T.-H. Peng

A global ocean carbon climatology: Results from Global Data Analysis Project (GLODAP)

[1]xa0During 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.

One-dimensional ecosystem model of the equatorial Pacific upwelling system. Part I: model development and silicon and nitrogen cycle

Abstract A one-dimensional ecosystem model was developed for the equatorial Pacific upwelling system, and the model was used to study nitrogen and silicon cycle in the equatorial Pacific. The ecosystem model consisted of 10 components (nitrate, silicate, ammonium, small phytoplankton, diatom, micro- and meso-zooplankton, detrital nitrogen and silicon, and total CO 2 ). The ecosystem model was forced by the area-averaged (5°S–5°N, 90°W–180°, the Wyrtki Box) annual mean upwelling velocity and vertical diffusivity obtained from a three-dimensional circulation model. The model was capable of reproducing the low-silicate, high-nitrate, and low-chlorophyll (LSHNLC) conditions in the equatorial Pacific. The linkage to carbon cycle was through the consumption of assimilated nitrate and silicate (i.e. new productions). Model simulations demonstrated that low-silicate concentration in the equatorial Pacific limits production of diatoms, and it resulted in low percentage of diatoms, 16%, in the total phytoplankton biomass. In the area of 5°S–5°N and 90°W–180°, the model produced an estimated sea-to-air CO 2 flux of 4.3xa0molxa0m −2 xa0yr −1 , which is consistent with the observed results ranging of 1.0–4.5xa0molxa0m −2 xa0yr −1 . The ammonium inhibition played an important role in determining the nitrogen cycle in the model. The modeled surface nitrate concentration could increase by a factor of 10 (from 0.8 to 8.0xa0mmolxa0m −3 ) when the strength of the ammonium inhibition increased from ψ =1.0 to 10.0xa0(mmolxa0m −3 ) –1 . The effects of both micro- and meso-zooplankton grazing were tested by varying the micro- and meso-zooplankton maximum grazing rates, G1 max and G2 max . The modeled results were quite sensitive to the zooplankton grazing parameters. The current model considered the role of iron implicitly through the parameters that determine the growth rate of diatoms. Several iron-enrichment experiments were conducted by changing the parameter α (the initial slope of the photosynthetic rate over irradiance at low irradiance), K Si(OH) 4 (half-saturation concentration of silicate uptake by diatom), and μ 2 max (the potential maximum specific diatom growth rate) in the regulation terms of silicate uptake by diatom. Within the first 5 days in the modeled iron-enrichment experiment, the diatom biomass increased from 0.08 to 2.5xa0mmolxa0m −3 , more than a factor of 30 increase. But the diatom populations crashed 2 weeks after the experiment started, due to exhaustion of available silicate and increased mesozooplankton population. The modeled iron-enrichment experiments produced several ecological behaviors similar to these observed during the IronEx-2.

In situ calcium carbonate dissolution in the Pacific Ocean

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 mmol kg1 yr1 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 mmol kg1 yr1). 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 40S, is 157 Pg C. This amounts to an average dissolution rate of approximately 0.31 Pg C yr1. This estimate is approximately 74% of the export production of CaCO3 estimated for the Pacific Ocean. These estimates should be considered tomorexa0» be upper limits for in situ carbonate dissolution in the Pacific Ocean, since a portion of the alkalinity increase results from inputs from sediments.«xa0less

Distribution of anthropogenic CO2 in the Pacific Ocean

[1]xa0This 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 ΔC* 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.

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

Calcium carbonate budget in the Atlantic Ocean based on water column inorganic carbon chemistry

[1]xa0Recent 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.

One-dimensional ecosystem model of the equatorial Pacific upwelling system. Part II: sensitivity analysis and comparison with JGOFS EqPac data

