A weaker Atlantic Meridional Overturning Circulation at the Last Glacial Maximum led to a greater deep ocean carbon content

2020 ◽  
Author(s):  
Laurie Menviel ◽  
Paul Spence ◽  
Luke Skinner ◽  
Kazuyo Tachikawa ◽  
Tobias Friedrich ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The North Atlantic ◽  
Ocean Carbon ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>While paleoproxy records and modelling studies consistently suggest that North Atlantic  Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than during pre-industrial times, its strength is still subject to debate partly due to different signals across the North Atlantic. Here, using a series of LGM experiments performed with a carbon isotopes enabled Earth system model, we show that proxy records are consistent with a shallower and weaker NADW. A significant equatorward advance of sea-ice over the Labrador Sea and the Nordic Seas shifts the NADW convection sites to the south of the Norwegian Sea. While the deep western boundary current in the Northwest Atlantic weakens with NADW, a change in density gradients strengthens the deep southward flow in the Northeast Atlantic. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic despite its transport being reduced. This resultant globally weaker oceanic circulation leads to an increase in deep ocean carbon of ~500 GtC, thus significantly contributing to the lower LGM atmospheric CO<sub>2</sub> concentration.</p><p> </p>

scholarly journals A coupled model study of the Last Glacial Maximum: Was part of the North Atlantic relatively warm?

2001 ◽  
Vol 28 (8) ◽  
pp. 1571-1574 ◽  
Author(s):  
Chris D. Hewitt ◽  
Anthony J. Broccoli ◽  
John F. B. Mitchell ◽  
Ronald J. Stouffer
Keyword(s):  
Last Glacial Maximum ◽  
North Atlantic ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
Model Study ◽  
The North Atlantic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

scholarly journals Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model (<i>i</i>LOVECLIM) comparison

2014 ◽  
Vol 10 (6) ◽  
pp. 1939-1955 ◽  
Author(s):  
T. Caley ◽  
D. M. Roche ◽  
C. Waelbroeck ◽  
E. Michel
Keyword(s):  
Last Glacial Maximum ◽  
Data Model ◽  
Model Comparison ◽  
Greenland Ice Sheet ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use the fully coupled atmosphere–ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 years). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data–model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data–model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a strong mean annual cooling in the area south of Iceland and Greenland between the LGM and present (> 6 °C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data–model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and the present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and the present are not spatially homogeneous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data–model comparison supports a heterogeneous cooling of a few degrees (2–4 °C) in the LGM Ocean.

scholarly journals Constraining the Last Glacial Maximum climate by data-model (<i>i</i>LOVECLIM) comparison using oxygen stable isotopes

2014 ◽  
Vol 10 (1) ◽  
pp. 105-148 ◽  
Author(s):  
T. Caley ◽  
D. M. Roche ◽  
C. Waelbroeck ◽  
E. Michel
Keyword(s):  
Last Glacial Maximum ◽  
Data Model ◽  
Model Comparison ◽  
Greenland Ice Sheet ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The North ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. We use the fully coupled atmosphere-ocean three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 yr). By using a model that is able to explicitly simulate the sensor (δ18O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that iLOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ18O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice-sheet. We observe a general pattern toward more enriched values for continental calcite δ18O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data-model comparison for sea surface temperature indicates that iLOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data-model comparison for calcite δ18O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a trong mean annual cooling between the LGM and present (> 6°C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data-model comparison also reveals that large positive calcite δ18O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ18Osw anomaly for the north Indian Ocean that contrasts with a large negative δ18Osw anomaly in the China Sea between the LGM and present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ18Osw between the LGM and present are not spatially homogenous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ18O data. Nonetheless, our data-model comparison support a heterogeneous cooling of few degrees (2–4°C) in the LGM Ocean.

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