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International audience; Nutrient trapping is a chronic problem found in global carbon cycle models with particle-only remineralization schemes. It is defined as the excess of subsurface nutrient concentrations relative to observations and occurs principally in the eastern equatorial Pacific. Previous studies reduced excess simulated nutrients by increasing the complexity of modeled biogeochemistry, i.e., by adding pools for nutrients (and carbon) either in dissolved organic form or as plankton. Conversely, our study suggests that deficiencies in modeled circulation fields from global coarse-resolution ocean models are mostly responsible. This new interpretation stems from our use of an ocean general circulation model with higher resolution, which offers a more realistic equatorial circulation. We used the same biogeochemical model Hamburg ocean carbon cycle model, version 3, as in some of the previous studies. Our model-predicted distribution of PO43- in the equatorial Pacific agrees reasonably well with the observations both at the surface and in the subsurface. Subsurface PO43- concentrations in our model's eastern equatorial Pacific exceed observations by, at most, 15%, unlike coarser-resolution models. Improvement is due to enhanced meridional resolution (0.5°) near the equator, which allows the model to simulate a vigorous equatorial undercurrent that brings in low-nutrient water from the western basin. Furthermore, the model upwells no nutrient-rich abyssal water into the surface equatorial Pacific. Our results suggest that dissolved organic carbon plays a minor role in the carbon budget of the equatorial Pacific.

The Ocean Carbon-Cycle Model Intercomparison Project (OCMIP) began in 1995 and is now in its 2nd, 3-year phase. What has motivated this effort? DOI: 10.1034/j.1600-0889.1999.00026.x

The effect of variable concentrations of dissolved molecular carbon dioxide, [CO 2,aq], on C : N : P ratios in marine phytoplankton was studied in batch cultures under high light, nutrient-replete conditions at different irradiance cycles. The elemental composition in six out of seven species tested was affected by variation in [CO 2,aq]. Among these species, the magnitude of change in C : N : P was similar over the experimental CO2 range. Differences in both cell size and day length-dependent growth rate had little effect on the critical CO 2 concentration below which a further decrease in [CO2,aq] led to large changes in C : N : P ratios. Significant CO 2-related changes in elemental ratios were observed at [CO2,aq] , 10 mmol kg 21 and correlated with a CO2-dependent decrease in growth rate. At [CO2,aq] typical for ocean surface waters, variation in C : N : P was relatively small under our experimental conditions. No general pattern for CO2-related changes in the elemental composition could be found with regard to the direction of trends. Either an increase or a decrease in C : N and C : P with increasing [CO2,aq] was observed, depending on the species tested. Diurnal variation in C : N and C : P, tested in Skeletonema costatum, was of a similar magnitude as CO2-related variation. In this species, the CO 2 effect was superimposed on diurnal variation, indicating that differences in elemental ratios at the end of the photoperiod were not caused by a transient buildup of carbon-rich storage compounds due to a more rapid accumulation of carbohydrates at high CO2 concentrations. If our results obtained under high light, nutrient-replete conditions are representative for natural phytoplankton populations, CO 2related changes in plankton stoichiometry are unlikely to have a significant effect on the oceanic carbon cycle.

Black carbon (BC) enters the ocean through aerosol and river deposition. BC makes up 12 to 31 percent of the sedimentary organic carbon (SOC) at two deep ocean sites, and it is 2400 to 13,900 carbon-14 years older than non-BC SOC deposited concurrently. BC is likely older because it is stored in an intermediate reservoir before sedimentary deposition. Possible intermediate pools are oceanic dissolved organic carbon (DOC) and terrestrial soils. If DOC is the intermediate reservoir, then BC is 4 to 22 percent of the DOC pool. If soils are the intermediate reservoir, then the importance of riverine carbon in the ocean carbon cycle has been underestimated.

The goals of this project were to understand the processes controlling the ocean carbon cycle and atmospheric, sea floor, and boundary exchanges. In addition, prediction of the ocean response to anthropogenic perturbations is a major goal, especially in regard to climate change.

Results of an intercomparison among terrestrial biogeochemical models (TBMs) are reported, in which one diagnostic and five prognostic models have been run with the same long-term climate forcing. Monthly fields of net ecosystem production (NEP), which is the difference between net primary production (NPP) and heterotrophic respiration R-H, at 0.5 degrees resolution have been generated for the terrestrial biosphere, The monthly estimates of NEP in conjunction with seasonal CO2 flux fields generated by the seasonal Hamburg Model of the Oceanic Carbon Cycle (HAMOCC3) and fossil fuel source fields were subsequently coupled to the three-dimensional atmospheric tracer transport model TM2 forced by observed winds. The resulting simulated seasonal signal of the atmospheric CO2 concentration extracted at the grid cells corresponding to the locations of 27 background monitoring stations of the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory network is compared with measurements from these sites. The Simple Diagnostic Biosphere Model(SDBM1), which is tuned to the atmospheric CO2 concentration at five monitoring stations in the northern hemisphere, successfully reproduced the seasonal signal of CO2 at the other monitoring stations. The SDBM1 simulations confirm that the north-south gradient in the amplitude of the atmospheric CO2 signal results from the greater northern hemisphere land area and the more pronounced seasonality of radiation and temperature in higher latitudes. In southern latitudes, ocean-atmosphere gas exchange plays an important role in determining the seasonal signal of CO2. Most of the five prognostic models (i.e., models driven by climatic inputs) included in the intercomparison predict in the northern hemisphere a reasonably accurate seasonal cycle in terms of amplitude and, to some extent, also with respect to phase. In the tropics, however, the prognostic models generally tend to overpredict the net seasonal exchanges and stronger seasonal cycles than indicated by the diagnostic model and by observations. The differences from the observed seasonal signal of CO2 may be caused by shortcomings in the phenology algorithms of the prognostic models or by not properly considering the effects of land use and vegetation fires on CO2 fluxes between the atmosphere and terrestrial biosphere. [References: 80]

