Bibliography - Robert M Key

1. Moore, W S., Jorge L Sarmiento, and Robert M Key, May 2008: Submarine groundwater discharge revealed by ²²⁸Ra distribution in the upper Atlantic Ocean. Nature Geoscience, 1, doi:10.1038/ngeo183.
   [ Abstract ]

   Submarine groundwater discharge is defined as any flow of water at continental margins from the seabed to the coastal ocean, regardless of fluid composition or driving force1. The flux of submarine groundwater discharge has been hypothesized to be a pathway for enriching coastal waters in nutrients, carbon and metals. Here, we estimate the submarine groundwater flux from the inventory of ²²⁸Ra in the upper Atlantic Ocean, obtained by interpolating measurements at over 150 stations. Only 46% of the loss in ²²⁸Ra from radioactive decay is replenished by input from dust, rivers and coastal sediments. We infer that the remainder must come from submarine groundwater discharge. Using estimates of ²²⁸Ra concentrations in submarine groundwater discharge, we arrive at a total flux from submarine groundwater discharge of 2–4x10¹³ m³ yr^-1, between 80 and 160% of the amount of freshwater entering the Atlantic Ocean from rivers. Submarine groundwater discharge is not a freshwater flux, but a flux of terrestrial and sea water that has penetrated permeable coastal sediments. Our assessment of the volume of submarine groundwater discharge confirms that this flux represents an important vehicle for the delivery of nutrients, carbon and metal to the ocean.

2. McNeil, B I., N Metzl, Robert M Key, R Matear, and A Corbiere, 2007: An empirical estimate of the Southern Ocean air-sea CO2 flux. Global Biogeochemical Cycles, 21, GB3011, doi:10.1029/2007GB002991.
   [ Abstract ]

   Despite improvements in our understanding of the Southern Ocean air-sea flux of CO₂, discrepancies still exist between a variety of differing ocean/atmosphere methodologies. Here we employ an independent method to estimate the Southern Ocean air-sea flux of CO₂ that exploits all available surface ocean measurements for dissolved inorganic carbon (DIC) and total alkalinity (ALK) beyond 1986. The DIC concentrations were normalized to the year 1995 using coinciding CFC measurements in order to account for the anthropogenic CO₂ signal. We show that independent of season, surface-normalized DIC and ALK can be empirically predicted to within ~8 µmol/kg using standard hydrographic properties. The predictive equations were used in conjunction with World Ocean Atlas (2001) climatologies to give a first estimate of the annual cycle of DIC and ALK in the surface Southern Ocean. These seasonal distributions will be very useful in both validating biogeochemistry in general circulation models and for use in situ biological studies within the Southern Ocean. Using optimal CO₂  dissociation constants, we then estimate an annual cycle of pCO₂ and associated net air-sea CO₂ flux. Including the effects of sea ice, we estimate a Southern Ocean (>50°S) CO₂ sink of 0.4 ± 0.25 Pg C/yr. Our analysis also indicates a substantial CO₂ sink of 1.1 ± 0.6 Pg C/yr within the sub-Antarctic zone (40°S–50°S), associated with strong cooling and high winds. Our results imply the Southern Ocean CO₂ flux south of 50°S to be very similar to those found by Takahashi et al. (2002), but on the higher end of a range of atmospheric/oceanic CO₂ inversion methodologies. This paper estimates for the first time basic seasonal carbon cycle parameters within the circumpolar Southern Ocean, which have up to now been extremely difficult to measure and sparse. The application of such an empirical technique using more widely available hydrographic parameters in the Southern Ocean provides an important independent estimate to not only CO₂ uptake, but also for other future biogeochemical studies. Refining and testing these empirical methods with new carbon measurements will be important to further reduce uncertainties and extend our understanding of Southern Ocean CO₂ dynamics.

3. Sarmiento, Jorge L., J Simeon, Anand Gnanadesikan, N Gruber, Robert M Key, and R Schlitzer, 2007: Deep ocean biogeochemistry of silicic acid and nitrate. Global Biogeochemical Cycles, 21, GB1S90, doi:10.1029/2006GB002720.
   [ Abstract ]

   Observations of silicic acid and nitrate along the lower branch of the global conveyor belt circulation show that silicic acid accumulation by diatom opal dissolution occurs at 6.4 times the rate of nitrate addition by organic matter remineralization. The export of opal and organic matter from the surface ocean occurs at a Si:N mole ratio that is much smaller than this almost everywhere (cf. Sarmiento et al., 2004). The preferential increase of silicic acid over nitrate as the deep circulation progresses from the North Atlantic to the North Pacific is generally interpreted as requiring deep dissolution of opal together with shallow remineralization of organic matter (Broecker, 1991). However, Sarmiento et al. (2004) showed that the primary reason for the low silicic acid concentration of the upper ocean is that the waters feeding the main thermocline from the surface Southern Ocean are depleted in silicic acid relative to nitrate. By implication, the same Southern Ocean processes that deplete the silicic acid in the surface Southern Ocean must also be responsible for the enhanced silicic acid concentration of the deep ocean. We use observations and results from an updated version of the adjoint model of Schlitzer (2000) to confirm that this is indeed the case.

4. Sweeney, C, M Gloor, A R Jacobson, Robert M Key, Galen McKinley, Jorge L Sarmiento, and R Wanninkhof, 2007: Constraining global air-sea gas exchange for CO2 with recent bomb 14C measurements. Global Biogeochemical Cycles, 21, GB2015, doi:10.1029/2006GB002784.
   [ Abstract ]

   The ¹⁴CO₂ released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO₂. Using the most complete database of dissolved inorganic radiocarbon, DI¹⁴C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI¹⁴C in the global ocean and confirm that there is a 25% decrease from previous estimates using older DI¹⁴C data sets. Additionally, we find a 33% lower globally averaged gas transfer velocity for CO₂ compared to previous estimates (Wanninkhof, 1992) using the NCEP/NCAR Reanalysis 1 1954–2000 where the global mean winds are 6.9 m s⁻¹. Unlike some earlier ocean radiocarbon studies, the implied gas transfer velocity finally closes the gap between small-scale deliberate tracer studies and global-scale estimates. Additionally, the total inventory of bomb-produced radiocarbon in the ocean is now in agreement with global budgets based on radiocarbon measurements made in the stratosphere and troposphere. Using the implied relationship between wind speed and gas transfer velocity k _s = 0.27 u ₁₀ ² (Sc/660)^−0.5 and standard partial pressure difference climatology of CO₂ we obtain an net air-sea flux estimate of 1.3 ± 0.5 PgCyr⁻¹ for 1995. After accounting for the carbon transferred from rivers to the deep ocean, our estimate of oceanic uptake (1.8 ± 0.5 PgCyr⁻¹) compares well with estimates based on ocean inventories, ocean transport inversions using ocean concentration data, and model simulations.

