scholarly journals Author's response to Anonymous Referee #1 for Variable C/P composition of organic production and its effect on ocean carbon storage in glacial model simulations

2019 ◽  
Author(s):  
Malin Ödalen
Keyword(s):  
Carbon Storage ◽  
Organic Production ◽  
Model Simulations ◽  
Ocean Carbon

scholarly journals Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations

2020 ◽  
Vol 17 (8) ◽  
pp. 2219-2244 ◽  
Author(s):  
Malin Ödalen ◽  
Jonas Nycander ◽  
Andy Ridgwell ◽  
Kevin I. C. Oliver ◽  
Carlye D. Peterson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Storage ◽  
Co2 Storage ◽  
Organic Production ◽  
Phosphate Concentration ◽  
Atmospheric Co2 ◽  
Carbon Uptake ◽  
Biological Pump ◽  
Redfield Ratio ◽  
Model Simulations

Abstract. During the four most recent glacial maxima, atmospheric CO2 has been lowered by about 90–100 ppm with respect to interglacial concentrations. It is likely that most of the atmospheric CO2 deficit was stored in the ocean. Changes in the biological pump, which are related to the efficiency of the biological carbon uptake in the surface ocean and/or of the export of organic carbon to the deep ocean, have been proposed as a key mechanism for the increased glacial oceanic CO2 storage. The biological pump is strongly constrained by the amount of available surface nutrients. In models, it is generally assumed that the ratio between elemental nutrients, such as phosphorus, and carbon (C∕P ratio) in organic material is fixed according to the classical Redfield ratio. The constant Redfield ratio appears to approximately hold when averaged over basin scales, but observations document highly variable C∕P ratios on regional scales and between species. If the C∕P ratio increases when phosphate availability is scarce, as observations suggest, this has the potential to further increase glacial oceanic CO2 storage in response to changes in surface nutrient distributions. In the present study, we perform a sensitivity study to test how a phosphate-concentration-dependent C∕P ratio influences the oceanic CO2 storage in an Earth system model of intermediate complexity (cGENIE). We carry out simulations of glacial-like changes in albedo, radiative forcing, wind-forced circulation, remineralization depth of organic matter, and mineral dust deposition. Specifically, we compare model versions with the classical constant Redfield ratio and an observationally motivated variable C∕P ratio, in which the carbon uptake increases with decreasing phosphate concentration. While a flexible C∕P ratio does not impact the model's ability to simulate benthic δ13C patterns seen in observational data, our results indicate that, in production of organic matter, flexible C∕P can further increase the oceanic storage of CO2 in glacial model simulations. Past and future changes in the C∕P ratio thus have implications for correctly projecting changes in oceanic carbon storage in glacial-to-interglacial transitions as well as in the present context of increasing atmospheric CO2 concentrations.

scholarly journals Supplementary material to "Variable C/P composition of organic production and its effect onocean carbon storage in glacial model simulations"

2019 ◽  
Author(s):  
Malin Ödalen ◽  
Jonas Nycander ◽  
Andy Ridgwell ◽  
Kevin I. C. Oliver ◽  
Carlye D. Peterson ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Organic Production ◽  
Model Simulations ◽  
Supplementary Material

scholarly journals Variable C/P composition of organic production and its effect onocean carbon storage in glacial model simulations

2019 ◽  
Author(s):  
Malin Ödalen ◽  
Jonas Nycander ◽  
Andy Ridgwell ◽  
Kevin I. C. Oliver ◽  
Carlye D. Peterson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Storage ◽  
Co2 Storage ◽  
Organic Production ◽  
Phosphate Concentration ◽  
Atmospheric Co2 ◽  
Carbon Uptake ◽  
Biological Pump ◽  
Redfield Ratio ◽  
Model Simulations

Abstract. During the four most recent glacial maxima, atmospheric CO2 has been lowered by about 90--100 ppm with respect to interglacial concentrations. It is likely that most of the atmospheric CO2 deficit was stored in the ocean. Changes of the biological pump, which are related to the efficiency of the biological carbon uptake in the surface ocean and/or of the export of organic carbon to the deep ocean, have been proposed as a key mechanism for the increased glacial oceanic CO2 storage. The biological pump is strongly constrained by the amount of available surface nutrients. In models, it is generally assumed that the ratio between elemental nutrients, e.g. phosphorus, and carbon (C/P ratio) in organic material is fixed according to the classical Redfield ratio. The constant Redfield ratio appears to hold approximately when averaged over basin scales, but observations document highly variable C/P ratios on regional scales and between species. If the C/P ratio decreases when nutrient availability is scarce, as observations suggest, this has the potential to further increase glacial oceanic CO2 storage in response to changes in surface nutrient distributions. In the present study, we perform a sensitivity study to test how a phosphate--concentration dependent C/P ratio influences the oceanic CO2 storage in an Earth system model of intermediate complexity (cGENIE). We carry out simulations of glacial--like changes in albedo, radiative forcing, wind--forced circulation, remineralisation depth of organic matter, and mineral dust deposition. Specifically, we compare model versions with with the classical constant Redfield ratio and an observationally-motivated variable C/P ratio, in which the carbon uptake increases with decreasing phosphate concentration. While a flexible C/P ratio does not impact the model's ability to simulate benthic d13C patterns seen in observational data, our results indicate that, in production of organic matter, flexible C/P can further increase the oceanic storage of CO2 in glacial model simulations. Past and future changes in the C/P ratio thus have implications for correctly projecting changes in oceanic carbon storage in glacial-to-interglacial transitions as well as in the present context of increasing atmospheric CO2 concentrations.