We present a method for testing the performance of global ocean carbon cycle models using measurements of atmospheric O-2 and CO2 concentration. We combine these measurements to define a tracer, atmospheric potential oxygen (APO approximate to O-2 + CO2), which is conservative with respect to terrestrial photosynthesis and respiration. We then compare observations of APO to the simulations of an atmospheric transport model which uses ocean-model air-sea fluxes and fossil fuel combustion estimates as lower boundary conditions. We present observations of the annual-average concentrations of CO2, O-2, and APO at 10 stations in a north-south transect. The observations of APO show a significant interhemispheric gradient decreasing towards the north. We use air-sea CO2, O-2, and N-2 fluxes from the Princeton ocean biogeochemistry model, the Hamburg model of the ocean carbon cycle, and the Lawrence Livermore ocean biogeochemistry model to drive the TM2 atmospheric transport model. The latitudinal variations in annual-average APO predicted by the combined models are distinctly different from the observations. All three models significantly underestimate the interhemispheric difference in APO, suggesting that they underestimate the net southward transport of the sum of O-2 and CO2 in the oceans. Uncertainties in the model-observation comparisons include uncertainties associated with the atmospheric measurements, the atmospheric transport model, and the physical and biological components of the ocean models. Potential deficiencies in the physical components of the ocean models, which have previously been suggested as causes for anomalously large heat fluxes out of the Southern Ocean, may contribute to the discrepancies with the APO observations. These deficiencies include the inadequate parameterization of subgrid-scale isopycnal eddy mixing, a lack of subgrid-scale vertical convection, too much Antarctic sea-ice formation, and an overestimation of vertical diffusivities in the main thermocline. [References: 55]

The long term abiological sinks for anthropogenic CO2 will be dissolution in the oceans and chemical neutralization by reaction with carbonates and basic igneous rocks. We use a detailed ocean/sediment carbon cycle model to simulate the response of the carbonate cycle in the ocean to a range of anthropogenic CO2 release scenarios. CaCO3 will play only a secondary role in buffering the CO2 concentration of the atmosphere because CaCO3 reaction uptake capacity and kinetics are limited by the dynamics of the ocean carbon cycle. Dissolution into ocean water sequesters 70–80% of the CO2 release on a time scale of several hundred years. Chemical neutralization of CO2 by reaction with CaCO3 on the sea floor accounts for another 9–15% decrease in the atmospheric concentration on a time scale of 5.5–6.8 kyr. Reaction with CaCO3 on land accounts for another 3–8%, with a time scale of 8.2 kyr. The final equilibrium with CaCO3 leaves 7.5–8% of the CO2 release remaining in the atmosphere. The carbonate chemistry of the oceans in contact with CaCO3 will act to buffer atmospheric CO2 at this higher concentration until the entire fossil fuel CO2 release is consumed by weathering of basic igneous rocks on a time scale of 200 kyr.

The major emphasis of our DOE funded research was to study the redistribution of anthropogenic carbon in the climate system and to constrain the global budgets of anthropogenic carbon and the carbon isotopes {sup 13}C and {sup 14}C for the historical period. We have continued the development of box models of the ocean carbon cycle (HILDA model) and the land biota. The coupled model (Bern model) was chosen as the reference model for scenario calculations and the calculations of global warming potential by the Intergovernmental Panel on Climate Change. These models were applied (1) to estimate the uptake of anthropogenic carbon by the ocean and the land biosphere for the last 200 years; (2) to investigate uncertainties in deconvolved fertilization fluxes into the land biota due to uncertainties in ice core CO{sub 2} data; (3) to study the relationship between future atmospheric CO{sub 2} levels and carbon emissions; (4) to investigate the budgets of bomb-produced radiocarbon and fossil {sup 13}C. We assessed the utility of bomb-produced and natural {sup 13}C observations to validate ocean models of anthropogenic CO{sub 2} uptake and tested the eddy diffusion parameterization of large-scale vertical transport in ocean box models. For this, vertical tracer transport in box-diffusion models and the 3-D ocean general circulation model from GFDL/Princeton was compared. We analyzed the distribution of the conservative property {Delta}C* to obtain a direct estimate based on marine measurements of the uptake of anthropogenic CO{sub 2} by the North Atlantic. We contribute to the missing sink debate by using atmospheric CO{sub 2} and {sup 13}C levels to disentangle the net carbon fluxes into the land biota and the ocean. A simplified representation for 4 different ocean models of anthropogenic CO{sub 2} uptake based on mixed-layer pulse response functions was developed.

As gas phase atmospheric ammonia reacts with acidic aerosol particles it affects the chemical, physical, and optical properties of the particles. A knowledge of the source strengths of NH3 is useful in determining the effect of NH3 on aerosol properties on a regional basis. Here, an attempt is made to determine the direction and magnitude of the air/sea flux of ammonia for the North Atlantic Basin from both measured and modeled seawater and atmospheric ammonia concentrations. Previously reported measured seawater concentrations range from less than 30 to 4600 nM with the highest concentrations reported for the Caribbean Sea, the North Sea, and the Belgium coast. Measured atmospheric ammonia concentrations range from 2 to 500 nmol m-3 with the largest values occurring over the Sargasso Sea, the Caribbean Sea, and the North Sea. For comparison to the measurements, seawater ammonia concentrations were calculated by the Hamburg Model of the Ocean Carbon Cycle (HAMOCC3). HAMOCC3 open ocean values agree well with the limited number of reported measured concentrations. Calculated coastal values are lower than those measured, however, due to the coarse resolution of the model. Atmospheric ammonia concentrations were calculated by the Acid Deposition Model of the Meteorological Synthesizing Center (MSC-W) and by the global 3-dimensional model Moguntia. The two models predict similar annually averaged values but are about an order of magnitude lower than the measured concentrations. Over the North Sea and the NE Atlantic, the direction and magnitude of the air/sea ammonia flux calculated from MSC-W and Moguntia agree within the uncertainty of the calculations. Flux estimates derived from measured data are larger in both the positive and negative direction than the model derived values. The discrepancies between the measured and modeled concentrations and fluxes may be a result of sampling artifacts, inadequate chemistry and transport schemes in the models, or the difficulty in comparing point measurements to time-averaged model values. Sensitivity tests were performed which indicate that, over the range of values expected for the North Atlantic, the accuracy of the calculated flux depends strongly on seawater and atmospheric ammonia concentrations. Clearly, simultaneous and accurate measurements of seawater and atmospheric ammonia concentrations are needed to reduce the uncertainty of the flux calculations, validate the model results, and characterize the role of oceanic ammonia emissions in aerosol processing and nitrogen cycling for the North Atlantic.

