Sequential changes in ocean circulation and biological export productivity during the last glacial–interglacial cycle: a model–data study

Abstract. We conduct a model–data analysis of the marine carbon cycle to understand and quantify the drivers of atmospheric CO2 concentration during the last glacial–interglacial cycle. We use a carbon cycle box model, “SCP-M”, combined with multiple proxy data for the atmosphere and ocean, to test for variations in ocean circulation and Southern Ocean biological export productivity across marine isotope stages spanning 130 000 years ago to the present. The model is constrained by proxy data associated with a range of environmental conditions including sea surface temperature, salinity, ocean volume, sea-ice cover and shallow-water carbonate production. Model parameters for global ocean circulation, Atlantic meridional overturning circulation and Southern Ocean biological export productivity are optimized in each marine isotope stage against proxy data for atmospheric CO2, δ13C and Δ14C and deep-ocean δ13C, Δ14C and CO32-. Our model–data results suggest that global overturning circulation weakened during Marine Isotope Stage 5d, coincident with a ∼ 25 ppm fall in atmospheric CO2 from the last interglacial period. There was a transient slowdown in Atlantic meridional overturning circulation during Marine Isotope Stage 5b, followed by a more pronounced slowdown and enhanced Southern Ocean biological export productivity during Marine Isotope Stage 4 (∼ −30 ppm). In this model, the Last Glacial Maximum was characterized by relatively weak global ocean and Atlantic meridional overturning circulation and increased Southern Ocean biological export productivity (∼ −20 ppm during MIS 3 and MIS 2). Ocean circulation and Southern Ocean biological export productivity returned to modern values by the Holocene period. The terrestrial biosphere decreased by 385 Pg C in the lead-up to the Last Glacial Maximum, followed by a period of intense regrowth during the last glacial termination and the Holocene (∼ 600 Pg C). Slowing ocean circulation, a colder ocean and to a lesser extent shallow carbonate dissolution contributed ∼ −70 ppm to atmospheric CO2 in the ∼ 100 000-year lead-up to the Last Glacial Maximum, with a further ∼ −15 ppm contributed during the glacial maximum. Our model results also suggest that an increase in Southern Ocean biological export productivity was one of the ingredients required to achieve the Last Glacial Maximum atmospheric CO2 level. We find that the incorporation of glacial–interglacial proxy data into a simple quantitative ocean transport model provides useful insights into the timing of past changes in ocean processes, enhancing our understanding of the carbon cycle during the last glacial–interglacial period.

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Sequential changes in ocean circulation and biological export productivity during the last glacial cycle: a model-data study

10.5194/cp-2019-146 ◽

2019 ◽

Author(s):

Cameron M. O'Neill ◽

Andrew McC. Hogg ◽

Michael J. Ellwood ◽

Bradley N. Opdyke ◽

Stephen M. Eggins

Keyword(s):

Southern Ocean ◽

Last Glacial Maximum ◽

Ocean Circulation ◽

Glacial Maximum ◽

Meridional Overturning Circulation ◽

Atmospheric Co2 ◽

Overturning Circulation ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract. We conduct a model-data analysis of the ocean, atmosphere and terrestrial carbon system to understand their effects on atmospheric CO2 during the last glacial cycle. We use a carbon cycle box model SCP-M, combined with multiple proxy data for the atmosphere and ocean, to test for variations in ocean circulation and biological productivity across marine isotope stages spanning 130 thousand years ago to the present. The model is constrained by proxy data associated with a range of environmental conditions including sea surface temperature, salinity, ocean volume, sea ice cover and shallow water carbonate production. Model parameters for global ocean circulation, Atlantic meridional overturning circulation and Southern Ocean biological export productivity are optimised in each marine isotope stage, against proxy data for atmospheric CO2, δ13C and ∆14C and deep ocean δ13C, ∆14C and carbonate ion. Our model-data results suggest that global overturning circulation weakened at marine isotope stage 5d, coincident with a ∼ 25 ppm fall in atmospheric CO2 from the penultimate interglacial level. This change was followed by a further slowdown in Atlantic meridional overturning circulation and enhanced Southern Ocean biological export productivity at marine isotope stage 4 (∼−30 ppm). There was also a transient slowdown in Atlantic meridional overturning circulation at MIS 5b. In this model, the last glacial maximum was characterised by relatively weak global ocean and Atlantic meridional overturning circulation, and increased Southern Ocean biological export productivity (∼−15–20 ppm during MIS 2–4). Ocean circulation and Southern Ocean biology rebounded to modern values by the Holocene period. The terrestrial biosphere decreased by ∼ 500 Pg C in the lead up to the last glacial maximum, followed by a period of intense regrowth during the Holocene (∼ 750 Pg C). Slowing ocean circulation, a cooler ocean and, to a lesser extent, shallow carbonate dissolution, contributed ∼−75 ppm to atmospheric CO2 in the ∼ 100 thousand-year lead-up to the last glacial maximum, with a further ∼−10 ppm contributed during the glacial maximum. Our model results also suggest that an increase in Southern Ocean biological productivity was one of the ingredients required to achieve the last glacial maximum atmospheric CO2 level. The incorporation of longer-timescale data into quantitative ocean transport models, provides useful insights into the timing of changes in ocean processes, enhancing our understanding of the last glacial maximum and Holocene carbon cycle transition.