5. Orr, James C., V J Fabry, O Aumont, L Bopp, S C Doney, R A Feely, Anand Gnanadesikan, N Gruber, A Ishida, F Joos, Robert M Key, K Lindsay, E Maier-Reimer, R Matear, Patrick Monfray, A Mouchet, R G Najjar, G-K Plattner, K B Rodgers, C L Sabine, Jorge L Sarmiento, R Schlitzer, Richard D Slater, I J Totterdell, M-F Weirig, Y Yamanaka, and A Yool, 2005: Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437(7059), doi:10.1038/nature04095.
   [ Abstract ]

   Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms such as corals and some plankton will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean-carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.

6. Gnanadesikan, Anand, John Dunne, Robert M Key, K Matsumoto, Jorge L Sarmiento, Richard D Slater, and P S Swathi, 2004: Oceanic ventilation and biogeochemical cycling: Understanding the physical mechanisms that produce realistic distributions of tracers and productivity. Global Biogeochemical Cycles, 18(4), GB4010, doi:10.1029/2003GB002097.
   [ Abstract ]

   Differing models of the ocean circulation support different rates of ventilation, which in turn produce different distributions of radiocarbon, oxygen, and export production. We examine these fields within a suite of general circulation models run to examine the sensitivity of the circulation to the parameterization of subgridscale mixing and surface forcing. We find that different models can explain relatively high fractions of the spatial variance in some fields such as radiocarbon, and that newer estimates of the rate of biological cycling are in better agreement with the models than previously published estimates. We consider how different models achieve such agreement and show that they can accomplish this in different ways. For example, models with high vertical diffusion move young surface waters into the Southern Ocean, while models with high winds move more young North Atlantic water into this region. The dependence on parameter values is not simple. Changes in the vertical diffusion coefficient, for example, can produce major changes in advective fluxes. In the coarse-resolution models studied here, lateral diffusion plays a major role in the tracer budget of the deep ocean, a somewhat worrisome fact as it is poorly constrained both observationally and theoretically.

7. Key, Robert M., A Kozyr, C L Sabine, K Lee, R Wanninkhof, J L Bullister, R A Feely, F J Millero, C Mordy, and T-H Peng, 2004: A global ocean carbon climatology: Results from Global Data Analysis Project (GLODAP). Global Biogeochemical Cycles, 18(4), 1-23.
   [ Abstract PDF ]

   During the 1990s, ocean sampling expeditions were carried out as part of the World Ocean Circulation Experiment (WOCE), the Joint Global Ocean Flux Study (JGOFS), and the Ocean Atmosphere Carbon Exchange Study (OACES). Subsequently, a group of U.S. scientists synthesized the data into easily usable and readily available products. This collaboration is known as the Global Ocean Data Analysis Project (GLODAP). Results were merged into a common format data set, segregated by ocean. For comparison purposes, each ocean data set includes a small number of high-quality historical cruises. The data were subjected to rigorous quality control procedures to eliminate systematic data measurement biases. The calibrated 1990s data were used to estimate anthropogenic CO2, potential alkalinity, CFC watermass ages, CFC partial pressure, bomb-produced radiocarbon, and natural radiocarbon. These quantities were merged into the measured data files. The data were used to produce objectively gridded property maps at a 1 resolution on 33 depth surfaces chosen to match existing climatologies for temperature, salinity, oxygen, and nutrients. The mapped fields are interpreted as an annual mean distribution in spite of the inaccuracy in that assumption. Both the calibrated data and the gridded products are available from the Carbon Dioxide Information Analysis Center. Here we describe the important details of the data treatment and the mapping procedure, and present summary quantities and integrals for the various parameters.

8. Matsumoto, K, Jorge L Sarmiento, Robert M Key, O Aumont, J L Bullister, K Caldeira, J-M Campin, S C Doney, H Drange, J-C Dutay, M Follows, Y Gao, Anand Gnanadesikan, N Gruber, A Ishida, F Joos, K Lindsay, E Maier-Reimer, J Marshall, R Matear, Patrick Monfray, A Mouchet, R G Najjar, G-K Plattner, R Schlitzer, Richard D Slater, P S Swathi, I J Totterdell, M-F Weirig, Y Yamanaka, A Yool, and James C Orr, 2004: Evaluation of ocean carbon cycle models with data-based metrics. Geophysical Research Letters, 31, L07303, doi:10.1029/2003GL018970.
   [ Abstract ]

   New radiocarbon and chlorofluorocarbon-11 data from the World Ocean Circulation Experiment are used to assess a suite of 19 ocean carbon cycle models. We use the distributions and inventories of these tracers as quantitative metrics of model skill and find that only about a quarter of the suite is consistent with the new data-based metrics. This should serve as a warning bell to the larger community that not all is well with current generation of ocean carbon cycle models. At the same time, this highlights the danger in simply using the available models to represent the state-of-the-art modeling without considering the credibility of each model.

