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). ble, but changes can be detected over spatial scales. To discriminate ana- For example, concentrations of ni­ longer time scales of seasons to years lytes against the large background of trate near the sea surface can be (16,17). major ions, efficient methods of high at the end of winter because of Chemical distributions also show chemical separation must be em­ frequent storms that bring deep, nu­ large variations over all spatial ployed. Time-series measurements trient-rich water to the surface. So­ scales. Concentrations may increase over periods from seconds to years lar heating during the spring pro­ or decrease from the surface to the are required to interpret ongoing duces a density stratification that sea floor (average ocean depth is chemical processes in the ocean. stabilizes the water column. This 3800 m), depending on whether the Chemical measurements must often thermal stratification allows phyto- chemical cycle is dominated by re­ be made over length scales from mil­ plankton to remain within the sunlit lease from or uptake by sinking par­ limeters to thousands of kilometers. portion of the water column (euphot- ticles (18). Large vertical concentra­ ic zone) where they grow rapidly and tion gradients can be found over Chemical tracers of ocean consume the available plant nutri­ distances of a few meters. Further­ circulation ents such as nitrates, phosphates, more, water circulates between each Chemical and biological coupling in and silicates. of the major ocean basins in a dis­ the ocean are often regulated by the After such spring blooms, which tinctive pattern. This produces a physical processes that transport usually last only a few weeks, photo- unique lateral distribution of dis­ water, plankton, and chemicals in synthetic rates are controlled by solved chemicals on a scale whose the sea. To some degree, the major physicochemical processes (e.g., up- length is tens of thousands of kilo­ circulation of seawater can be de­ welling, diffusion, and atmospheric meters for many chemicals. In addi­ scribed as a conveyor belt (Figure 2) deposition) that slowly resupply nu­ tion, important chemical variability (20). A strong density gradient (pyc- trients to the sunlit surface layer. Bi­ may occur over distances of < 1 mm nocline) at a depth of 50-200 m, ological processes such as grazing because of the presence of microenvi- caused by a rapid temperature de­ and microbial decomposition also re­ ronments such as anoxic fecal pellets crease with increasing depth, iso­ lates the surface wind-mixed layer from the colder and denser deep wa­ ters. The major source of the deep water below the pycnocline is in the high latitudes of the North Atlantic. From there it flows south through the Atlantic to the Antarctic cir- cumpolar current, then north through both the Indian and Pacific oceans. Deep water returns to the surface ocean by turbulent mixing and upwelling in zones located on the eastern coastal margins and equato­ rial belt of the major ocean basins. The average time needed to replace -i \\\ \ ' \\ V^ ^ /.Pacific U \ the deep waters of the entire ocean system is 500 years, and deep water in the North Pacific is thought to be >Λ\\ Atlantic ;c ' / /^ί\ ^è^^ _—~r—"-r^Cwarm about 1500 years old (21). \ Λ\\\ Ocean 'Si// ) L·^ JSÎr*"C?\~") ) shallow I ' )\V\ \ {M/ SÎ/κ x / t / current Much of our knowledge of advec- tive and diffusive processes in the ocean is obtained from measure­ ments of chemical tracers rather than from direct measurements of ~~—'————— QQid ancj sany jeep current the motion of water masses (18). Cir­ ff Antarctic circumpolar current culation tracers are chemicals whose s _—· - - ^ concentrations change in a well- defined manner with time. They are excellent tools for the study of deep Figure 2. Conveyor belt of oceanic surface and deep-water currents, illustrating circulation because they integrate the major pattern of deep-sea circulation deduced from chemical tracer the turbulent fluctuations that dom­ measurements. inate the flow of water in the deep (Adapted with permission from Reference 20, courtesy Joe LeMonnier.) sea. Without the information pro-

ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1067 A REPORT vided by circulation tracers, an inor­ tion will allow better temporal erator MS has eliminated the need dinately large number of velocity resolution when dating water that for decay counting (24) and will revo­ measurements would be required to has left the surface in the past 20 lutionize the ability of oceanogra- describe the time-averaged circula­ years, when the atmospheric Freon- phers to date deep seawater samples. tion of the ocean. 11/12 ratio has been relatively con­ At present, accelerator MS can be The general circulation of sea- stant. Freon-113 concentrations are, used to measure 14C concentrations water along the conveyor was ini­ however, below the detection limit of by direct atomic counting of the inor­ tially deduced from measurements of most current measurement tech­ ganic carbon extracted from 200 mL biochemically reactive tracer com­ niques, primarily because of contam­ of seawater. A national accelerator pounds such as oxygen and plant nu­ ination problems. MS facility for océanographie re­ trients. Determination of the rates at The utility of 14C, another oceanic search has just begun operation at which seawater flows along the con­ tracer, has recently been enhanced the Woods Hole Océanographie Insti­ veyor requires measurements of ra­ by new analytical techniques. 14C, tution. However, difficult contamina­ diotracers with appropriate half- tion problems still exist in the deter­ which has a half-life of 5720 years, is 14 lives or chemicals with well-known, naturally produced in the strato­ mination of natural levels of C in time-dependent source functions. samples collected on research vessels sphere by cosmic-ray interaction 14 These tracers exist only in extremely with nitrogen. Unlike CFCs, which where large spikes of C02 are used low concentrations. Their utility has can be tracked in the environment to determine rates of primary pro­ come about mainly through advances for no more than 60 years, 14C can be ductivity. in analytical instrumentation and used to determine the time elapsed contamination control. since a water mass left the surface in Inorganic carbon the oldest portions of the oceanic Two examples of chemical tracers 14 The concentration of C02 in the at­ that can be used to determine the conveyor (21). C measurements mosphere has increased rapidly since patterns and rates of deep-sea circu­ have not been made routinely, how­ the industrial revolution because of lation are chlorofluorocarbons ever, because decay-counting tech­ the burning of fossil fuels and the de­ (CFCs) and 14C. CFCs were first pro­ niques require that inorganic carbon struction of tropical rain forests. It is duced in the 1930s, and their concen­ be stripped and concentrated from predicted that this concentration will trations in the atmosphere have in­ > 200 L of seawater for each analy­ double during the 21st century. Con­ sis. This is an expensive process that creased almost exponentially since centrations of C02 in the upper that time. CFCs dissolved in surface requires specialized sampling appa­ ocean must also have increased. To­ seawater are in equilibrium with the ratus at sea and time-consuming tal inorganic carbon in the ocean is atmosphere; present-day concentra­ analyses. The development of accel- defined as tions are ~5 pM for CC13F (Freon- 11) and CC12F2 (Freon-12) (22). The [TC02] = [HCO3] + [CO*"] + [C02]aq increase in CFC concentrations has • • • However, direct measurements of the been paralleled by a changing ratio PCo2 ^atm) increase in TOC are not yet feasible of Freon-11 to Freon-12. This time- because its spatial and temporal dependent ratio makes it possible to 150 350 550 750 variability requires a massive num­ determine when a seawater sample o F—Γ~6 1 ber of samples to assess the TC02 in­ was last in equilibrium with the at­ • ventory of a single ocean. • • mosphere. CFC measurements have The rate at which C0 is absorbed now been used to trace the flow of 2 100 - m from the atmosphere by the ocean is water as it enters the deep sea. For not well known, and considerable example, CFC measurements show variability exists in recent estimates that water leaving the surface of the 200 - •> of the amount of fossil fuel COz that North Atlantic during winter reaches m •ë. 300 - a has entered the ocean (8). Measure­ the equator in 23 years and is diluted £ É • ments of a time-dependent change in only fivefold during this time (23). ο. Ι 13 12 S 400 - · .' the ratio of C/ C in seawater, be­ • Detection of low CFC concentra­ • cause of dilution of oceanic carbon by I • fossil fuel carbon with a different iso- tions in seawater became feasible 500 - • H only after the invention of the elec­ topic composition, demonstrate that tron capture detector (ECD) for GC \ the ocean is receiving fossil fuel and the adoption of strict procedures 600 - S carbon (25). A direct assessment of to control contamination from the at­ C02 uptake by the ocean is critically mosphere and the CFC-rich labora­ 700 I I important because it will allow limits tory environment. Samples are to be placed on the magnitudes of purged, cold-trapped, and analyzed other global carbon sources (e.g., by GC using an ECD. Because of the Figure 3. Atmospheric C02 increase tropical forest clearing) and sinks high sensitivity of this approach, reflected in the Pcc>2 of the North (e.g., uptake by boreal forests) (8). ECD-based analyses can accurately Atlantic Ocean at a station between In lieu of direct measurements of measure CFCs down to concentra­ Florida and Bermuda. the rate at which C02 enters the tions of 0.005 pM (grams per cubic Measured PCOz values (dark blue squares) ocean because of fossil fuel burning, kilometer) in seawater (22). increase with depth because of remineralization oceanographers have attempted to of organic carbon. Correction of the measured Further development of CFC mea­ values for respiration (yellow squares), using the measure the change in TC02 or Pco suring techniques is still needed. For observed depletion of oxygen, demonstrates that as seawater flows along the con­ shallower waters are equilibrated with the modern example, Freon-113 (CC12FCC1F2) veyor. Old water that has moved far atmosphere (Pco = 350 μΆ\π\); older, deep water along the conveyor should have has been produced in large quanti­ is equilibrated with the pre-industrial atmosphere, ties only during the past two de­ which had a Pcc,2 of only 270 μαΙπ\. (Data from equilibrated with the pre-industrial cades. A method for its determina­ Reference 26.) atmosphere and have a lower Pco

1068 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 and TC02. However, respiration of tine precision of 0.1% with the devel­ routine basis. Such a system may organic carbon and dissolution of opment of a coulometric titration form the basis for an optical sensor CaC03 from particles sinking into procedure that could be used aboard that can be deployed on océano­ the deep sea also increase the Pco2 ship (28). This has become the stan­ graphie moorings for long periods of and TC02 as seawater ages. The dard analytical procedure for global time to observe changes in oceanic TC02 concentration increases by ocean science programs. It will be carbon chemistry. ~20% during the time water spends difficult, however, to achieve inter- in the deep sea. Respiration of or­ laboratory agreement at the 99.9% Organic compounds ganic carbon produces the largest level until seawater standards for Large gaps occur in our most funda­ change in TC02 in the deep sea TC02 become readily available. mental knowledge of DOC com­ («70%). If concentrations of TC02 Measurements of TC02 alone can­ pounds in seawater. The total con­ and titration alkalinity, defined as not completely define the state of the centration of DOC is classically inorganic carbon system in seawater. determined by chemical oxidation of TA = [HCO3] + 2[CO|-] + [B(OH)2 + One additional chemical parameter, organic molecules with persulfate or [OH ] - [H+] such as pH, Pcc,2, or TA must also be by ultraviolet photooxidation and are measured with a precision better determined. As with the coulometric subsequent determination of the C02 than 0.1%, it is possible to detect the TC02 determination, these measure­ that is produced. This technique change in PCo2 and TC02 concentra­ ments must be made with extremely yields ocean DOC concentrations tions because of the increase in C02 in high precision and accuracy to detect that are quite low (30-100 μΜ). the recent atmosphere. Such measure­ the small temporal changes occur­ However, results obtained with re­ ments have been used to detect the ex­ ring in the ocean. The spectrophoto- cently developed high-temperature tent of penetration of fossil fuel C02 metric determination of pH by using combustion methods have suggested into the Atlantic Ocean (Figure 3) (26, indicator dyes may be the simplest that the total DOC concentration in 27). measurement that can be made to seawater has been underestimated The analytical difficulties in rou­ fully define the seawater carbonate by a factor of 2 or more (30). DOC tinely measuring the TC02 concen­ system (29). The narrow pH range of values obtained by high-temperature tration and the TA or pH with errors seawater (7.4-8.9) is well suited to combustion methods in surface wa­ < 0.1% throughout the ocean are sub­ spectrophotometric measurement ters can reach 300 μΜ. The excess, stantial. Recently, significant with an acid-base indicator of the relative to that obtained by low- progress was made in measuring appropriate τρΚα. Precision better temperature oxidation, amounts to a TC02 levels of seawater with a rou­ than 0.001 pH can be obtained on a pool of organic carbon that is greater in mass than the total amount of carbon stored on land in soils and vegetation, when averaged over the volume of the ocean (31). Although many investigators have turned their analytical efforts toward the recently developed high-temper­ ature combustion method, a recent interlaboratory comparison failed to Radiation resolve the discrepancies among the budget various methods for DOC analysis. Other laboratories have reported confirmation of a much larger DOC Cloud albedo pool (31), but the original paper re­ porting the high-temperature com­ bustion method has been withdrawn, leaving the field in a state of disar­ Cloud condensation Global temperature nuclei ray. Much work in this important area remains to be done. t + \ Temporal variability of individual Sulfate aerosol organic compounds or compound m classes, their spatial distributions, Î + Climate feedbacks and their roles in biogeochemical cy­

