Inferring ocean circulation during the Last Glacial Maximum and last deglaciation using data and models

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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A 3000-yr Annually Laminated Stalagmite Record of the Last Glacial Maximum from Hulu Cave, China

Quaternary Research ◽

10.1016/j.yqres.2015.01.003 ◽

2015 ◽

Vol 83 (2) ◽

pp. 360-369 ◽

Cited By ~ 15

Author(s):

Fucai Duan ◽

Jiangying Wu ◽

Yongjin Wang ◽

R. Lawrence Edwards ◽

Hai Cheng ◽

...

Keyword(s):

Last Glacial Maximum ◽

Ocean Circulation ◽

Hydrological Cycle ◽

Glacial Maximum ◽

Solar Cycles ◽

Last Glacial ◽

The North ◽

Annual Layer ◽

The Last Glacial Maximum ◽

The Last Glacial

A high-resolution, annual layer-counted and 230Th-dated multi-proxy record is constructed from a stalagmite in Hulu Cave, China. These proxies, including δ18O, annual layer thickness (ALT), gray level (GL) and Sr/Ca, cover a time span of ~ 3000 yr from 21 to 24 ka. The physical proxies (ALT and GL) and the geochemical index (Sr/Ca), all primarily reflecting karst hydrological processes, vary in concert and their coherence is supported by wavelet analyses. Variations in the δ18O data agree with fluctuations in the ALT and Sr/Ca records on multi-decadal to centennial scales, suggesting that the Hulu δ18O signal is strongly associated with varying local rainfall amounts on short timescales. A monsoon failure event at ~ 22.2 ka correlates with a decrease in tropical rainfall, a reduction in global CH 4 and an ice-rafted event in the North Atlantic. This correlation highlights roles of the Asian monsoon and tropical hydrological cycle in modulating global CH 4, because the high-latitude emission was inhibited during the Last Glacial Maximum (LGM). Spectral analysis of the δ18O record displays peaks at periodicities of 139, 59, 53, 43, 30, 23 and 19"15 yr. The absence of typical centennial solar cycles may be related to muted changes in ocean circulation during the LGM.

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The Biological Pump During the Last Glacial Maximum

Annual Review of Marine Science ◽

10.1146/annurev-marine-010419-010906 ◽

2020 ◽

Vol 12 (1) ◽

pp. 559-586 ◽

Cited By ~ 3

Author(s):

Eric D. Galbraith ◽

Luke C. Skinner

Keyword(s):

Carbon Storage ◽

Last Glacial Maximum ◽

Ocean Circulation ◽

Marine Ecosystem ◽

Glacial Maximum ◽

Ice Age ◽

Natural Experiments ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial

Much of the global cooling during ice ages arose from changes in ocean carbon storage that lowered atmospheric CO2. A slew of mechanisms, both physical and biological, have been proposed as key drivers of these changes. Here we discuss the current understanding of these mechanisms with a focus on how they altered the theoretically defined soft-tissue and biological disequilibrium carbon storage at the peak of the last ice age. Observations and models indicate a role for Antarctic sea ice through its influence on ocean circulation patterns, but other mechanisms, including changes in biological processes, must have been important as well, and may have been coordinated through links with global air temperature. Further research is required to better quantify the contributions of the various mechanisms, and there remains great potential to use the Last Glacial Maximum and the ensuing global warming as natural experiments from which to learn about climate-driven changes in the marine ecosystem.

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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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A modeling sensitivity study of the influence of the Atlantic meridional overturning circulation on neodymium isotopic composition at the Last Glacial Maximum

Climate of the Past ◽

10.5194/cp-4-191-2008 ◽

2008 ◽

Vol 4 (3) ◽

pp. 191-203 ◽

Cited By ~ 25

Author(s):

T. Arsouze ◽

J.-C. Dutay ◽

M. Kageyama ◽

F. Lacan ◽

R. Alkama ◽

...

Keyword(s):

Isotopic Composition ◽

Last Glacial Maximum ◽

Ocean Circulation ◽

Glacial Maximum ◽

Meridional Overturning Circulation ◽

Oceanic Circulation ◽

Last Glacial ◽

The Last Glacial Maximum ◽

The Last Glacial ◽

Modern Control

Abstract. Using a simple parameterisation that resolves the first order global Nd isotopic composition (hereafter expressed as εNd in an Ocean Global Circulation Model, we have tested the impact of different circulation scenarios on the εNd in the Atlantic for the Last Glacial Maximum (LGM), relative to a modern control run. Three different LGM freshwater forcing experiments are performed to test for variability in the εNd oceanic distribution as a function of ocean circulation. Highly distinct representations of the ocean circulation are generated in the three simulations, which drive significant differences in εNd, particularly in deep waters of the western part of the basin. However, at the LGM, the Atlantic is more radiogenic than in the modern control run, particularly in the Labrador basin and in the Southern Ocean. A fourth experiment shows that changes in Nd sources and bathymetry drive a shift in the εNd signature of the basin that is sufficient to explain the changes in the εNd signature of the northern end-member (NADW or GNAIW glacial equivalent) in our LGM simulations. All three of our LGM circulation scenarios show good agreement with the existing intermediate depth εNd paleo-data. This study cannot indicate the likelihood of a given LGM oceanic circulation scenario, even if simulations with a prominent water mass of southern origin provide the most conclusive results. Instead, our modeling results highlight the need for more data from deep and bottom waters from western Atlantic, where the εNd change in the three LGM scenarios is the most important (up to 3 εNd. This would also aid more precise conclusions concerning the evolution of the northern end-member εNd signature, and thus the potential use of εNd as a tracer of past oceanic circulation.

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