9. Roussenov, V, R G Williams, M Follows, and Robert M Key, 2004: Role of bottom water transport and diapycnic mixing in determining the radiocarbon distribution in the Pacific. Journal of Geophysical Research, 109(C6), C06015, doi:10.1029/2003JC002188.
   [ Abstract ]

   The mechanisms controlling the distribution of radiocarbon over the deep Pacific are examined using, firstly, a simplified one-and-a-half-layer model and, secondly, an isopycnic circulation model with parameterized radiocarbon sources and sinks. Two mechanisms control the radiocarbon at depth: relatively fast, lateral transport of bottom waters determining the horizontal distribution and a slower balance between advection-diffusion and radio decay in the vertical. In the isopycnic model, there is a strong topographic control of the bottom water spreading, which is more complex than in the idealized model. Sensitivity studies reveal that altering the bottom intensified diapycnic mixing leads to significant changes in the radiocarbon distribution through both the direct diapycnic transfer and, indirectly, by modifying the bottom water transport and northward penetration of young radiocarbon waters.

10. Sabine, C L., R A Feely, N Gruber, Robert M Key, K Lee, J L Bullister, R Wanninkhof, C S Wong, D W R Wallace, B Tilbrook, F J Millero, T-H Peng, A Kozyr, T Ono, and A F Rios, 2004: The oceanic sink for anthropogenic CO2. Science, 305(5682), 367-371.
    [ Abstract PDF ]

    Using inorganic carbon measurements from an international survey effort in the 1990s and a tracer-based separation technique, we estimate a global oceanic anthropogenic carbon dioxide (CO2) sink for the period from 1800 to 1994 of 118 ± 19 petagrams of carbon. The oceanic sink accounts for ~ 48% of the total fossil-fuel and cement-manufacturing emissions, implying that the terrestrial biosphere was a net source of CO2 to the atmosphere of about 39" 28 petagrams of carbon for this period. The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential.

11. Chung, S-N, K Lee, R A Feely, C L Sabine, F J Millero, R Wanninkhof, J L Bullister, Robert M Key, and T-H Peng, 2003: Calcium carbonate budget in the Atlantic Ocean based on water column inorganic carbon chemistry. Global Biogeochemical Cycles, 17(4), 1093, doi:10.1029/2002GB002001.
    [ Abstract ]

    Recent independent lines of evidence suggest that the dissolution of calcium carbonate (CaCO₃) particles is substantial in the upper ocean above the calcite 100% saturation horizon. This shallow-water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic CaCO₃ at shallow water depths. Here we use more than 20,000 sets of carbon measurements in conjunction with CFC and ¹⁴C data from the WOCE/JGOFS/OACES global CO₂ survey to estimate in situ dissolution rates of CaCO₃ in the Atlantic Ocean. A dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface. The in situ CaCO₃ dissolution increases rapidly at the aragonite 100% saturation horizon. Estimated dissolution rates north of 40ºN are generally higher than the rates to the south, which is partly attributable to the production of exported CaCO₃ being higher in the North Atlantic than in the South Atlantic. As more CaCO₃ particles move down the water column, more particles are available for in situ dissolution. The total water column CaCO₃ dissolution rate in the Atlantic Ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5.6 × 10¹² mol C yr^-1 from CaCO₃-rich sediments. The resulting water column dissolution rate of CaCO₃ for the Atlantic Ocean is approximately 11.1 × 10¹² mol C yr^-1. This corresponds to about 31% of a recent estimate (35.8 × 10¹² mol C yr^-1) of net CaCO₃ production by Lee [2001] for the same area. Our calculation using a large amount of high-quality water column alkalinity data provides the first basin-scale estimate of the CaCO₃ budget for the Atlantic Ocean.

12. Lee, K, S-D Choi, G-H Park, R Wanninkhof, T-H Peng, Robert M Key, C L Sabine, R A Feely, J L Bullister, F J Millero, and A Kozyr, 2003: An updated anthropogenic CO₂ inventory in the Atlantic Ocean. Global Biogeochemical Cycles, 17(4), 1116, doi:10.1029/2003GB002067.
    [ Abstract PDF ]

    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 ΔC* 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.

13. Matsumoto, K, Anand Gnanadesikan, N Gruber, Robert M Key, and Jorge L Sarmiento, 2003: Inconsistent model uptake of anthropogenic tracers in the Southern Ocean. Geochimica et Cosmochimica Acta, 67(18), Suppl 1, A278.
    [ PDF ]
14. McNeil, B I., R Matear, Robert M Key, J L Bullister, and Jorge L Sarmiento, 2003: Anthropogenic CO₂ uptake by the ocean based on the Global Chlorofluorocarbon Data Set. Science, 299(5604), 235-239.
    [ Abstract PDF ]

    We estimated the oceanic inventory of anthropogenic carbon dioxide (CO₂) from 1980 to 1999 using a technique based on the global chorofluorocarbon data set. Our analysis suggests that the ocean stored 14.8 petagrams of anthropogenic carbon from mid-1980 to mid-1989 and 17.9 petagrams of carbon from mid-1990 to mid-1999, indicating an oceanwide net uptake of 1.6 and 2.0 ± 0.4 petagrams of carbon per year, respectively. Our results provide an upper limit on the solubility-driven anthropogenic CO₂ flux into the ocean, and they suggest that most ocean general circulation models are overestimating oceanic anthropogenic CO₂ uptake over the past two decades.

15. Toggweiler, J R., and Robert M Key, 2003: Ocean Circulation / Thermohaline Circulation In Encyclopedia of Atmospheric Sciences, Vol. 4, San Diego, CA, Academic Press, 1549-1555.
16. Watson, A J., James C Orr, Anand Gnanadesikan, Robert M Key, Jorge L Sarmiento, and Richard D Slater, 2003: Carbon dioxide fluxes in the global ocean In Ocean Biogeochemistry: A Synthesis of the Joint Global Ocean Flux Study (JGOFS), Berlin, Germany, Springer-Verlag, 123-143.
17. Feely, R A., C L Sabine, K Lee, and Robert M Key, et al., 2002: In situ calcium carbonate dissolution in the Pacific Ocean. Global Biogeochemical Cycles, 16(4), 1144, doi:10.1029/2002GB001866.
    [ Abstract PDF ]

