Kitack Lee

Distribution of alkalinity in the surface waters of the major oceans

Abstract In recent years the total alkalinity (TA) of seawater has been measured with high precision (∼±2 μ mol kg −1 ) in the Atlantic, Pacific, and Indian oceans. In this paper we have analyzed the surface alkalinity of the major ocean basins using these measurements as well as those obtained during the GEOSECS and TTO studies. The salinity normalized alkalinity (NTA=TA×35/ S ) in subtropical gyres between 30°S and 30°N is remarkably invariable except in upwelling areas (e.g., the Eastern Equatorial Pacific). The NTA increases toward high latitudes (>30°) and is inversely proportional to sea surface temperature (SST). This increase in NTA with latitude (or decreasing temperature) is attributed to the upward transport of deep waters with higher NTA due to the dissolution of CaCO 3 (s). The distribution of surface NTA in the major ocean basins shows that the major basins can be divided into regions where different trends of NTA are observed and boundaries between the regions are similar to those of the major ocean currents. The linear behavior of NTA (∼±5 μ mol kg −1 ) with respect to SST makes it possible to provide regional maps of NTA. These maps can be used to estimate TA in surface waters in large areas of the ocean from values of SST and salinity ( S ). By combining the estimates of TA using SST and S (from the Climatological Atlas of the World Ocean) with underway f CO 2 measurements (by ships, moorings, and satellites), it is possible to map the detailed distribution of TCO 2 for surface waters over a large area of the ocean. Calculations of TCO 2 from measurements of f CO 2 , SST, and S in the subtropical Pacific Ocean agree with the coulometrically measured values to ±5 μ mol kg −1 .

Titration alkalinity of seawater

Abstract The titration system is described that was used to measure the total alkalinity of seawater (TA) during the Joint Global Ocean Flux Study (JGOFS) sponsored by the National Oceanic and Atmospheric Administration (NOAA) in the equatorial Pacific. It consists of a piston titrator, a pH meter, and a glass thermostated cell. Since the new pH meters and titrators have RS232 interfaces the system can be easily connected to a personal computer. The computer programs used to carry out the titration and to determine TA, pH sw (pH on the seawater scale), and TCO 2 from the full titration curve are described. A typical titration takes 20 min and consists of 25 points. Six separate titration cells were calibrated to be used on three systems at sea. The reliability of the electrodes was examined by titrations of 0.7 m NaCl with HCl at a pH near 3 and using seawater buffers at a pH near 8. Although most electrodes did not have Nernstian behavior over the entire pH range, all gave precise values of TA for a given solution. The individual cells were calibrated using standard Na 2 CO 3 and seawater standards prepared in our laboratory and Certified Reference Material (CRM) provided by Dickson. The cells gave reliable values of TA, but the values of pH sw were low (0.02) and values of TCO 2 were high (20 μmol kg −1 ) due to the non-Nernstian behavior of the electrodes at a pH near 8.0. If the slope determined from the buffers is used, the titrations yield reliable values of TA, TCO 2 and pH sw . Measurements on Dickson standards with the three cells at sea indicate that the systems have a reproducibility of ±2–4 μ mol kg −1 in TA. The titration values of TCO 2 determined on the CRMs and the samples collected at sea were about 17 ± 6 μ mol kg −1 (fall) and 20 ± 6 μ mol kg −1 (spring) too high. This offset in TCO 2 is independent of depth and is due to the non-Nernstian behavior of the electrodes. The offset is not due to unknown protolytes.

Low interannual variability in recent oceanic uptake of atmospheric carbon dioxide

An improved understanding of the partitioning of carbon between the atmosphere, terrestrial biosphere, and ocean allows for more accurate predictions of future atmospheric CO2 concentrations under various fossil-fuel CO2-emission scenarios. One of the more poorly quantified relevant processes is the interannual variability in the uptake of fossil-fuel CO2 from the atmosphere by the terrestrial biosphere and ocean. Existing estimates, based on atmospheric measurements, indicate that the oceanic variability is large. Here we estimate the interannual variability in global net air–sea CO2 flux using changes in the observed wind speeds and the partial pressure of CO2 (pCO2) in surface sea water and the overlying air. Changes in seawater pCO2 are deduced from interannual anomalies in sea surface temperature and the regionally and seasonally varying temperature-dependence of seawater pCO2, assuming that variations in sea surface temperature reflect seawater pCO2 changes caused by thermodynamics, biological processes and water mixing. The calculated interannual variability in oceanic CO2 uptake of 0.4 Gt C yr−1 (2σ) is much less than that inferred from the analysis of atmospheric measurements. Our results suggest that variable sequestration of carbon by the terrestrial biosphere is the main cause of observed year-to-year variations in the rate of atmospheric CO2 accumulation.