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

Climate of the Past ◽

10.5194/cp-5-695-2009 ◽

2009 ◽

Vol 5 (4) ◽

pp. 695-706 ◽

Cited By ~ 72

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.

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A large increase in the carbon inventory of the land biosphere since the Last Glacial Maximum: constraints from multi-proxy data

10.5194/cp-2018-167 ◽

2018 ◽

Author(s):

Aurich Jeltsch-Thömmes ◽

Gianna Battaglia ◽

Olivier Cartapanis ◽

Samuel L. Jaccard ◽

Fortunat Joos

Keyword(s):

Monte Carlo ◽

Mass Balance ◽

Last Glacial Maximum ◽

Glacial Maximum ◽

Atmospheric Co2 ◽

Proxy Data ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial ◽

Carbon Inventory

Abstract. Atmospheric CO2 increased by about 90 ppm across the transition from the Last Glacial Maximum (LGM) to the end of the preindustrial (PI) period. The contribution of changes in land carbon stocks to this increase remains uncertain. Estimates of the PI-LGM difference in land biosphere carbon inventory (∆land) range from −400 to &plus;1,500 GtC, based on upscaling of scarce paleo soil carbon or pollen data. A perhaps more reliable approach infers ∆land from reconstructions of the stable carbon isotope ratio in the ocean and atmosphere assuming isotopic mass balance with recent studies yielding ∆land values of about 300–400 GtC. Surprisingly, however, earlier studies considered a mass balance for the ocean–atmosphere–land biosphere system only. Thereby, these studies neglect carbon exchange with sediments, weathering-burial flux imbalances, and the influence of the deglacial reorganization on the isotopic budgets. We show this neglect to significantly bias low deglacial ∆land in simulations using the Bern3D Earth System Model of Intermediate Complexity v.2.0s. We constrain ∆land to ∼ 850 GtC (median estimate; 450 to 1250 GtC 1σ range) by using reconstructed changes in atmospheric δ13C, marine δ13C, deep Pacific carbonate ion concentration, and atmospheric CO2 as observational targets in a Monte Carlo ensemble with half a million members. Sensitivities of the target variables to changes in individual deglacial carbon cycle processes are established from factorial simulations over the past 21,000 years with the Bern3D model. These are used in the Monte Carlo ensemble and provide forcing–response relationships for future model–model and model–data comparisons. Uncertainties in the estimate of ∆land remain considerable due to model and proxy data uncertainties. Yet, it is likely that ∆land is larger than 450 GtC and highly unlikely that the carbon inventory in the land biosphere was larger for the LGM than during the recent preindustrial period.

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

Climate of the Past Discussions ◽

10.5194/cpd-5-1463-2009 ◽

2009 ◽

Vol 5 (3) ◽

pp. 1463-1491 ◽

Cited By ~ 1

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 can attribute over 90% of the change in atmospheric CO2 to such factors. The lesser role for circulation means that when all plausible factors are accounted for, over half 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.

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Climate of the last glacial maximum: sensitivity studies and model-data comparison with the LOVECLIM coupled model

Climate of the Past Discussions ◽

10.5194/cpd-2-1105-2006 ◽

2006 ◽

Vol 2 (6) ◽

pp. 1105-1153 ◽

Cited By ~ 4

Author(s):

D. M. Roche ◽

T. M. Dokken ◽

H. Goosse ◽

H. Renssen ◽

S. L. Weber

Keyword(s):

