1 Fundamental Problems in Oceanographic
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Analysis DAVID N . H U M E Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass. 02139
The success of studies on ocean chemistry usually hinges on the availability of adequate analytical methodology and expertise. The nature of the chemical problems involved; the size and heterogeneity of the ocean; the extremes of concentration, composition, temperature, and pressure; and the dynamic interactions at its interfaces with the lithosphere, atmosphere, and biosphere create challenging and often unique analytical problems. Current analytical methods are limited, and improved capability in referee, routine, monitoring, and in situ analyses is needed. Valid sampling, the use of reliable standards in calibration, and the collaborative evaluation of methods under real-world conditions are important.
*~T*he chemistry of the oceans involves a vast number of intricately and intimately interrelated systems and reactions. T o be understood, many of these require precise and accurate analytical data, which is often unattainable by conventional means. This symposium has brought together oceanographers and analytical chemists for meaningful com munication. W e hope that the oceanographers can give an overview of the fundamental chemical problems of the ocean i n terms of the equi librium, dynamic, biological, hydrological, geological, and meteorological systems involved and that the chemists can speak cogently i n terms of what approaches may be effective i n generating valid data under the unusual and extreme conditions which characterize the natural ocean. I n short, we w i l l discuss what ocean chemistry is all about, what questions need answering, what the difficulties are, and what analytical chemists may be able to do to help. A
1 Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
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ANALYTICAL METHODS IN OCEANOGRAPHY
W h e n one considers the size of the ocean—its 10 1. of water covers 7 1 % of the earth's surface—and its importance as the climatic mediator, as the source of food and materials, and as the ultimate sink for many of our pollutants, it is surprising how little is actually known about it. Only i n very recent years has the volume of ocean research, chemical and otherwise, started increasing rapidly. W i t h this increase has come an awareness of the inadequacy of our methodology. 21
The Ocean as an Object and a System The ocean is a large mass of water containing about 3.5% salt i n a fairly uniform mixture. It is layered with respect to temperature, being warm enough at the surface i n many places for swimming but close to 4 ° C throughout most of its depths. There are various horizontal and vertical currents, which produce gradual mixing. F r o m the standpoint of a chemist it is almost a static system because the mixing time is about 1600 years, although this constitutes rapid turnover to a geologist who consequently views it as a well mixed dynamic system. W h i l e there are local variations i n total salinity because of evaporation, rainfall, and input from rivers, the relative proportions of the major constituents are remarkably uniform (Table I ) ( I ) . The bulk of the dissolved salts ( > 99.99% ) is made up of only 11 elements which vary only slightly i n their relative amounts. Most of the rest of the dissolved salts consist of the minor constituents (Table II) (2) which vary considerably i n their relative and absolute amounts, largely as the result of biological activity. W h a t is left is a little bit of everything else i n the periodic table at con centrations of a few parts per billion and less. It would be a considerable challenge just to establish accurately the composition and chemical properties of an isolated sample of seawater, but the sea is not isolated. It has three important interfaces with its environment: the atmosphere, the lithosphère, and the biosphere. E a c h of these interfaces involves active transport of matter and energy, each Table I.
Concentrations of the Major Nonvolatile Constituents of 35%o Salinity Seawater
Constituent Chloride Sodium Sulfate Magnesium Calcium Potassium
Concentration (mg/kg) 19,350 10,760 2,710 1,290 413 387
Constituent Bicarbonate Bromide Strontium Boron Fluoride
Concentration (mg/kg) 142 67 8 5 1
Gibb; Analytical Methods in Oceanography Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
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Problems in Océanographie
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Analysis
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Table II. Approximate Concentrations of the Minor Nonvolatile Constituents of 35%o Salinity Seawater" Constituent Silicon Nitrogen Lithium Rubidium Potassium Iodine
Concentration ^g/kg) ~3000 —1000 170 120 —70 60
Constituent Barium Aluminum Iron Zinc Molybdenum
Concentration 30 —10 —10 —10 —10
° All remaining elements