Increasing N Abundance in the Northwestern Pacific Ocean Due to Atmospheric Nitrogen Deposition

Nitrogen deposition from the atmosphere has altered the nitrate:phosphorus ratio in the marginal seas of the northwestern Pacific Ocean. The relative abundance of nitrate (N) over phosphorus (P) has increased over the period since 1980 in the marginal seas bordering the northwestern Pacific Ocean, located downstream of the populated and industrialized Asian continent. The increase in N availability within the study area was mainly driven by increasing N concentrations and was most likely due to deposition of pollutant nitrogen from atmospheric sources. Atmospheric nitrogen deposition had a high temporal correlation with N availability in the study area (r = 0.74 to 0.88), except in selected areas wherein riverine nitrogen load may be of equal importance. The increase in N availability caused by atmospheric deposition and riverine input has switched extensive parts of the study area from being N-limited to P-limited.

An updated anthropogenic CO2 inventory in the Atlantic Ocean

[1] This paper presents a comprehensive analysis of the basin-wide inventory of anthropogenic CO2 in the Atlantic Ocean based on high-quality inorganic carbon, alkalinity, chlorofluorocarbon, and nutrient data collected during the World Ocean Circulation Experiment (WOCE) Hydrographic Program, the Joint Global Ocean Flux Study (JGOFS), and the Ocean-Atmosphere Carbon Exchange Study (OACES) surveys of the Atlantic Ocean between 1990 and 1998. Anthropogenic CO2 was separated from the large pool of dissolved inorganic carbon using an extended version of the DC* method originally developed by Gruber et al. [1996]. The extension of the method includes the use of an optimum multiparameter analysis to determine the relative contributions from various source water types to the sample on an isopycnal surface. Total inventories of anthropogenic CO2 in the Atlantic Ocean are highest in the subtropical regions at 20� –40� , whereas anthropogenic CO2 penetrates the deepest in high-latitude regions (>40� N). The deeper penetration at high northern latitudes is largely due to the formation of deep water that feeds the Deep Western Boundary Current, which transports anthropogenic CO2 into the interior. In contrast, waters south of 50� S in the Southern Ocean contain little anthropogenic CO2. Analysis of the data collected during the 1990– 1998 period yielded a total anthropogenic CO2 inventory of 28.4 ± 4.7 Pg C in the North Atlantic (equator-70� N) and of 18.5 ± 3.9 Pg C in the South Atlantic (equator-70� S). These estimated basin-wide inventories of anthropogenic CO2 are in good agreement with previous estimates obtained by Gruber [1998], after accounting for the difference in observational periods. Our calculation of the anthropogenic CO2 inventory in the Atlantic Ocean, in conjunction with the inventories calculated previously for the Indian Ocean [Sabine et al., 1999] and for the Pacific Ocean [Sabine et al., 2002], yields a global anthropogenic CO2 inventory of 112 ± 17 Pg C that has accumulated in the world oceans during the industrial era. This global oceanic uptake accounts for approximately 29% of the total CO2 emissions from the burning of fossil fuels, land-use changes, and cement production during the past 250 years. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1635 Global Change: Oceans (4203); 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4806 Oceanography: Biological and Chemical: Carbon cycling; KEYWORDS: anthropogenic CO2, Atlantic Ocean, air-sea disequilibrium

The recommended dissociation constants for carbonic acid in seawater

A coherent representation of carbonate dissociation constants and measured inorganic carbon species is essential for a wide range of environmentally important issues such as oceanic uptake of anthropogenic CO2 and carbon cycle depictions in ocean circulation models. Previous studies have shown varying degrees of discordance between calculated and measured CO2-system parameters. It is unclear if this is due to errors in thermodynamic models or in measurements. In this work, we address this issue using a large field dataset (15,300 water samples) covering all ocean basins. Our field data, obtained using laboratory-calibrated measurement protocols, are most consistent with calculated parameters using the dissociation constants of Mehrbach et al. [1973] as refit by Dickson and Millero [1987]. Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collected during the global CO2 survey during the 1990s and for characterization of the carbonate system in seawater.