Abstract A one-dimensional model of the equatorial Pacific upwelling ecosystem that incorporates two phytoplankton components, two grazers, and three nutrients, Si(OH)4, NO3, and NH4 (Chai et al., Deep-Sea Research II (2002) 2713–2745), was designed to consider the effects of Si(OH)4 limitation on the diatom growth and ecosystem functioning. Model output was obtained for a range of source concentrations of Si(OH)4, 3–15xa0mmolxa0m−3, coinciding with the range measured at 120xa0m depth during JGOFS EqPac. NO3 was held at 12xa0mmolxa0m−3, reflecting the relatively greater concentrations of NO3 compared to Si(OH)4 in the JGOFS data. The model was shown to function as a chemostat-like system with the loss rates, provided largely from zooplankton grazing, controlling growth rates of the phytoplankton. When different source concentrations of Si(OH)4 were applied, surface concentrations of Si(OH)4 varied within a narrow range compared to NO3 as would occur in a chemostat with limiting Si(OH)4 and non-limiting NO3 in the feed water. Vertical profiles of nutrients compared well with field data. Model results are compared with field data for new and total nitrogen production and export of N, Si, and C, and with other models, although none consider Si(OH)4 specifically. The model suggests that the stability of the equatorial system with its narrow range of biological and chemical variables is conferred by the action of diatoms providing food for mesozooplankton whose grazing also depletes the picoplankton. Diatoms increase with source Si(OH)4 concentrations, and picoplankton population and NO3 consumption decrease, resulting in a maximum surface TCO2 and increased CO2 flux to the atmosphere at intermediate source Si(OH)4 concentrations. Diatoms function in the equatorial system as a silica pump to export silica. This means that sedimented biogenic silica under the equatorial upwelling area should be viewed as an amplifier of changes in surface properties, with important consequences to paleoequatorial productivity.

Meridional asymmetry of source nutrients to the equatorial Pacific upwelling ecosystem and its potential impact on ocean–atmosphere CO2 flux; a data and modeling approach

Si(OH)4, NO3, and TCO2 are shown to be distributed asymmetrically in a north/south direction about the equatorial Pacific using data from WEPOCS III and JGOFS EqPac cruises. Equatorial SiOH4 concentrations are shown to be the product of both geochemical and physical interactions with chemical processes, occurring in at least three regions remote from the equatorial Pacific, and physical delivery processes from the equatorial undercurrent (EUC) to the surface layer varying over a range of time scales. The EUC was partitioned into upper and lower portions, the upper providing source water to the central upwelling area and the lower crossing the Pacific without upwelling and thought to reenter the surface along the coast of Peru and to the eastern equatorial upwelling area. The source waters from the North Pacific, the north equatorial countercurrent (NECC) and from the South Pacific, the New Guinea coastal undercurrent (NGCUC) also were partitioned according to source for the upper and lower EUC. Mean concentrations and ranges of nutrients for each source partition were obtained from field data. Current flow and advective data output from a 3-D physical model were used with the field nutrient data to calculate nutrient fluxes into the EUC. Although the inflow of water from the north and south were approximately equal, the stronger asymmetric distribution of Si(OH)4 compared to NO3 resulted in identifying the South Pacific source as only 30% of the total supply of Si(OH)4 to the EUC and the cause of a low Si(OH)4:NO3 condition. These results suggest a coupling between Southern Ocean productivity, equatorial productivity, and the efflux of CO2 to the atmosphere from the equatorial upwelling system.

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.

Temporal variations of bomb radiocarbon inventory in the Pacific Ocean

The natural and anthropogenic components of the radiocarbon measurements from seawater samples can be successfully separated by an improved method, which is based on a very well-defined relationship between natural radiocarbon and dissolved silica observed mainly during the GEOSECS survey for waters beneath 1000 m depth. This relationship is further reconfirmed by the l4 C measurements from large volume samples taken in the deep waters in the Pacific Ocean during the recent WOCE survey program. Analysis of upper ocean 14 C measurements made along 152°W, and north of 20°N, in the northeastern Pacific Ocean during the NOAAs CGC91 cruises which is a part of the WOCE survey program, indicates that the bomb l4 C inventory in this part of the ocean has increased by 22% since the GEOSECS measurements made in 1974. This increase is consistent with the model prediction of 25% for the northern hemisphere ocean. Change of the surface water bomb Δ 14 C values during this period is insignificant. This feature is also consistent with the model simulation. Results of this new analysis will provide useful information of the temporal variations of bomb l4 C inventory in the ocean, in addition to the spatial distribution, which can be used as powerful constraints in calibrating the global ocean carbon cycle models, especially those based on three-dimensional ocean general circulation models, for estimating the uptake of CO 2 by the ocean.