Carbon Cycle Variations During the Past 50,000 Years: Atmospheric 14 C/12 C Ratio as an Isotopic Indicator

2013 ◽  
pp. 221-233 ◽  
Author(s):  
Devendra Lal
Keyword(s):  
Carbon Cycle ◽  
The Past

scholarly journals Mid-Pleistocene transition in glacial cycles explained by declining CO2and regolith removal

2019 ◽  
Vol 5 (4) ◽  
pp. eaav7337 ◽  
Author(s):  
M. Willeit ◽  
A. Ganopolski ◽  
R. Calov ◽  
V. Brovkin
Keyword(s):  
Climate Variability ◽  
Carbon Cycle ◽  
Northern Hemisphere ◽  
Seasonal Variations ◽  
Ice Sheets ◽  
Glacial Cycles ◽  
Solar Insolation ◽  
The Past ◽  
Transient Simulations

Variations in Earth’s orbit pace the glacial-interglacial cycles of the Quaternary, but the mechanisms that transform regional and seasonal variations in solar insolation into glacial-interglacial cycles are still elusive. Here, we present transient simulations of coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. We show that a gradual lowering of atmospheric CO2and regolith removal are essential to reproduce the evolution of climate variability over the Quaternary. The long-term CO2decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations, while the combined effect of CO2decline and regolith removal controls the timing of the transition from a 41,000- to 100,000-year world. Our results suggest that the current CO2concentration is unprecedented over the past 3 million years and that global temperature never exceeded the preindustrial value by more than 2°C during the Quaternary.

scholarly journals New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Netta Shalev ◽  
Tomaso R. R. Bontognali ◽  
C. Geoffrey Wheat ◽  
Derek Vance
Keyword(s):  
Low Temperature ◽  
Carbon Cycle ◽  
Oceanic Crust ◽  
Isotope Fractionation ◽  
Hydrothermal Fluids ◽  
Carbonate Precipitation ◽  
Magnesium Isotopes ◽  
Conventional View ◽  
The Past ◽  
Dolomite Formation

AbstractThe oceanic magnesium budget is important to our understanding of Earth’s carbon cycle, because similar processes control both (e.g., weathering, volcanism, and carbonate precipitation). However, dolomite sedimentation and low-temperature hydrothermal circulation remain enigmatic oceanic Mg sinks. In recent years, magnesium isotopes (δ26Mg) have provided new constraints on the Mg cycle, but the lack of data for the low-temperature hydrothermal isotope fractionation has hindered this approach. Here we present new δ26Mg data for low-temperature hydrothermal fluids, demonstrating preferential 26Mg incorporation into the oceanic crust, on average by εsolid-fluid ≈ 1.6‰. These new data, along with the constant seawater δ26Mg over the past ~20 Myr, require a significant dolomitic sink (estimated to be 1.5–2.9 Tmol yr−1; 40–60% of the oceanic Mg outputs). This estimate argues strongly against the conventional view that dolomite formation has been negligible in the Neogene and points to the existence of significant hidden dolomite formation.

Mineral dust coupled with climate‐carbon cycle on orbital timescales over the past 4 Ma

2021 ◽  
Author(s):  
Mengmeng Cao ◽  
Zhixiang Wang ◽  
Yu Sui ◽  
Yanzhen Li ◽  
Ze Zhang ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Mineral Dust ◽  
The Past

Toward an improved characterisation of climate and environmental changes during warm periods of the past: First results from the MOPGA HOTCLIM project 

2021 ◽  
Author(s):  
Etienne Legrain ◽  
Emilie Capron ◽  
Frederic Parrenin
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Environmental Changes ◽  
Temporal Structure ◽  
Ice Cores ◽  
Environmental Data ◽  
Interglacial Period ◽  
Climate Projections ◽  
The Past ◽  
First Results