The use of buffers to measure the pH of seawater

The pH of seawater can be measured in the field using potentiometric and spectrophotometric methods. The use of pH standards or buffers is an important aspect of the calibration of both methods in a laboratory on a common concentration scale. The buffers can also be used to monitor the performance of pH meter and spectrophotometer during a cruise. A procedure is described for the determination of the pH of seawater, where the proton concentration is expressed as moles kg-H2O−1 using seawater buffers. The buffers are prepared in synthetic seawater in the laboratory by the methods outlined by Bates and coworkers. We have prepared four buffers (Bis, Tris, Morpholine and 2-Aminopyridine) that cover a pH range from 6.8 to 8.8. The emf values of the buffers were measured with a H2, Pt/AgCl, Ag electrode system after their preparation and bottling for use at sea. The measured emf values were found to be in good agreement (±0.05 mV) with the original measurements of Bates and coworkers from 0 to 45°C. The measured pH of these buffers are in good agreement (±0.001 pH units) with the values calculated from the equations of Dickson on the total pH scale based on Bates et al. Studies are underway to access the long term stability of these buffers. We have also used these buffers to calibrate systems used to make potentiometric and spectrophotometric measurements of pH on seawater relative to the H2, Pt/Ag, AgCl electrode from 5 to 45°C.

Increasing anthropogenic nitrogen in the North Pacific Ocean

The recent increase in anthropogenic emissions of reactive nitrogen from northeastern Asia and the subsequent enhanced deposition over the extensive regions of the North Pacific Ocean (NPO) have led to a detectable increase in the nitrate (N) concentration of the upper ocean. The rate of increase of excess N relative to phosphate (P) was found to be highest (∼0.24 micromoles per kilogram per year) in the vicinity of the Asian source continent, with rates decreasing eastward across the NPO, consistent with the magnitude and distribution of atmospheric nitrogen deposition. This anthropogenically driven increase in the N content of the upper NPO may enhance primary production in this N-limited region, potentially leading to a long-term change of the NPO from being N-limited to P-limited. Atmospheric deposition of nitrogen from Asian pollution has increased the nitrate concentration of the upper North Pacific Ocean. Polluting the way to more productivity Most biologically available nitrogen comes from the recycling of organic matter and nitrogen fixation. However, airborne anthropogenic nitrogen—air pollution—can also provide a source of such nitrogen. Kim et al. reconstructed changes in the N content of surface water across the North Pacific Ocean for the past four decades. N concentrations have increased markedly. This trend could enhance microbial growth in the ocean and eventually increase production of the greenhouse gas N2O. Science, this issue p. 1102

Heterotrophic feeding as a newly identified survival strategy of the dinoflagellate Symbiodinium

Survival of free-living and symbiotic dinoflagellates (Symbiodinium spp.) in coral reefs is critical to the maintenance of a healthy coral community. Most coral reefs exist in oligotrophic waters, and their survival strategy in such nutrient-depleted waters remains largely unknown. In this study, we found that two strains of Symbiodinium spp. cultured from the environment and acquired from the tissues of the coral Alveopora japonica had the ability to feed heterotrophically. Symbiodinium spp. fed on heterotrophic bacteria, cyanobacteria (Synechococcus spp.), and small microalgae in both nutrient-replete and nutrient-depleted conditions. Cultured free-living Symbiodinium spp. displayed no autotrophic growth under nitrogen-depleted conditions, but grew when provided with prey. Our results indicate that Symbiodinium spp.’s mixotrophic activity greatly increases their chance of survival and their population growth under nitrogen-depleted conditions, which tend to prevail in coral habitats. In particular, free-living Symbiodinium cells acquired considerable nitrogen from algal prey, comparable to or greater than the direct uptake of ammonium, nitrate, nitrite, or urea. In addition, free-living Symbiodinium spp. can be a sink for planktonic cyanobacteria (Synechococcus spp.) and remove substantial portions of Synechococcus populations from coral reef waters. Our discovery of Symbiodinium’s feeding alters our conventional views of the survival strategies of photosynthetic Symbiodinium and corals.

Consistency and synthesis of Pacific Ocean CO2 survey data

Between 1991 and 1999, carbon measurements were made on twenty-five WOCE/JGOFS/OACES cruises in the Pacific Ocean. Investigators from 15 different laboratories and four countries analyzed at least two of the four measurable ocean carbon parameters (DIC, TAlk, fCO2, and pH) on almost all cruises. The goal of this work is to assess the quality of the Pacific carbon survey data and to make recommendations for generating a unified data set that is consistent between cruises. Several different lines of evidence were used to examine the consistency, including comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements. With the adjustments proposed here, the data can be combined to generate a Pacific Ocean data set, with over 36,000 unique sample locations analyzed for at least two carbon parameters in most cases. The best data coverage was for DIC, which has an estimated overall accuracy of ∼3 μmol kg−1. TAlk, the second most common carbon parameter analyzed, had an estimated overall accuracy of ∼5 μmol kg−1. To obtain additional details on this study, including detailed crossover plots and information on the availability of the compiled, adjusted data set, visit the Global Data Analysis Project web site at: http://cdiac.esd.ornl.gov/oceans/glodap.