Dependence of the ocean-atmosphere partitioning of carbon on temperature and alkalinity

Omta, Anne Willem; Dutkiewicz, Stephanie; Follows, Michael J.

doi:10.1029/2010gb003839

Cited by 21 publications

(24 citation statements)

References 39 publications

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“…Without external forcing, the alkalinity goes through sawtooth‐shaped cycles with slow increases and steep declines, at which the calcifiers exhibit spikes (Figure ). The amplitude of the illustrated alkalinity cycles is about 0.06 mol eq/m 3 , corresponding to variations in atmospheric p CO 2 of about 75 ppmv [ Omta et al ., ]; the period of the cycles is about 20 kyr which is considerably shorter than the observed 100 kyr periodicity. The cycles slowly damp toward an equilibrium state with A =2.0 mol eq/m 3 and P =4.0×10 −5 mol eq/m 3 .…”

Section: Model Formulation and Resultsmentioning

confidence: 99%

On the potential role of marine calcifiers in glacial‐interglacial dynamics

Omta

Voorn

Rickaby

et al. 2013

Global Biogeochemical Cycles

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[1] Ice core measurements have revealed a highly asymmetric cycle in Antarctic temperature and atmospheric CO 2 over the last 800 kyr. Both CO 2 and temperature decrease over 100 kyr going into a glacial period and then rise steeply over less than 10 kyr at the end of a glacial period. There does not yet exist wide agreement about the causes of this cycle or about the origin of its shape. Here we explore the possibility that an ecologically driven oscillator plays a role in the dynamics. A conceptual model describing the interaction between calcifying plankton and ocean alkalinity shows interesting features: (i) It generates an oscillation in atmospheric CO 2 with the characteristic asymmetric shape observed in the ice core record, (ii) the system can transform a sinusoidal Milankovitch forcing into a sawtooth-shaped output, and (iii) there are spikes of enhanced calcifier productivity at the glacial-interglacial transitions, consistent with several sedimentary records. This suggests that ecological processes might play an active role in the observed glacial-interglacial cycles.

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Section: Model Formulation and Resultsmentioning

confidence: 99%

On the potential role of marine calcifiers in glacial‐interglacial dynamics

Omta

Voorn

Rickaby

et al. 2013

Global Biogeochemical Cycles

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“…Increased alkalinity shifts the buffered carbon equilibrium away from dissolved CO 2 and towards carbonate and bicarbonate ions, allowing greater oceanic uptake of CO 2 from the atmosphere and increasing the size of the C sat reservoir (e.g. Omta et al 2011). In summary, increased Southern Ocean residual circulation generally decreases the C sat reservoir and acts to increase atmospheric CO 2 , while decreased residual circulation has the opposite effect (Table 2).…”

Section: Anomaly Of the Saturated Dic Concentration DC Satmentioning

confidence: 99%

Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2

et al. 2013

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The effect of idealized wind-driven circulation changes in the Southern Ocean on atmospheric CO 2 and the ocean carbon inventory is investigated using a suite of coarse-resolution, global coupled ocean circulation and biogeochemistry experiments with parameterized eddy activity and only modest changes in surface buoyancy forcing, each experiment integrated for 5,000 years. A positive correlation is obtained between the meridional overturning or residual circulation in the Southern Ocean and atmospheric CO 2 : stronger or northward-shifted westerly winds in the Southern Hemisphere result in increased residual circulation, greater upwelling of carbon-rich deep waters and oceanic outgassing, which increases atmospheric pCO 2 by *20 latm; weaker or southward-shifted winds lead to the opposing result. The ocean carbon inventory in our model varies through contrasting changes in the saturated, disequilibrium and biogenic (soft-tissue and carbonate) reservoirs, each varying by O(10-100) PgC, all of which contribute to the net anomaly in atmospheric CO 2 . Increased residual overturning deepens the global pycnocline, warming the upper ocean and decreasing the saturated carbon reservoir.

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“…The buffer capacity of the CO 2 -system varies with temperature and the distribution of total inorganic carbon and alkalinity (e.g. Omta et al, 2010Omta et al, , 2011. Biogeochemical processes, namely the organic tissue pump and the CaCO 3 counter pump, strongly affect the ocean's internal cycling and distribution of carbon and alkalinity, which in turn influences the surface ocean buffer capacity and hence the ocean's ability to take up anthropogenic CO 2 .…”

Section: Introductionmentioning

confidence: 99%

Methods to evaluate CaCO<sub>3</sub> cycle modules in coupled global biogeochemical ocean models

et al. 2014

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Abstract. The marine CaCO 3 cycle is an important component of the oceanic carbon system and directly affects the cycling of natural and the uptake of anthropogenic carbon. In numerical models of the marine carbon cycle, the CaCO 3 cycle component is often evaluated against the observed distribution of alkalinity. Alkalinity varies in response to the formation and remineralization of CaCO 3 and organic matter. However, it also has a large conservative component, which may strongly be affected by a deficient representation of ocean physics (circulation, evaporation, and precipitation) in models. Here we apply a global ocean biogeochemical model run into preindustrial steady state featuring a number of idealized tracers, explicitly capturing the model's CaCO 3 dissolution, organic matter remineralization, and various preformed properties (alkalinity, oxygen, phosphate). We compare the suitability of a variety of measures related to the CaCO 3 cycle, including alkalinity (TA), potential alkalinity and TA * , the latter being a measure of the time-integrated imprint of CaCO 3 dissolution in the ocean. TA * can be diagnosed from any data set of TA, temperature, salinity, oxygen and phosphate. We demonstrate the sensitivity of total and potential alkalinity to the differences in model and ocean physics, which disqualifies them as accurate measures of biogeochemical processes. We show that an explicit treatment of preformed alkalinity (TA 0 ) is necessary and possible. In our model simulations we implement explicit model tracers of TA 0 and TA * . We find that the difference between modelled true TA * and diagnosed TA * was below 10 % (25 %) in 73 % (81 %) of the ocean's volume. In the Pacific (and Indian) Oceans the RMSE of A * is below 3 (4) mmol TA m −3 , even when using a global rather than regional algorithms to estimate preformed alkalinity. Errors in the Atlantic Ocean are significantly larger and potential improvements of TA 0 estimation are discussed. Applying the TA * approach to the output of three state-of-the-art ocean carbon cycle models, we demonstrate the advantage of explicitly taking preformed alkalinity into account for separating the effects of biogeochemical processes and circulation on the distribution of alkalinity. In particular, we suggest to use the TA * approach for CaCO 3 cycle model evaluation.

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Dependence of the ocean-atmosphere partitioning of carbon on temperature and alkalinity

Cited by 21 publications

References 39 publications

On the potential role of marine calcifiers in glacial‐interglacial dynamics

On the potential role of marine calcifiers in glacial‐interglacial dynamics

Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2

Methods to evaluate CaCO<sub>3</sub> cycle modules in coupled global biogeochemical ocean models

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Dependence of the ocean-atmosphere partitioning of carbon on temperature and alkalinity

Cited by 21 publications

References 39 publications

On the potential role of marine calcifiers in glacial‐interglacial dynamics

On the potential role of marine calcifiers in glacial‐interglacial dynamics

Wind-driven changes in Southern Ocean residual circulation, ocean carbon reservoirs and atmospheric CO2

Methods to evaluate CaCO&lt;sub&gt;3&lt;/sub&gt; cycle modules in coupled global biogeochemical ocean models

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Methods to evaluate CaCO<sub>3</sub> cycle modules in coupled global biogeochemical ocean models