This paper is written to facilitate dialogue between molecular biologists and marine microbial ecologists on research strategies in understanding the role of marine microbes in the oceanic carbon cycle. We think molecular biology can revolutionize marine microbial ecology and biogeochemistry, but at this early stage the challenge is to articulate fundamental unsolved problems in a way that shows how molecular approaches might be applied. In this paper we discuss one of the central problems in oceanic carbon cycling, namely bacteria-organic matter coupling. We will explain why bacteria-organic matter coupling is an important problem, stress the need for studying the problem in a suitable ecosystem context, formulate hypotheses for future research, and suggest how molecular approaches might be of value.

Long-term time series observations are a powerful tool for investigating biogeochemical processes in the ocean. Oceanic ecosystems are variable on a wide range of time and space scales (Dickey 1991). This variability arises from a combination of physical and biological processes and has important consequences for the measurement and interpretation of the upper ocean carbon cycle. The seasonal cycle of ocean mixing and phytoplankton primary production are the most obvious temporal patterns. Interannual variations in the seasonal cycle provide natural experiments on the relationship between the physical forcings and the biological response. Maintaining a high-quality oceanic time series study with consistent data quality over many decades is a scientific and logistical challenge. The ocean near Bermuda is unique in terms of the diversity and duration of the ocean and atmospheric time series that have been successfully maintained over decadal time scales.

The general objective of the project calcareous plankton as a monitor of a natural CO2 experiment during the last glacial-interglacial cycle (Geological subprogram of “Calcareous plankton and the oceanic carbon cycle: Emiliania huxleyi as a model system”) is to quatify natural changes in plankton production and its role in the global carbon cycle. More specifically the research concentrates on 1) the reconstruction of long-term carbonate production during the last glacial cycle (150,000 years) at 48°N and 25°W, and 2) the determination of regional trends in carbonate production in the Northeast Atlantic during times of rapid climatic change. To estimate past primary productivity using biogenic carbonate accumulation on the seafloor, one needs to quantify the amount of detrital and biogenic carbonate as well as the loss of calcium carbonate by dissolution. We developed a new method to quantify dissolution using recent sediments from a range of oceanic water depths which represent different degrees of dissolution. This can be applied to deep water piston cores to determine temporal variation in carbonate dissolution. Our time series of reconstructed surface ocean productivity of the last 150,000 years, based on biogenic carbonate accumulation at 48°N, 25°W, indicates that during interglacials (warm periods) primary productivity is generally high, whereas during glacials (cold periods) it is low. This corresponds to times of high and low atmospheric CO2 respectively, as suggested by the VOSTOK ice core record. The regional reconstruction of oceanic primary productivity shows that the contrast in productivity values between warm and cold periods decreases going from 60°N to 45°N. Published reconstruction's at low latitudes (i.e. upwelling off NW Africa) indicate a continuation of this trend, ending in the tropics with high productivity during glacials and low productivity during interglacial periods which is the opposite of the higher latitude situation. This will be of importance when modelling global oceanic carbon flux.

Marine carbonate system plays an important role in the air-sea CO2 gas exchange. The aim of the present study is to investigate the air-sea flux of CO2 in Nasik Strait, Belitung. Field observation was carried out during April, 2010, where the observed parameters are consisted of temperature, salinity, pH, dissolved inorganic carbon (DIC), total alkalinity (TA), primary productivity of phytoplankton and nutrients (phosphate and silicate). Partial pressure of CO2 (pCO2) in sea surface was particularly calculated using ABIOTIC model of the ocean carbon cycle model intercomparison project phase-2. Analysis results of the marine carbonate system show that generally Nasik Strait waters is played as a source (release) of CO2 to the atmosphere. The CO2 flux in mangrove waters, coral reef waters and coastal waters (non mangrove and coral reef) ranged between 3.06–3.19, 0.96–1.45 and 2.77–2.98 mmolC/m2/day, respectively. The present study found that the CO2 uptake by phytoplankton (photosynthesis) was not significantly affect the CO flux, however the decomposition of particulate organic carbon tended to give significant contribution to the CO2 flux.

We investigate the response of a three-dimensional ocean circulation model (Hamburg LSG) coupled on-line with an oceanic carbon cycle model (HAMOCC-3) to E1 Nifio-SouthernO scillation( ENSO) inducedf luctuationso f the wind field. During E1 Nifio 1982/1983, when upwelling and biological productivity in the equatorial Pacific were strongly reduced and sea surface temperatures were increased, the oceanic C02 partial pressure in this region decreased significantly. Consequentlyin, 1982/1983t he C02 flux from the tropicalo ceani nto the atmosphere was reduced. However, in 1983 the interannual deviations from the long-term trend in atmospheric C02 showed in January low and in December high values with a total shift by more then 1.4 GtC. The model simulation supports the oceanic measurements and predicts a temporary uptake of 0.6 GtC during the ENSO year 1983. We conclude that the concurrent release of C02 from the land biosphere must have been about 2 GtC.