S02 cles are not well understood. Studies α of a few specific organic molecules, t + however, have demonstrated the tre­ DMS + or - mendous influence that these com­ k Atmosphere pounds can have, both in controlling global processes and as tools for Ocean studying physical and chemical pro­ DMS cesses in the ocean. Phytoplankton Marine For example, recent work by Bras- abundance and ecology + or speciation sell et al. has shown the potential of long-chain (»-C37) unsaturated alk- enone biomarkers as indicators of Figure 4. Proposed role of phytoplankton in the ocean-atmosphere sulfur cycle. surface temperatures in ancient Production of DMS in the ocean leads to increased atmospheric DMS. This link may serve as a negative oceans (32). Phytoplankton of the feedback mechanism for global warming. (Adapted with permission from Reference 36.) class Prymnesiophyceae biosynthesize

ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1069 A REPORT these alkenones, apparently storing sea. Ocean cloud cover has also been Recent advances in analytical meth­ them in cell membranes. The degree correlated with the concentration of ods, sample collection, and process­ of unsaturation is used to regulate phytoplankton (39). It has been sug­ ing techniques have led to dramatic membrane fluidity as a function of gested, in fact, that phytoplankton new understanding of the marine temperature. Measurements in may regulate the production of DMS biogeochemical behavior of trace ele­ plankton cultures, in suspended par­ in such a manner as to control the ments in seawater. The first accurate ticulate matter, and in surface sedi­ Earth's albedo and its climate (40). measurements of the total dissolved ments at different locations in the The identification and quantita­ concentrations of most trace ele­ ocean demonstrate that the ratio of tion of individual dissolved organic ments were made only in the past 15 the 37-carbon alkadienone to that of compounds at low nanomolar to pico- years (43), demonstrating that most the 37-carbon alkatrienone is lin­ molar concentrations continues to be trace elements are present at low na­ early related to the temperature of the chief obstacle in studies of or­ nomolar to picomolar concentrations the water in which these phyto­ ganic carbon cycling. Current meth­ in surface waters. In many cases, plankton live (32, 33). ods of analysis require large samples their vertical distribution in the oce­ These alkenones are refractory in or a time-consuming chromato­ anic water column mimics that of the marine sediments, and their ratio graphic separation and, even then, major plant nutrients such as ni­ apparently is preserved for > 650,000 concentrations are still often near trates, phosphates, and silicates years. Determination of the alkenone detection limits. The determination (Figure 6) (44). compounds in ancient sediments, of DMS involves purging and cold- Experiments using phytoplankton dated by isotopic measurements, can trapping a sample with liquid nitro­ cultures indicate that iron as well as be used to reconstruct the surface gen, which is difficult to maintain on zinc, manganese, copper, and cad­ temperature of the ocean during past long research cruises (41). Advances mium can exert strong selective glacial and interglacial periods (34). in MS that provide detection limits pressures that may regulate the dif­ The carbon isotopic ratios of these in the picomolar range (42) promise ferences in species composition of biomarker compounds in sediment to expand the number of compounds phytoplankton between metal-rich cores can be used to estimate the that can be detected. The develop­ coastal and metal-poor open ocean magnitude and direction of the atmo­ ment of other analytical schemes environments (45). Recent studies sphere-sea C02 flux in ancient that do not introduce isotopic frac­ with natural plankton samples dem­ oceans (35). This analysis has been tionation effects is still required. onstrate that iron may limit primary possible only through the coupling of Much of the development needs to be production in otherwise potentially capillary GC with isotope ratio MS focused on methods that can be used productive regions of the world's for measuring isotopes of specific aboard ship or in situ for real-time oceans (46). Addition of only 1 nM Fe compounds in a complex mixture. measurements of large numbers of to surface seawater samples, which Trace organic compounds may also samples and a limited suite of com­ typically contain < 0.1 nM Fe, can have a large impact on global chemi­ pounds, rather than a few measure­ cause a significant increase in pri­ cal cycles. For example, dimethylsul- ments of large numbers of com­ mary production. Estimates of the fide (DMS) produced in the ocean is pounds (37). potential productivity of ocean wa­ believed to play a critical role in the ters, based on phytoplankton cellular global sulfur cycle and the radiation Trace elements Fe:N:C ratios and dissolved iron and balance of the Earth (Figure 4) (36). Many trace elements are required nitrate in surface waters, indicate Dimethylsulfoniopropionate (DMSP), micronutrients in the enzyme and that substantial increases in global the precursor to DMS, is produced in electron transport systems present in carbon fixation could be realized if the surface layer of the ocean by all living organisms. Plant growth is modest amounts of iron were added some phytoplankton (Figure 5) (37). limited by trace element availability at the equator and at high latitudes. DMSP apparently is used to regulate in many terrestrial systems, yet the This scenario, known as the "Iron the internal osmotic pressure of the role of these elements in limiting Hypothesis" (11), has recently re­ plankton cell; it decomposes to DMS, phytoplankton growth in the ocean ceived much public attention because which is quite stable in seawater. has remained largely speculative. of the potential for iron fertilization DMS is lost primarily through trans­ port across the sea surface to the at­ mosphere and also to microbial con­ sumption. DMSP (nM) Chlorophyll a (mg/m3) DMS (nM) DMSO (nM) The radicals OH and N03 react with DMS in the atmospheric bound­ Ο 1 2 3 Ο 4 8 12 16 Ο 2 4 _ 6 Ο 40 80 —I -FS Ι Ι—Ι—ϊ—ΓΤΙ Ι Ι "Μ-^1 Ι \Ι Ι ary layer to produce methanesulfonic À acid, sulfur dioxide and, ultimately, +— _. * rfi*V-Fiee *^» sulfate. Biogenic DMS entering the •ρ- 10° "" " I Particulate f atmosphere from the oceans may add —ii ι ap sulfur at a concentration roughly £ ι g- 200 -, ,, t equivalent to the input from sulfur Q ι ι: ; dioxide derived from fossil fuel com­ I bustion. The sulfate aerosol provides ι ι ! 300 - ; the most significant source of nuclei for cloud condensation in the remote marine atmosphere. The concentra­ 400 Li tion of cloud condensation nuclei is now directly linked to the abundance Figure 5. Vertical profiles of organosulfur compounds. of methanesulfonic acid (38) and pre­ Distributions of DMS, DMSO (dimethylsulfoxide), DMSP, and chlorophyll a demonstrate that sumably the flux of DMS from the phytoplankton are the source of organosulfur compounds. (Adapted with permission from Reference 37.)

