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

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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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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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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Influence of the Atlantic thermohaline circulation on neodymium isotopic composition at the Last Glacial Maximum – a modelling sensitivity study

Climate of the Past Discussions ◽

10.5194/cpd-4-309-2008 ◽

2008 ◽

Vol 4 (2) ◽

pp. 309-333 ◽

Cited By ~ 1

Author(s):

T. Arsouze ◽

J.-C. Dutay ◽

M. Kageyama ◽

F. Lacan ◽

R. Alkama ◽

...

Keyword(s):

Isotopic Composition ◽

Last Glacial Maximum ◽

Ocean Circulation ◽

Glacial Maximum ◽

Oceanic Circulation ◽

Last Glacial ◽

Deep Waters ◽

The Impact ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract. The oceanic neodymium isotopic composition (hereafter expressed as ε Nd) is modeled for the Last Glacial Maximum (LGM) using the coarse resolution Ocean Global Circulation Model NEMO–ORCA2°. This study focuses on the impact of changes in the overturning cell and circulation patterns between LGM and Holocene on ε Nd in the Atlantic basin. Three different LGM freshwater forcing experiments are performed to test the variability in ε Nd oceanic distribution as a function of ocean circulation. Highly distinct representations of ocean circulation are generated in the three simulations, which drive significant differences in ε Nd, particularly in deep waters of the western part of the basin. However, mean Atlantic LGM ε Nd values are remain half a unit more radiogenic than for the modern control run. A fourth experiment shows that changes in Nd sources and bathymetry drive a shift in the ε Nd signature of Northern end-members (NADW or GNAIW glacial equivalent) that is sufficient to explain the shift in mean ε Nd during our LGM simulations. None of our three LGM circulation scenarios gives a better agreement with the existing ε Nd paleo-data, as the model fails in reproducing the dynamical features of the area. Therefore, this study cannot indicate the likelihood of a given LGM oceanic circulation scenario. Rather, our modeling results highlight the need for data from western Atlantic deep waters, where the ε Nd gradient in the three LGM scenarios is the most important (up to 3 ε Nd). This would also aid more precise conclusions concerning the north end-member ε Nd signature evolution, and thus the potential use of ε Nd as a tracer of past oceanic circulation.

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

Climate of the Past ◽

10.5194/cp-17-171-2021 ◽

2021 ◽

Vol 17 (1) ◽

pp. 171-201

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 ◽

Atmospheric Co2 ◽

Proxy Data ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial ◽

Export Productivity

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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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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The impact of tidal dissipation changes on the Last Glacial Maximum AMOC

10.5194/egusphere-egu2020-9930 ◽

2020 ◽

Author(s):

Sophie-Berenice Wilmes ◽

Mattias Green ◽

Andreas Schmittner

Keyword(s):

Last Glacial Maximum ◽

Glacial Maximum ◽

Meridional Overturning Circulation ◽

Tidal Mixing ◽

Tidal Dissipation ◽

Last Glacial ◽

Meridional Overturning ◽

The Impact ◽

The Last Glacial Maximum ◽

The Last Glacial

The global mean sea-level decrease of 120 &#8211; 130 m during the Last Glacial Maximum (LGM; 26 &#8211; 19 kyr BP) is thought to have substantially altered semidiurnal tidal dynamics in the glacial North Atlantic. This more than doubled global open ocean tidal dissipation in comparison to present day and increased the amount of energy available for diapycnal mixing which is important for driving the global meridional overturning circulation. Reconstructions of the glacial ocean have generally suggested a more sluggish Atlantic meridional overturning circulation (AMOC) during the LGM together with weaker mixing. Here, we investigate the impact of tidal dissipation changes on the LGM AMOC and the carbon cycle using the intermediate complexity ocean model UVic coupled to the biogeochemistry model MOBI forced with three different LGM dissipation estimates. The simulations are constrained with LGM &#948;13C and radiocarbon data from sediments. Our results suggest that our simulations, as previously inferred, most closely agree with a weakened LGM AMOC (8 &#8211; 9 Sv), and importantly, that the agreement is consistent with increased LGM tidal mixing. These results firstly imply that a weakened AMOC state can occur with stronger tidal mixing without hampering the agreement with the sediment isotope data. Secondly, this work highlights the importance of considering tidal dissipation changes when modelling the paleo-ocean.

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