An eleven-box model of the ocean-atmosphere subsystem of the global carbon cycle is developed to study the potential contribution of continental rock weathering and oceanic sedimentation to variations of atmospheric CO2 pressure over glacial-interglacial timescales. The model is capable of reproducing the distribution of total dissolved inorganic carbon, total alkalinity, phosphate, δ13C, and Δ14C between the various ocean basins today, as well as the partial pressure of atmospheric CO2. A simple sedimentation scheme at 20 different depth levels drives carbonate deposition and dissolution as a function of the depths of carbonate and aragonite lysoclines in each ocean basins considered (Atlantic, Antarctic and Indo-Pacific). The coral-reef erosion-deposition cycle is also taken into account. Furthermore, a simple cycle of oceanic strontium isotopes has been added to this model to take advantage of the 87Sr/86Sr data recently published by Dia et al. (1992) for the last 300,000 years. These data emphasize the importance of weathering of continental silicate rocks at glacial-interglacial timescales. They are used to construct several scenarios of changes of continental weathering over the last glacial cycles. They suggest that the flux of alkalinity delivered to the ocean from continental silicate weathering may have been substantially larger during glacial times than today. We show that such variations of continental weathering may explain at least in part the observed changes of the partial pressure of atmospheric CO2 between glacial and interglacial periods.

The Hamburg Oceanic Carbon Cycle Circulation Model as a global tracer model suited for glacial ocean studies is briefly described. Experimental strategies for paleoclimatic model experiments are outlined. In sensitivity experiments the effect of a hydrography shift due to a change in sea level on the marine carbon cycle is investigated.

The global ocean chlorophyll archive produced by the Coastal Zone Color Scanner (CZCS) was revised using compatible algorithms with the Sea-viewing Wide Field-of-view Sensor (SeaWIFS), and both were blended with in situ data. This methodology permitted a quantitative comparison of decadal changes in global ocean chlorophyll from the CZCS (1979-1986) and SeaWiFS (Sep. 1997-Dec. 2000) records. Global seasonal means of ocean chlorophyll decreased over the two observational segments, by 8% in winter to 16% in autumn. Chlorophyll in the high latitudes was responsible for most of the decadal change. Conversely, chlorophyll concentrations in the low latitudes increased. The differences and similarities of the two data records provide evidence of how the Earth's climate may be changing and how ocean biota respond. Furthermore, the results have implications for the ocean carbon cycle.

[1] Exchanges of carbon dioxide (CO2) between the atmosphere and the oceans play an important role in the global carbon cycle and in determining how much CO2 is stored in the atmosphere and how much is stored in the ocean. A new study shows that rain can be an important, though often overlooked, factor in this exchange. Rain can contribute to the air-sea carbon exchange in several ways. Rain dilutes the CO2 in the surface layer of the ocean, increases the speed at which gas is transferred between the atmosphere and ocean, and deposits carbon from the atmosphere into the ocean. To determine the effects of rain on the air-sea carbon flux in the western equatorial Pacific, Turk et al. analyzed rain measurements from a buoy at 0°, 156°E during 2002 as well as a dilution model based on observational ocean studies and output from an ocean carbon cycle model. (Geophysical Research Letters, doi:10.1029/2010GL045520, 2010)

International audience; Two box models, one analytical and one numerical, are used to investigate systematically a broad range of oceanic circulation changes on the atmospheric carbon dioxide (CO2) concentration. A number of oceanic carbon cycle models have failed to reproduce the 30% increase in CO2 partial pressure (pCO2) during the last deglaciation as reconstructed from polar ice cores. We apply therefore this approach of exploring the model's parameter space to examine the effect of long-lived dissolved organic matter on the system. The results from the two models complement each other, in terms of insight versus detail. Carbon is usually assumed to be transported from the surface into the deep ocean through the sedimentation of particulate matter. If there exists in the ocean a pool of dissolved organic matter (DOM) with a regeneration time comparable with the advection time, then the associated carbon can also be advected, resulting in a different clistribution. Such a DOM reservoir acts as a smoother on the spatial distribution of nutrients in the sea, particularly in the equatorial intermediate waters. We establish the role of intermediate waters as one of the key components of the oceanic carbon cycle and show that DOM reduces the sensitivity of the carbon cycle to oceanic circulation pattern changes, mainly because of its smoothing effect. Consequently, the possible existence of DOM species with a time constant of the order of a century tends to reduce, rather than enhance, the glacial-interglacial difference in pCO2 levels due to changes in the thermohaline circulation. 1Also at Centre des Faibles Radioactivitts, Domaine du

A state-of-the-art report is given of the Hamburg model of the oceanic carbon cycle. The model advects geochemical tracers important to the carbon cycle by the currents of a general circulation model. The geochemical cycling is driven by a Michaelis - Menten type production kinetics. The model is an extension of the Bacastow and Maier-Reimer (1990) model. It is based-on-a more realistic current field and includes a mechanism of lysocline - sediment interaction. Principal variables are SIGMACO2, alkalinity. phosphate, oxygen, and silicate. The carbon variables are defined for C-12, C-13, and C-14 separately. In addition to these carbon isotopes, 39A and deltaO-18 of dissolved oxygen are predicted. The model predicts realistic global patterns of tracer distribution. In the equatorial eastern Pacific, however, the structures are exaggerated due to a strong upwelling which is a common feature of coarse resolution models of the general circulation of the ocean.

The distribution of cadmium in the modern ocean gives imipritant information about ocean circulation and nutrient distributions. As the Cd/Ca-ratio of foraminiferal shells is proportional to that of seawater, Cd/Ca-records of benthic foraminifera have been used to reconstruct the Glacial oceanic distributions of dissolved Cd and PO4quantitatively. The results, in turn, have served as boundary conditions for ocean carbon cycle models. This quantitative reconstruction, however, requires that the present oceanic Cd-PO4 relationship and the distribution coefficient converting Cd/Ca-ratios into dissolved Cd and PO4 concentrations, remain constant through geological time. We have constructed a multi-box model ( menu : metal-nutrients) to test various hypotheses about the biogeochemical mechanisms determining the modern oceanic Cd-PO4 relationship and its behaviour in time. The results indicate that the oceanic Cd-PO4 relatiohship may change in response to changing oceanic conditions, such as circulation, productivity changes and upwelling intensity, for example during a glacial period. In addition, we discuss the frequent omission in the literature of statistical considerations pertaining to regression analysis, resulting in an unduly optimistic estimate of the distribution coefficient, thereby neglecting uncertainties on the order of 30% or more. In combination with spatial variability of the distribution coefficient, this conceivably poses intrinsic restrictions to its use as a conversion factor. We conclude that, awaiting a significant reduction of the aforementioned uncertainties, interpretation of the sedimentary Cd/Ca record should be performed only qualitatively.

