scholarly journals Response of the carbon cycle to the different orbital configurations of the last 9 interglacials

2016 ◽  
Author(s):  
Nathaelle Bouttes ◽  
Didier Swingedouw ◽  
Didier Roche ◽  
Maria Sanchez-Goni ◽  
Xavier Crosta
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Atmospheric Co2 ◽  
Oceanic Circulation ◽  
Co2 Concentrations ◽  
Before And After ◽  
Ocean Carbon ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Atmospheric CO2 levels during interglacials prior to the Mid Bruhnes Event (MBE, ~ 430 ka BP) have lower values of around 40 ppm than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to differences in external forcing before and after the MBE, might have increased the ocean carbon storage and thus explained the lower CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings and atmospheric CO2 concentrations over the nine last interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few ppm. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 is slightly smaller in these pre-MBE simulated interglacials including ice sheet variations, but the magnitude is still far too small. These results suggest a possible mis-representation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, that could explain the lower atmospheric CO2 concentrations during pre-MBE interglacials.

scholarly journals Response of the carbon cycle in an intermediate complexity model to the different climate configurations of the last nine interglacials

2018 ◽  
Vol 14 (2) ◽  
pp. 239-253 ◽  
Author(s):  
Nathaelle Bouttes ◽  
Didier Swingedouw ◽  
Didier M. Roche ◽  
Maria F. Sanchez-Goni ◽  
Xavier Crosta
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Atmospheric Co2 ◽  
Oceanic Circulation ◽  
Intermediate Complexity ◽  
Co2 Concentrations ◽  
Co2 Levels ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Atmospheric CO2 levels during interglacials prior to the Mid-Brunhes Event (MBE, ∼ 430 ka BP) were around 40 ppm lower than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to different external forcings before and after the MBE, might have increased the ocean carbon storage in pre-MBE interglacials, thus lowering atmospheric CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings, ice sheet configurations and atmospheric CO2 concentrations over the last nine interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few parts per million. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 levels are lower during these pre-MBE simulated interglacials including all these effects, but the magnitude is still far too small. These results suggest a possible misrepresentation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, to fully account for the lower atmospheric CO2 concentrations during pre-MBE interglacials.

scholarly journals Heterogeneous CO<sub>2</sub> and CH<sub>4</sub> content of glacial meltwater from the Greenland Ice Sheet and implications for subglacial carbon processes

2021 ◽  
Vol 15 (3) ◽  
pp. 1627-1644
Author(s):  
Andrea J. Pain ◽  
Jonathan B. Martin ◽  
Ellen E. Martin ◽  
Åsa K. Rennermalm ◽  
Shaily Rahman
Keyword(s):  
Greenhouse Gas ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mineral Weathering ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
Co2 Concentrations ◽  
Geochemical Models ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Accelerated melting of the Greenland Ice Sheet has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of Greenland Ice Sheet meltwater on Arctic greenhouse gas budgets. We evaluate subglacial discharge from the Greenland Ice Sheet for carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks. We compare discharge from southwest (a sub-catchment of the Isunnguata Glacier, sub-Isunnguata, and the Russell Glacier) and southern Greenland (Kiattut Sermiat). Meltwater CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat. In contrast, meltwaters from southwest sites are supersaturated, even though oxidation reduces CH4 concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at sub-Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites; however, differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. At the sub-Isunnguata site, the predominant source of CO2 is organic matter (OM) remineralization. However, multiple or heterogeneous subglacial CO2 sources maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat, where CO2 is undersaturated. These results highlight a previously unrecognized degree of heterogeneity in greenhouse gas dynamics under the Greenland Ice Sheet. Future work should constrain the extent and controls of heterogeneity to improve our understanding of the impact of Greenland Ice Sheet melt on Arctic greenhouse gas budgets, as well as the role of continental ice sheets in greenhouse gas variations over glacial–interglacial timescales.

scholarly journals A missing link in the carbon cycle: phytoplankton light absorption

