of the first open ocean iron enrichment experiment (IronEx I) near the Galapagos Islands in October 1993. The development and results of these methodologies are presented. In the IronEx I equatorial experiment, a Lagrangian coordinate system was established using a drogued buoy (equipped with GPS and packet radio) and the iron-enriched area (64 km 2 containing 443 kg of Fe) was tagged with the inert chemical tracer sulfurhexafluoride (SF 6). This strategy resulted in a fairly rectangular, homogeneous enriched patch initially detectable by both Fe and SF 6 determination. Shipboard analysis and airborne observations confirmed good spatial agreement between the Lagrangian drifter and the biological and chemical signatures in the patch. Biological and chemical sampling of the enriched area showed an increase in chlorophyll, primary production, biomass and photosynthetic energy conversion efficiency relative to waters outside the patch, supporting the hypothesis that iron limits phytoplankton growth and biomass in a ‘bottom up’ manner in this area. The ability to create a coherent patch and track it over time led to this first open-ocean test of the iron hypothesis.

Surface textural analysis of quartz sand grains from ODP Site 918 off the southeast coast of Greenland suggests glaciation of southern Greenland at 11 Ma

Shipboard analysis of the 1,183-m sedimentary section recovered at Site 918 in the Irminger Basin during Ocean Drilling Program Leg 152 revealed material of glacial origin (diamictons, ice-rafted debris (IRD) and dropstones) as deep as 543 m below sea floor (bsf). The sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 Ma, pushing back the date for the onset of glaciation on southern Greenland by 5 Ma. Thin layers of fine sand were found as much as 60 m deeper in the core, raising the possibility of an even earlier date for glaciation. To determine the sedimentary history of these deeper sand layers, the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope. The results suggest that the grains in the 60-m interval below the deepest dropstone have a glacial history. At that level, an 11-Ma Sr-isotope date was obtained from planktonic foraminifers. This late Miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages, indicating a new minimum age for the onset of glaciation on southern Greenland and in the North Atlantic.

Dual-detector system for the shipboard analysis of halocarbons in sea-water and air for oceanographic tracer studies

The measurement of chlorofluorocarbons (CFCs) has become well established as a technique for tracing oceanographic processes, providing time-dependent information about the mixing and transport of water masses. Until recently, sea-water analyses have been confined to CFC-11 and CFC-12, using a packed column electron capture detector–GC system. Recent changes in CFC use, together with the desire to extend the timescale covered by this technique, has necessitated the broadening of the range of compounds measured to include CFC-113 and tetrachloromethane. This has involved the development of a new chromatographic strategy based on a DB-624 megabore column together with a redesigned sample trapping/injection system. In addition, a dual-detector configuration, permitting increased sample throughput, has been designed. The new instrument also includes a more sophisticated standard/air injection system, providing the ability to cover a wider range of concentrations, but with a greater number of calibration points if required. Increased automation helps to ensure analytical quality whilst enhancing the instrument's usability. Results from the first field trials of this instrument, on RRS Discovery cruise 213, are reported. These indicate that the system has detection limits of 0.05, 0.005, 0.015 and 0.015 mol l–1 for CFC-12, CFC-11, CFC-113 and tetrachloromethane, respectively.

Shipboard analytical flow cytometry of oceanic ultraphytoplankton.

Shipboard analysis of marine ultraphytoplankton by flow cytometry is a powerful method to classify these cells according to in vivo fluorescence characteristics and size. At present, this ataxonomic-allometric approach allows recognition of phycoerythrin-containing cyanobacteria, cryptomonads, very small red-fluorescing cells (presumably prochlorophytes), and eukaryotic algae of various sizes in many open ocean samples. The speed at which flow cytometric analysis can be performed on freshly collected samples permits a high degree of sampling resolution in both space and time. A flow cytometric view is presented of the vertical distribution of ultraphytoplankton at various sites in the north Atlantic and of experiments wherein phytoplankton were incubated in an artificial light gradient and under simulated in situ conditions.

New venting in TAG Field

The Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field, which lies on the east wall of the Mid‐Atlantic Ridge at about 26°N, has been a focus of study since low‐temperature hydrothermal activity was discovered there in 1973. In July 1985, scientists making an intensive investigation of the site discovered the first black smokers on the ridge (Eos, 66, October 1, 1985, p. 682).The smokers appeared in images from a towed deep‐sea photovideo camera. Water temperature anomalies were recorded by a near‐bottom thermister array mounted on the camera. A conductivity‐temperaturedepth (CTD)/nephelometer package sent real‐time data of plume depth, distribution, and concentration. Shipboard analysis provided total reactive Mn.