    Over the past several years researchers have been working to synthesize the WOCE/JGOFS global CO2 survey data to better understand carbon cycling processes in the oceans. The Pacific Ocean data set has over 35,000 sample locations with at least two carbon parameters, oxygen, nutrients, CFC tracers, and hydrographic parameters. In this paper we estimate the in situ CaCO3 dissolution rates in the Pacific Ocean water column. Calcium carbonate dissolution rates ranging from 0.01–1.1 µmol kg-1 yr-1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon. In the North Pacific Intermediate Water between 400 and 800 m, CaCO3 dissolution rates are more than 7 times faster than observed in middle and deep water depths (average = 0.051 µmol kg-1 yr-1). The total amount of CaCO3 that is dissolved within the Pacific is determined by integrating excess alkalinity throughout the water column. The total inventory of CaCO3 added by particle dissolution in the Pacific Ocean, north of 40°S, is 157 Pg C. This amounts to an average dissolution rate of approximately 0.31 Pg C yr-1. This estimate is approximately 74% of the export production of CaCO3 estimated for the Pacific Ocean. These estimates should be considered to be upper limits for in situ carbonate dissolution in the Pacific Ocean, since a portion of the alkalinity increase results from inputs from sediments.

18. Keller, K, Richard D Slater, M Bender, and Robert M Key, 2002: Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization. Deep-Sea Research, Part II, 49(1-3), 345-362.
    [ Abstract PDF ]

    We analyze North Pacific GEOSECS (1970s) and WOCE (1990s) observations to examine potential decadal trends of the marine biological carbon pump. Nitrate concentrations ([NO3]) and apparent oxygen utilization (AOU) decreased significantly in intermediate waters (by -0.6 and -2.9 μmol kg-1, respectively, at = 27.4 kg m-3, corresponding to 1050 m). In shallow waters (above roughly 750 m) [NO3] and AOU increased, though the changes were not statistically significant. A sensitivity study with an ocean general circulation model indicates that reasonable perturbations of the biological carbon pump due to changes in export production or remineralization efficiency are insufficient to account for the intermediate water tracer trends. However, changes in water ventilation rates could explain the intermediate water tracer trends and would be consistent with trends of water age derived from radiocarbon. Trends in AOU and [NO3] provide relatively poor constraints on decadal scale trends in the marine biological carbon pump for two reasons. First, most of the expected changes due to decadal scale perturbations of the marine biota occur in shallow waters, where the available data are typically too sparse to account for the strong spatial and temporal variability. Second, alternative explanations for the observed tracer trends (e.g., changes in the water ventilation rates) cannot be firmly rejected. Our data analysis does not disprove the null-hypothesis of an unchanged biological carbon pump in the North Pacific.

19. Key, Robert M., P D Quay, P Schlosser, A P McNichol, K F von Reden, R J Schneider, K L Elder, M Stuiver, and H Göte Ostlund, 2002: WOCE Radiocarbon IV: Pacific Ocean results. Radiocarbon, 44(1), 239-392.
    [ Abstract PDF ]

    The World Ocean Circulation Experiment, carried out between 1990 and 1997, provided the most comprehensive oceanic survey of radiocarbon to date. Approximately 10,000 samples were collected in the Pacific Ocean by U.S. investigators for both conventional large volume ß counting and small volume accelerator mass spectrometry analysis techniques. Results from six cruises are presented. The data quality is as good or better than previous large-scale surveys. The 14C distribution for the entire WOCE Pacific data set is graphically described using mean vertical profiles and sections, and property-property plots.

20. Lamb, M F., C L Sabine, R A Feely, R Wanninkhof, and Robert M Key, et al., 2002: Consistency and synthesis of Pacific Ocean CO2 survey data. Deep-Sea Research, Part II, 49(1-3), 21-58.
    [ Abstract PDF ]

    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 :mol kg-1. TAlk, the second most common carbon parameter analyzed, had an estimated overall accuracy of ~5 :mol 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.

21. Millero, F J., D Pierrot, K Lee, R Wanninkhof, R A Feely, C L Sabine, Robert M Key, and T Takahashi, 2002: Dissociation constants for carbonic acid determined from field measurements. Deep-Sea Research, Part I, 49(10), 1705-1723.
    [ Abstract PDF ]

    A number of workers have recently shown that the thermodynamic constants for the dissociation of carbonic acid in seawater of Mehrbach et al. are more reliable than measurements made on artificial seawater. These studies have largely been confined to looking at the internal consistency of measurements of total alkalinity (TA), total inorganic carbon dioxide (TCO2) and the fugacity of carbon dioxide (fCO2). In this paper, we have examined the field measurements of pH, fCO2, TCO2 and TA on surface and deep waters from the Atlantic, Indian, Southern and Pacific oceans to determine the pK1, pK2 and pK2-pK1. These calculations are possible due to the high precision and accuracy of the field measurements. The values of pK2 and pK2-pK1 over a wide range of temperatures (-1.6–38°C) are in good agreement (within ±0.005) with the results of Mehrbach et al. The measured values of pK1 at 4°C and 20°C are in reasonable agreement (within ±0.01) with all the constants determined in laboratory studies. These results indicate, as suggested by internal consistency tests, that the directly measured values of pK1+pK2 of Mehrbach et al. on real seawater are more reliable than the values determined for artificial seawater. It also indicates that the large differences of pK2-pK1 (0.05 at 20°C) in real and artificial seawater determined by different investigators are mainly due to differences in pK2. These differences may be related to the interactions of boric acid with the carbonate ion. The values of pK2-pK1 determined from the laboratory measurements of Lee et al. and Lueker et al. at low fCO2 agree with the field-derived data to ±0.016 from 5°C to 25°C. The values of pK2-pK1 decrease as the fCO2 or TCO2 increases. This effect is largely related to changes in the pK2 as a function of fCO2 or TCO2. The values of fCO2 calculated from an input of TA and TCO 2, which require reliable values of pK2-pK1, also vary with fCO2. The field data at 20°C has been used to determine the effect of changes of TCO2 on pK2 giving an empirical relationship: pK2TCO2=pK2-1.6×10-4(TCO2-2050) which is valid at TCO2>2050 :mol kg-1. This assumes that the other dissociation constants such as KB for boric acid are not affected by changes in TCO2. The slope is in reasonable agreement with the laboratory studies of Lee et al. and Lueker et al. (–1.2x10-4 to –1.9x10-4). This equation eliminates the dependence of the calculated ƒCO2 on the level of ƒCO2 or TCO2 in ocean waters (` =29.7 :atm in ƒCO2). An input of pH and TCO2 yields values of ƒCO2 and TA that are in good agreement with the measured values ("22.3 F atm in ƒCO2 and "4.3 :mol kg-1 in TA). The cause of the decrease in pK2 at high ƒCO2 is presently unknown. The observed inconsistencies between the measured and computed ƒCO2 values may be accounted for by adding the effect of organic acid (~8 :mol kg-1) to the interpretation of the TA. Further studies are needed to elucidate the chemical reactions responsible for this effect.