1070 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 of the oceans to offset the effects of thermal ionization MS (TIMS). In­ trace measurements. Only recently, increased atmospheric C02 and glo­ ductively coupled plasma MS is be­ the techniques developed for océano­ bal warming. This hypothesis is still coming widely accepted for océano­ graphie analyses have been extended the subject of much scientific debate, graphie analyses because it is highly to measurements taken in freshwa­ mainly because very few laboratories sensitive, can determine multiple el­ ter systems. These measurements, can accurately measure iron in sea- ements, and requires small samples. using methods developed by chemical water at ambient concentrations or It is especially useful for measuring oceanographers, demonstrate that perform uncontaminated enrichment the refractory elements, such as tita­ dissolved metal concentrations are experiments. nium and the rare earths (47). overestimated in freshwater lakes Two major advances have made it These developments led to dra­ and rivers by as much as 3 orders of possible to determine total concen­ matic decreases in the reported con­ magnitude (49). trations of dissolved trace elements centrations of most trace elements Measurements of total element in seawater. First was the realization dissolved in seawater; in some cases, concentrations, however, are insuffi­ of the extraordinary efforts required the reported concentrations dropped cient to define chemical behavior. to carry a seawater sample through several orders of magnitude. These The chemical speciation of an ele­ each step of the sampling and ana­ changes led to the concept of océano­ ment will determine its biological lytical processes without contamina­ graphie consistency as a criterion for availability, toxicity, and geochemi- tion (43). Second was the adaptation accepting trace chemical measure­ cal reactivity in seawater. The oxida­ of analytical methodologies with suf­ ments (48). This concept states that tion states of a variety of trace ele­ ficient sensitivity and selectivity to element concentrations measured in ments (e.g., arsenic, tin, antimony, determine trace metals at extremely the open ocean should show smooth and tellurium) have been success­ low concentrations. variations that are related to known fully determined by using techniques The analytical methods most com­ physical, chemical, and biological such as selective hydride generation monly used in oceanography involve processes. Trace element concentra­ coupled with AAS or GC (50). preconcentration and separation tions change smoothly because of the Complexation of metals by organic steps with use of ion-exchange resins long time scale for mixing of sea­ and inorganic ligands can also have a or chelation and solvent extraction. water (> 100 years) and the long dis­ marked effect on the reactivity of Even after concentration by factors tances between strong sources of chemicals in the ocean. Copper, for of 100 to 1000, most trace elements trace elements at the oceans' mar­ example, is present in surface sea­ in seawater can be detected only by gins and interior. Océanographie water at concentrations of < 1 nM. It using graphite furnace atomic ab­ consistency has been a highly suc­ is bound by an unidentified ligand, sorption spectrometry (GFAAS) or cessful means of identifying reliable which appears to be produced by or­ ganisms in the upper ocean, that has a high specificity for the metal (51). The ligand is also present at concen­ trations of ~1 nM and regulates the Silicate (μΜ) Zinc (nM) copper(II) aquo-ion concentration. Concentrations of the copper aquo- 0 50 100 150 200 0 2 4 6 8 10 ion are calculated to be on the order of 1 χ 10"14 M, which is undetectable by any analytical method now avail­ able (Figure 7). Studies of this sys­ tem must be performed at total metal and ligand concentrations < 1 nM. 1000 -1 , - - k . Electrochemical methods such as dif­ Atlantic \ Atlantic \ ferential pulse anodic stripping vol- tammetry (DPASV) at a thin mer­ cury film/glassy carbon electrode or differential pulse cathodic stripping Î voltammetry (DPCSV) methods us­ ing a hanging mercury drop electrode are employed most often in these 1 \ ) I studies (52, 53). 2000 -1 - « Much of the focus in the analytical t Pacific I ° Pacific \ chemistry of trace metals in sea­ 3000 - · - · water is on the development of meth­ ods that can be used aboard ship to produce large data sets (53). Ship­ board methods have, in general, pre­ cluded AAS and MS because the in­ 4000 I 1 I ' - struments are sensitive to the constant vibrations. Instead, a vari­ ety of methods have been developed, including atomic fluorescence (for Figure 6. Profiles of total dissolved zinc and silicate in the North Atlantic and mercury) (54), GC (for aluminum, be­ North Pacific oceans. ryllium, arsenic, and selenium) (55), Zinc distributions are similar to those of the plant nutrient silicate—depleted at the surface and enriched and flow injection analysis (FIA) us­ at depth. Biological activity depletes dissolved zinc to subnanomolar levels. The interocean differences are the same for the two analytes, indicating a constant composition of sinking plankton as seawater ing chemiluminescence and fluoro- passes along the oceanic conveyor. (Data from Reference 44.) metric detection (for a suite of met-

ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1071 A REPORT als, including cobalt and manganese The determination of 234Th has rium can be extracted in situ by [56, 57]). DPASV and DPCSV are typically been achieved through a pumping seawater through car­ also used at sea for the determina­ long coprecipitation, ion-exchange, tridges filled with acrylic fibers that tion of zinc, cadmium, copper, lead, and electrodeposition process. This is have been impregnated with manga­ cobalt, nickel, and iron (53). Many of followed by alpha particle counting of nese oxide (58), thus eliminating the these techniques can discriminate a 230Th yield tracer using silicon sur­ need to process thousands of liters of between the various chemical forms face barrier detectors and beta parti­ seawater aboard ship. Second, 234Th of the element (e.g., the oxidation cle counting of the 234Pa product of emits a gamma particle that can be state and the degree of complexation 234Th using low-background, antico­ detected with use of a low-back­ by organic ligands), which more ac­ incidence, gas-flow proportional de­ ground well-type germanium-lithium curately reflects the chemical reac­ tectors (60). The particles and pro­ detector. The acrylic fibers on which tivity and the biological availability cesses that remove thorium are thorium is concentrated can be or toxicity of the metal (51). How­ heterogeneously distributed in the melted into a puck and inserted di­ ever, shipboard sampling (with the surface waters, and many measure­ rectly into the detector to obtain possible exception of surface water ments are required to characterize 234Th activities while still at sea (61). pumping) permits only a few samples these rates accurately. Furthermore, Third, TIMS is now being used to de­ to be collected, and the possibility of 234Th has only a 24.1-day half-life, tect the longer-lived thorium and contamination still exists. Future and some of the activities are very other uranium-series radionuclides. work must focus on in situ measure­ low (< 0.2 decay per minute per liter), The direct determination of the mo­ ments of metal concentrations where necessitating that the isotopes in lecular abundance of 230Th and 232Th greater sampling resolution and less samples collected on long cruises be by using TIMS greatly improves the likelihood of contamination can be separated and counted at sea. The detection limit, which reduces the achieved. other isotopes of thorium that are volume of water needed for an analy­ useful in determining rates of metal sis from 1000 to about 10 L (62). Fur­ Radioisotopes interactions with particles, 230Th ther improvements in concentration More than 60 radionuclides occur and 232Th, have long half-lives and and detection techniques will in­ naturally in the marine environ­ require thousands of liters to be pro­ crease the utility of radioisotopes as ment, in addition to the fission prod­ cessed for each sample before the iso­ tracers of chemical processes within ucts of thermonuclear power genera­ topes can be measured by conven­ the oceans. tion and weapons detonation. Of the tional methods of alpha particle natural radionuclides, 14 are pro­ detection. Chemical sensors and analyzers duced by cosmic rays and 49 by decay These difficulties have prompted A long-term series of chemical obser­ of primordial isotopes. Radioisotopes several recent analytical advances in vations is required to identify the have the unique feature of allowing thorium isotope detection. First, tho­ processes that lead to natural vari- oceanographers to elucidate rates of mixing and chemical transforma­ tions in the ocean. The parent/product activity ratios Copper (M) of the natural uranium and thorium 9 decay series isotopes have proved 10-15 10-12 ΙΟ" 10- particularly useful in studies of dis­ 0 solved metal-particle interactions (58). The primordial isotope 238U ex­ ists principally as the dissolved 238 U02(C03)3~ species in seawater and shows a low affinity for chemical Hyd rated Total reaction or sorption onto sinking aquo-ion concentration particles. Uranium therefore is dis­ activity 500 tributed in a uniform manner throughout the water column. In con­ trast, 234Th, the immediate product of 238U, exists as the hydrolysis prod­ 234 < 4 + uct Th(0H) „ -'" and is highly CD particle reactive. Radioactive dis- D equilibria between the dissolved 234Th and its 238U parent (shown in 1000 the shaded region of Figure 8) can be used to calculate rates at which tho­ rium is scavenged from the dissolved to the particulate phase and the rate at which particles are removed from the water column. These measure­ ments show the importance of inter­ 1500 actions with plankton in removing metals from the surface ocean (Fig­ Figure 7. Vertical profiles of total dissolved copper (right) and the Cu(ll) aquo-ion ure 8) (59). By measuring other ele­ (left) activity in the North Pacific Ocean. ments associated with particles Organic ligands produced near the surface suppress the Cu(ll) ion activity in the upper ocean by carrying thorium, various elemental > 3 orders of magnitude relative to the value in organic-free seawater. (Adapted with permission from removal rates can be calculated. Reference 51.)