Dissolved organic matter (DOM) has an important role in ocean chemistry, in the remineralization of inorganic nutriens, feed web by heterotrophic organisms or as ligand of trace metals. Recent measurements of dissolved organic carbon (DOC) concentration in seawater using a high temperature catalytic oxidation (HTCO) method influenced strongly the biogeochemical ocean community. The HTCO method produced substantially higher values with more possibilities to be related to the consumption of oxygen. The first diel observations of DOC concentrations were done during the bloom study of JGOFS in 1989. DOC concentrations changed from 20 μM C to 50 μM C. This change is primarily due to the physical mixing of water and to biological processes. It was observed that there is a very weak negative correlation between the DOC inventory (0–50 m depth) and primary production. It seems that the rate of decomposition of DOC or DOM affects the rate of primary production. Using a two box model the DOM downward flux was calculated. It is likely that the DOM downward flux of about 5 GtC yr-1 plays an important role in the oceanic carbon cycle. The turnover time of DOC is calculated to be 2.9 years in the upper ocean layers and 170 years in the deep waters.

The Joint Global Ocean Flux Study (JGOFS) is a major international scientific program with the aim of understanding the role of biological processes in the ocean carbon cycle (the “biological pump”). One of the major aims of this project is to be able to model the effect of the biological pump on carbon dioxide drawdown from the atmosphere and to determine its geographical and seasonal variation and what part this pump may play in climatic change (Fasham et al., 1991). This is an ambitious undertaking and it will be some years before we can judge its success. The first requirement is to develop a model of biological production that possesses some geographical generality; the assumption being that the underlying structure of the marine ecosystem is similar throughout the world ocean but that different physical forcing scenarios give rise to different seasonal cycles and the relative concentrations of the individual components of the food web. One of the problems with developing such a generic model is that even simple biological models contain a large number of parameters which are often difficult to measure and, in any event, represent some average value over the diverse species that make up the phytoplankton, Zooplankton, and bacterial populations. It is still an open question whether such a model can be produced but in the meantime we should investigate candidate models for their agreement with observations and also determine the senstitvity of the models to the parameter set.

The earth’s climate is regulated by the radiative balance between the solar energy received by the earth-atmosphere system and the thermal radiation sent back to space. While most of the former is absorbed by the earth’s surface, most of the latter originates from the atmosphere. As a result, thermal exchanges across the ocean-atmosphere interface directly influence the atmospheric density as well as the surface ocean density, thus forcing oceanic and atmospheric circulations. The continuous exchange of gases and energy across the ocean-atmosphere interface strongly influences the physical and biological processes in the upper ocean. Penetration of heat and light in the surface seawater intensifies not only biological activity, but also ocean stratification and circulation which in turn influences the penetration of greenhouse gases into the ocean, thus modulating the global warming of our planet. CO2 gas is the major natural and anthropogenic greenhouse gas and therefore has played both a primordial role and a contemporary role in the intensity of the global warming.

Carbon dioxide is an important greenhouse gas, and its atmospheric increase causes concern because of a potential impact on the global climate. A prerequisite for assessing possible future climatic changes is a means to estimate the future development of the atmospheric CO2 concentration, given some energy consumption scenarios. For this purpose, models have been developed which represent the global carbon cycle and the processes which are important for the redistribution of anthropogenic CO2. This paper describes the carbon cycle mechanisms which are relevant in this context, the way in which they are integrated in models and some model results.

Many studies of patch dynamics develop from provocative observations: hence, the scales of interest are those at which observations were practical. If further work suggests that patchiness at scales outside the range observed may be important, then the observation capabilities may be expanded into these ranges of scales. Recently, oceanographers have taken on a daunting challenge where the choice of scale selection has been removed. The ocean is important to climate change and global warming—as a storer and transporter of heat and carbon—but our understanding of the operative processes is inadequate to make predictions with the required skill. We cannot choose the observational “window” where we are most capable: we must address all scales that contribute to the global climate. In particular, to assess the role of the marine ecosystem in the ocean carbon cycle, we have had initially to extrapolate to ocean basin scales (105 km) from, for example, a few tens of sediment traps (1 m diameter) or water samples (10 cm, based on a 1 L sample). How do we bridge over 9 orders of magnitude to address problems of global scale from water samples typically of 1 L volume?

The ocean plays a central role in the climate of the Earth. Storage and transport, by oceanic circulation, control the temporal evolution of climate change resulting from the increase in greenhouse gases in the atmosphere, and affect the magnitude and regional distribution of the changes. Chemical and biological processes in the ocean are also strongly coupled to climate change, particularly through the global carbon cycle. This text contains a series of lectures discussing the complex processes and interactions that link the ocean to the climate system. It covers topics from the fields of physical, chemical and biological oceanography as well as meteorology. Emphasis is placed on modelling ocean circulation dynamics, hydrological processes in the atmosphere, tropical ocean-atmosphere interactions, and the oceanic carbon cycle.

In the global oceanic carbon cycle, there are three main methane sources. Biogenically formed CH4 in the reduced sediments of shelf and continental slopes (δ13C from −58.2 to −87.0‰). “Fossil” CH4 coming from fluid and gas seeps (δ13C from −43.0 to −71.0‰). Abiogenically produced CH4 coming from hydrothermal vents of Mid Oceanic Ridges and Back Arc spreading rift zones (δ13C from −15.0 to −18.2‰). The main part of oceanic methane is oxidized by methanotrophic bacteria with formation of CO2 and carbonate minerals. Biomass of methanotrophic bacteria serves as an additional source of organic matter. But some part of the CH4 from shallow sediments and from gas seeps can enter to the atmosphere.