22. Rubin, S I., and Robert M Key, 2002: Separating natural and bomb-produced radiocarbon in the ocean: the potential alkalinity method. Global Biogeochemical Cycles, 16(4), doi:10.1029/2001/GB001432.
    [ Abstract PDF ]

    the use of radiocarbon as a tracer for oceanic processes generally requires differentiation of naturally occurring radiocarbon from the bomb component produced by atmospheric nuclear weapons testing. We present a new separation method based on the strong linear correlation between radiocarbon and potential alkalinity. Unlike previous techniques the new algorithm is applicable at all latitudes. Additionally, the potential alkalinity method provides an estimate of surface ocean prebomb radiocarbon concentrations. Predictions with the technique appear to be unbiased and have uncertainties which are less than previous techniques.

23. Sabine, C L., R A Feely, Robert M Key, J L Bullister, F J Millero, K Lee, T-H Peng, B Tilbrook, T Ono, and C S Wong, 2002: Distribution of anthropogenic CO2 in the Pacific Ocean. Global Biogeochemical Cycles, 16(4), 1083, doi:10.1029/2001GB001639.
    [ Abstract ]

    This work presents an estimate of anthropogenic CO2 in the Pacific Ocean based on measurements from the WOCE/JGOFS/OACES global CO2 survey. These estimates used a modified version of the C* technique. Modifications include a revised preformed alkalinity term, a correction for denitrification, and an evaluation of the disequilibrium terms using an optimum multiparameter analysis. The total anthropogenic CO2 inventory over an area from 120°E to 70°W and 70°S to 65°N (excluding the South China Sea, the Yellow Sea, the Japan/East Sea, and the Sea of Okhotsk) was 44.5 ± 5 Pg C in 1994. Approximately 28 Pg C was located in the Southern Hemisphere and 16.5 Pg C was located north of the equator. The deepest penetration of anthropogenic CO2 is found at about 50°S. The shallowest penetration is found just north of the equator. Very shallow anthropogenic CO2 penetration is also generally observed in the high-latitude Southern Ocean. One exception to this is found in the far southwestern Pacific where there is evidence of anthropogenic CO2 in the northward moving bottom waters. In the North Pacific a strong zonal gradient is observed in the anthropogenic CO2 penetration depth with the deepest penetration in the western Pacific. The Pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area. The lack of deep and bottom water formation in the North Pacific means that the North Pacific inventories are smaller than the North Atlantic.

24. Sabine, C L., Robert M Key, R A Feely, and D Greeley, 2002: Inorganic carbon in the Indian Ocean: distribution and dissolution processes. Global Biogeochemical Cycles, 16(4), 1067, doi:10.1029/2002GB001869.
    [ Abstract ]

    This study uses nearly 25,000 carbon measurements from the WOCE/JGOFS global CO2 survey to examine the distribution of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the Indian Ocean. Shallow and intermediate distributions of inorganic carbon do not strictly follow temperature and salinity because of differing surface gradients and vertical biological processes that work to modify the circulation derived features. Anthropogenic CO2 has increased the shallow DIC by as much as 3%, decreasing the vertical DIC gradient. Deep ocean DIC and TA increase toward the north because of the decomposition and dissolution of organic and inorganic particles. Calcite saturation depths range from 2900–3900 m with the deepest saturation depth in the central Indian Ocean. Variations of aragonite saturation depth (200–1400 m) are similar to calcite, but the deepest saturations are in the southwestern Indian Ocean. The shallowest aragonite saturation depths are found in the Bay of Bengal. In the northern Arabian Sea and Bay of Bengal, the current aragonite saturations are 100 and 200 m shallower, respectively, than in preindustrial times. Estimates of carbonate dissolution rates on isopycnal surfaces range from 0.017 to 0.083 µmol kg-1 yr-1 in deep waters. Upper water column dissolution rates range from 0 to 0.73 µmol kg-1 yr-1, with a local maximum occurring in intermediate waters just below the aragonite saturation horizon. Dissolution is also generally higher north of the Chemical Front at 10–20°S. There is some evidence for significant sedimentary sources in the northern Indian Ocean.

25. Sarmiento, Jorge L., John Dunne, Anand Gnanadesikan, Robert M Key, K Matsumoto, and Richard D Slater, 2002: A new estimate of the CaCO3 to organic carbon export ratio. Global Biogeochemical Cycles, 16(4), doi:10.1029/2002/GB001919.
    [ Abstract ]

    We use an ocean biogeochemical-transport box model of the top 100 m of the water column to estimate the CaCO3 to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate. We find a global average molar export ratio of 0.06 ± 0.03. This is substantially smaller than earlier estimates of 0.25 on which a majority of ocean biogeochemical models had based their parameterization of CaCO3 production. Contrary to the pattern of coccolithophore blooms determined from satellite observations, which show high latitude predominance, we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres. Our results suggest a dominant contribution to global calcification by low-latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods.

