REPORT Analytical Chemistry in Oceanography such as sewage plants or runoff from 1 Kenneth S. Johnson , farmland (e.g., ammonia, nitrates, Kenneth H. Coale, and and phosphates) can lead to in­ Hans W. Jannasch2 creased rates of plant production, or Moss Landing Marine Laboratories eutrophication, in surface waters. P.O. Box 450 Eutrophication is linked to toxic phy- Moss Landing, CA 95039 toplankton blooms (e.g., red tides) and greater oxygen demand in the Chemical measurements in the ocean subsurface waters. Increasing anoxia involve a unique set of challenges re­ in the water column attributable to lated to the distinctive composition eutrophication has had a negative of seawater, the large spatial and impact on marine resources in both temporal scales over which measure­ the New York Bight (3) and the ments are made, and the frequent Chesapeake Bay (4). A single episode need to perform analyses while at of anoxia in the New York Bight re­ sea under difficult conditions. These sulted in a $60 million loss to surf- problems are not familiar to many clam fishery alone (3). In many cases, analytical chemists, in part because the impacts of these perturbations it is unusual to find chemical ocean - are not recognized or understood be­ ographers or geochemists in close cause we lack records of natural contact with their chemistry col­ chemical variability in the marine leagues (J). environment or an adequate means Chemical oceanography has been to monitor it (5). practiced primarily in departments On a global scale, the flow of chem­ or institutions oriented toward ma­ icals through the ocean system is rine or environmental sciences. Our closely linked to the Earth's climate. chemical understanding of the The ocean holds 60 times more inor­ oceans is, however, directly linked to ganic carbon than does the atmo­ the development of the latest analyt­ sphere, and perturbations in the flow ical tools and advances in chemistry of C02 through the ocean are related and engineering. A report soon to be to changes in atmospheric C02 and issued by the National Research global temperature (6). Release of Council states that a significant in­ C02 from the burning of fossil fuels, crease is needed in our abilities to which has resulted in a 30% increase ζ observe ocean chemistry and to study in atmospheric C02 since 1850, has g the biological, physical, and chemical the potential to produce even greater (biogeochemical) processes that con­ climatic changes than were experi­ (Λ Ζ trol the flow of chemicals through the enced over the last glacial cycle (7). Ο χ ocean and its linkage with the atmo­ Much of this C02 will enter the < sphere (2). Rapid improvements in ocean, but the rates of C02 absorp­ 8 the methods of chemical analysis tion in seawater are not yet well <ζ LU available to oceanographers are known (8). Rapid changes in ocean 8 needed, particularly with respect to circulation may produce large C02 LU Ο sensors that can operate in situ and fluxes between the ocean and the at­ Ι CO unattended for long periods of time mosphere (9); small changes in ocean ο on deep-sea moorings. These ad­ chemistry may also draw large 8 vances will require much closer coop­ amounts of C0 from the atmosphere ω> 2 LU en eration between the analytical chem­ and regulate climate (10). ID Ο Ο istry and chemical oceanography Despite the importance of these cy- <" communities. Q Increasing attention has been fo­ s cused on ocean chemistry because of 'Also affiliated with Monterey Bay Aquarium m Research Institute, 160 Central Ave., Pacific 2 civilization's impact on the flow of Grove, CA 95039 > chemicals through the sea. On a local 2Present address: Monterey Bay Aquarium Re­ CD Ο scale, nutrient loading from sources search Institute Ο Ι ο. 0003-2700/92/0364-1065A/$03.00/0 ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1065 A © 1992 American Chemical Society REPORT cles, there are large gaps in our most humic material, a poorly character­ particles affect the cycling of chemi­ fundamental understanding of the ized substance of high molecular cals in the sea. Many elements and processes that drive the flow of weight with extensive unsaturation compounds are passively adsorbed to chemicals through the ocean. For ex­ and polymerization. the exterior of particles, whereas ample, we do not understand what Seawater cannot be considered as others are actively taken up and combination of processes controls the an assemblage of dissolved elements transformed by the biota. Biologi­ rates at which phytoplankton fix dis­ and compounds alone. Particles of cally mediated reactions are one of solved C02 into organic carbon in every size drift, sink, and swim the major forces that control the large areas of the ocean (11). Yet this through the sea. Furthermore, many chemical cycling of dissolved trace el­ "biological