1072 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 ability in ocean chemistry and to as­ sess the human impacts on bio- 3 ( Pigments (mg/m ) ' 234Th/238U geochemical cycles. Analysis of temporal trends in chemical concen­ 0.1 0.3 0.5 0.2 0.6 1.0 trations in the ocean now requires 0 ! ! ! ! __^ that a ship be on station to collect the \ I Mixed layer ; ! samples. The cost of operating a modern research vessel capable of working on the high seas ($7000 to $18,000 per day) makes this a pro­ hibitively expensive undertaking, and long-term océanographie studies are done at very few locations (63). As a result, our understanding of J» \ Euphotic zone 1^ ocean processes is severely limited. ω The high production that occurs f / \ \ during the few weeks of a spring bloom may never be sampled by sci­ entists constrained by ship schedules 200 - I - {( and finite budgets. Wintertime sam­ pling in many high-latitude areas of I Particles Dissolved Total the ocean is completely lacking be­ cause of extremely unfavorable weather conditions. Few long-term series of oceanographically consis­ tent data have been collected with 300 y ~L automated chemical measurement systems. Difficulties with sensor Figure 8. Vertical profiles of (a) phytoplankton pigments and (b) activity ratio of drift and biofouling have compro­ 233Th:238U in the dissolved and particulate (> 0.45 μηπ) fractions in the central mised their use on deep-sea moor­ North Pacific. ings where sensors must operate un­ attended for months at a time, (a) Phytoplankton are concentrated near 100 m because nutrient concentrations are too low at shallower 234 although recent progress has been depths, and there is insufficient light below 150 m to support growth, (b) Low dissolved Th activities in the 100-m region (highest biological activity) are an indication of the role of phytoplankton in removing made (64). A new generation of metals from surface waters. (Adapted with permission from Reference 59.) chemical measurement systems must be developed for long-term (1-12 months) operation on océanographie moorings. Two approaches are being tested -3 -1 Temperature anomaly (m'C) ι Light attenuation anomaly (10 m ) for the design of chemical measure­ ment systems that can operate in the deep sea. One method uses chemical sensor systems in which the analyte interacts with the active surface of the sensor by diffusion. The second approach is to adapt continuous-flow ΟΑΓ\(\ ' valley wall spreading valley wall chemical analyzers, which transport D<22 Π 34-46 Η 58-70 H>82 D<5 D 25-45 Θ65-85 sample and reagents mechanically, D 22-34 Π 46-58 Β 70-82 D5-25 Ο 45-65 H>85 for in situ operations over long peri­ ods of time. Both techniques have significant advantages and disad­ Iron (nM) . . Manganese (nM) vantages. 1800 - ' ^/ - ' . Sensor systems, such as electrodes, fiber-optic sensors, and chemical field-effect transistors promise to play an important role in the future (65). These systems are mechanically simple and can potentially be manu­ 2400 I 1 i 1 I factured at low cost. Fiber-optic sys­ D<10 D 20-30 Β 40-50 Η 60-70 D <25 Π 75-125 Β 175-225 tems also allow the electronics to be D 10-20 D 30-40 S 50-60 B>70 D 25-75 D125-175 B>225 placed in a remote location. The only chemical sensors regularly used are oxygen and pH electrodes. These sen­ Figure 9. Temperature anomaly, light attenuation anomaly, dissolved iron, and sors have been particularly valuable dissolved manganese measured in situ over a hydrothermally active segment of for measurements of small-scale the Juan de Fuca Ridge. (< 1 mm) chemical gradients across The sawtooth line in the temperature anomaly plot (1000 m °C = 1 °C) shows the tow path of the the sediment-water interface (66). instrument package. More than 3700 determinations for iron and manganese were performed at depths Development of other chemical sen­ > 2000 m in real time, enabling the acquisition of chemical data at similar resolution to physical measurements. (Adapted with permission from Reference 69.) sor systems has been hindered be-

ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1073 A REPORT

cause they usually require a revers­ patchiness that requires continuous (13) Chester, R. Marine Geochemistry; Un- ible chemistry that will respond observations (71). The present gener­ win Hyman: London, 1990. (14) Barber, R. T.; Chavez, F. P. Science rapidly to changes in dissolved chem­ ation of instrumentation is oriented 1983 222 1203 ical concentration and yet have suffi­ primarily toward analyses of dis­ (15) PÎatt, T.; Sathyendranath, S.; Ulloa, cient sensitivity and selectivity to cretely collected samples in ship- and O.; Harrison, W. G.; Hoepffner, N.; detect dissolved chemicals present at shore-based laboratories. The need Goes, J. Nature 1992, 356, 229. a concentration of 0.1 μΜ. Few such (16) Brewer, P. G.; Broecker, W. S.; for a new generation of chemical ob­ Rhinnes, P. R.; Jenkins, W. J.; Rooth, chemistries are known. serving systems to better monitor the C. G.; Swift, J. H.; Takahashi, T.; It is also possible to determine the changing ocean is now widely recog­ Williams, R. T. Science 1983, 222, 1237. concentrations of a suite of dissolved nized. Global science initiatives, in­ (17) Sansone, F. J.; Smith, S. V.; Price, cluding the Joint Global Ocean Flux J. M.; Walsh, T. W.; Daniel, T. H.; An­ chemicals in situ by using unseg- drews, C. C. Nature 1988, 332, 714. mented, continuous-flow analyzers Study (72) and the Ridge Inter- (18) Broecker, W. S.; Peng, T-H. Tracers (67). These submersible chemical an­ Disciplinary Global Experiments in the Sea; Eldgio Press: Palisades, NY, alyzers (scanners) are based on the (73), have identified developments in 1982. principles of FIA, although without chemical sensing that are required to (19) Alldredge, A. L.; Cohen, Y. Science 1987 235 689 the injection valve. Continuous-flow meet their scientific objectives. Many (20) Broecker, W. S. Nat. Hist. Mag. 1987, analyzers modified to operate under­ of these needs are outlined in a Na­ 97, 