26. Deutsch, Curtis A., N Gruber, Robert M Key, Jorge L Sarmiento, and A Ganachaud, 2001: Denitrification and N₂ fixation in the Pacific Ocean. Global Biogeochemical Cycles, 15(2), 483-506.
    [ Abstract PDF ]

    We establish the fixed nitrogen budget of the Pacific Ocean based on nutrient fields from the recently completed World Ocean Circulation Experiment (WOCE). The budget includes denitrification in the water column and sediments, nitrogen fixation, atmospheric and riverine inputs, and nitrogen divergence due to the large-scale circulation. A water column denitrification rate of 48 ± 5 Tg N yr^-1 is calculated for the Eastern Tropical Pacific using N* [Gruber and Sarmiento, 1997] and water mass age tracers. On the basis of rates in the literature, we estimate sedimentary denitrification to remove an additional 15 ± 3 Tg N yr^-1 . We then calculate the total nitrogen divergence due to the large scale circulation through the basin, composed of flows through a zonal transect at 32°S, and through the Indonesian and Bering straits. Adding atmospheric deposition and riverine fluxes results in a net divergence of nitrogen from the basin of -4 ± 12 Tg N yr^-1 . Pacific nitrogen fixation can be extracted as a residual component of the total budget, assuming steady state. We find that nitrogen fixation would have to contribute 59 ± 14 Tg N yr^-1 in order to balance the Pacific nitrogen budget. This result is consistent with the tentative global extrapolations of Gruber and Sarmiento [1997], based on nitrogen fixation rates estimated for the North Atlantic. Our estimated mean areal fixation rate is within the range of direct and geochemical rate estimates from a single location near Hawaii [Karl et al., 1997]. Pacific nitrogen fixation occurs primarily in the western part of the subtropical gyres where elevated N* signals are found. These regions are also supplied with significant amounts of iron via atmospheric dust deposition, lending qualitative support to the hypothesis that nitrogen fixation is regulated in part by iron supply.

27. Key, Robert M., 2001: Radiocarbon In Encyclopedia of Ocean Sciences, Academic Press, 2338-2353.
    [ PDF ]
28. Orr, James C., E Maier-Reimer, U Mikolajewicz, Patrick Monfray, Jorge L Sarmiento, J Robert Toggweiler, N K Taylor, J Palmer, N Gruber, C L Sabine, C Le Quéré, Robert M Key, and J Boutin, 2001: Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models. Global Biogeochemical Cycles, 15(1), 43-60.
    [ Abstract PDF ]

    We have compared simulations of anthropogenic CO₂ in the four three-dimensional ocean models that participated in the first phase of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), as a means to identify their major differences. Simulated global uptake agrees to within ± 19%, giving a range of 1.85±0.35 Pg C yr ^-1 for the 1980-1989 average. Regionally, the Southern Ocean dominates the present-day air-sea flux of anthropogenic CO₂ in all models, with one third to one half of the global uptake occurring south of 30°S. The highest simulated total uptake in the Southern Ocean was 70% larger than the lowest. Comparison with recent data-based estimates of anthropogenic CO₂ suggest that most of the models substantially overestimate storage in the Southern Ocean; elsewhere they generally underestimate storage by less than 20%. Globally, the OCMIP models appear to bracket the real ocean's present uptake, based on comparison of regional data-based estimates of anthropogenic CO₂ and bomb ¹⁴C. Column inventories of bomb ¹⁴C have become more similar to those for anthropogenic CO₂ with the time that has elapsed between the Geochemical Ocean Sections Study (1970s) and World Ocean Circulation Experiment (1990s) global sampling campaigns. Our ability to evaluate simulated anthropogenic CO₂ would improve if systematic errors associated with the date-based estimates could be provided regionally.

29. Toggweiler, J R., and Robert M Key, 2001: Thermohaline Circulation In Enclyclopedia of Ocean Sciences, 2941-2947.
    [ PDF ]
30. Gruber, N, K Keller, and Robert M Key, 2000: What story is told by oceanic tracer concentrations? Science, 290(5491), 455-456.
31. Ortiz, J D., A C Mix, P A Wheeler, and Robert M Key, 2000: Anthropogenic CO2 invasion into the northeast Pacific based on concurrent 13CDIC and nutrient profiles from the California Current. Global Biogeochemical Cycles, 14(3), 917-929.
    [ Abstract PDF ]

    The stable isotopic signature of dissolved inorganic carbon ( 13CDIC ) in the northeast Pacific Ocean is lower in near-surface waters by 1.1‰ relative to values predicted from global oceanic trends of 13CDIC versus nutrients. A combination of anthropogenic carbon uptake from the atmosphere and thermodynamic, air-sea gas exchange processes in different water mass source areas account for the isotopic depletion. Here we evaluate the efficacy of using a concurrent nutrient- 13C strategy to separate these two effects, with the goal of improving estimates of anthropogenic carbon uptake over the course of the Industrial Revolution. In depth profiles from the sea surface to 2500 m at four stations across the California Current (42°N), nitrate, rather than phosphate, is best correlated to 13CDIC providing the best choice for this experiment. On the basis of an assumption of no anthropogenic carbon in North Pacific Deep Waters between 1000-2500m depth (potential densities, ~ 27.3-27.7), the "anthropogenic - preanthropogenic" carbon isotope shift 13Ca-p ) in near-surface waters of the northeast Pacific is inferred to be -0.62 ± 0.17‰, while the thermodynamic air-sea gas exchange signature is estimated at -0.48 ± 0.17‰. Values of 13 Ca-p (similar to the regional patterns of 14C and Tritium penetration) approach zero for >26.8, indicating little penetration of anthropogenic carbon into the North Pacific Intermediate Water or the upper North Pacific Deep Water. Our results suggest an upper North Pacific sink of anthropogenic carbon over the past ~200 years that is ~40% greater than that estimated for the interval between ~1970 and ~1990 by Quay et al., [1992]. Our estimate of the North Pacific inventory of anthropogenic carbon, added to published estimates from the North Atlantic and Indian Ocean, is smaller than model predictions of the total carbon sink, suggesting that a significant portion of anthropogenic carbon enters the deep sea via the Southern Ocean.