A state-of the art report is given of the Hamburg model of the oceanic carbon cycle. The model treats geochemical tracers important to the carbon cycle advected by the currents of a general circulation model. The model is an extension of the Bacastow and Maier-Reimer (1990) model. It is based on a more realistic current field and includes a mechanism of lysocline — sediment interaction with alkalinity, dissolved inorganic carbon, phosphate, oxygen and silicium as prognostic variables. The carbon variables are defined for 12C, δ13C, and Δ14C separately.

Understanding the oceanic uptake of carbon from the atmosphere is essential for better constraining the global budget, as well as for predicting the air-borne fraction of CO 2 emissions and thus degree of climate change. Gaining this understanding is difficult, because the ‘natural’ carbon cycle, the part of the global carbon cycle unaltered by CO 2 emissions, also responds to climate change and ocean acidification. Using a global climate model of intermediate complexity, we assess the evolution of the natural carbon cycle over the next few centuries. We find that physical mechanisms, particularly Atlantic meridional overturning circulation and gas solubility, alter the natural carbon cycle the most and lead to a significant reduction in the overall oceanic carbon uptake. Important biological mechanisms include reduced organic carbon export production due to reduced nutrient supply, increased organic carbon production due to higher temperatures and reduced CaCO 3 production due to increased ocean acidification. A large ensemble of model experiments indicates that the most important source of uncertainty in ocean uptake projections in the near term future are the upper ocean vertical diffusivity and gas exchange coefficient. By year 2300, the model's climate sensitivity replaces these two and becomes the dominant factor as global warming continues. DOI: 10.1111/j.1600-0889.2010.00461.x

The delta(13)C value of the dissolved inorganic carbon in the surface waters of the Pacific Ocean has decreased by about 0.4 per mil between 1970 and 1990. This decrease has resulted from the uptake of atmospheric CO(2) derived from fossil fuel combustion and deforestation. The net amounts of CO(2) taken up by the oceans and released from the biosphere between 1970 and 1990 have been determined from the changes in three measured values: the concentration of atmospheric CO(2), the delta(13)C of atmospheric CO(2) and the delta(13)C value of dissolved inorganic carbon in the ocean. The calculated average net oceanic CO(2) uptake is 2.1 gigatons of carbon per year. This amount implies that the ocean is the dominant net sink for anthropogenically produced CO(2) and that there has been no significant net CO(2) released from the biosphere during the last 20 years.

Public concern about the inadvertent interference by man in the processes that conspire to produce the earth’s climate — the general problem of “global change” — has emphasised the need for scientists to gain a deeper understanding of the planet as a compound biogeochemical system. In particular it has become recognised that we must improve our knowledge of the global carbon cycle, including the part of it that lies in the oceans. It is in this context that a rather obscure concept in biological oceanography has been projected into the scientific limelight and has given a household word (“new production”) to those institutions where research on global-change issues is carried out, written about, read about, or worried about. For understanding the oceanic carbon cycle, and the role of the oceans in the planetary carbon cycle, the concept of new production is central and fundamental.

The flux of organic carbon associated with new production has been modeled by advection of dissolved organic carbon in addition to falling particulate organic carbon, in a carbon cycle model that is based on an oceanic general circulation model. Model predictions of chemical species involved in the carbon cycle are compared with observations. Relative to a model in which new production is carried only by falling particulate organic carbon, there is significantly better agreement between predicted and observed oceanic phosphate and oxygen concentrations if a large part of the new production flux is carried by dissolved organic carbon. copyright 1991 by the American Geophysical Union.

By discussing the impact of feedbacks between the physical climate system and the oceanic carbon cycle, Keeling's comment ([ 1 ][1]) addresses a crucial issue in the determination of the air-sea balance of CO2 beyond the direct oceanic uptake of anthropogenic CO2. These feedbacks were already

The oceans and the atmosphere are intimately linked in determining global climate. The greenhouse gas carbon dioxide is a key player in this, its concentration in the atmosphere being dynamically controlled via generation from the biosphere, geosphere and hydrosphere, and through ‘draw down’ into carbon reservoirs of short-term historical and long-term geological timescales. Physical and biological processes in the oceans play a central role in atmospheric carbon dioxide regulation. Hence, public concern over climate change immediately confronts our knowledge of the oceanic carbon cycle, both now and in the past. The North Atlantic is of special interest, being an extremely dynamic ocean with an enormous effect on the heat and humidity balance of the Northern Hemisphere and, in consequence, on the agriculture and lifestyles of the populations of North America, Europe and Asia. There is considerable controversy over the role of the North Atlantic in drawing down man-made CO 2 from the atmosphere and hence in determining climate. Predicting the impact of the increased levels of atmospheric CO 2 which are being generated anthropogenically depends upon quantification of sources, sinks and the processes inter-relating them.

Carbonates are the largest reservoirs of carbon on Earth. From mid-Mesozoic time, the biologically catalyzed precipitation of calcium carbonates by pelagic phytoplankton has been primarily due to the production of calcite by coccolithophorids. In this paper we address the physical and chemical processes that select for coccolithophorid blooms detected in Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color imagery. Our primary goal is to develop both diagnostic and prognostic models that represent the spatial and temporal dynamics of coccolithophorid blooms in order to improve our knowledge of the role of these organisms in mediating fluxes of carbon between the ocean, the atmosphere, and the lithosphere. On the basis of monthly composite images of classified coccolithophorid blooms and global climatological maps of physical variables and nutrient fields, we developed a probability density function that accounts for the physical chemical variables that predict the spatiotemporal distribution of coccolithophorids in the world oceans. Our analysis revealed that areas with sea surface temperatures (SST) between 3° and 15°C, a critical irradiance between 25 and 150 µmol quanta m-2 s-1, and decreasing nitrate concentrations (N/t < 0) are selective for upper ocean large-scale coccolithophorid blooms. While these conditions favor both Northern and Southern Hemisphere blooms of the most abundant coccolithophorid in the modern oceans, Emiliania huxleyi, the Northern and Southern Hemisphere populations of this organism are genetically distinct. Applying amplified fragment length polymorphism as a marker of genetic diversity, we identified two major taxonomic clades of E. huxleyi; one is associated with the Northern Hemisphere blooms, while the other is found in the Southern Hemisphere. We suggest a rule of “universal distribution and local selection”: that is, coccolithophorids can be considered cosmopolitan taxa, but their genetic plasticity provides physiological accommodation to local environmental selection pressure. Sea surface temperature, critical irradiance, and N/t were predicted for the years 2060–2070 using the NCAR Community Climate System Model to generate future monthly probability distributions of coccolithophorids based upon the relationships observed between the environmental variables and coccolithophorid blooms in modern oceans. Our projected probability distribution analysis suggests that in the North Atlantic, the largest habitat for coccolithophorids on Earth, the areal extent of blooms will decrease by up to 50% by the middle of this century. We discuss how the magnitude of carbon fluxes may be affected by the evolutionary success of coccolithophorids in future climate scenarios.