scholarly journals Deglacial carbon cycle changes observed in a compilation of 127 benthic <i>δ</i><sup>13</sup>C time series (20–6 ka)

2018 ◽  
Vol 14 (8) ◽  
pp. 1229-1252 ◽  
Author(s):  
Carlye D. Peterson ◽  
Lorraine E. Lisiecki
Keyword(s):  
Time Series ◽  
Carbon Cycle ◽  
Carbon Storage ◽  
Large Scale ◽  
Deep Ocean ◽  
Atmospheric Co2 ◽  
Last Deglaciation ◽  
Terrestrial Biosphere ◽  
Spatial Coverage ◽  
Ocean Carbon

Abstract. We present a compilation of 127 time series δ13C records from Cibicides wuellerstorfi spanning the last deglaciation (20–6 ka) which is well-suited for reconstructing large-scale carbon cycle changes, especially for comparison with isotope-enabled carbon cycle models. The age models for the δ13C records are derived from regional planktic radiocarbon compilations (Stern and Lisiecki, 2014). The δ13C records were stacked in nine different regions and then combined using volume-weighted averages to create intermediate, deep, and global δ13C stacks. These benthic δ13C stacks are used to reconstruct changes in the size of the terrestrial biosphere and deep ocean carbon storage. The timing of change in global mean δ13C is interpreted to indicate terrestrial biosphere expansion from 19–6 ka. The δ13C gradient between the intermediate and deep ocean, which we interpret as a proxy for deep ocean carbon storage, matches the pattern of atmospheric CO2 change observed in ice core records. The presence of signals associated with the terrestrial biosphere and atmospheric CO2 indicates that the compiled δ13C records have sufficient spatial coverage and time resolution to accurately reconstruct large-scale carbon cycle changes during the glacial termination.

scholarly journals The influence of the ocean circulation state on ocean carbon storage and CO<sub>2</sub> drawdown potential in an Earth system model

2017 ◽  
Author(s):  
Malin Ödalen ◽  
Jonas Nycander ◽  
Kevin I. C. Oliver ◽  
Laurent Brodeau ◽  
Andy Ridgwell
Keyword(s):  
Carbon Storage ◽  
Wind Stress ◽  
Ocean Circulation ◽  
System Model ◽  
Biological Pump ◽  
Earth System ◽  
Heat Diffusivity ◽  
Initial States ◽  
Ocean Carbon ◽  
Atmospheric Heat

Abstract. During the four most recent glacial cycles, atmospheric CO2 during glacial maxima has been lowered by about 90–100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is however still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to constrain the range in ocean carbon storage for an ensemble of ocean circulation equilibrium states. We do a set of simulations where we run the model to pre-industrial equilibrium, but where we achieve different ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air-sea CO2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO2 disequilibrium component. We also relate these contributions to differences in strength of ocean overturning circulation. In cases with weaker circulation, we see that the ocean's capacity for carbon storage is larger. Depending on which ocean forcing parameter that is tuned, the origin of the change in carbon storage is different. When wind stress or ocean vertical diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean horizontal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Finally, we do a drawdown experiment, where we investigate the capacity for increased carbon storage by maximising the efficiency of the biological pump in our ensemble members. We conclude that different initial states for an ocean model result in different capacities for ocean carbon storage, due to differences in the ocean circulation state. This could explain why it is difficult to achieve comparable responses of the ocean carbon pumps in model intercomparison studies, where the initial states vary between models. The drawdown experiment highlights the importance of the strength of the biological pump in the control state for model studies of increased biological efficiency.

scholarly journals Glacial – interglacial atmospheric CO<sub>2</sub> change: a simple "hypsometric effect" on deep-ocean carbon sequestration?

2006 ◽  
Vol 2 (5) ◽  
pp. 711-743 ◽  
Author(s):  
L. C. Skinner
Keyword(s):  
Carbon Sequestration ◽  
Carbon Storage ◽  
Ocean Circulation ◽  
Deep Water ◽  
Deep Sea ◽  
Storage Capacity ◽  
Deep Ocean ◽  
Contributing Factors ◽  
Carbon Reservoir ◽  
Ocean Carbon