32. Sabine, C L., Robert M Key, K M Johnson, F J Millero, A Poisson, Jorge L Sarmiento, D W R Wallace, and C D Winn, 1999: Anthropogenic CO₂ inventory of the Indian Ocean. Global Biogeochemical Cycles, 13(1), 179-198.
    [ Abstract PDF ]

    This study presents basin-wide anthropogenic CO₂ inventory estimates for the Indian Ocean based on measurements from the World Ocean Circulation Experiment/Joint Global Ocean Flux Study global survey. These estimates employed slightly modified d C* and time series techniques originally proposed by Gruber et al. [1996] and Wallace [1995], respectively. Together, the two methods yield the total oceanic anthropogenic CO₂ and the carbon increase over the past 2 decades. The highest concentrations and the deepest penetrations of anthropogenic carbon are associated with the Subtropical Convergence at around 30° to 40°S. With both techniques, the lowest anthropogenic CO₂ column inventories are observed south of 50°S. The total anthropogenic CO₂ inventory north of 35°S was 13.6 ± 2 Pg C in 1995. The inventory increase since GEOSECS (Geochemical Ocean Sections Program) was 4.1 ± 1 Pg C for the same area. Approximately 6.7 ± 1 Pg C are stored in the Indian sector of the Southern Ocean, giving a total Indian Ocean inventory of 20.3 ± 3 Pg C for 1995. These estimates are compared to anthropogenic CO₂ inventories estimated by the Princeton ocean biogeochemistry model. The model predicts an Indian Ocean sink north of 35°S that is only 0.61-0.68 times the results presented here; while the Southern Ocean sink is nearly 2.6 times higher than the measurement-based estimate. These results clearly identify areas in the models that need further examination and provide a good baseline for future studies of the anthropogenic inventory.

33. Broecker, W, S L Peacock, S Walker, R Weiss, M Schroeder, U Mikolajewicz, C Heinze, Robert M Key, T-H Peng, S I Rubin, and E Fahrbach, 1998: How much deep water is formed in the Southern Ocean? Journal of Geophysical Research, 103(C8), 15,833-15,843.
    [ Abstract PDF ]

    Three tracers are used to place constraints on the production rate of ventilated deep water in the Southern Ocean. The distribution of the water mass tracer PO4* ("phosphate star") in the deep sea suggests that the amount of ventilated deep water produced in the Southern Ocean is equal to or greater than the outflow of North Atlantic Deep Water from the Atlantic. Radiocarbon distributions yield an export flux of water from the North Atlantic which has averaged about 15 Sv over the last several hundred years. CFC inventories are used as a direct indicator of the current production rate of ventilated deep water in the Southern Ocean. Although coverage is as yet sparse, it appears that the CFC inventory is not inconsistent with the deep water production rate required by the distributions of PO4* and radiocarbon. It has been widely accepted that the major part of the deep water production in the Southern Ocean takes place in the Weddell Sea. However, our estimate of the Southern Ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the Weddell Sea, which lie in the range 1-5 Sv. Possible reasons for this difference are discussed.

34. Cochran, J K., and Robert M Key, et al., 1995: Natural and anthropogenic radionuclide distributions in the Nansen Basin, Arctic Ocean: Scavenging rates and circulation timescales. Deep-Sea Research, Part II, 42(6), 1495-1517.
    [ Abstract PDF ]

    Determination of the naturally occurring radionuclides ²³²Th, ²³⁰Th, ²²⁸Th and 210Pb, and the anthropogenic radionuclides ²⁴¹Am, ^239,240Pu, ¹³⁴Cs and ¹³⁷Cs in water samples collected across the Nansen Basin from the Barents Sea slope to the Gakkel Ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the Arctic Ocean. Large volume water samples ( ~ 1500 l) were filtered in situ to separate particulate (> 0.5 µm) and dissolved Th isotopes and ²⁴¹Am. Thorium-230 displays increases in both particulate and dissolved activities with depth, with dissolved ²³⁰Th greater and particulate ²³⁰Th lower in the deep central Nansen Basin than at the Barents Sea slope. Dissolved ²²⁸Th activities also are greater relative to ²²⁸Ra, in the central basin. Residence times for Th relative to removal from solution onto particles are ~ 1 year in surface water, ~ 10 years in deep water adjacent to the Barents Sea slope, and ~ 20 years in the Eurasian Basin Deep Water. Lead-210 in the central basin deep water also has a residence time of ~ 20 years with respect to its removal from the water column. This texture of scavenging is reflected in distributions of the particle-reactive anthropogenic radionuclide ²⁴¹Am, which shows higher activities relative to Pu in the central Nansen Basin than at the Barents Sea slope. Distributions of ¹³⁷Cs show more rapid mixing at the basin margins (Barents Sea slope in the south, Gakkel Ridge in the north) than in the basin interior. Cesium-137 is mixed throughout the water column adjacent to the Barents Sea slope and is present in low but detectable activities in the Eurasian Basin Deep Water in the central basin. At the time of sampling (1987) the surface water at all stations had been labeled with ¹³⁴Cs released in the 1986 accident at the Chernobyl nuclear power station. In the ~ 1 year since the introduction of Chernobyl ¹³⁴Cs to the Nansen Basin, it had been mixed to depths of ~ 800 m at the Barents Sea Slope and to ~ 300 m in the central basin. "Pre-Chernobyl" inventories of ¹³⁷Cs (as well as ^{239, 240}Pu) are 10 times those expected from global atmospheric fallout from nuclear weapons testing and are derived principally from releases from the Sellafield, U.K., nuclear fuel reprocessing facility on the Irish Sea. Based on the sources of ¹³⁷Cs to the Nansen Basin, mixing time scales are 9 - 18 years for the upper water column (to 1500 m) and ~ 40 years for the deep water. These mixing time scales, combined with more rapid scavenging at the basin margin relative to the central basin, produce residence times of particle-reactive radionuclides in the Nansen Basin comparable to other open ocean areas (e.g., north-west Atlantic) despite the presence of permanent ice cover and long periods of low-light levels that limit productivity in the Arctic.