2021 ◽  
Author(s):  
Rémy Asselot ◽  
Frank Lunkeit ◽  
Philip Holden ◽  
Inga Hense
Keyword(s):  
Carbon Cycle ◽  
Co2 Emissions ◽  
Light Absorption ◽  
Climate System ◽  
Atmospheric Co2 ◽  
Co2 Concentrations ◽  
Recent Climate ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Marine biota and biogeophysical mechanisms, such as phytoplankton light absorption, have attracted increasing attention in recent climate studies. Under global warming, the impact of phytoplankton on the climate system is expected to change. Previous studies analyzed the impact of phytoplankton light absorption under prescribed future atmospheric CO2 concentrations. However, the role of this biogeophysical mechanism under freely-evolving atmospheric CO2 concentration and future CO2 emissions remain unknown. To shed light on this research gap, we perform simulations with the EcoGEnIE Earth system model and prescribe CO2 emissions following the four Representative Concentration Pathways (RCP) scenarios. Under all the RCP scenario, our results indicate that phytopankton light absorption increases the surface chlorophyll biomass, the sea surface temperature, the atmospheric CO2 concentrations and the atmospheric temperature. Under the RCP2.6, RCP4.5 and RCP6.0 scenarios, the magnitude of changes due to phytoplankton light absorption are similar. However, under the RCP8.5 scenario, the changes in the climate system are less pronounced due to the temperature limitation of phytoplankton growth, highlighting the reduced effect of phytoplankton light absorption under strong warming. Additionally, this work evidences the major role of phytoplankton light absorption on the climate system, suggesting a highly uncertain feedbacks on the carbon cycle with uncertainties that are in the range of those known from the land biota.

scholarly journals Heterogenous CO<sub>2</sub> and CH<sub>4</sub> content of glacial meltwater of the Greenland Ice Sheet and implications for subglacial carbon processes

2020 ◽  
Author(s):  
Andrea J. Pain ◽  
Jonathan B. Martin ◽  
Ellen E. Martin ◽  
Shaily Rahman
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Mineral Weathering ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
Co2 Concentrations ◽  
Geochemical Models ◽  
Carbon Dioxide Co2 ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Accelerated melting of the Greenland Ice Sheet (GrIS) has increased freshwater delivery to the Arctic Ocean and amplified the need to understand the impact of GrIS meltwater on Arctic greenhouse gas (GHG) budgets. We measured carbon dioxide (CO2) and methane (CH4) concentrations and δ13C values and use geochemical models to evaluate subglacial CH4 and CO2 sources and sinks in water discharging from three subglacial outlets of the GrIS in southwest (Isunnguata and Russell Glaciers) and southern Greenland (Kiattut Sermiat). CH4 concentrations vary by orders of magnitude between sites and are saturated with respect to atmospheric concentrations at Kiattut Sermiat, but are supersaturated at southwest sites, even though oxidation reduces concentrations by up to 50 % during periods of low discharge. CO2 concentrations range from supersaturated at Isunnguata to undersaturated at Kiattut Sermiat. CO2 is consumed by mineral weathering throughout the melt season at all sites, however differences in the magnitude of subglacial CO2 sources result in meltwaters that are either sources or sinks of atmospheric CO2. The predominant source of CO2 at Isunnguata is organic matter (OM) remineralization, but Russell and Kiattut Sermiat sites have multiple or heterogeneous subglacial CO2 sources that maintain atmospheric CO2 concentrations at Russell but not at Kiattut Sermiat where CO2 is undersaturated. These results highlight the variability in GHG dynamics under the GrIS. Constraining this variability will improve our understanding of the impact of GrIS melt on Arctic GHG budgets, as well as the role of continental ice sheets in GHG variations over glacial-interglacial timescales.

scholarly journals 23rd Century surprises: Long-term dynamics of the climate and carbon cycle under both high and net negative emissions scenarios

2021 ◽  
Author(s):  
Charles Koven ◽  
Vivek K. Arora ◽  
Patricia Cadule ◽  
Rosie A. Fisher ◽  
Chris D. Jones ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Carbon Emissions ◽  
Global Climate ◽  
Climate Projections ◽  
Earth System ◽  
Global Mean Temperature ◽  
Co2 Concentrations ◽  
Ocean Carbon ◽  
Atmospheric Co2 Concentrations ◽  
Emissions Scenario

Abstract. Future climate projections from Earth system models (ESMs) typically focus on the timescale of this century. We use a set of four ESMs and one Earth system model of intermediate complexity (EMIC) to explore the dynamics of the Earth’s climate and carbon cycles under contrasting emissions trajectories beyond this century, to the year 2300. The trajectories include a very high emissions, unmitigated fossil-fuel driven scenario, as well as a second mitigation scenario that diverges from the first scenario after 2040 and features an “overshoot”, followed by stabilization of atmospheric CO2 concentrations by means of large net-negative CO2 emissions. In both scenarios, and for all models considered here, the terrestrial system switches from being a net sink to either a neutral state or a net source of carbon, though for different reasons and centered in different geographic regions, depending on both the model and the scenario. The ocean carbon system remains a sink, albeit weakened by climate-carbon feedbacks, in all models under the high emissions scenario, and switches from sink to source in the overshoot scenario. The global mean temperature anomaly generally follows the trajectories of cumulative carbon emissions, except that 23rd-century warming continues after the cessation of carbon emissions in several models, both in the high emissions scenario and in one model in the overshoot scenario. While ocean carbon cycle responses qualitatively agree both in globally integrated and zonal-mean dynamics in both scenarios, the land models qualitatively disagree in zonal-mean dynamics, in the relative roles of vegetation and soil in driving C fluxes, in the response of the sink to CO2, and in the timing of the sink-source transition, particularly in the high emissions scenario. The lack of agreement among land models on the mechanisms and geographic patterns of carbon cycle feedbacks, alongside the potential for lagged physical climate dynamics to cause warming long after CO2 concentrations have stabilized, point to the possibility of surprises in the climate system beyond the 21st century time horizon, even under relatively mitigated global warming scenarios, which should be taken into consideration when setting global climate policy.