Abstract. Given the magnitude and dynamism of the deep marine carbon reservoir, it is almost certain that past glacial – interglacial fluctuations in atmospheric CO2 have relied at least in part on changes in the carbon storage capacity of the deep sea. To date, physical ocean circulation mechanisms that have been proposed as viable explanations for glacial – interglacial CO2 change have focussed almost exclusively on dynamical or kinetic processes. Here, a simple mechanism is proposed for increasing the carbon storage capacity of the deep sea that operates via changes in the volume of southern-sourced deep-water filling the ocean basins, as dictated by the hypsometry of the ocean floor. It is proposed that a water-mass that occupies more than the bottom 3 km of the ocean will essentially determine the carbon content of the marine reservoir. Hence by filling this interval with southern-sourced deep-water (enriched in dissolved CO2 due to its particular mode of formation) the amount of carbon sequestered in the deep sea may be greatly increased. A simple box-model is used to test this hypothesis, and to investigate its implications. It is suggested that up to 70% of the observed glacial – interglacial CO2 change might be explained by the replacement of northern-sourced deep-water below 2.5 km water depth by its southern counterpart. Most importantly, it is found that an increase in the volume of southern-sourced deep-water allows glacial CO2 levels to be simulated easily with only modest changes in Southern Ocean biological export or overturning. If incorporated into the list of contributing factors to marine carbon sequestration, this mechanism may help to significantly reduce the "deficit" of explained glacial – interglacial CO2 change.

Ocean carbon storage uniquely linked to ocean heat 

2021 ◽  
Author(s):  
Ben Bronselaer ◽  
Laure Zanna
Keyword(s):  
Carbon Storage ◽  
Large Scale ◽  
Climate Models ◽  
Circulation Pattern ◽  
Secondary Importance ◽  
Large Scale Circulation ◽  
Excess Carbon ◽  
Excess Heat ◽  
Surface Ocean ◽  
Ocean Carbon

&lt;p&gt;As the climate warms due to greenhouse gas emissions, the ocean absorbs excess heat and carbon. The patterns of ocean excess heat and carbon storage appear tightly linked when the large-scale circulation is fixed. This unique link is not shared with any other ocean tracer, such as &lt;span&gt;Chlorofluorocarbons&lt;/span&gt; (CFCs). At the same time, ocean excess carbon storage patterns are mostly unchanged whether the large-scale circulation is free to evolve, or fixed to the pre-industrial circulation pattern, as the climate warms. Here, we interpret the reason for this behavior by breaking ocean carbon storage into two parts: uptake of atmospheric anomalies by the surface ocean, and subsequent internal storage by the ocean&amp;#8217;s circulation. We show that the patterns of surface ocean carbon anomalies are dictated by mean state biogeochemical properties and therefore mostly unchanged by circulation changes. Furthermore, surface biogeochemical properties are strongly shaped by the ocean temperature, providing a link between ocean heat and carbon uptake. CFCs on the hand, lack chemical buffering and therefore the patterns of CFC storage do not correlate with heat as much as carbon patterns do. The patterns of surface anomalies ultimately explain most of the differences in how temperature, carbon and CFCs are stored by the ocean, while changes in internal pathways are of secondary importance. Furthermore, the ratio of total ocean carbon and heat storage is roughly constant across warming scenarios and climate models, which might have further implications for relating ocean carbon storage to important climate metrics, such as the transient response to cumulative emissions.&lt;/p&gt;

scholarly journals Response of the Ocean Natural Carbon Storage to Projected Twenty-First-Century Climate Change

2014 ◽  
Vol 27 (5) ◽  
pp. 2033-2053 ◽  
Author(s):  
Raffaele Bernardello ◽  
Irina Marinov ◽  
Jaime B. Palter ◽  
Jorge L. Sarmiento ◽  
Eric D. Galbraith ◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Carbon Storage ◽  
Wind Stress ◽  
First Century ◽  
High Latitudes ◽  
Co2 Solubility ◽  
Natural Carbon ◽  
Twenty First Century ◽  
Ocean Carbon

Abstract The separate impacts of wind stress, buoyancy fluxes, and CO2 solubility on the oceanic storage of natural carbon are assessed in an ensemble of twentieth- to twenty-first-century simulations, using a coupled atmosphere–ocean–carbon cycle model. Time-varying perturbations for surface wind stress, temperature, and salinity are calculated from the difference between climate change and preindustrial control simulations, and are imposed on the ocean in separate simulations. The response of the natural carbon storage to each perturbation is assessed with novel prognostic biogeochemical tracers, which can explicitly decompose dissolved inorganic carbon into biological, preformed, equilibrium, and disequilibrium components. Strong responses of these components to changes in buoyancy and winds are seen at high latitudes, reflecting the critical role of intermediate and deep waters. Overall, circulation-driven changes in carbon storage are mainly due to changes in buoyancy fluxes, with wind-driven changes playing an opposite but smaller role. Results suggest that climate-driven perturbations to the ocean natural carbon cycle will contribute 20 Pg C to the reduction of the ocean accumulated total carbon uptake over the period 1860–2100. This reflects a strong compensation between a buildup of remineralized organic matter associated with reduced deep-water formation (+96 Pg C) and a decrease of preformed carbon (−116 Pg C). The latter is due to a warming-induced decrease in CO2 solubility (−52 Pg C) and a circulation-induced decrease in disequilibrium carbon storage (−64 Pg C). Climate change gives rise to a large spatial redistribution of ocean carbon, with increasing concentrations at high latitudes and stronger vertical gradients at low latitudes.

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