35. Key, Robert M., and J Robert Toggweiler, 1993: First results in from Pacific 14C Program. WOCE Notes, 5(3), 1-8.
36. Sarmiento, Jorge L., G Thiele, Robert M Key, and W S Moore, 1990: Oxygen and nitrate new production and remineralizaion in the North Atlantic subtropical gyre. Journal of Geophysical Research, 95(C10), 18,303-18,315.
    [ Abstract PDF ]

    New estimates are obtained of oxygen utilization rates on isopycnal surfaces in the North Atlantic subtropical gyre thermocline based on tritium inventories (2.4-3.5 mol m^-2yr^-1) and ²²⁸Ra measurements (8.5 ± 0.8 mol m^-2yr^-1). Arguments are given for why the tritium inventory oxygen utilization rate estimate may be too low. The ²²⁸Ra results are combined with recent estimates of oxygen utlization within the thermocline (Jenkins, 1987) as well as estimates of oxygen production in the mixed layer (Spitzer and Jenkins, 1989; Musgrave et al., 1988), to suggest a tentative overall oxygen balance for the whole water column. The new production of oxygen in the surface ocean (~4.6 ± 1.6 mol m^-2yr^-1) appears to be lower than the estimated utilization within the thermocline (~8.5 ± 0.8 mol m^-2yr^-1), suggesting that there may be a net lateral import of organic matter into the thermocline equivalent to a new production of ~3.9 ± 1.8 mol m^-2yr^-1. The nitrogen balance is consistent with these results. An estimate for the total nitrogen remineralization rate in the thermocline is obtained from the oxygen utilization rate by using an -O₂:N Redfield ratio of 9.1 ± 0.4 for remineralization (Minster and Boulahdid, 1987), giving a nitrogen remineralization rate of ~0.93 ± 0.10 mol m^-2yr^-1. Subtracting off the estimated lateral export of nitrate of ~0.51 ± 0.21 mol m^-2yr^-1, which is presumed to be balanced by a lateral import of dissolved organic nitrogen (Rintoul and Wunsch, 1990), gives a nitrate flux into the surface of ~0.42 ± 0.23 mol m^-2yr^-1, which is comparable to the estimate of 0.6 ± 0.2 mol m^-2yr^-1 obtained by Jenkins (1988) near Bermuda as well as the 100-m particulate nitrogen flux of 0.33 mol m^-2yr^-1 obtained Altabet (1989) near Bermuda.

37. Moore, W S., Jorge L Sarmiento, and Robert M Key, 1986: Tracing the Amazon component of surface Atlantic water using ²²⁸Ra, salinity and silica. Journal of Geophysical Research, 91(C2), 2574-2580.
    [ Abstract PDF ]

    High ²²⁸Ra/²²⁶Ra activity ratios characteristic of waters in the Amazon estuary provide a sensitive indicator of the presence of these waters in the Atlantic Ocean. A conservative mixing model utilizing the ²²⁸Ra/²²⁶activity ratio (AR) tied to absolute measurements in the estuary allows us to estimate that 20-34% of the surface water east of the Antilles during June, 5-9% from the same area during December, and 15-20% of the eastern Caribbean surface water during December are derived from the Amazon estuary. Differences in ²²⁸Ra input occur in response to variable stratification of water near the river mouth. During high discharge, intense vertical mixing enriches the water in the estuary in ²²⁸Ra. A large fraction of this water moves to the north and east of Antilles, where its relatively high ²²⁸Ra/²²⁶ AR distinguishes it over 1500 km from its source. During low discharge (northern hemisphere fall) a significant fraction of river water passes northwest of the zone of intense mixing into a vertically stratified region where ²²⁸Ra gain is lower. This water is transported by the Guiana Current along the coast of South America and into the Caribbean.

38. Key, Robert M., R F Stallard, W S Moore, and Jorge L Sarmiento, 1985: Distribution and flux of ²²⁶Ra and ²²⁸Ra in the Amazon River estuary. Journal of Geophysical Research, 90(C4), 6995-7004.
    [ Abstract PDF ]

    Measurements of ²²⁶Ra and ²²⁸Ra in the Amazon River estuary show that desorption from river-borne suspended particulate matter in the estuary increases the riverine flux of both isotopes to the ocean by a factor of approximately 5 over the flux attributable to radium dissolved in the river water alone. The total Amazon flux supplies approximately 0.20% of the ²²⁶Ra and approximately 2.6% of the ²²⁸Ra standing crops in the near-surface Atlantic (0-200 m). Diffusive flux from estuarine and shelf sediments and desorption from resuspended sediments in the region of the estuary approximately double the estuarine ²²⁶Ra concentration and quadruple the estuarine ²²⁸Ra concentration above that caused by the dissolved and desorbed river components alone.

39. Moore, W S., Robert M Key, and Jorge L Sarmiento, 1985: Techniques for precise mapping of ²²⁶Ra and ²²⁸Ra in the Ocean. Journal of Geophysical Research, 90(C4), 6983-6994.
    [ Abstract ]

    Improvements in the analyses of ²²⁶Ra and ²²⁸Ra in seawater made possible by better extraction and processing techniques reduce significantly the errors associated with these measurements. These improvements and the extensive sampling for Ra isotopes conducted on the TTO North Atlantic Study should enable us to use the distribution of ²²⁸Ra to study mixing processes on a 3-15 year time scale in both the upper and deep North Atlantic. The ²²⁸Ra profiles already analyzed show a closer resemblance to GEOSECS tritium data than to TTO tritium data in the upper ocean. This is because the transient tracer tritium was responding on a 10-year time scale during GEOSECS and a 20-year time scale during TTO. The steady state tracer ²²⁸Ra should always respond on a time scale of 8 years. Thus the ²²⁸Ra data obtained on TTO should provide a means to extend the features of the GEOSECS tritium field to the regions of the TTO study. The ²²⁶Ra data are of high enough quality to identify features associated with different water masses. Changes in the positions of the deep-water masses since the GEOSECS cruise are revealed by the ²²⁶Ra data

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