Applications of Analytical Chemistry to Oceanic Carbon Cycle Studies (1993) / Chapter Skim
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Oceanographic Measurements
Oceanographic Measurements
Pages 13-32
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From page 13... ...
The list of analyses was divided into four categories, with emphasis being placed on the relative importance to understanding the oceanic carbon cycle: Priority 1 Quantifying the Anthropogenic Carbon Input Priority 2a Understanding the Biological Pump Priority 2b Tracing Water Masses Priority 3 Other Analytes of Interest Priority 3 analyses were suggested by chemical oceanographers who responded to a questionnaire. These parameters are of interest to many oceanographers and could benefit from attention by the analytical chemistry community, even though they are not necessarily related to the carbon cycle directly.
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From page 15... ...
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From page 18... ...
Priority 1 Quantifying the Anthropogenic Carbon Input The carbon dioxide reservoir in seawater is presumably increasing in size in response to the burning of fossil fuels at a rate of approximately 1 micromole per kilogram per year in surface waters; increases are less in the deep ocean. The magnitude of this change could be estimated by measurements of the carbon dioxide flux into the ocean or measurements of the concentration of carbon dioxide.
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From page 19... ...
OCEANOGRAPHIC MEASUREMENTS TABLE 2 Technologies for Chemical Measurements 19 Techniques Analytes That Could Be Measured Mass spectrometry 313C A14C iron 615N, argon-39, 3He/3H, zinc, copper, aluminum, lead, manganese, 3He, Th isotopes Electrochemical techniques Potentiometry Constant potential techniques at steady state Pulse voltammetry Stripping voltammetry Coulometry Spectrophotometry Absorbance Luminescence Raman Fiber optics Refractive index Piezoelectric mass sensors New chemistry Chromatography and electrophoresis Flow injection analysis and continuous flow analysis pCO2, pH, ammonium PCO2, O2 Iron, O2, zinc, copper, aluminum, lead, DMS, manganese Iron, zinc, copper, aluminum, lead, DMS, manganese TCO2, DOC, POC, ammonium pCO2, pH, nitrate, phosphate, iron, ammonium, zinc, copper, aluminum, lead, LMW compounds pCO2, pH, DOC, nitrate, iron, ammonium, O2, zinc, copper, aluminum, lead, manganese CFCs, LMW compounds DOC, nitrate, phosphate, silicate, iron, ammonium, algal pigments, O2, zinc, copper, aluminum, lead, DMS, LMW compounds, manganese Alkalinity DOC pCO2, pH, DOC, nitrate, phosphate, silicate, iron, ammonium, algal pigments, O2, zinc, copper, aluminum, lead, DMS, LMW compounds, manganese, algal toxins DOC, nitrate, phosphate, CFCs, DMS, LMW compounds pCO2, pH, nitrate, phosphate, silicate, iron, ammonium, zinc, copper, aluminum, LMW compounds, manganese DOC = Dissolved organic carbon POC = Particulate organic carbon CFCs = Chlorofluorocarbons DMS = Dimethyl sulfide LMW = Low molecular weight Th isotopes = Thorium isotopes (234Th and 230Th)
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From page 20... ...
To determine a valid parameterization of the air-sea gas transfer constant, the actual rate of gas transfer should be measured simultaneously with relevant parameters, such as l\pCO2, wind speed, temperature difference between water and air, sea surface roughness, and possibly other factors. Measurements of TCO2 require a precision and accuracy of better than 1 micromole per kilogram per year to be useful in detecting, within a few years, the signal of anthropogenic carbon input to the ocean from combustion of fossil fuels.
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From page 21... ...
It is necessary to improve our capability for measuring the spatial and temporal distributions of a variety of chemical compounds, to gain a better understanding of how the biological pump operates, and to be able to predict future changes in the ocean carbon cycle. Biological activity in the upper and deep ocean results in the formation and breakdown of particulate and dissolved organic carbon and nitrogen (POC, PON, DOC and DON)
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From page 22... ...
However, we do not yet have an accurate estimate of the mass of DOC or a detailed understanding of what controls its rate of turnover, much less its composition or function in microbial food webs. There is not yet a generally accepted analytical method to characterize DOC, although there is much interest in improving high-temperature combustion methods using discrete samples.
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From page 23... ...
In recent years, flow cytometry has been adapted from medical use to sort and count phytoplankton cells containing different pigment types, increasing the level of information about phytoplankton communities. Knowledge of pigment concentrations is necessary to study the coupling of primary productivity with higher levels of the oceanic food web, such as the productivity of marine fisheries.
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From page 24... ...
With this technique, the time since a water mass left the surface can be determined within a range from several months to 30 years. Priority 3 Other Analytes of Interest Analytes in this category are not necessarily related to the carbon cycle, but are of interest to chemical oceanographers.
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From page 25... ...
are excluded from biological cycles, they often serve as useful tools in oceanography for tracing physical mechanisms and processes. The difference in the ratios of these gases, as well as nitrogen, in air and in surface ocean water has been used to study air-sea gas transfer mechanisms, such as air injection via gas bubbles.
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From page 26... ...
In general, most chemical analyses benefit from minimal sample manipulation, making in situ measurements preferable to ship-based measurements, which in turn are usually better than those in which the sample is brought back to a landbased laboratory. Conversely, the difficulties of performing chemical analyses multiply as the analytical method and instrumentation are brought from land-based laboratories to ships, and perhaps ultimately incorporated into an immersible device.
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From page 27... ...
Presently, most shipboard chemical analyses are carried out with instruments not designed for shipboard use. Instruments designed for use on ships must endure a humid, corrosive atmosphere; withstand shock and violent motions of the ship; survive greater extremes of temperature than in the usual laboratory; and function with limited and poor quality power and water supplies.
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From page 28... ...
An additional benefit of using in situ sensors is the potential savings in labor cost per sample. In general, adapting chemical analyses for use in the ocean is much harder than adapting methods and instrumentation for shipboard use.
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From page 29... ...
Sea surface temperature may be determined very precisely from satellites, providing additional physical oceanographic information. Physical oceanographic information is an important adjunct to chemical and biological measurements because temperature affects chemical reaction rates, gas solubilities, and organism growth.
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From page 30... ...
The major constraint to using satellite remote sensing is the relative opacity of the ocean and clouds to electromagnetic radiation. Thus, satellite measurements are limited to the very top layer of the ocean and usually provide little evidence about processes occurring below the ocean surface.
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From page 31... ...
This automation pertains principally to the supporting instrumentation necessary for operation of the sensor and for signal processing. Power requirements, on-board data handling, and data storage must all be configured appropriately for the particular application.
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From page 32... ...
Most sensors will depend upon a chemically selective layer attached to an appropriate transducer element. The system of chemical reactions contained within the selective layer must be stable or reversible or, if irreversible, be based on a renewed or continuously delivered reagent that maintains the ability of the sensor to detect the desired analyte.
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