[1] It has been suggested that much of the observed glacial-interglacial variability in the atmospheric mixing ratio of CO2 (xCO2) could potentially be driven by a perturbation of the marine Si cycle. To date, only relatively simple steady-state analysis has been made of this hypothesis. In this study, we develop a description of the ocean carbon cycle, incorporating novel descriptions for the recycling of Si, both within the water column and in deep-sea sediments. A high degree of computational efficiency enables model integrations over multiple glacial-interglacial cycles, driven by a time-varying input of dissolved Si to the ocean. Due to the long time constant (∼23 ka) of atmospheric xCO2 response to perturbation in Si supply and the highly nonlinear nature of opal preservation in deep-sea sediments, we find that reduction in the deposition rate of aeolian silicates at the surface ocean can explain little (

[1] Using a simple box model, we investigate the effects of a reduced Si:N uptake ratio by Antarctic phytoplankton on the marine silica cycle and atmospheric pCO2. Recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added [Hutchins and Bruland, 1998; Takeda, 1998; Franck et al., 2000]. The Southern Ocean may have supported diatoms with reduced Si:N uptake ratios compared to today during the dustier glacial times [Petit et al., 1999]. A similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as Phaeocystis. Our model shows that reduced Si:N export ratios in the Southern Ocean create excess silicic acid, which may then be leaked out to lower latitudes. Any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes CaCO3 production and therefore diminishes the carbonate pump. In our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric CO2 from the interglacial 277 to 230–242 ppm, depending on where the excess silicic acid is consumed. By comparison, the atmospheric pCO2 sensitivity of general circulation models to carbonate pump forcing is ∼3.5–fold greater, which, combined with carbonate compensation, can account for peak glacial atmospheric pCO2. We discuss the importance of the initial rain ratio of CaCO3 to organic carbon on atmospheric pCO2 and relevant sedimentary records that support and constrain this “silicic acid leakage” scenario.

Over the past decade there has been a surge of studies on ocean biogeochemistry, and the carbon cycle in particular. The results were the central topic of a meeting in April, one message being that it is the biological aspects of the oceanic carbon cycle that are the trickiest to quantify.

Recent studies ([1][1], [2][2]) have suggested that respiration exceeds photosynthetic oxygen production in large areas of the oceans. If correct, the conclusion has profound implications for our understanding of the oceanic carbon cycle. C. M. Duarte and S. Augusti conclude that four-fifths of the

The assessment of direct effects of anthropogenic CO 2 increase on the marine biota has received relatively little attention compared to the intense research on CO 2 -related responses of the terrestrial biosphere. Yet, due to the rapid air–sea gas exchange, the observed past and predicted future rise in atmospheric CO 2 causes a corresponding increase in seawater CO 2 concentrations, [CO 2 ], in upper ocean waters. Increasing [CO 2 ] leads to considerable changes in the surface ocean carbonate system, resulting in decreases in pH and the carbonate concentration, [CO 2 −3 ]. These changes can be shown to have strong impacts on the marine biota. Here we will distinguish between CO 2 -related responses of the marine biota which (a) potentially affect the ocean's biological carbon pumps and (b) are relevant to the interpretation of diagnostic tools (proxies) used to assess climate change on geological times scales. With regard to the former, three direct effects of increasing [CO 2 ] on marine plankton have been recognized: enhanced phytoplankton growth rate, changing elemental composition of primary produced organic matter, and reduced biogenic calcification. Although quantitative estimates of their impacts on the oceanic carbon cycle are not yet feasible, all three effects increase the ocean's capacity to take up and store atmospheric CO 2 and hence, can serve as negative feedbacks to anthropogenic CO 2 increase. With respect to proxies used in palaeo-reconstructions, CO 2 -sensitivity is found in carbon isotope fractionation by phytoplankton and foraminifera. While CO 2 - dependent isotope fractionation by phytoplankton may be of potential use in reconstructing surface ocean p CO 2 at ancient times, CO 2 -related effects on the isotopic composition of foraminiferal shells confounds the use of the difference in isotopic signals between planktonic and benthic shells as a measure for the strength of marine primary production. The latter effect also offers an alternative explanation for the large negative swings in δ 13 C of foraminiferal calcite between glacial and interglacial periods. Changes in [CO 2 −3 ] affect the δ 18 O in foraminiferal shells. Taking this into account brings sea surface temperature estimates for the glacial tropics closer to those obtained from other geochemical proxies. DOI: 10.1034/j.1600-0889.1999.00023.x