74. water can use many of the chemis­ tional Research Council report (2). (21) Stuiver, M.; Quay, P. D.; Ostlund, tries developed for use in the labora­ What is now needed is an exchange H. G. Science 1983, 219, 849. of ideas and technology between the (22) Gammon, R. H.; Cline, J.; Wise- tory with little modification required. garver, D. / Geophys. Res. 1982, 87, 9441. Scanners are the only instruments chemical oceanographer and analyti­ (23) Weiss, R. F.; Bullister, J. L.; Gam­ available that can be used to deter­ cal chemist to foster the development mon, R. H.; Warner, M. J. Nature 1985, mine dissolved nutrient elements in of new techniques for a clearer vision 314, 608. of the global ocean and our planet as (24) Nelson, D. E.; Korteling, R. G.; Stott, situ. Nitrate concentrations from the W. R. Science 1977, 198, 507. surface to depths of 2000 m have a whole. (25) Quay, P. D.; Tilbrook, B.; Wong, been determined in situ with a scan­ C. S. Science 1992, 256, 74. (26) Brewer, P.; Goyet, C, Monterey Bay ner tethered to a research vessel (68). We wish to acknowledge the contributions of The concentration of nitrate is deter­ Aquarium Research Institute, personal our many colleagues at Moss Landing Marine communication, 1992. mined classically by reducing it to ni­ Laboratories and Monterey Bay Aquarium Re­ (27) Brewer, P. G. Geophys. Res. Lett. 1978, trite and forming an azo dye. Mea­ search Institute. They have inspired and en­ 5, 997. couraged our work on marine analytical chem­ (28) Johnson, K. M.; Sieburth, J. M.; surements of redox reactive species istry. Greg Cutter, Stuart Wakeham, and one such as sulfide, manganese, and iron Williams, P.J.L.; Braendstroem, L. Mar. anonymous reviewer had many useful com­ Chem. 1987, 21, 117. also have been made in deep-sea hy­ ments on an early version of this report. We (29) Robert-Baldo, G.; Morris, M. J.; drothermal systems at depths of apologize to those chemical oceanographers Byrne, R. H. Anal. Chem. 1985, 57, 2564. whose areas of study were not presented or 2500 m with scanners mounted on mentioned only briefly here, but we thank all (30) Sugimura, Y.; Suzuki, Y. Mar. Chem. manned submersibles or towed from who have made this field what it is today. This 1988, 24, 105. a research vessel (Figure 9) (69). work is supported by Office of Naval Research (31) Martin, J. H.; Fitzwater, S. E. Nature grant N00014-89-J-1070 and National Science 1992, 356, 699. Scanner systems can easily be cal­ Foundation grant OCE8923057. (32) Brassell, S. C; Eglinton, G.; Mar­ lowe, I. T.; Pflaumann, U.; Sarnthein, ibrated in situ by substituting stan­ M. Nature 1986, 320, 129. dards for the seawater input at regu­ References (33) Prahl, F. G.; Wakeham, S. G. Nature lar intervals. Analyzer systems are, 1987, 330, 367. however, inherently more complex (1) Bard, Α.; Goldberg, E. D.; Spencer, (34) Eglinton, G.; Bradshaw, S. Α.; Rosell, Α.; Sarnthein, M.; Pflaumann, than sensor systems. This has a D. W. Appl. Geochem. 1988, 3, 3. (2) Chemical Measurement Technologies for U.; Teiedemann, R. Nature 1992, 356, marked impact on their long-term Ocean Sciences; National Research Coun­ 423. reliability and operating life. Signifi­ cil: Washington, DC, in press. (35) Jasper, J. P.; Hayes, J. M. Nature cant progress in reducing the com­ (3) Falkowski, P. G.; Hopkins, T. S.; 1990, 347, 462. plexity of scanner systems has been Walsh, J. J. J. Mar. Res. 1980, 38, 479. (36) Andreae, M. Mar. Chem. 1990, 30, 1. (4) Officer, C. B.; Biggs, R. B.; Taft, J. L.; (37) Lee, C; Wakeham, S. G. In Chemical made by replacing mechanical pumps Cronin, L. E.; Tyler, Μ. Α.; Boynton, Oceanography; Riley, J. P., Ed.; Aca­ with osmotic pumps (70). W. R. Science 1984, 223, 22. demic: London, 1988; Vol. 9, pp. 1-51. (5) Managing Troubled Waters: The Role of (38) Ayers, G. P.; Gras, J. L. Nature 1991, Conclusions Marine Environmental Monitoring; Na­ 353, 834. tional Research Council: Washington, (39) Falkowski, P. G.; Kim, Y.; Kolber, Z.; Our vision of the ocean is seen DC, 1990. Wilson, C; Wirick, C; Cess, R. Science through lenses crafted by the tools of (6) The Carbon Cycle and Atmospheric C02: 1992, 256, 1311. our discipline. The picture of ocean Natural Variations Archean to Present; (40) Charlson, R. J.; Lovelock, J. E.; An­ dreae, M. O.; Warren, S. G. Nature 1987, chemical cycles developed by ocean- Sundquist, E. T.; Broecker, W. S., Eds.; American Geophysical Union: Washing­ 326, 655. ographers has been focused by ad­ ton, DC, 1985. (41) Andreae, M. O.; Barnard, W. R. Anal. vances in analytical chemistry. In (7) Lorius, C; Jouzel, J.; Raynaud, D.; Chem. 1983, 55, 608. many ways, however, our knowledge Hansen, J.; Le Treut, H. Nature 1990, (42) Burlingame, A. L.; Millington, D. S.; of ocean chemistry still remains very 347, 139. Norwood, D. L.; Russell, D. H. Anal. (8) Sarmiento, J. L.; Sundquist, Ε. Τ. Na­ Chem. 1990, 62, 268 R. superficial. The influence of organ­ ture 1992, 356, 589. (43) Bruland, K. W. In Chemical Oceanog­ isms, one of the most important fac­ (9) Broecker, W. S.; Denton, G. H. Geo- raphy; Riley, J. P.; Chester, R., Eds.; Ac­ tors in controlling the composition of chim. Cosmochim. Acta 1989, 53, 2465. ademic: London, 1983; Vol. 8, pp. 157- seawater, is often treated by chemi­ (10) Martin, J. H. Paleoceanogr. 1990, 5, 1. 220. (11) Martin, J. H.; Gordon, R. M.; Fitz- (44) Bruland, K. W.; Franks, R. P. In cal oceanographers as a black box. water, S.; Broenkow, W. W. Deep-Sea Res. Trace Metals in Sea Water; Wong, C. S.; This lack of knowledge arises be­ 1989, 36, 649. Boyle, E.; Bruland, K. W.; Burton, J. D.; cause ocean chemistry is under sam­ (12) Marine Particles: Analyses and Charac­ Goldberg, E. D., Eds.; Plenum: New pled on all time and space scales. terization; Hurd, D. C; Spencer, D. W., York, 1983; pp. 395-414. Eds.; Geophysical Monograph No. 63; (45) Bruland, K. W.; Donat, J. R.; The ocean is a dynamic system American Geophysical Union: Washing­ Hutchins, D. Â. Limnol. Oceanogr. 1991, with fronts, eddies, and biological ton, DC, 1991. 36, 1555.