A high sensitivity method for the determination of nanomolar concentrations of Nitrate and Nitrite in seawater with a technicon autoanalyzer II

A high sensitivity manifold for the determination of trace quantities (nanomolar concentrations) of nitrate+nitrite and nitrite alone is described. The method uses a classical Technicon AutoAnalyzer II usually employed for shipboard analysis. A reproducibility of ± 1 nmol dm −3 for nitrate plus nitrite and nitrite alone was obtained, with an analytical rate of 40 samples h −1.

Analysis of seawater for dissolved cadmium, copper and lead: An intercomparison of voltammetric and atomic absorption methods

An intercomparison study of voltammetric and atomic absorption spectrometric methods for determining cadmium, lead and copper in seawater samples was conducted. The voltammetric approach utilizes differential pulse anodic stripping voltammetry using a rotating, glassy carbon, mercury film electrode under conditions developed to minimize contamination sources and to enhance sensitivity for seawater matrices. The atomic absorption approach involves a concentration step using either an organic solvent extraction of metal dithiocarbamate chelates or a Chelex-100 column with detection by graphite furnace atomic absorption spectrometry. Similar and consistent results were obtained using both methods for the three trace metals studied on a wide range of natural seawater samples. Both methods are comparable in sensitivity for cadmium and copper, however the voltammetric method is better suited for the analysis of lead in seawater because of its enhanced sensitivity and low blank. An advantage of the voltammetric approach is its amenability towards real-time shipboard analysis.

Shipboard calibration of an infrared absorption gas analyser for total carbon dioxide determination in sea water

A new method for shipboard calibration of an infrared absorption carbon dioxide analyser was devised, utilizing the oxidative decomposition reaction of oxalic acid by permanganate in acid solution. With the present method, shipboard analysis of total carbon dioxide in 2 ml of sea water can be carried out with an error of less than 0.5 %. Some improvements in the analyser system are also presented.

Cretaceous Black Shales in Angola Basin of South Atlantic Ocean: ABSTRACT

Conditions favorable to deposition of black shales in the deep ocean occurred several times during the Cretaceous. Anoxic sediments were laid down in the South Atlantic during two distinct periods, the Aptian-early Albian and the late Albian-Coniacian. At site 530 of DSDP Leg 75 in the Angola Basin, black shales averaging 5.1% and containing up to 16.5% organic carbon were found in a late Albian-Coniacian turbidite sequence. Shipboard analysis shows most of the organic matter to be of marine origin, although several layers contain some terrigenous material. Based upon Rock Eval pyrolysis and the absence of significant amounts of light hydrocarbons, all of this organic matter is classified as immature. Thicknesses of the black shale layers are generally several centimeters or less, and they are separated by fine-grained turbidites containing less than 0.3% organic carbon. These Aptian-Coniacian shales seem to be the result of downslope density flows of shelf-edge sediments rich in organic matter. Preservation of organic matter was a result of rapid burial, not by stagnant basin waters. Furthermore, this mode of preservation appears to be responsible for the Cretaceous black shales throughout the South Atlantic. End_of_Article - Last_Page 958------------

Shipboard analysis of strontium-90 in seawater on Geosecs II

Strontium-90 in seawater samples was analyzed aboard the USS Knorr by direct extraction of the 90Y daughter. The extraction was made in two 17-gallon heavy-walled glass bottles. Yttrium carrier was added and the 90Y was extracted with HDEHP in toluene, back-extracted with HCl, and purified with a second HDEHP extraction. The Y was mounted as the oxalate and counted in a methane end window system. Check analyses were performed in a shorebased laboratory equipped with low background beta counters. The results of the sea and shore analyses were consistent within the limits of error. The test demonstrates that 90Sr analyses can be performed satisfactorily at sea, and that a better equipped laboratory and counting facility would improve the performance considerably.

Quick Statistical Methods for Analysing the Sequences of Fish Counts Provided by Digital Echo Counters

The data records of digital echo counters consist mainly of sequences of overlapping counts. To estimate target density and the total number of distinct targets present, one should make appropriate allowances for the redundancy induced by overlapping. With this in mind, point and interval estimation methods are suggested for use in the hand analysis of such sequences. The techniques were developed in response to the need for ship-board analysis of data when there is an immediate requirement to gauge variations in target density as fish surveys are being conducted.