pump" is one of the most of the particles studied by geochem- ements in the ocean (13). significant processes that acts to re­ ists are actually living organisms. A The natural cycles of many chemi­ distribute dissolved and particulate typical milliliter of surface seawater cals are characterized by large tem­ chemicals throughout the sea. contains on the order of 10 million poral changes in concentration. Daily Our goal in this REPORT is to high­ viruses, 1 million bacteria, 100,000 variability in the surface waters is light some of the current issues and phytoplankton, and 10,000 zooplank- driven by photosynthesis, respira­ problems in chemical oceanography. ton. All of these living and nonliving tion, photochemical reaction, tidal It will focus on both the océano­ graphie questions and the analytical methods used to address them. This article will concentrate primarily on the determination of dissolved chem­ icals. However, cycling of particles in the marine environment is an Fe - I— m- Na equally important subject that can­ Xe - • - Mg not be easily separated from studies Ti - I • - SOf- of dissolved chemicals (12). The areas Ge - | • - Ca in which significant advances in an­ Pb - I • - Κ alytical technology are required will Co - I • - TCOz be emphasized. We do not pretend to W - • - N2 offer a comprehensive treatment of TI - • - Br this subject in so few pages, but we Ag - I I • - 02 hope to offer the analytical chemist a La - I- • - Β sense of the enormous challenge fac­ Ga - h I • - Si ing the chemical oceanographer, with Be - 1— • - Sr an appreciation for the complexity of Ce - h • - F the marine system and the power of Sn - I I • - NOj analytical chemistry to unravel the Nd - h • - Li ocean's secrets. Sc - I- m - Ar Background Pr - h • - Rb The analytical challenges involved in Dy - I- !-• - 1 studying ocean chemistry are formi­ Yb - h l-B - Ba dable. Only seven ions are present in Gd - h • - Mo seawater at concentrations > 1 mM. Er - I • - AI These major ion electrolytes consti­ Sm - fB - V tute > 99.5% of the dissolved chemi­ Ho - I— l-B - As cals in seawater and dramatically af­ Lu - I I—• - Ni fect the rates and equilibria of Tm - 1 • - U chemical reactions in the sea. Hidden Tb - H I • - Zn within this matrix of major ions are Th - I • • - Ne infinitesimally small quantities of Te - h- I • - Cu the remaining elements (Figure 1). tn — I— • i-B - Cr Determination of these trace chemi­ Pt - h >-• - Kr cals is often complicated by the major Eu - h I • - Μη ion matrix. Despite their low concen­ Pd - h- I • - Se tration, the remaining elements may Bi - I • - Cs have a significant influence on global Au - H • - He chemical cycling. A single iron atom, • - Sb for instance, is required for each 15 12 9 6 3 100,000 molecules of C02 that are 10~ 10~ 10~ 10~ 1(Γ 1 fixed into organic carbon. Lack of iron, therefore, may control the fate Concentration (M) of enormous amounts of carbon in the ocean (10, 11). Figure 1. Plot of concentrations of seawater components, spanning 15 orders of The sea is also a weak organic soup magnitude. that contains up to 300 μΜ dissolved The horizontal bar spans the range of concentrations that have been detected in open ocean waters. In organic carbon (DOC), of which many cases, low concentrations represent detection limits and even lower concentrations are likely to < 10% has been identified (13). Much occur. Yellow squares refer to the left y-axis; dark blue squares refer to the right y-axis. TC02 refers to of the remaining organic carbon is total inorganic carbon. Concentrations are taken from current literature. 1066 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 mixing, and overturn of the water lease nutrient elements stored in found in oxygenated surface waters column initiated by solar heating. cells (15). Fall and winter storms vig­ (19). Reduced compounds produced in Variations in concentration also oc­ orously mix plant nutrients into sur­ these environments may have an im­ cur on a seasonal cycle because of face waters, but productivity does pact on chemical cycles. changes in light, temperature, verti­ not increase until the water column Thus the challenge for the chemi­ cal mixing rates, and growth of phy- again stabilizes during the spring. cal oceanographer is to develop or toplankton. Interannual changes in The few weeks of high primary pro­ apply analytical methodologies with chemical distributions over large ar­ duction during the spring bloom can the sensitivity and specificity to de­ eas of the ocean basins occur because dominate the annual carbon produc­ termine a wide variety of chemical of climatic processes such as the tion cycle (15). The chemical compo­ substances within a complex medium well-known weather phenomenon sition of the deep water is more sta­ over a large range of temporal and "El Nino" (14).