Ocean carbon cycle feedbacks in CMIP6 models: contributions from different basins

Abstract. The ocean response to carbon emissions involves the combined effect of an increase in atmospheric CO2, acting to enhance the ocean carbon storage, and climate change, acting to decrease the ocean carbon storage. This ocean response can be characterised in terms of a carbon–concentration feedback and a carbon–climate feedback. The contribution from different ocean basins to these feedbacks on centennial timescales is explored using diagnostics of ocean carbonate chemistry, physical ventilation and biological processes in 11 CMIP6 Earth system models. To gain mechanistic insight, the dependence of these feedbacks on the Atlantic Meridional Overturning Circulation (AMOC) is also investigated in an idealised climate model and the CMIP6 models. For the carbon–concentration feedback, the Atlantic, Pacific and Southern oceans provide comparable contributions when estimated in terms of the volume-integrated carbon storage. This large contribution from the Atlantic Ocean relative to its size is due to strong local physical ventilation and an influx of carbon transported from the Southern Ocean. The Southern Ocean has large anthropogenic carbon uptake from the atmosphere, but its contribution to the carbon storage is relatively small due to large carbon transport to the other basins. For the carbon–climate feedback estimated in terms of carbon storage, the Atlantic and Arctic oceans provide the largest contributions relative to their size. In the Atlantic, this large contribution is primarily due to climate change acting to reduce the physical ventilation. In the Arctic, this large contribution is associated with a large warming per unit volume. The Southern Ocean provides a relatively small contribution to the carbon–climate feedback, due to competition between the climate effects of a decrease in solubility and physical ventilation and an increase in accumulation of regenerated carbon. The more poorly ventilated Indo-Pacific Ocean provides a small contribution to the carbon cycle feedbacks relative to its size. In the Atlantic Ocean, the carbon cycle feedbacks strongly depend on the AMOC strength and its weakening with warming. In the Arctic, there is a moderate correlation between the AMOC weakening and the carbon–climate feedback that is related to changes in carbonate chemistry. In the Pacific, Indian and Southern oceans, there is no clear correlation between the AMOC and the carbon cycle feedbacks, suggesting that other processes control the ocean ventilation and carbon storage there.

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Controls of ocean carbon cycle feedbacks from different ocean basins and meridional overturning in CMIP6

10.5194/bg-2020-487 ◽

2021 ◽

Author(s):

Anna Katavouta ◽

Richard G. Williams

Keyword(s):

Climate Change ◽

Atlantic Ocean ◽

Carbon Cycle ◽

Southern Ocean ◽

Carbon Storage ◽

Carbon Concentration ◽

Climate Feedback ◽

Meridional Overturning ◽

Ocean Carbon ◽

Southern Oceans

Abstract. The ocean response to carbon emissions involves a competition between the increase in atmospheric CO2 acting to enhance the ocean carbon storage, characterised by the carbon-concentration feedback, and climate change acting to decrease the ocean carbon storage, characterised by the carbon-climate feedback. The contribution from different ocean basins to the carbon cycle feedbacks and its control by the ocean carbonate chemistry, physical ventilation and biological processes is explored in diagnostics of 10 CMIP6 Earth system models. To gain mechanist insight, the dependence of these feedbacks to the Atlantic Meridional Overturning Circulation (AMOC) is also investigated in an idealised climate model and the CMIP6 models. The Atlantic, Pacific and Southern Oceans contribute equally to the carbon-concentration feedback, despite their different size. This large contribution from the Atlantic Ocean relative to its size is associated with an enhanced carbon storage in the ocean interior due to a strong local physical ventilation and an influx of carbon transported from the Southern Ocean. The Atlantic Ocean provides the largest contribution to the carbon-climate feedback relative to its size, which is primarily due to climate change acting to reduce the physical ventilation. The Southern Ocean provides a relatively small contribution to the carbon-climate feedback, due to a compensation between the climate effects of the combined decrease in solubility and physical ventilation, and the increase in accumulation of regenerated carbon in the ocean interior. In the Atlantic Ocean, the AMOC strength and its weakening with warming has a strong control on the carbon cycle feedbacks that leads to a moderate dependence of these feedbacks to AMOC on global scale. In the Pacific, Indian and Southern Oceans there is no clear correlation between AMOC and the carbon cycle feedbacks, suggesting that other processes control the ocean ventilation and carbon storage there.

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Changes in the Arctic Ocean carbon cycle with diminishing ice cover

10.1002/essoar.10502603.1 ◽

2020 ◽

Cited By ~ 1

Author(s):

Michael D. DeGrandpre ◽

Wiley Evans ◽

Mary-Louise Timmermans ◽

Richard A. Krishfield ◽

William J Williams ◽

...

Keyword(s):

Carbon Cycle ◽

Arctic Ocean ◽

Ice Cover ◽

The Arctic ◽

Ocean Carbon Cycle ◽

The Arctic Ocean ◽

Ocean Carbon

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Deglacial carbon cycle changes observed in a compilation of 127 benthic δ13C time series (20–6 ka)

Climate of the Past ◽

10.5194/cp-14-1229-2018 ◽

2018 ◽

Vol 14 (8) ◽

pp. 1229-1252 ◽

Cited By ~ 4

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.