1074 A · ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 (46) What Controls Phytoplankton Production con, M. P.; Livingston, H. D.; Casso, in Nutrient-Rich Areas of the Open Sea? S.A.; Hirschberg, D.; Hartman, M. C; Chisholm, S. W.; Morel, F.M.M., Eds.; Fleer, A. P. Deep-Sea Res. 1992, 39, 1103. Say Goodbye to Limnol. Oceanogr. 1991, 36, 1507-1965. (62) Chen, J. H.; Edwards, R. L.; Wasser- (47) Orians, K. J.; Boyle, Ε. Α.; Bruland, burg, G. J. Earth Planet. Sci. Lett. 1986, Either/Or K. W. Nature 1990, 348, 322. 80, 241. (48) Boyle, Ε. Α.; Sclater, F. R.; Edmond, (63) Karl, D. M.; Winn, C. D. Environ. Sci. J. M. Earth Planet. Sci. Lett. 1977, 37, 38. Technol. 1991, 25, 1977. Electrochemistry (49) Windom, H. L.; Byrd, J. T.; Smith, (64) Wallace, D.W.R.; Wirick, C. D. Na­ R. G.; Huan, F. Environ. Sci. Technol. ture 1992, 356, 694. 1991 25 1137 (65) Goyet, C; Walt, D. R.; Brewer, P. G. (50) Cutter, L. S.; Cutter, G. Α.; San Di- Deep-Sea Res. 1992, 39, 1015. ego-McGlone, M.L.C. Anal. Chem. 1991, (66) Reimers, C. E. Deep-Sea Res. 1987, 34, 63, 1138. 2019. (51) Coale, K. H.; Bruland, K. W. Limnol. (67) Johnson, K. S.; Beehler, C. L.; Saka­ Oceanogr. 1988, 33, 1084. moto-Arnold, C. M. Anal. Chim. Acta Square Wave Stripping (52) Van Den Berg, C.M.G. In Chemical 1986, 179, 245. 80 ppb Lead Oceanography; Riley, J. P., Ed.; Aca­ (68) Johnson, K. S.; Sakamoto-Arnold, Mercury Microelecrrude demic: London, 1988; Vol. 9, pp. 197- C. M.; Beehler, C. L. Deep-Sea Res. 1990, 245. 36, 1407. (53) Donat, J. R.; Bruland, K. W. In Trace (69) Coale, K. H.; Chin, C. S.; Massoth, Metals in Natural Waters; Steinnes, E.; G. J.; Johnson, K. S.; Baker, Ε. Τ. Nature Salbu, B., Eds.; CRC Press: Boca Raton, 1991, 352, 325. FL, in press; Chapter 12. (70) Jannasch, H. W.; Johnson, K. S. In (54) Gill, G. Α.; Bruland, K. W. Environ. Proceedings of the MarChem '91 Workshop ost electrochemical software is Sci. Technol. 1990, 24, 1392. on Marine Chemistry; Martin, S. J.; Codis- designed to do either sophisti­ (55) Measures, C. I.; Edmond, J. M. Anal. poti, L. Α.; Johnson, D. H., Eds.; Office M Chem. 1989, 61, 544. of Naval Research Report No. OCNR cated research or routine measure­ (56) Sakamoto-Arnold, C. M.; Johnson, 12492-510; Office of Naval Research: ments. In the past, if your lab did K. S. Anal. Chem. 1987, 59, 1789. Arlington, VA. both, you were stuck. (57) Chapin, T. P.; Johnson, K. S.; Coale, (71) Dickey, T.; Marra, J.; Granata, T.; Κ. Η. Anal. Chim. Acta 1991, 249, 469. Langdon, C; Hamilton, M.; Wiggert, J.; Either you had to buy two separate (58) Bacon, M. P.; Anderson, R.F. /. Geo- Siegel D.; Bratkovich, A. / Geophys. Res. phys. Res. 1982, 37, 2045. 1991, 96, 8643. packages, which meant satisfying (59) Coale, K. H.; Bruland, K. W. Limnol. (72) Global Ocean Flux Study; National the compatibility requirements for Oceanogr. 1987, 32, 189. Academy Press: Washington, DC, 1984. both and learning two very different (60) Coale, K. H.; Bruland, K. W. Limnol. (73) Ridge Inter-Disciplinary Global Experi­ Oceanogr. 1985, 30, 22. ments: Initial Science Plan; Ridge Office, environments. Or you had to buy (61) Buesseler, K. 0.; Cochran, J. K.; Ba­ University of Washington: Seattle, 1989. one package and make do. Well say goodbye to either/or electro­ chemistry. The Model 270 Electro­ chemical Analysis software from EG&G Princeton Applied Research is unmatched on all counts—power, versatility, and ease of use. Consider just this small selection of Model 270 advantages: • Both time-tested hardware (Model 273 Potentiostat) and state-of-the- art computer environment (IBM platform, pull-down menus) • Automatic control of both the PARC Model 303A SMDE and a se­ lection of microelectrodes The authors in front of the National Science Foundation's research vessel, R/V Point Sur, operated by Moss Landing Marine Laboratories (MLML). • Traditional voltammetry/polarog- Kenneth S. Johnson (left) is professor of chemical oceanography at MLML of the Cali­ raphy and fast Square Wave fornia State University and a senior scientist at the Monterey Bay Aquarium Research In­ • Easy-to-learn Standard Mode for stitute (MBARI). He received his B.S. degrees in chemistry and oceanography from the routine use and feature-rich Expert University of Washington in 1975 and a Ph.D. in oceanography from Oregon State Uni­ Mode for finer experimental control versity in 1979. His research interests include the development of automated methods for shipboard and in situ trace chemical analysis and application of these systems to the study So if you typically do ground-break­ of chemical cycling in the ocean. ing research one day and routine Kenneth H. Coale (center) is a research scientist and adjunct professor at MLML. He measurements the next, say hello to received his B.S. degree and his Ph.D. (1988) from the University of California, Santa total electrochemistry. Call for infor­ Cruz. His research interests include trace element biogeochemistry in marine and fresh­ mation today at 1-609-530-1000. water systems, the application of naturally occurring U/Th series radionuclides to study chemical cycling and age dating of marine specimens, and the development of analytical methods for shipboard and in situ determination of trace metals in seawater. EGzG PARC Hans W. Jannasch (right) is an assistant scientist at MBARI. Before his joint postdoc at MBARI and MLML, he received his Sc.B. degree in chemistry from Brown University P.O. BOX 2565 · PRINCETON, NJ 08543-2565 in 1978 and a Ph.D. in chemical oceanography from the University of Washington in (609) 530-1000 · FAX: (609) 883-7259 1990. His research interests include trace metal scavenging, behavior of marine particles, Circle 25 for Literature. and the development of in situ chemical instrumentation. Circle 26 for Sales Representative.

ANALYTICAL CHEMISTRY, VOL. 64, NO. 22, NOVEMBER 15, 1992 · 1075 A