408 



74 OCEANOGRAPHY IN THE NEXT DECADE 



causes are inferred from measured distributions, that is, as an 

 inverse problem. Variations in measured concentrations reflect 

 changes in the relative importance of these causes. This inver- 

 sion is constrained by different chemical properties of the ele- 

 ments of the periodic table, their valence states, their isotopes, 

 and the compounds they form. It follows that this strategy re- 

 quires the measurement of a vast array of chemical properties. 

 Although technology development is required for measuring some 

 of these properties, each of the elements and forms is not equally 

 important diagnostically. Extraction of all the information useful 

 in constraining the inversion is a prodigious analytical task. 



Until recently, each available instrument could analyze only a 

 few elements at the sensitivity, precision, and accuracy levels 

 necessary for their concentration in natural samples. Thus no 

 laboratory could perform more than a small fraction of possible 

 measurements. Over the past 10 years, the sensitivity of instru- 

 ments has increased vastly. Accurate and precise multielement 

 analyses on single samples are now feasible, and multiple collec- 

 tor thermal ionization mass spectrometers have increased the sen- 

 sitivity for a wide range of elements and isotopes. High-energy 

 accelerator mass spectrometry allows the measurement of the cos- 

 mogenic radioisotopes in the study of a wide range of geochrono- 

 logical questions; it also allows exploitation of the unique proper- 

 ties of these isotopes in a variety of tracer studies. Plasma source 

 mass spectrometry makes it possible to perform accurate multielement 

 analyses on extremely small amounts of material. This technol- 

 ogy eases measurement of refractory elements that, because of 

 their low volatility or high ionization potential, are difficult to 

 measure with conventional techniques. 



Mass spectrometry for the measurement of 6^^0, 8^^C, and 

 other light isotope systems are well established, as are methods 

 for determining radiogenic isotopes. New developments in high- 

 resolution thermal ionization mass spectrometry for the measure- 

 ment of ^-^OTh, ^^^Th, ^^"^U, and ^^^U and the negative thermal 

 ionization mass spectrometric measurement of ^^'^Os/^^^Os have 

 improved our capacity to use these isotopes in marine geochemi- 

 cal studies. 



Improving Our Knowledge of Fluxes 



Much more research needs to be done to quantify continental 

 inputs to the oceanic reactor. An important adjunct to studies of 

 fluxes will be long time-series measurements that will allow an 