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

Journal of Climate ◽

10.1175/jcli-d-13-00343.1 ◽

2014 ◽

Vol 27 (5) ◽

pp. 2033-2053 ◽

Cited By ~ 29

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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Sustained growth of the Southern Ocean carbon storage in a warming climate

Geophysical Research Letters ◽

10.1002/2015gl064320 ◽

2015 ◽

Vol 42 (11) ◽

pp. 4516-4522 ◽

Cited By ~ 13

Author(s):

Takamitsu Ito ◽

Annalisa Bracco ◽

Curtis Deutsch ◽

Hartmut Frenzel ◽

Matthew Long ◽

...

Keyword(s):

Southern Ocean ◽

Carbon Storage ◽

Sustained Growth ◽

Warming Climate ◽

Ocean Carbon

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The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

10.5194/bg-2016-367 ◽

2016 ◽

Cited By ~ 3

Author(s):

Célia J. Sapart ◽

Natalia Shakhova ◽

Igor Semiletov ◽

Joachim Jansen ◽

Sönke Szidat ◽

...

Keyword(s):

Water Column ◽

Large Scale ◽

Age Determination ◽

Arctic Shelf ◽

Climate Feedback ◽

The Arctic ◽

Small Contribution ◽

Isotope Data ◽

Siberian Arctic ◽

Subsea Permafrost

Abstract. Methane (CH4) is a strong greenhouse gas emitted by human activity and natural processes that are highly sensitive to climate change. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS) overlays large areas of subsea permafrost that is degrading. The release of large amount of CH4 originally stored or formed there could create a strong positive climate feedback. Large scale CH4 super-saturation has been observed in the ESAS waters, pointing to leakages of CH4 through the sea floor and possibly to the atmosphere, but the origin of this gas is still debated. Here, we present CH4 concentration and triple isotope data analyzed on gas extracted from sediment and water sampled over the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 μM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon CH4 isotope data reveal the predominant presence of CH4 that is not of thermogenic/natural gas origin as it has long been thought, but resultant from microbial CH4 formation using as primary substrate glacial water and old organic matter preserved in the subsea permafrost or below. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment. CH4 will then rapidly migrate through the very shallow water column of the ESAS to escape to the atmosphere generating a positive radiative feedback.

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Showcasing the compact Earth system model OSCAR v3.1 with CMIP6 simulations

10.5194/egusphere-egu21-15630 ◽

2021 ◽

Author(s):

Yann Quilcaille ◽

Thomas Gasser

Keyword(s):

Carbon Cycle ◽

Atmospheric Chemistry ◽

Coupled Model ◽

Climate Feedback ◽

Large Set ◽

Earth System ◽

Ocean Carbon Cycle ◽

Intercomparison Project ◽

Reduced Complexity ◽

Ocean Carbon

While Earth system models (ESM) provide spatially detailed process-based outputs, they present heavy computational costs. Reduced complexity models such as OSCAR are calibrated on those complex models and provide an alternative with faster calculations but lower resolutions. Yet, reduced-complexity models need to be evaluated and validated. We diagnose the newest version of OSCAR (v3.1) using observations and results from ESMs and the current Coupled Model Intercomparison Project 6. A total of 99 experiments are selected for simulation with OSCAR v3.1 in a probabilistic framework, reaching a total of 567,700,000 simulated years. Here, we showcase these results. A first highlight of this exercise is the unstability of the model for high-warming scenarios, which we attribute to the ocean carbon cycle module. The diverging runs caused by this unstability were discarded in the post-processing. The ensuing main results were further obtained by weighting each physical parametrizations based on their performance to replicate a set of observations. Overall, OSCAR v3.1 qualitively behaves like complex ESMs, for all aspects of the Earth system, although we observe a number of quantitative differences with state-of-the-art models. Some specific features of OSCAR contribute in these differences, such as its fully interactive atmospheric chemistry and endogenous calculations of biomass burning, wetlands and permafrost emissions. Nevertheless, the low sensitivity of the land carbon cycle to climate change, the unstability of the ocean carbon cycle, the seemingly over-constrained climate module, and the strong climate feedback over short-lived species, all call for an improvement of these aspects in OSCAR. Beyond providing a key diagnosis of the model in the context of the reduced-complexity models intercomparison project (RCMIP), this work is also meant to help with the upcoming calibration of OSCAR on CMIP6 results, and to provide a large set of CMIP6 simulations all run consistently with a probalistic model.

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Climate–Carbon Cycle Feedback Analysis: Results from the C4MIP Model Intercomparison

Journal of Climate ◽

10.1175/jcli3800.1 ◽

2006 ◽

Vol 19 (14) ◽

pp. 3337-3353 ◽

Cited By ~ 2085

Author(s):

P. Friedlingstein ◽

P. Cox ◽

R. Betts ◽

L. Bopp ◽

W. von Bloh ◽

...

Keyword(s):

Climate Change ◽

Carbon Cycle ◽

Net Primary Productivity ◽

Future Climate ◽

Climate Feedback ◽

Future Climate Change ◽

Ocean Carbon Cycle ◽

Intergovernmental Panel ◽

Ocean Carbon ◽

The Impact

Abstract Eleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C. All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.

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