<p>The current and future anthropogenic-induced high-latitude warming will have global climatic implications due to polar ice mass loss, sea level rise and ocean circulation changes. However, uncertainty remains on future climate projections mainly due to an incomplete understanding of climate, cryosphere and carbon cycle feedback processes occurring at centennial to millennial- timescales. Progress can be achieved by exploring climate and environmental changes that occurred in the past. In the HOTCLIM project, we are studying past warm periods, also referred to as interglacials, which exhibit a polar warming comparable to that projected by 2100 due to specific combinations of orbital and CO<sub>2</sub> forcing. Especially, we are investigating the link between the carbon cycle dynamics and climate changes. To do so, we are combining (i) new analyses on the air trapped in Antarctic deep ice cores to inform on past changes in Antarctic climate and atmospheric CO2 concentrations (ii) climate and environmental data synthesis looking into the lower latitudes using terrestrial and oceanic archives (sea surface temperature, hydrological cycles, ocean circulation) (iii) an evaluation of outputs from climate models using the new comparison of the paleoclimatic datasynthesis and models output. The HOTCLIM project will improve our understanding of the natural climate variability and the processes involved during past periods associated with temperature changes comparable to projected future warming, hence helping improve climate projections</p><p>Here, we present the first results from the HOTCLIM project which is a multi-archive synthesis focused on the warm interval occurring between 190 and 243 ka BP, also refered to as Marine Isotopic Stage 7 (MIS 7). This warm period is of special interest because it follows the fastest transition between a cold (glacial) and a hot (interglacial) period of the last 800 000 ka, with a polar warming of 10 degrees in less than 5ka. We have compiled more than 30 oceanic cores, 9 speleothems and 3 ice cores covering the MIS 7 period. To compare them, we are now building a common chronology to these records. The use of combined continental (ice cores, speleothems) and oceanic (sediment cores) archives located on the whole surface of the Earth will allows to characterize (i) the amplitude and the temporal structure of the surface warming across the globe (ii) the contrast between oceanic and continental warming.</p>

Carbon Cycle in the Past 300 Years and Future Projections

2000 ◽  
Vol 7 (4) ◽  
pp. 214-215
Author(s):  
F. T. Mackenzie ◽  
A. Lerman
Keyword(s):  
Carbon Cycle ◽  
Future Projections ◽  
The Past ◽  
Past 300 Years

scholarly journals Orbital pacing of carbon fluxes by a ∼9-My eccentricity cycle during the Mesozoic

2015 ◽  
Vol 112 (41) ◽  
pp. 12604-12609 ◽  
Author(s):  
Mathieu Martinez ◽  
Guillaume Dera
Keyword(s):  
Carbon Cycle ◽  
Orbital Forcing ◽  
Time Intervals ◽  
Sea Level Fluctuations ◽  
The Past ◽  
Paleoenvironmental Changes ◽  
Chaotic Diffusion ◽  
Orbital Cycles ◽  
Short Time

Eccentricity, obliquity, and precession are cyclic parameters of the Earth’s orbit whose climatic implications have been widely demonstrated on recent and short time intervals. Amplitude modulations of these parameters on million-year time scales induce ‟grand orbital cycles,” but the behavior and the paleoenvironmental consequences of these cycles remain debated for the Mesozoic owing to the chaotic diffusion of the solar system in the past. Here, we test for these cycles from the Jurassic to the Early Cretaceous by analyzing new stable isotope datasets reflecting fluctuations in the carbon cycle and seawater temperatures. Our results document a prominent cyclicity of ∼9 My in the carbon cycle paced by changes in the seasonal dynamics of hydrological processes and long-term sea level fluctuations. These paleoenvironmental changes are linked to a great eccentricity cycle consistent with astronomical solutions. The orbital forcing signal was mainly amplified by cumulative sequestration of organic matter in the boreal wetlands under greenhouse conditions. Finally, we show that the ∼9-My cycle faded during the Pliensbachian, which could either reflect major paleoenvironmental disturbances or a chaotic transition affecting this cycle.

Goal and products of PAGES LandCover6k 2018-2020: Past Global Land Cover and Land Use for Climate Modelling

2020 ◽  
Author(s):  
Marie-Jose Gaillard ◽  
Andria Dawson ◽  
Ralph Fyfe ◽  
Esther Githumbi ◽  
Emily Hammer ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Carbon Cycle ◽  
Climate Model ◽  
Climate Modelling ◽  
Model Simulations ◽  
Lulc Changes ◽  
The Past ◽  
Per Capita ◽  
Past Land Use