scholarly journals The impact of spatiotemporal variability in atmospheric CO<sub>2</sub> concentration on global terrestrial carbon fluxes

2018 ◽  
Author(s):  
Eunjee Lee ◽  
Fan-Wei Zeng ◽  
Randal D. Koster ◽  
Brad Weir ◽  
Lesley E. Ott ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Temporal Variability ◽  
Gross Primary Production ◽  
Carbon Fluxes ◽  
Atmospheric Co2 ◽  
Spatiotemporal Variability ◽  
Terrestrial Carbon ◽  
Diurnal Variability ◽  
Co2 Concentrations ◽  
The Impact

Abstract. Land carbon fluxes, e.g., gross primary production (GPP) and net biome production (NBP), are controlled in part by the responses of terrestrial ecosystems to atmospheric conditions near the Earth's surface. The Coupled Model Intercomparison Project Phase 6 (CMIP6) has recently proposed increased spatial and temporal resolutions for the surface CO2 concentrations used to calculate GPP, and yet a comprehensive evaluation of the consequences of this increased resolution for carbon cycle dynamics is missing. Here, using global offline simulations with a terrestrial biosphere model, the sensitivity of terrestrial carbon cycle fluxes to multiple facets of the spatiotemporal variability of atmospheric CO2 is quantified. Globally, the spatial variability of CO2 is found to increase the mean global GPP by 0.2 PgC year−1, as more vegetated land areas benefit from higher CO2 concentrations induced by the inter-hemisphere gradient. The temporal variability of CO2, however, compensates for this increase, acting to reduce overall global GPP; in particular, consideration of the diurnal variability of atmospheric CO2 reduces multi-year mean global annual GPP by 0.5 PgC year−1 and net land carbon uptake by 0.1 PgC year−1. The relative contribution of the different facets of CO2 variability to GPP are found to vary regionally and seasonally, with the seasonal variation in atmospheric CO2, for example, having a notable impact on GPP in boreal regions during fall. Overall, in terms of estimating global GPP, the magnitudes of the sensitivities found here are minor, indicating that the common practice of applying spatially-uniform and annually increasing CO2 (without higher frequency temporal variability) in offline studies is a reasonable approach – the small errors induced by ignoring CO2 variability are undoubtedly swamped by other uncertainties in the offline calculations. Still, for certain regional- and seasonal-scale GPP estimations, the proper treatment of spatiotemporal CO2 variability appears important.

scholarly journals The impact of spatiotemporal variability in atmospheric CO<sub>2</sub> concentration on global terrestrial carbon fluxes

2018 ◽  
Vol 15 (18) ◽  
pp. 5635-5652 ◽  
Author(s):  
Eunjee Lee ◽  
Fan-Wei Zeng ◽  
Randal D. Koster ◽  
Brad Weir ◽  
Lesley E. Ott ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Temporal Variability ◽  
Gross Primary Production ◽  
Carbon Fluxes ◽  
Atmospheric Co2 ◽  
Spatiotemporal Variability ◽  
Terrestrial Carbon ◽  
Diurnal Variability ◽  
Co2 Concentrations ◽  
The Impact

