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.

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.

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

&lt;p&gt;While paleoproxy records and modelling studies consistently suggest that North Atlantic&amp;#160; 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&lt;sub&gt;2&lt;/sub&gt; concentration.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions

2010 ◽  
Vol 292 (3-4) ◽  
pp. 290-300 ◽  
Author(s):  
Katharine R. Hendry ◽  
R. Bastian Georg ◽  
Rosalind E.M. Rickaby ◽  
Laura F. Robinson ◽  
Alex N. Halliday
Keyword(s):  
Last Glacial Maximum ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Isotopic Compositions ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Northern Sourced Water dominated the Atlantic Ocean during the Last Glacial Maximum

2020 ◽  
Author(s):  
Frerk Pöppelmeier ◽  
Patrick Blaser ◽  
Marcus Gutjahr ◽  
Samuel Jaccard ◽  
Martin Frank ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Water Mass ◽  
Stable Carbon Isotope ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Ice Age ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;Increased carbon sequestration in the ocean subsurface is commonly assumed to have been one of the main causes responsible for lower glacial atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations. This carbon must have been stored away from the atmosphere for thousands of years, yet the water mass structure accommodating such increased carbon storage continues to be debated. Here we present new sediment derived bottom water neodymium isotope data that allow fingerprinting of water masses and their mixtures and provide a more complete picture of the Atlantic overturning circulation geometry during the Last Glacial Maximums. These results suggest that the vertical and meridional structure of the Atlantic deep water mass distribution only experienced minor changes since the last ice age. In particular, we find no compelling evidence supporting glacial southern sourced water substantially expanding to shallower depths and farther into the northern hemisphere than today, which has been inferred from stable carbon isotope reconstructions. We argue that depleted &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values observed in the deep Northwest Atlantic do not necessarily indicate the presence of southern sourced water. Instead, these values may represent a northern sourced water mass with lower than modern preformed &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C values that were further modified downstream by increased sequestration of remineralized carbon, facilitated by a more sluggish glacial deep circulation. If proven to be correct, the glacial water mass structure inferred from Nd isotopes has profound implications on our understanding of the deep ocean carbon storage during the Last Glacial Maximum.&lt;/p&gt;

scholarly journals Ice-age ice-sheet rheology: constraints from the Last Glacial Maximum form of the Laurentide ice sheet

2000 ◽  
Vol 30 ◽  
pp. 163-176 ◽  
Author(s):  
W. Richard Peltier ◽  
David L. Goldsby ◽  
David L. Kohlstedt ◽  
Lev Tarasov
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Glacial Maximum ◽  
Ice Age ◽  
Laurentide Ice Sheet ◽  
Last Glacial ◽  
Flow Law ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractState-of-the-art thermomechanical models of the modern Greenland ice sheet and the ancient Laurentide ice sheet that covered Canada at the Last Glacial Maximum (LGM) are not able to explain simultaneously the observed forms of these cryospheric structures when the same, anisotropy-enhanced, version of the conventional Glen flow law is employed to describe their rheology. The LGM Laurentide ice sheet, predicted to develop in response to orbital climate forcing, is such that the ratio of its thickness to its horizontal extent is extremely large compared to the aspect ratio inferred on the basis of surface-geomorphological and solid-earth-geophysical constraints. We show that if the Glen flow law representation of the rheology is replaced with a new rheology based upon very high quality laboratory measurements of the stress-strain-rate relation then the aspect ratios of both the modern Greenland ice sheet and the Laurentide ice sheet, that existed at the LGM, are simultaneously explained with little or no retuning of the flow law.

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