<p>The question of whether prehistoric human impacts on land cover (i.e. anthropogenic land cover change due to land use, LULC) were sufficiently large to have a major impact on regional cli-mates is still a matter of debate. Climate model simulations have shown that LULC datasets can have large regional impacts on climate in recent and prehistoric time<sup> (1)</sup>. But there are major differences between the available LULC scenarios/datasets such as HYDE (History Database of the Global En-vironment) and Kaplan’s KK10 <sup>(2)</sup>, and diagnoses of inferred carbon-cycle impacts show that none of the scenarios are realistic <sup>(3)</sup>. The only way to provide a useful assessment of the potential for LULC changes to affect climate in the past, is to provide more realistic LULC data based on palaeovegetation and archaeological evidence to improve the LULC datasets used in climate modelling<sup>(4)</sup>. We use the REVEALS model to reconstruct LC from pollen data at a regional scale, and archaeological data to map LU types and distribution, and estimate per capita LU. The archaeology-based LU maps and per-capita LU estimates are used to improve LULC datasets. Pollen-based REVEALS LC estimates are then used to evaluate/validate the new, improved LULC datasets. These new datasets will be used to implement past land use in palaeoclimate and carbon cycle model simulations. Such simulations are necessary to assess the impact of LULC changes in the past and understand the effect of ecosys-tem management on future climate. We present results from five years of PAGES LandCover6k activities. </p><p>(1) Strandberg G, Kjellström E, Poska A, Wagner S, Gaillard M-J et al. (2014) Regional climate model sim-ulations for Europe at 6 and 0.2 k BP: sensitivity to changes in anthropogenic deforestation. Clim. Past 10, 661–680.<br>(2) Gaillard M-J, Sugita S, Mazier F et al (2010) Holocene land-cover reconstructions for studies on land cover-climate feedbacks. Clim. Past 6, 483-499.<br>(3) Stocker B, Yud Z, Massae C, Joos F (2017) Holocene peatland and ice-core data constraints on the tim-ing and magnitude of CO2 emissions from past land use. www.pnas.org/cgi/doi/10.1073/ pnas.1613889114.<br>(4) Harrison S P, Gaillard M-J, Stocker B D, Vander Linden M, Klein Goldewijk K, Boles O, Braconnot P, Dawson A, Fluet-Chouinard E, Kaplan J O, Kastner T, Pausata F S R, Robinson E, Whitehouse N J, Madella M, and Morrison K D (2019) Development and testing of scenarios for implementing Holocene LULC in Earth Sys-tem Model Experiments, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-125, in review, 2019.</p><p><sup> </sup></p><p> </p><p> </p>

scholarly journals Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

2017 ◽  
Vol 13 (12) ◽  
pp. 1695-1716 ◽  
Author(s):  
Andrey Ganopolski ◽  
Victor Brovkin
Keyword(s):  
Carbon Cycle ◽  
Ice Sheets ◽  
Co2 Concentration ◽  
System Model ◽  
Model Parameters ◽  
Orbital Forcing ◽  
Earth System ◽  
Glacial Cycles ◽  
The Past ◽  
Paleoclimate Reconstructions

Abstract. In spite of significant progress in paleoclimate reconstructions and modelling of different aspects of the past glacial cycles, the mechanisms which transform regional and seasonal variations in solar insolation into long-term and global-scale glacial–interglacial cycles are still not fully understood – in particular, in relation to CO2 variability. Here using the Earth system model of intermediate complexity CLIMBER-2 we performed simulations of the co-evolution of climate, ice sheets, and carbon cycle over the last 400 000 years using the orbital forcing as the only external forcing. The model simulates temporal dynamics of CO2, global ice volume, and other climate system characteristics in good agreement with paleoclimate reconstructions. These results provide strong support for the idea that long and strongly asymmetric glacial cycles of the late Quaternary represent a direct but strongly nonlinear response of the Northern Hemisphere ice sheets to orbital forcing. This response is strongly amplified and globalised by the carbon cycle feedbacks. Using simulations performed with the model in different configurations, we also analyse the role of individual processes and sensitivity to the choice of model parameters. While many features of simulated glacial cycles are rather robust, some details of CO2 evolution, especially during glacial terminations, are sensitive to the choice of model parameters. Specifically, we found two major regimes of CO2 changes during terminations: in the first one, when the recovery of the Atlantic meridional overturning circulation (AMOC) occurs only at the end of the termination, a pronounced overshoot in CO2 concentration occurs at the beginning of the interglacial and CO2 remains almost constant during the interglacial or even declines towards the end, resembling Eemian CO2 dynamics. However, if the recovery of the AMOC occurs in the middle of the glacial termination, CO2 concentration continues to rise during the interglacial, similar to the Holocene. We also discuss the potential contribution of the brine rejection mechanism for the CO2 and carbon isotopes in the atmosphere and the ocean during the past glacial termination.

Modelling the global carbon cycle for the past and future evolution of the earth system

1999 ◽  
Vol 159 (1-4) ◽  
pp. 305-317 ◽  
Author(s):  
Siegfried Franck ◽  
Konrad Kossacki ◽  
Christine Bounama
Keyword(s):  
Carbon Cycle ◽  
Global Carbon Cycle ◽  
Earth System ◽  
Future Evolution ◽  
The Past ◽  
The Earth ◽  
Global Carbon
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