Last Glacial Maximum ◽

Glacial Maximum ◽

Future Climate Change ◽

Oceanic Circulation ◽

Coupled Models ◽

Proxy Data ◽

Last Glacial ◽

The Last Glacial Maximum ◽

Last Glacial Maximum Climate ◽

The Last Glacial

Abstract. The Last Glacial Maximum climate is one of the classic benchmarks used both to test the ability of coupled models to simulate climates different from that ot the present-day and to better understand the possible range of mechanisms that could be involved in future climate change. It also bears the advantage of being one of the most well documented periods with respect to palaeoclimatic records, allowing a thorough data-model comparison. We present here an ensemble of Last Glacial Maximum climate simulations obtained with the Earth System model LOVECLIM, including coupled dynamic atmosphere, ocean and vegetation components. The climate obtained using standard parameter values is then compared to available proxy data for the surface ocean, vegetation, oceanic circulation and atmospheric conditions. Interestingly, the oceanic circulation obtained resembles that of the present-day, but with increased overturning rates. As this result is in contradiction with the "classic" palaeoceanographic view, we ran a range of sensitivity experiments to explore the response of the model and the possibilities for other oceanic circulation states. After a critical review of our LGM state with respect to available proxy data, we conclude that the balance between water masses obtained is consistent with the available data although the specific characteristics (temperature, salinity) are not in full agreement. The consistency of the simulated state is further reinforced by the fact that the mean surface climate obtained is shown to be generally in agreement with the most recent reconstructions of vegetation and sea surface temperatures, even at regional scales.

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Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: δ13C evidence from laminated Ethmodiscus rex mats in tropical West Pacific

Global and Planetary Change ◽

10.1016/j.gloplacha.2013.06.003 ◽

2013 ◽

Vol 108 ◽

pp. 1-14 ◽

Cited By ~ 14

Author(s):

Zhifang Xiong ◽

Tiegang Li ◽

Xavier Crosta ◽

Thomas Algeo ◽

Fengming Chang ◽

...

Keyword(s):

Last Glacial Maximum ◽

Potential Role ◽

Glacial Maximum ◽

Atmospheric Co2 ◽

Marine Diatoms ◽

West Pacific ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

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Influence of dynamic vegetation on climate change and terrestrial carbon storage in the Last Glacial Maximum

Climate of the Past ◽

10.5194/cp-9-1571-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1571-1587 ◽

Cited By ~ 12

Author(s):

R. O'ishi ◽

A. Abe-Ouchi

Keyword(s):

Carbon Storage ◽

Last Glacial Maximum ◽

Glacial Maximum ◽

Atmospheric Co2 ◽

Terrestrial Carbon ◽

Dynamic Global Vegetation Model ◽

Vegetation Feedback ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract. When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

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PMIP-carbon: towards a multi-models comparison of climate-carbon interactions at the Last Glacial Maximum

10.5194/egusphere-egu2020-13279 ◽

2020 ◽

Author(s):

Nathaelle Bouttes ◽

Ruza Ivanovic ◽

Ayako Abe-Ouchi ◽

Hidetaka Kobayashi ◽

Laurie Menviel ◽

...

Keyword(s):

Carbon Cycle ◽

Carbon Isotopes ◽

Last Glacial Maximum ◽

Ocean Circulation ◽

Ice Cores ◽

Glacial Maximum ◽

Last Glacial ◽

Intercomparison Project ◽

The Last Glacial Maximum ◽

The Last Glacial

More and more climate models now include the carbon cycle, but multi-models studies of climate-carbon simulations within the Climate Model Intercomparison Project (CMIP) are limited to present and future time periods. In addition, the carbon cycle is not considered in the simulations of past periods analysed within the Paleoclimate Modelling Intercomparison Project (PMIP). Yet, climate-carbon interactions are crucial to anticipate future atmospheric CO2 concentrations and their impact on climate. Such interactions can change depending on the background climate, it is thus necessary to compare model results among themselves and to data for past periods with different climates such as the Last Glacial Maximum (LGM).The Last Glacial Maximum, around 21,000 years ago, was about 4&#176;C colder than the pre-industrial, and associated with large ice sheets on the American and Eurasian continents. It is one of the best documented periods thanks to numerous paleoclimate archives such as marine sediment cores and ice cores. Despite this period having been studied for years, no consensus on the causes of the lower atmospheric CO2 concentration at the time (around 180 ppm) has been reached and models still struggle to simulate these low CO2 values. The ocean, which contains around 40 times more carbon than the atmosphere, likely plays a key role, but models tend to simulate ocean circulation changes in disagreement with proxy data, such as carbon isotopes.This new project aims at comparing, for the first time, the carbon cycle representation at the Last Glacial Maximum from general circulation models and intermediate complexity models. We will explain the protocol and present first results in terms of carbon storage in the main reservoirs (atmosphere, land and ocean) and their link to key climate variables such as temperature, sea ice and ocean circulation. The use of coupled climate-carbon models will not only allow to compare changes in the carbon cycle in models and analyse their causes, but it will also enable us to better compare to indirect data related to the carbon cycle such as carbon isotopes.

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