Cells of Emiliania huxleyi are surrounded by ‘coccoliths', minute, elegant scales of calcium carbonate. In all the oceans, particularly at mid-latitudes, this species forms gigantic blooms, readily visualized by satellite imagery. Coccolith-bearing organisms, of which E. huxleyi is by far the most abundant representative, are the major contributors to the ocean floor limestone sediments, and this in turn is the largest long-term sink of inorganic carbon on earth. In addition, E. huxleyi blooms emit vast amounts of dimethyl-sulphide (DMS), a gas which, on oxidation, is a dominant source of cloud nuclei. The profusion of E. huxleyi and its intimate involvement with the global biogeochemical cycles of both carbon and sulphur make it a key component of the greenhouse effect (CO2), natural acid rain and albedo regulation.E. huxleyi blooms are often almost monospecific. They can be visualized by satellite imagery and leave highly characteristic skeletal and macromolecular markers which accumulate on the deep-sea floor as a long-term record of their history. The organism is easily cultured in the laboratory and molecular genetical, biochemical and physiological studies are underway.We focus on Emiliania huxleyi as a model organism to study interactions between oceanic plankton and climate. Benefits of this approach are: (1) to highlight the idiosyncratic non-linear character of these interactions; (2) to reveal the intimate coupling of the oceanic carbon cycle and DMS productivity; and (3) to allow an integrated modelling and experimental approach, integrating multi-disciplinary studies that range from the global down to the macromolecular level and through geological time. E. huxleyi coccoliths and specific biomarkers preserved in the geological archive not only provide information on the distribution of this organism in the geological past. The connection with extensive neontological research offers a unique opportunity to reconstruct the development of the entire E. huxleyi system, including its multifarious climatic interactions, through geological time.The ‘Global Emiliania Modeling Initiative’ (GEM), started in 1990, is a European research program intended to investigate and model the Emiliania huxleyi system.

Determining the effect of tropical land use on the carbon dioxide (CO2) content of the atmosphere requires: (a) estimates of the rates of land use change, (b) estimates of the difference between the carbon stored in forests and that stored in pastures and cultivated fields, and (c) a consideration of the fate of carbon stored in the cleared vegetation. The first article of this series analyzed land use in four tropical countries and estimated the carbon released to the atmosphere as a consequence of changes in land use. This article estimates the carbon released from the entire tropical region based on the two published studies of land use change for the tropics as a whole that distinguish between temporary and permanent land use: Seiler and Crutzen (1980) and Lanly (1982). We combine these estimates with two estimates of the difference in carbon storage between forests and fields derived from Whittaker and Likens (1975) and Brown and Lugo (1982), and the two scenarios of the fate of cleared vegetation, developed in the previous article, to produce several complete sets of data describing the necessary parameters to calculate carbon exchange. These data sets, entered into our model, produce a range of estimates of the annual release of carbon from tropical vegetation in 1980 of from 0.6 to 1.8 BMT/year, with the more likely range being 0.9–1.2 BMT/year. Our preliminary analysis suggests that the release from tropical soils due to land use change adds about an additional 0.3 BMT C/year, so that the total release is probably between 1.2 and 1.5 BMT C/year. Peng and others (1983) reported that new models of the oceanic carbon cycle can accommodate at least 1.2 BMT C/year in 1980 from forests and soils. Our results indicate that, given the uncertainties in the size of both the biotic release and oceanic uptake, the global carbon budget may be balanced if there is no significant release from nontropical ecosystems due to land use change and all mature ecosystems are in collective equilibrium with the atmosphere.

Mechanisms are identified whereby processes internal to the oceans can give rise to rapid changes in atmospheric P CO2 . One such mechanism involves exchange between the atmosphere and deep ocean through the high-latitude outcrop regions of the deep waters. The effectiveness of communication between the atmosphere and deep ocean is determined by the rate of exchange between the surface and deep ocean against the rate of biological uptake of the excess carbon brought up from the abyss by this exchange. Changes in the relative magnitude of these two processes can lead to atmospheric p co2 values ranging between 165 p.p.m. (by volume) and 425 p.p.m. compared with1 2 a pre-industrial value of 280 p.p.m. Another such mechanism involves the separation between regeneration of alkalinity and total carbon that occurs in the oceans because of the fact that organic carbon is regenerated primarily in the upper ocean whereas CaCO 3 is dissolved primarily in the deep ocean. The extent of separation depends on the rate of CaCO 3 formation at the surface against the rate of upward mixing of deep waters. This mechanism can lead to atmospheric values in excess of 20000 p.p.m., although values greater than 1100 p.p.m. are unlikely because calcareous organisms would have difficulty surviving in the undersaturated surface waters that develop at this point. A three-dimensional model that is being developed to further study these and other problems provides illustrations of them and also suggests the possibility that there is a long-lived form of non-sinking carbon playing a major role in carbon cycling.

Particulate organic carbon fluxes were measured with free-floating particle traps at nine locations during VERTEX and related studies. Examination of these data indicated that there was relatively little spatial variability in open ocean fluxes. To obtain mean rates representative of the oligotrophic environment, flux data from six stations were combined and fitted to a normalized power function, F = F 100 ( z /100) b ; e.g. the open ocean composite C flux in mol m −2 y −1 = 1.53 ( z /100 −0.858 with depth z in meters. It is shown that the vertical derivative of particulate fluxes may indicate solute regeneration rates, and accordingly regeneration rates for C, H and N were estimated. Oxygen utilization rates were also estimated under the assumption that 1.5, 1.0 and 0.25 moles of O 2 were used for each mole of N, C and H regenerated. Regeneration ratios of these elements were depth-dependent: i.e. N:C:H:−O 2 = 1.0 N: 6.2 ( z /100) 0.130 C: 10.0( z /100) 0.146 H: [1.5 + 6.2 ( z /100) 0.130 + 2.5 ( z /100) 0.146 ]− O 2 . Comparisons of our rates with those in the literature indicate that trap-derived new productivities in the open Pacific (≈1.5 mol C m −2 y −1 ) are substantially less than those estimated from oxygen utilization rates in the Sargasso Sea (≈4 mol C m −2 y −1 ). A hypothesis is presented which attempts to explain this discrepancy on the basis of the lateral transport and decomposition of slow or non-sinking POC in the Sargasso Sea. Data gathered during the VERTEX studies are also used for various global estimates. Open ocean primary productivities are estimated at 130 g C m −2 y −1 which results in a global open ocean productivity of 42 Gt y −1 . Organic C removal from the surface of the ocean via particulate sinking (new production) is on the order of 6 Gt y −1 . Fifty percent of this C is regenerated in the upper 300 m of the water column. The ratio of new production (measured with traps) to total primary production (measured via 14 C) is 0.14. It is concluded that the 14 C technique yields reasonable estimates of primary productivity provided that care is taken to prevent heavy metal contamination.