Abstract. Land carbon fluxes, e.g., gross primary production (GPP) and net biome production (NBP), are controlled in part by the responses of terrestrial ecosystems to atmospheric conditions near the Earth's surface. The Coupled Model Intercomparison Project Phase 6 (CMIP6) has recently proposed increased spatial and temporal resolutions for the surface CO2 concentrations used to calculate GPP, and yet a comprehensive evaluation of the consequences of this increased resolution for carbon cycle dynamics is missing. Here, using global offline simulations with a terrestrial biosphere model, the sensitivity of terrestrial carbon cycle fluxes to multiple facets of the spatiotemporal variability in atmospheric CO2 is quantified. Globally, the spatial variability in CO2 is found to increase the mean global GPP by a maximum of 0.05 Pg C year−1, as more vegetated land areas benefit from higher CO2 concentrations induced by the inter-hemispheric gradient. The temporal variability in CO2, however, compensates for this increase, acting to reduce overall global GPP; in particular, consideration of the diurnal variability in atmospheric CO2 reduces multi-year mean global annual GPP by 0.5 Pg C year−1 and net land carbon uptake by 0.1 Pg C year−1. The relative contributions of the different facets of CO2 variability to GPP are found to vary regionally and seasonally, with the seasonal variation in atmospheric CO2, for example, having a notable impact on GPP in boreal regions during fall. Overall, in terms of estimating global GPP, the magnitudes of the sensitivities found here are minor, indicating that the common practice of applying spatially uniform and annually increasing CO2 (without higher-frequency temporal variability) in offline studies is a reasonable approach – the small errors induced by ignoring CO2 variability are undoubtedly swamped by other uncertainties in the offline calculations. Still, for certain regional- and seasonal-scale GPP estimations, the proper treatment of spatiotemporal CO2 variability appears important.

scholarly journals Quantifying the roles of ocean circulation and biogeochemistry in governing ocean carbon-13 and atmospheric carbon dioxide at the last glacial maximum

2009 ◽  
Vol 5 (4) ◽  
pp. 695-706 ◽  
Author(s):  
A. Tagliabue ◽  
L. Bopp ◽  
D. M. Roche ◽  
N. Bouttes ◽  
J.-C. Dutay ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Last Glacial ◽  
Carbon 14 ◽  
Ocean Carbon ◽  
The Impact ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use a state-of-the-art ocean general circulation and biogeochemistry model to examine the impact of changes in ocean circulation and biogeochemistry in governing the change in ocean carbon-13 and atmospheric CO2 at the last glacial maximum (LGM). We examine 5 different realisations of the ocean's overturning circulation produced by a fully coupled atmosphere-ocean model under LGM forcing and suggested changes in the atmospheric deposition of iron and phytoplankton physiology at the LGM. Measured changes in carbon-13 and carbon-14, as well as a qualitative reconstruction of the change in ocean carbon export are used to evaluate the results. Overall, we find that while a reduction in ocean ventilation at the LGM is necessary to reproduce carbon-13 and carbon-14 observations, this circulation results in a low net sink for atmospheric CO2. In contrast, while biogeochemical processes contribute little to carbon isotopes, we propose that most of the change in atmospheric CO2 was due to such factors. However, the lesser role for circulation means that when all plausible factors are accounted for, most of the necessary CO2 change remains to be explained. This presents a serious challenge to our understanding of the mechanisms behind changes in the global carbon cycle during the geologic past.

scholarly journals Systematic study of the impact of fresh water fluxes on the glacial carbon cycle

2012 ◽  
Vol 8 (2) ◽  
pp. 589-607 ◽  
Author(s):  
N. Bouttes ◽  
D. M. Roche ◽  
D. Paillard
Keyword(s):  
Carbon Cycle ◽  
Fresh Water ◽  
Climate Changes ◽  
Water Flux ◽  
Ice Cores ◽  
Atmospheric Co2 ◽  
Water Fluxes ◽  
Oceanic Circulation ◽  
Fresh Water Flux ◽  
The Impact

Abstract. During glacial periods, atmospheric CO2 concentration increases and decreases by around 15 ppm. At the same time, the climate changes gradually in Antarctica. Such climate changes can be simulated in models when the AMOC (Atlantic Meridional Oceanic Circulation) is weakened by adding fresh water to the North Atlantic. The impact on the carbon cycle is less straightforward, and previous studies give opposite results. Because the models and the fresh water fluxes were different in these studies, it prevents any direct comparison and hinders finding whether the discrepancies arise from using different models or different fresh water fluxes. In this study we use the CLIMBER-2 coupled climate carbon model to explore the impact of different fresh water fluxes. In both preindustrial and glacial states, the addition of fresh water and the resulting slow-down of the AMOC lead to an uptake of carbon by the ocean and a release by the terrestrial biosphere. The duration, shape and amplitude of the fresh water flux all have an impact on the change of atmospheric CO2 because they modulate the change of the AMOC. The maximum CO2 change linearly depends on the time integral of the AMOC change. The different duration, amplitude, and shape of the fresh water flux cannot explain the opposite evolution of ocean and vegetation carbon inventory in different models. The different CO2 evolution thus depends on the AMOC response to the addition of fresh water and the resulting climatic change, which are both model dependent. In CLIMBER-2, the rise of CO2 recorded in ice cores during abrupt events can be simulated under glacial conditions, especially when the sinking of brines in the Southern Ocean is taken into account. The addition of fresh water in the Southern Hemisphere leads to a decline of CO2, contrary to the addition of fresh water in the Northern Hemisphere.

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